Manual of qualitative chemical analysis, by Dr. C. Remigius Fresenius ...
Fresenius, C. Remigius, 1818-1897.

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Page  II Bntered according to Act of Congress, in the year 189?, by JOHN WILEY, In the Office of the Librarian of Congress at Washington. TROW'S PRINTING AND BOOKBINDING CO, PRINTERS AND BOOKBINDERS, 205-213 East 12th St., 4gIW YORK*

Page  III EDITOR'S PREFACE. THE matter of this new American edition of Fresenitus' Manual of Qualitative Analysis, for the most part faithfully represents the'last (fourteenth) German edition. The editor has added a few paragraphs, has condensed, altered, or rewritten some others, and has expunged the scheme for the "Analysis of Simple Compounds," after becoming convinced by experience that this omission not only greatly simplifies the analytical course, but really facilitates its mastery by the student. A series of very brief analytical tables has been appended to this edition. These tables are borrowed, with some changes, from fMr. Vacher's English edition of 1869. INo such tables, however elaborate, can take the place of Fresenius' systematic course, in the real work of the careful analyst, but they may be made very serviceable to the beginner in enabling him to survey his ground, as well as to the experienced chemist, when, being out of practice, he may need a brief outline of the order of operations to sharpen his memory. In form the book is quite changed by the use throughout of the lanlguage and notation of "nmodern chemistry," a chaunge called for by the universal adoption of the "New System," as well as by its inherent advant ad ages. For the convenience of tile studellt, various developed formulae are given on page 42, alcd in numerous foot-notes. In these formlle each dash, either horizontal, vertical or inclined, indicates a " bond " or unit of quanltivalence, anld implies chemical combination between t!he atoms or groupings whose symbols are thus connected. The + sign and period are used to express " molecular combinatioln, i.e., combination not amenable to the usually received quanti valences, as in case of crystal water.

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Page  V CONTENTS. PART I. INTRODUCTORY PART. PAGU PRELIMINARY REARKS...................................... SECTION I. OPERATIONS,~ 1..............3......... 3 1. Solution, ~ 2..3 2. Crystallization, ~ 3 5..............................5... 8 3. Precipitation, ~ 4........................................ 6 4. Filtration, ~ 5..................................7........ 5. Decantation, ~ 6............................... 10 6. Washing, ~ 7.................................... 10 7. Dialysis, ~ 8.......................................... 11 8. Evaporation, ~ 9........................................... 12 9. Distillation, ~ 10...................................... 14 10. Ignition, ~ 11............................................... 14 11. Sublimatibn, ~ 12........................................... 15 12. Fusion, ~ 13................................................ 15 13. Deflagration, ~ 14...................1........................ 16 14. The use of the blowpipe, ~ 15................................ 17 15. The use of lamps, particularly of gas-lamps, ~ 16............... 21 16. Observation of the coloration of flame by certain bodies, and spectrum analysis, ~ 17....................................... 29 Appendix to the First Section. Apparatus, ~ 18................................................ 33 SECTION IL REAGENTS, ~ 19....................................... 35 A. REAGENTS IN THE WET WAY. I. SIMPLE SOLVENTS. 1. Water, ~ 20.............................................. 38 2. Alcohol, ~ 21.............................................38 3. Ether. ~ 22............................................. 39 4. Chloroform....................................................... 39 5 Carben disulphide.......................................... 39 [I. COLORING MATTERS AND INDIFFERENT VEGETABLE SUBSTANCES. 1. Test-papers, ~ 23.......................................... 40 2. Indigo solution. ~ 24................................. 41

Page  VI Vi CONTENTS. PAGE' JI. ACIDS AND HALOGENS, ~ 25.................................. 41 a. Oxygen acids. 1. Sulphuric acid, ~ 26.................................... 43 2. Nitric acid, ~ 27............................................ 45 3. Acetic acid. ~ 28................. 46 4. Tartaric acid, ~ 29......................................... 46 b. Hydrogen acids and halogens. 1. Hydrochloric acid, ~ 30..................................... 47 2. Chlorine and chlorine water, ~ 31............................. 48 3. Nitrohydrochloric acid, ~ 32................................. 49 4. Hydrofluosilicic acid, ~ 33................................... 50 c. Sulphur acids. 1. Hydrogen sulphide, or hydrosulphuric acid, ~ 34............... 51 [V. BASES, METALS, AND SULPHIDES, ~ 35.......................... 56 a. Oxygen bases. a. Alkalies. 1. Potassium hydroxide, or potassa and sodium hydroxide, or soda, ~ 36..................................................... 56 2. Ammonia and ammonium hydroxide, ~ 37.................... 59 3. Alkali earths. 1. Barium hydroxide, or baryta, ~ 38........................... 60 2. Calcium hydroxide, or lime, ~ 39............................. 61 y. Heavy metals and their oxides and hydroxides. 1. Zinc, ~ 40................................................. 61 2. Iron..................................................... 62 3. Copper. 62 4. Lead dioxide, ~ 41......................................... 62 5. Bismuthous hydroxide, ~ 42................................. 63 b. Suiphides. 1. Ammonium sulphide, ~ 43.................................. 63 2. Sodium sulphide, ~ 44...................................... 65 V. SALTS. a. Salts of the alkali metals. 1. Potassium sulphate, ~ 45.................................... 66 2. Sodium phosphate, ~ 46.................................... 66 3. Aimmnium oxalate, ~ 47................................... 67 4. Sodium acetate, ~ 48....................................... 67 5. Sodium carbonate, ~ 49.................................... 6. Ammonium carbonate, ~ 50................................ 6 7. Hydrogen sodium sulphite, ~ 51............................. 70 8. Potassium nitrate, ~ 52...... 71 9. Potassium bichromate, ~ 53........................ 71 10. Potassium pyroantimonate, ~ 54............................. 71 11. Ammonium nolybdate, ~ 55.......... 72 12. Ammonium chloride, ~ 56.................................. 73 13. Potassium cyanide, ~ 57.................................... 74 14. Potassium ferrocyanide, ~ 58................................ 75 15. Potassium ferricyanide, ~ 59................................ 75 16. Potassium stulphocyanate, ~ 60............................ 76

Page  VII CONTENTS. vil PAGE b. Salts of the alkali-earth metals. 1. Barium chloride, ~.61.................................. 76 2. Barium nitrate, ~ 62...................................... 77 3. Barium carbonate, ~ 63......................... 78 4. Calcium sulphate, ~ 64...................................... 78 5. Calcium chloride, ~ 65...................................... 79 6. Magnesium sulphate, ~ 66................................... 79 c. Salts of the heavy metals. 1. Ferrous sulphate, ~ 67...................................... 8C 2. Ferric chloride, ~ 68........................................ 81 3. Silver nitrate, ~ 69.............................. 81 4. Lead acetate, ~ 70........................................ 82 5. Mercurous nitrate, ~ 71.................................... 82 6. Mercuric chloride, ~ 72.................................... 83 7. Copper sulphate, ~ 73...................................... 83 8. Stannous chloride, ~ 74...................................... Q 9. Platinic chloride, ~ 75..................................... 85 10. Sodium palladio-chloride, ~ 76.............................. 85 11. Auric chloride, ~ 77..............................-......... 85 B. REAGENTS TN THE DRY WAY. I. Fluxes and decomposing agents. 1. Sodium carbonate, ~ 78..................................... 86 2. Calcium carbonate, ~ 79..................................... 87 3. Ammonium chloride, ~ 80................................... 87 4. Sodium nitrate, ~ 81........................................ 88 5. Sodium disulphate, ~ 82......................... 88 II. Blowpipe reagents. 1. Sodium carbonate, ~ 83.................................... 89 2. Potassium cyanide, ~ 84.. 89 3. Sodium tetraborate, ~ 85.......... 90 4. HIydrbtgen sodium ammonium phosphate, ~ 85 a.. 91 5. Cobalt nitrate, ~ 85 b....................................... 92 SECTION III. REACTIONS, ~ 86................................... 93 A. REACTIONS OF THE METALLIC OXIDES AND THEIR RADICALS, ~ 8]7..... 94 FIRST GROUP,~ 88...........................I.............. 95 a. Potassium, ~ 89............................................ 95 b. Sodium, ~ 90............................................. 97 c. Ammonium ~ 91.......................................... 99 Recapitulation andl remarks, ~ 92................................. 1CO Cusium, rubidium, lithium, ~ 93................................ 102 SECOND GROUP, ~ 94........................................ 104 a. Barium, ~ 95.............................................. 105 b. Strontium, ~ 96............................................ 107 c. Calcium, ~ 97........................ 109 d. Magnesium, ~ 98..8....'...................... 111 Recapitulation and remarks, ~ 99................................. 113 THIRD GROUP, ~ 100......................................... 115 a. Aluminium, ~ 101........................................... 116

Page  VIII V111 CONTENTS. PAGl b. Chromium, ~ 102......................................... 118 Recapitulation and remarks, ~ 103................................ 120 Beryllium, thorium, zirconium, yttrium, erbium, cerium, lanthanium, didymnium, titanium, tantalum, niobium, ~ 104.................. 120 FOURTH GROUP, ~ 105....................................... 130 a Zinc, ~ 106........................................ 131 b. Manganese, ~ 107.......................................... 133 c. Nickel, ~ 108.............................................. 135 d. Cobalt, ~ 109.............................................. 138 e. Iron, ferrous compounds, ~ 110.......................4....... 10 f. Iron, ferric compounds, ~ 1ll................................ 142 Recapitulation and remarks, ~ 112................................ i44 Uranium, thallium, indium, and vanadium, ~ 113.................. 146 FIFTH GROUP, ~ 114......................................... 150 First Division. a. Silver, ~ 115...................................... 150 b. Mercury, mercurous compounds, ~ 116........................ 152 c. Lead, ~ 1177................................................ 153 Recapitulation and remarks, ~ 118................................ 155 Second Division. a. Mercury, mercuric compounds, ~ 119......................... 156 b. Copper, ~ 120.............................................. 157 c. Bismuth, ~ 121........................................... 160 d. Cadmium, ~ 122........................................... 162 Recapitulation and remarks, ~ 123............... 164 Palladium, rhodium, osmium, and ruthenium, ~ 124........... 165 SIXTH GROUP, ~ 126......................................... 168 First Division. a. Gold, ~ 126.......................... 169 b. Platinum, ~ 127............................................ 170 Recapitulation and remarks, ~ 128................................ 172 Second Division. a. Tin, stannous compounds, ~ 129............................. 172 b. Tin, stannic compounds, ~ 130................................ 174 c. Antimony, ~ 131........................................... 1175 d. Arsenic and arsenious compounds, ~ 132...................... 180 e. Arsenic compounds, ~ 133............................... 189 Recapitulation and remarks, ~ 134.......................... 191 Iridium, molybdenum, tungsten, tellurium, and selenium, ~ 135.... 194 B. REACTIONS OF THE ACIDS AND THEIR RADICALS, ~ 136............. 199 Classification of acids in groups................................. 199 I. INORGANIC ACIDS. FIRST GROUP, ~ 137.......................................... 200 First Division. Chromic acid, ~ 138........................................... 201 Sulphurous, thiosulphuric (hyposulphurous), iodic acid, ~ 139....... 203

Page  IX CONTENTS. ix Second Division. PAGI Sulphuric acid, ~ 140......................................... 205 Hydrofluosilicic acid, ~ 141.................................... 207 Third Division. a. Orthophosphoric acid, ~ 142................................. 207 Pyro- and meta-phosphoric acid, ~ 143...................... 212 b. Boric acid, ~ 144.................... 213 c. Oxalic acid, ~ 145.......................................... 215 d. Hydrofluoric acid, ~ 146.................................... 216 Recapitulation and remarks, ~ 147................................ 219 Phosphorous acid, ~ 148....................................... 221 Fourth Division. a. Carbonic acid, ~ 149.................................. 221 b. Silicic acid, ~ 150........................................ 223 Recapitulation and remarks, ~ 151................................. 225 SECOND GROUP. a. Hydrochloric acid, ~ 152.................................... 226 b. Hydrobromic acid, ~ 153.................................... 228 c. Hydriodic acid, ~ 154....................................... 230 d. Hydroc yanic acid, ~ 5.............................. 223 Hydroferrocyanic and hydroferricyanic acid.................. 235 e. Hydrosulphuric acid, ~ 156.................................. 236 Recapitulation and remarks, ~ 157.......................... 238 Nitrous, hypochlorous, cliorous, hypophosphorous acid, ~ 158 240 THIRD GROUP. a. Nitric acid, ~ 159.......................................... 243 b. Chloric acid, ~ 160......................................... 244 Recapitulation and remarks, ~ 161................................ 245 Perchloric acid, ~ 162......................................... 246 II. ORGANIC ACIDS FIRST GROUP. a. Oxalic acid..................................... 247 b. Tartaric acid, ~ 163........................................ 247 c. Citric acid, ~ 164........................................... 249 d.'Malic acid, ~ 165........................................... 251 Recapitulation and remarks, ~ 166................................ 252 Racemic acid, ~ 167.................................... 254 SECOND GROUP. a. Succinic acid, ~ 168.................................. 254 b. Benzoic acid, ~ 169......................................... 255 Recapitulation and remarks, ~ 170................................ 256 THIRD GROUP. a. Acetic acid, ~ 171.......................................... 256 b. Formic acid, ~ 172......................................... 258 Recapitulation and remarks, ~ 173............ 259 Lactic, propionic, and butyric acids, ~ 174....................... 250

Page  X x CONTENTS. PART II. COURSE OF ANALYSIS. PACE Preliminary remarks on the course of qualitative analy sis........... 262 SECTION I. PRACTICAL PROCESS FOR THE ANALYSIS OF COMPOUNDS AND Ml ITURES IN GENERAL. i. Preliminary examination, ~ 175............................. 264 A. The substance is solid. 1. It is neither a pure metal nor an alloy, ~ 176......... 265 2. It is a metal or an alloy, ~ 177... 272 B. The substance is a fluid, ~ 178..................... 272 II. The solution of bodies, or classification of substances according to their deportment with certain solvents, ~ 179............... 273 A. The substance is neither a metal nor an alloy, ~ 180..... 274 B. The substancb is a metal or an alloy, ~ 181... 276 III. ACTUAL ANALYSIS. A. Substances soluble in water or in hydrochloric acid, nitric acid, or nitrohydrochloric acid. Detection of the metals, ~ 182. I. Soluition in water. Detection of silver and mercury in mercurous compounds.... 277 II. Solution in hydrochloric acid or aqua regia................. 280 III. Solution in nitric acid. Detection of silver and mercury in mercurous compounds.... 280 Treatment with hydrosulphuric acid, precipitation of the metals of Group V., 2d division, and of Group VI., ~ 183.............. 281 Treatament of the precipitate produced by hydrosulphuric acid with ammonium sulphide; separation of the 2d division of Group V. from Group VI., ~ 184............................... 282 Detection of the metals of Group VI.: Arsenic, antimony, tin, gold, platinum, ~ 18............................................. 283 Detection of the metals of Group V., 2d division: Lead, bismuth, copper, cadmium, mercury, ~ 186................... 286 Precipitation with ammonium sulphide, detection and separation of the metals of Groups IlI. and IV.: Aluminium, chlor-iium, zinc, manganese, nickel, cobalt, iron; and also of those salts of the alkaliearth metals which are precipitated by aminonia fiorom their solution in hydrochloric acid: Phosphates, borates, oxa!ates, silicates, and fluorides, ~ 187.......................... 288 Separation and detection of the metals of Group II., which are precipitated by ammonium carbonate in presence of ammonium chloride: Barium, strontium, calcium, ~ 188....................... 296 Examination for magnesium, ~ 189..................... 298 Examination for potassitum and sodium, ~ 190.................... 299 Examination for ammonium, ~ 191............................ 299

Page  XI CONTENTS. Xi PAGX A. ]. Substances soluble in water. Detection of acids. I. In the absence of organic acids, ~ 192......................... 300 II. In presence of organic acids, ~ 193......................... 303 A. 2. Substances insoluble in water, but soluble in hydrochloric acid, nitric acid, or nitrohydrochloric acid. Detection of acids. I. In the absence of organic acids, ~ 194........................ 306 II. In presence of organic acids, ~ 195.................. 307 B. Substances insoluble or sparingly soluble both in water and acids. Detection of the bases, acids, and non-metallic elements, ~ 196... 308 SECTION II. PRACTICAL COURSE IN PARTICULAR CASES. I. Special method of effecting the analysis of cyanides, ferrocyanides, etc., insoluble in water, ~ 197............................... 312 II. Analysis of silicates, ~ 198................................. 314 A. Silicates decomposable by acids, ~ 199....................... 315 a. Decomposable by hydrochloric or nitric ac id. b. Decomposable by concentrated sulphuric acid. B. Silicates whic(h are not decomposed by acids, ~ 200............ 317 C. Silicates which are partially decomposed by acids, ~ 201........ 319 III. Analysis of natural waters, ~ 202............................. 319 A. Analysis of potable waters, ~ 203............................ 320 B. Analysis of mineral iwaters, ~ 204............................ 324 1. Examination of the water. a. Operations at the spring, ~ 205............................. 324 b. Operations in the laboratory, ~ 206.......................... 325 2. Examination of the sinter deposit, ~ 207............ 330 IV. Analysis of soils, ~ 208...................................... 333 1. Preparation and examination of the aqueous extract, ~ 209...... 334 2. Preparation and examination of the acid extract, ~ 210.......... 336 3. Examination of the inorganic constituents insoluble in water and acids, ~ 211.............................................. -337 4. Examination of the organic constituents of the soil, ~ 212...... 337 V. Detection of inorganic substances in presence of organic substances, ~ 213.............................................. 338 1. Genleral rules for the detection of inorganic substances inl presence of organic matters, ~ 214.............................. 338 2. Detection of inorganic poisons in articles of food, in dead bodies, etc., ~ 215................................................ 341 Toxical analysis. I. Detection of arsenic, ~ 216.................................... 342 A. Detection of undissolved arsenious oxide..................... 343 B. Detection of soluble arsenical and other metallic compounds, by means of dialysis, ~ 217................................... 343 C. Method for the detection of arsenic in whatever form, its quantitative determination and detection of other metallic poisons, ~ 218............................................ 345 11. Detection of hjdrocyanic acid, ~ 219.......................... 353 III. Detection of phosphorus, ~ 220............................. 355 3. Examination of the inorganic constituents of plants, animals, or parts of the same, of manures, etc. (analysis of ashes), ~ 221... 361

Page  XII CONTENTS. PAGR A. Preparation of the ash.................................... 361 B. Examination of the ash................................... 362 a. Examination of the part soluble in water................... 362 b. Examination of the part soluble in hydi ochloric acid.......... 363 c. Examination of the residue insoluble in hydrochloric acid...... 364 SECTION III. EXPLANATORY NOTES AND ADDITIONS TO TIE SYSTEMATIC COURSE OF ANALYSIS. I. Additional remarks to the preliminary examination. To ~~ 175-178. 365 II. Additional remarks to the solution of substances, &c. To ~~ 179181.................................................... 366 III. Additional remarks to the actual examination. To ~~ 182-196. A. General reviJw and explanation of the analytical course. a. Detection of the metals................................... 368 b. Detection of the acids........ 371 B. Special remarks and additions to the systematic course of analysis. To ~ 182... 374 ~~ 183 and 184..................................... 376 ~ 18.................................................. 378 ~ 186.378 187............................................ 379 ~~ 188 —191......................38............. 380 ~ 196.................................................. 381 ~ 197.................................................. 381 APPENDIX. L. Deportment of the most important medicinal alkaloids with reagents, and systematic method of effecting the detection of these substances, ~ 222....................................................... 384 A. General reagents for alkaloids, ~ 223................ 384 B. Reactions of individual alkaloids............................. 387 I. Volatile alkaloids. 1. Nicotin, ~ 224..................................... 387 2. Conin, ~ 225.................................... 389 II. Non-volatile alkaloids. FIRST GROUP. Iorphin, ~ 226........................................... 390 SECOND GROUP. a. Narcotin, ~ 227............................................ 394 b. Quinin, ~ 228.......................................... 395 c. Cinchonin, ~ 229................................... 397 Recapitulation and remarks, ~ 230.......................... 398 THIRD GRO UP. a. Strychnin, ~ 231........................................... 399 b. Brucin, ~ 232............................................. 402 c. Veratrin, ~ 233........................... 03 d. Atropin, ~ 234.................................. 405

Page  XIII CONTENTS. xl11 PAGA Recapitulation and remarks, ~ 235.......... 406 C. Reactions of non-azotized bodies, allied to alkaloids. a. Salicin, ~ 236.......................................... 406 b. D'gitalin, ~ 237.......................................... 407 c. Picrotoxin, ~ 238......................................... 408 Systematic course for the detection of allkaloids: and of salicin, digitalin, and picrotoxin. L Detection of the non-volatile alkaloids, &c.. in solutions supposed to contain only one of these substances, ~ 239.... 409 II. Detection of the non-volatile, alkaloids. &c., in solutions supposed to contain several or all of these substances, ~ 240............ 411 III. Detection of alkaloids and of digitalin and picrotoxin in presence of coloring and extractive vegetable or animal matters...... 414 1. STAS'S method of detecting poisonous alkaloids (also digitalin and picrotoxin), modified by OTTO, ~ 241.......................... 414 2. Methods of detecting strychnin, based upon the use of chloroform, ~ 242..............................418 3. Method of detecting strychnin in beer, by GRAHAM and HIOFFMANN, ~ 243..................................................... 419 4. Separation by dialysis, ~ 244................................ 420 II. General plan of the order in which substan-lces should be analyzed for practice, ~ 245....................................... 420 III. Arrangement of the results of analysis performed for practice, ~ 246............................. 422 IV. Table of the solubility of compounds, ~ 247............425-426 V. Analytical tables, ~ 248.................................... 428 INDEX........................................................ 435

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Page  1 PART I. INTRO DUCTORY. PIRELIMINARIY RtEIARlKS. ANALYTICAL chemistry is divided into two branches-vi:.. qualitative analysis, which studies the nture and properties of the component parts of bodies; and quantitGCtivw analysis, which ascertains the qucantity of every individual elemlent present. The office of qualitative analysis is to exhibit the constituent parts of a substance of unknown, composition in forms of tknown composition, from which the constitution of the body examined, and the presence of its several component elements, may be positively inferred. The efficiency of its method depends upon two conditions-viz., it must attain the object in view with unerring certainty, and in the most expeditious nmanner. The object of quantitative analysis, on the other hand, is to exhibit the elements revealed by the qualitative investigation in forms *Which will permit the most accurate estimate of their weight, or to effect by other means the determination of their quantity. The study of qualitative analysis must be pursued separately from that of quantitative analysis, and must naturally precede it. For a successful pursuit of qualitative investigations, it is absolutely indispensable that the student should possess some knowledge of the chemical elements, and of their most impori taut combinations, as well as of the principles of chemistry in general; and that he should combine with this knowledge some readiness in the apprehension of chemical processes. The practical part of this science demands, moreover, strict order, great neatness, and a certain skill in manipulation. If the student joins to these qualifications the habit of invariably ascribing the failures with which he may happen to meet, to some error or defect in his operations, or, in other words, to the absencei of some condition indispensable to the success of the experimnent-and a firm reliance on the immutability of the laws of nature cannot fail to create this habit-he possesses every requisite to render his study of analytical chemistry successful.

Page  2 2 PRELIIINARY REJMARKS. AlthougE chemical analysis is based on general chemistry, and cannot be cultivated without some knowledge of the latter, yet, on the other hand, we have to look upon it as one of the main pillars upon which the entire structure of the science rests; since it is of almost equal importance for all branches of theoretical as well as of practical chemistry. This consideration would be sufficient reason to recommend a thorough stady of this branch of science, even if its cultivation lacked those attractions which it possesses for every one whllo devotes himself ardently to it. The mind is constantly striving for the attainment of truth; it delights in the solution of )roblems; and where do we meet with a greater variety of them, more or less difficult of solution, than in the province of chemistry? but as a problem to which, after long pondering, we fail to discover the key, wearies and discourages the mind: so do chemical investigations, if the object in view be not attained-if the results do not bear the stamp of unerring certainty. A half-knowledge is, therefore, to be considered worse than no knowledge at all; and a su}perJfcial cultivation of chemical analysis is to be particularly guarded against. A qualitative investigation may be made with a twofold view —viz., either, 1st, to prove that a certain body is or is not contained in a substance, e.g. lead in wine; or, 2d, to ascertain all the constituents of a chemical compound or mixture. Any substance whatever may of course become the object of a chemical analysis. In this work, those bodies which are most important in practical chemistry, from their wide distribution and their uses in medicine and the arts, are treated of in full detail; while, to facilitate the beginner's progress, the rarer elements are noticed more briefly, and in such a manner that they may be separately studied. The study of qualitative analysis is most properly divided into four principal parts-viz.: 1. CHIIEMICAL OPERATIONS. 2. REAGENTS AND THEIR USES. 3. DEPORTMENT OF THE VARIOUS BODIES WITH REAGENTS. 4. SYSTEMATIC COURSE OF QUALITATIVE ANALYSIS. It will be readily understood that the pursuit of chemical analysis requires practical skill and ability, as well as theoretical knowledge; and that mere speculative study can as little lead to success as purely empirical experiments. To attain the desired end, theory and practice must be judiciously combined.

Page  3 ~ 1, 2.1 SOLUTION. 3 SECTION I. OPERATIONS. ~ 1. THE operations of analytical chemistry are essentially the same as those of synthetical chemistry, though modified to a certain extent to adapt them to the different object in view, and to the small quantities operated upon in analytical investigations. The following are the principal operations in qualitative analysis. ~ 2. 1. SOLUTION. The term "solution," in its widest sense, denotes the union of a body, whether gaseous, liquid, or solid, with a fluid, resulting in a homogeneous liquid. When the substance dissolved is gaseous, the term "1 absorption" is more properly made use of; and the solution of one fluid in another is more generally called a mixture. The term solution, in its more usual sense, means the union of a solid body with a liquid. A solution is the more readily effected the more minutely the body to be dissolved is divided. The fluid by means of which the solution is effected, is the solvent. We call the solution chemical, where the solvent enters into chemical combination with the substance dissolved; simnple, where no definite combination takes place. In a simple solution the dissolved body is supposed to exist in the free state, and to retain all its original properties, except those dependent on its form and cohesion; since it separates unaltered when the solvent is withdrawn. Common salt dissolved in water is a familiar instance of a simple solution. The salt imparts its peculiar taste to the liquid. On evaporating the water, the salt is left behind in its original form. A simple solution is called saturated when the solvent contains all it can hold of the dissolved substance. But as fluids generally dissolve larger quantities of a substance the higher their temperature, the term saturated, as applied to simple solutions, is only relative, and refers invariably to a certain temperature. As a general rule, elevation of temperature facilitates and accelerates simple solution. This rule has but few exceptions. A chemical solution contains the dissolved substance not in

Page  4 4 OPERATIONS. [~ 2. the same state nor possessed of the same properties as before; the dissolved body is intimately combined with the solvent, which latter also has lost its original properties; a new substance has thus been producedi, and the solution, therefore, manifests the properties of this new substance. A chemical solution also may be usually acceleratecl by elevation of temperature, since heat generally promotes the action of bodies upon each other. But the _quantity of the dissolved body remains always the same in proportion to a given quantity of the solvent, the combining proportions of substances being invariable, and independent of the gradations of temperature. The reason of this is, that in a chemical solution the solvent and the body upon which it acts, have, more or less, opposite properties, which tend to neutralize each other. Solution ceases as soon as this tendency is satisfied. The solution is in this case also said to be saturated, or, more properly, neutralized, and the point which denotes it to be so is termed the point of saturation or neutralization. The substances which produce chemical solutions are, in most cases, either acids or alkalies. With few exceptions, they have first to be converted to the fluid state by means of a simple solvent. When the opposite properties of acid and base are mutually neutralized, and the new compound is formed, the actual transition to the fluid state will ensue only if the new compound possesses the property of forming a simple solution with the liquid present; e.g. when solution of acetic acid in water is brought into contact with lead oxide, there ensues, first, a chemical combination between the acid and the oxide, and then a simple solution of the new-formed lead acetate, in the water present. In pharmacy, solutions are often made in a mortar by triturating the body to be dissolved with the solvent added gradually in small quantities at a time; in chemical laboratories solutions are rarely made in this manner, but generally by digesting or heating the substance to be dissolved with the fluid in belaker-glasses, flasks, test-tubes, or capsules. In the preparation of chemical solutions, the best way generally is to mix the body to be dissolved in the first place with water (or with Mwhatever other indifferent fluid may happen to be used), and then gradually add the chemical agent. By this course of proceeding a large excess of the latter is avoided, an over-energetic action guarded against, the process greatly facilitated, and complete solution ensured, which is a matter of some importance, as it will not seldom happen in chemical combinations that the product formed refuses to dissolve if an excess of the chemical solvent is present; in which case the molecules first formed of the new salt, being insoluble in the menstruum present, gather round and enclose the portion still unacted on, weakening thereby or preventing altogether further chemical action upon

Page  5 ~;.] CRYSTA:LLIZATION. 5 them. Thus, for instance, Witherite (barium carbonate) dissolves readily when, after being reduced to powder, water is poured upon it, and hydrochloric acid gradually added; but it dissolves with difficulty and imperfectly when projected into a concentrated solution of hydrochloric acid in water, for barium chloride will indeed dissolve in water, but not in hydrochloric acid. CRYSTALLIZATION and PRECIPITATION are the reverse of solution, since they have for their object the conversion of a fluid or dissolved substance to the solid state. As both generally depend on the same cause, viz., on the absence of a solvent, it is impossible to assign exact limits to either; in many cases.they merge into one another. We must, however, consider them separately here, as they differ essentially in their extreme forms, and as the special objects which we purpose to attain by their application are generally very different. ~ 3. 2. CRYSTALLIZATION. We understand by the term crystallization, in a more general sense, every operation, or process, whereby bodies are made to pass from the fluid to the solid state, and to assume certain fixed, mathematically definable, regular forms. But as these forms, which we call crystals, are usually the more regular, anda consequently the more perfect, the more slowly the operations is carried on, we commonly connect with the term " crystallization" the accessory idea of a slow separation-of a graCdual conversion to the solid state. The formation of crystals depends on the regular arrangement of the constituent particles of bodies (molecules); it can only take place, therefore, if these molecules possess perfect freedom of motion, and thus, in general, only when a substance passes from the fluid or gaseous to the solid state. Those instances in which the mere ignition, olr the softening or moistening of a solid body, suffices to mlakethe tendency of the molecules to a regular arrangement (crystallization) prevail over the diminished force of cohesion — such as, for instance, the turning white and opaque of moistened barley-sugar-are to be regarded as exceptional cases. To induce crystallization, the causes of the fluid or gaseous form of a substance must be removed. These causes are either heat alone, e.g., in the case of fused metals; or solvents alone, as in the case of an aqueous solution of common salt; or both combined, as in the case of a hot saturated solution of potas. sium nitrate in water. In the first case we obtain crystals by

Page  6 6 OPERATIONS. [~ 4 cooling the fused mass; in the second, by evaporating off the inenstruum; and in the third, by either of these means. The imost frequently occurring case is that of crystallization by cooling hot saturated solutions. The liquors which remain after the separation of the crystals are called mother-liquors. The term amo2phous is applied to such solid bodies as have no crystalline form. WVe have recourse to crystallization generally either to obtain the crystallized substance in a solid form, or to separate it from other substances dissolved in the same menstruum. In many cases also the form of the crystals or their deportment in the air, viz., whether they remain unaltered or effloresce, or deliquesce, upon exposure to the air, will afford an excellent means of distinguishing between bodies otherwise resembling each other; for instance, between sodium sulphate and potassium sulphate. The process of crystallization is usually effected in dishes, or, in the case of very small quantities, in watch-glasses, or finally in microscopic work, on slips or slides of thin plain glass. Where the quantity of fluid to be operated upon is small, the surest way of getting well-formed crystals is to let the fluid evaporate in the air, or, better, under a bell-glass, over an open vessel half-filled with concentrated sulphuric acid. Minute crystals are examined best with a lens or microscope. ~4. 3. PRECIPITATION. This operation differs from the preceding one in that the dissolved body is suddcenly converted to the solid state, no matter whether the substance separating is crystalline or amorphous, whether it sinks to the bottom of the vessel, or ascends, or remains suspended in the liquid. Precipitation is either caused by a modification of the solvent-thus calcium sulphate (gypsum) separates immediately from its solution in water upon the addition of alcohol; or it ensues in consequence of the separation of an educt insoluble in the menstruum-thus when ammonia is added to a solution of aluminium sulphate, the latter salt is decomposed, and aluminium hydroxide, not being, soluble in water, precipitates. Precipitation takes place also when new compounds (products) are formed which are insoluble in the mnenstruum; thus calcium oxalate precipitates lupon adding oxalic acid to a solution of calciumn acetate; lead chromate, upon mixing potassium chromate with lead nitrate. In exchanges of this kind, one of the products remains generally in solution, and the same is sometimes the case also with the educt; thus, in the instances just mentioned, the amlilonium sulphate, the acetic acid, and the potassium nitrate remain iu

Page  7 ~ 5.] FILTRATION. 7 solution. It may, however, happen also that both the product and the educt, or two products, precipitate, and that nothing remains in solution; this is the case, for instance, when a solution of magnesium sulphate is mixed with water of baryta, or whllen a solution of silver sulphate is precipitated with barium chloride. Precipitation is resorted to for the same purposes as crystallization, viz., either to obtain a substance in the solid form, or to separate it from other dissolved substances. But in qualitative analysis we have recourse to this operation more particularly for the purpose of detecting and distinguishing substances by the color, properties, and general deportment which they exhibit when precipitated either in an isolated state or in comnbination with other substances. The solid body separated by this process is called the precipitate, and the substance whicll acts as the immediate cause of the separation is termed theprecipitant. Various terms are applied to precipitates by way of particularizing them according to their different nature; thus we distinguish crystalline, pulverulent, flocculent, curdy, gelatinous precipitates, etc. The terms turbid, turbidity, or cloudy and cloudiness, are made use of to designate the state of a fluid which contains a precipitate so finely divided and so inconsiderable in amount, that the suspended particles, although impairing the transparency of the fluid, yet cannot be clearly distinguished. The separation of floceulent precipitates may generally be promoted by vigorous shaking; that of crystalline precipitates, by stirring the fluid and rubbing the sides of the vessel with a glass rod; elevation of temperature is also an effective means of prom-oting the separation of most precipitates. The process is conducted, according to circumstances, either in test-tubes, flasks, or beakers. The two operations described respectively in ~ 5a and 6, viz., FILTRATION and DECANTATION, serve to effect the mechanical separation of fluids from matter suspended therein. ~ 5. FILTRATION. This operation consists simply in passing the fluid, fromn which we wish to remove the solid particles mechanically susended therein, through a filtering apparatus, formed usually y a properly arranged piece of unsized paper placed in a glass funnel; an apparatus of this description allows the fluid to trickle through, whilst it retains the solid particles. We eran

Page  8 8 oPERATIONS. [~ 5. ploy smooth filters and plcaited filters; the former in cases where the separated solid substance is to be made use of, the latter in cases where it is wished to clear the solution rapidly. [Smooth filters are prepared by folding a circular piece of filter paper first into halves, and then into quarters; then opening it out into a conicai cu-p w-ith three thicknesses on one side, and one on the other. In filtering, the filter should be opened, and pressed well down into the funnel so as to fit it closely. Piaited filters are folded, as just described, into eighths, the folds all being mlade on the saie side of the paper. Then each division is folded again upon itself on the opposite side of tile paper; but to avoid breaking the latter, the folds should not reach quite to the centre. At this stage the filter has the appearance of a paper fan when shut. It is carefully opened out into a ribbed cone, pressed into the funnel, and evenly mloistened from the vertex upwards, by aid of a gentle stream of water from the washingbottle, Fig. 4.-EDITOR.] In cases where the contents of the filter require washing, the pa-per must not project over the rim of the funnel. It isin nmost cases advisable to moisten the filter previously to passing the fluid throug. h it; since this not only tends to accelerate the process, but also renders the solid particles less liable to be carried through the pores of the filter. The paper selected for filters must be as free as possible from inorganic substances, especially such as are dissolved hy acids, e.g., calcium and iron compounds. The common filtering paper of commerce seldom comes up to our wants in this respect, and I would therefore always recommend to wash it carefully with dilute hydrochloric,1,n hacid whenever it is intended N1 for use in accurate aalyzases. For this purpose the apparatus a_ a shown in Fig. 1 will be found convenient. A is a bottle with the bottom out; a and b are glass pllates: between them lie the filters which have been previously cut and folded; d is a glass tube fitted into the cork c; e is a piece of flexible tube, which is closed by a piece of glass rod or a clip. The bottle is filled with a mixture of one part hydrochloric acid sp. gr. 1.12 and two parts water, in which the filters are allowed to soak twelve hours, the acid being then run off and rep]aced _____ ______=_ by ordinary water. After an hour this is replaced by fresh _-_ _ _, water, and so on till the wash__________=__ - ings are barely acid. The washing is continued with dis______ _______________ - tilled water till the washings are free from liydrochloric acid FIG. 1. — that is, till they cease to give any turbidity when mixed with a few drops of solution of silver nitrate. Finally, the filters are drained, turned out upon blotting-paper, covered with the same, and dried in a

Page  9 . 5.] FILTRATION. 9 sieve in a warm place. When we merely want to wash two or three filters, we place them in a funnel, as in filtering, one inside the other, moisten them with dilute hydrochloric or nitric acid, and after some time wash them wvell with distilled water. Filteringt -paper, to be considered good, must, besides being pure, also let fluids pass readily through; whilst yet completely retaining even the finest pulverulent precipitates, such as barium sulphate, calcli.m oxalate, etc. If a paper satisfying these requirements cannot be readily procured, it is advisable to keep two sorts, one of greater density for the separation of very finely divided precipitates, and one of greater porosity _ for the speedy separation of grosser particles. The stand shown in Fig. 2 FIG. 2. is adapted for supporting the smallsized funnels used in qualitative analyses. Funnels are also often sustained in the mouths of flasks, test-tubes, or narrow beakers. [Rapid Filtration, as made practical by BUNSEN, is described in the American Edition of Fresenius' Quantitative Analysis, pp. 66, 80. When hydrant water under high C! / pressure is at hand, the most efficient and cheapest exhausting apparatus is the Jet Aspirator perfected by RIcHARDS. * With water of low head, the JAGN pump t renders good service.-ED.] A very simple and, for many i purposes, sufficient apparatus is that of WEIL, the operation of which is:evident from Fig. 3. The prolong of the tube, A, may be one or several feet long. Its lower extremity being dipped in'water, the liquid is lifted to the fI' funnel by mouth-suction applied at the horizontal tube. The clamp, c, being then closed, the columni remains until the filter is emnpty, or until air passes it. The filter, d, blav be strengthened if needful' by being placed within a smaller one, a. FIG. 3. * Am. Jour. Sci. [3] VIII. p. 412. t Thorpe's Quant. Analysis, p. 61, and (Foote's Modification) Am. Jour. Bci. [31 VI. p. 360.

Page  10 10 OPERATIONS. [~~ 6, 7.. 6. 5. DECANTATION. This operation is frequently resorted to instead of filtration, in cases where the solid particles to be removed are of considerably greater specific gravity than the liquid in which they are. suspended; as they will in such cases speedily subside to the bottom, thereby rendering it easy either to decant the supernatant fluid by simply inclining the vessel, or to draw it off by means of a syphon or pipette. Certain slimy or gelatinous precipitates so clog the pores of paper as scarcely to admit of filtration. To obtain the liquid in which they have been formed quite clear, decantation is indispensable. Oftentimes the two processes may be advantageously combined by allowing the precipitate to settle as much as possible, and pouring off the still turbid liquid upon a filter. ~ 7. 6. WASHING. When filtration or decantation has been resorted to for the purpose of collecting a solid substance, the latter has to be freed afterward from the adhering liquid by repeated washing or edulcoration. The washing of precipitates collected on a filter is usually effected by means of a washing-bottle, such as shown in Fig. 4. This consists of a flask or bottle, closed with a twice-perforated, snuglzy-fitting rubber stopper, through which pass two glass tubes, as in the figure. The outer end of the tube, a, is drawn to a moderately fine point. By blowing into the other tube, a stream of water is driven out from a with considerable force, which adapts the apparatus to removing precipitates fronm the sides of vessels as well as to washing them on filters. This form of washingbottle serves for edulcoration with warm or even boiling water, provided the vessel itself has a uniformly thin bottom, so that it can be heated without fear of breaking. By binding about the neck a ring of cork, or A =_____ winding it closely with smooth cord, it umay be - handled with convenience when its contents are hot. [By cutting the exit tube at a, and, after FIG. 4. rounding their ends by fusion, uniting the two pieces with a bit of black rubber connector, the operator has it in his power to direct the outgoing stream upwards, oi

Page  11 ~ 8.] DIALYSIS. 11 otherwise as he may desire, by applying the forefinger to the base of the movable portion. By a similar device, that part of the exit tube -which enters the flask may be made flexible, so that the lower end shall remahi, immersed until all the water is expelled.-EnD.] As the success of an analysis often depends upon the complete or proper washing of a precipitate, the operator must accustom himself to continue the process patiently until he is certain that the object in view has been actually accomplished. In general, this is not the case until the precipitate has been perfectly freed from the liquor in which it was formed. The analyst must not be content to guess that a precipitate is thoroughly washed, but must prove that it is so, by applying appropriate tests, until experience enables him to know how long to continue the process in any given case. If the body to be removed is non-volatile, slow evaporation of a few drops of the last portions of the washings on a clean surface of glass or platinum'will usually serve to indicate the point at which the process may terminate. ~ 8. 7. DIaLYsIs. Dialysis is an operation which may be employed for certain separations, and depends upon the different behavior of bodies dissolved in water towards moist membranes. Bodies that are able to crystallize (crystalloids, GRAHAM) have the power of penetrating suitable membranes with which their solution may be placed in contact, whilst amorphous bodies, or colloids, viz., gumn, gelatin, starch, albumin, silicic acid, etc., do not possess that property. Hence the two classes may be separated by taking advantage of this action. The septum must consist of a colloid ratus for this operation. In Fig 5, the dialyser consists of the top of a bottle closed below with parchment paper; in Fig. 6, it consists of a gutta-percha hoop covered like __ a sieve with parchment-paper. 14 The disk of parchment-paper used -- slhlould measure three or four inches in ___-___________diameter more than the space to be covcred; it is moistened, stretched over and FIG. 5. fastened by a string or by an elastic band, but it should not be secured too firmly. The parchment-paper must

Page  12 12 OPEIZATIONS. [~ 9. not be porous; its soundness may b1 tested by sponging the upper side with water, andl observing whether w-et spots show on the other side. Defects may be remedied by applying liquid albumin and coagulating this by heat. [As MIoni suggests, the parchment paper may also be made into a plaited filter (~ 5), which, being supported in a funnel, is, with the latter, immersed in water contained in a beaker to the required depth. - -ED.] When the dialyser has thus been got ready, the mass to be examined is 111T ~ poured into it. The depth of fluid in —:____i_::: ___~ the dialysers above figured should not be more than half _________________ =- an inch, and the FIG. 6. membrane should.dip a little way below the surface of the water in the outer vessel, which should amount to at least four times the quantity of the fluid to be dialysed. [Mohr's dialyser may, of course, stand nearly its full depth in water.] After twenty-four hours, half or three-fourths of the crystalloids will be found in the external water, while the colloids remain in the dialyser-at most only traces pass into the external fluid. If the dialyser is'brought successively in contact with fresh supplies of water, the whole of the crystalloids may be finally separated from the colloids. This operation is sometimes of service in chemico-legal investigations for the extraction of poisonous crystalloids from parts of a dead body, food, vomit, etc. There are four operations which serve to separate volatile substances from less volatile or from fixed bodies, viz., EVAPORA.TION, DISTILLATION, IGNITION, and SUBLIMATION. ~ 9. 8. EVAPORATION. This operation, serves to separate volatile fluids from less volatile or from fixed bodies (solid or fluid), in cases where the residuary substance alone is of importance; thus we have re

Page  13 ~ 9.] EVAPORATIO. 13 course to evaporation for the purpose of removing from a saline solution part of the water, in order to bring about crystallization of the salt; also for removing the whole of the water from the solution of a non-crystallizable substance, so as to obtain the latter in a solid form, etc. The evaporated water is disregarded in these cases, the only object being to obtain in the one case a more concentrated fluid, and in the other a dry substance. These objects are attained by converting the fluid which is to be removed, to the gaseous state. This is generally done by the application of heat; sometimes by leaving the fluid for a time in contact with the atmosphere, or with an enclosed volume of air kept dry by hygroscopic substances, such as concentrated sulphuric acid, calcium chloride, etc.; or, lastly, by placing the fluid in rarefied air, with simultaneous application of hygroscopic substances. As it is of the utmost importance in qualitative analyses to guard against the least contamination, and as an evaporating fluid is the more liable to this the longer the operation lasts, the process is usually conducted with proper expedition, in porcelain or platinum dishes, over the flame of a spirit or gas lamp, in a place free from dust, preferably in a cuplboard or hood provided with a draught. If the operator has no place of the kind, he must have recourse to covering the dish; the best way of doing this is to place over the dish a large glass funnel secured by a retort-holder, in a manner to leave sufficient space between the rim of the funnel and the border of the dish; the funnel is placed slightly aslant, that the drops running down its sides may be received in a beaker. Or the dish may also be covered -with a sheet of filter-paper previously freed from inorganic substances by washing with dilute hydrochloric or nitric acid (see ~ 5); were common and unwashed filter-paper used for the purpose, the ferric oxide, lime, etc., contained in it would dissolve in the vapors evolved (more especially if acid), and the solution dripping down into the evaporating fluid would speedily contaminate it. These precautions are necessary, of course, only in Ad accurate analyses. Large quantities of fluid are evaporated best in flasks standing aslant, covered with a cap of pure filtering-paper, over a charcoal fire or gas; or also in tubulated retorts with "ic;: rising obliquely upward, and open tubulure. Evaporating processes at 100~ are con- FIG. 7. ducted in a suitable steam apparatus, or on the -ater-bath shown in Fig. 7. Evaporation to dryness is not usually conducted over the naked flame, but generally either on the water-bath or the sand-bath, or on an iron plate. It should be remembered that porcelain and glass vesselswhich we can hardly avoid using for the evaporation of large quantities of fluids-are always somewhat acted upon so that their contents become more or less contaminated. This action is but slight in case of most dilute acids or acid liquids, but the student should never evaporate alkaline fluids in glass, as al a boiling temperature they attack it considerably.

Page  14 14 OPERATIONS. [~~ 10, 11 ~ 10. 9. DISTILLATION. This operation serves to separate a volatile liquid from a less volatile or a non-volatile substance, where the object is to re cover the evaporating fluid. A distilling apparatus consists of three parts: 1st, a vessel in which the liquid to be distilled is heated, and thus converted into vapor; 2d, an apparatus in _ FrG. 8. which this vapor is cooled again or condensed, and thus reconverted to the fluid state; and 3d, a vessel to receive the fluid thus reproduced by the condensation of the vapor (the distillate). For the distillation of large quantities metallic apparatus are used (copper stills with head an4d condenser of tin), or large glass retorts; in analytical investigations we either use small retorts with receivers, or more usually an apparatus such as is shown in Fig. 8. The fluid to be distilled is boiled in A, and the vapor escapes through the tube which is fitted into the cork. The tube is surrounded with a wider tube which is filled with cold water, and is renewed continually or occasionally by pouring in through d, after placing a vessel under g to catch the hot water which will run out. A small flask serves as a receiver. ~ 11. 10. IGNITION. Ignition is, in a certain sense, for solid bodies what evaporation is to fluids; since it serves (at least generally) to separate

Page  15 ~~ 12, 13.] FUSION AND FLUXING. 15 volatile substances from less volatile or from fixed bodies in cases where the residuary substance alone is of importance. In some instances, substances are ignited simply for the purpose of modifying their state, without any volatilization taking place; thus chromic oxide is converted by ignition into the inso)uble modification, etc. Substances are often ignited also, that the operator may from their deportment at a red heat draw a conclusion as to their nature in general, their fixity, their fusibility, the presence or absence of organic matter, etc. Crucibles are the vessels generally made use of in ignition. In operations on a large scale, Hessian or black-lead crucibles are used, heated by charcoal or gas; in analytical. experiments small-sized.crucibles or dishes are selected, of porcelain, platinum, silver, or iron, or glass tubes sealed at one end, according to the nature of the substances to be ignited; these crucibles, dishes, or tubes are heated over a spirit or gas lamp, or a bellows blowpipe. ~ 12. 11. SUBLIMATION. The term sunimation designates the process which serves to convert solid bodies into vapor by the application of heat, and subsequently to recondense the vapor to the solid state by refrigeration;-the substance volatilized and recondensed is called a sublimate. Sublimation is consequently a distillation of solid bodies. We have recourse to this process mostly to effect the separation of substances possessed of different degrees of volatility. In sublimations'for analytical purposes we generally employ sealed glass tubes. When the sublimation is performed with the aid of a current of hydrogen or carbon-dioxide we use open glass tubes, which are usually made narrower just behind the part to which the heat is applied. ~ 13. 12. FUSION AND FLUXING. Simple fusion is the conversion of a solid substance into the fluid form by the application of heat; it is most frequently resorted to for the purpose of effecting the combination or the decomposition of bodies. The term is also applied in cases where substances insoluble or difficult of solution in water and acids are by fusion in conjunction with some other body modified, decomposed, or fluxed in such a manner that they or the new-formed compounds will subsequently dissolve in water or acids. Fusion is conducted either in porcelain, silver, or plat.

Page  16 16 OPERATI:ONS. [~ 14. inium crucibles. The crucible is supported on a triangle of moderately stout platinum wire, resting on, or attached to, the iron ring of the spirit or gas lamp. Triangles of thick iron wire, especially when laid upon the stouter brass ring of the lamp, carry off too much heat to allow of the production of very high temperatures. Small quantities of matter are also often fused in glass tubes sealed at one end. Resort to fusion is especially required for the analysis of various insoluble sulphates, silicates, and aluminium compounds. The flux most commonly used is sodium carbonate. In certain cases a mixture of calcium carbonate and alnmonium chloride is employed. For the fusion of aluminates, sodium disulphate is frequently used. A platinum crucible is used for the fusion in all these cases just narned. Precautionary rules for the prevention of damage to platinum vessels. -No substance evolving chlorine ought to be treated in platinum vessels; no sodiuml or potassium nitrate or hydroxide or cyanide, no metals, or sulphides of metals, should be fused in'such vessels; nor should readily (leoxidizable metallic oxides or organic salts of the heavy metals be ignited in them, or phosphates in presence of organic compounds. It is also detrimental to platinum crucil)les, and especially to their covers, to expose them direct to an intense charcoal fire, as the action of the ash is likely to lead to tile formation of platinum silicide, which renders the vessel brittle. It is always advisable to support platinum crucibles used in ignition or fusion on triangles of platinum wire. When a platinum crucible has been made white hot over the bellows blowpipe, it is unwise to cool it too quickly by suddenly turning off the gas, and allowing the cold blast to play upon it, since the crucible is under these circumstances very liable to become slightly cracked. [When platinum vessels are ignited in the inner blue gas flame, they are liable to assume a dull and soiled aspect externally, and after prolonged use often become cracked with rifts, that at first are scarcely perceptible, but shortly extend so as to ruin the vessel. This detriment is prevented, and generally most kinds of stains may be removed from platinum apparatus by gently rubbing the surface with wet sea-sand as often as thee lustre is impaired. The grains of sand must be polished and free from sharp angles. By the proper use of sand of good quality, the metal is not scoured, but lburnished.-ED.] If the stains or impurities in a platinum dish resist this treatment, sodium disulphate or borax should be heated in it to fusion for some time. The vessel is then cleaned with hot water, and finally, if needful, is burnished with sand as above described. ~ 14. 13. DEFLAGRATION. We understand by the term de fagration, in a more general sense, every process of decomposition attended with noise or detonation. We uce the same term, however, in a more restricted sense, to designate the oxidation of a substance in the

Page  17 ~ 15.] THE USE OF THE BLOWPIPE. 17 dry way, at the expense of the oxygen of another substance mixed with it (usually a nitrate or a chlorate), and conuect with it the idea of a sudden combustion attended with incandescence and detonation. Deflagration is resorted to either to produce a desired bodythus arsenious sulphide is deflagrated with potassium nitrate to obtain potassium arsenate; or it is applied as a means to prove the presence or absence of a certain substance-thus salts are tested for nitric or chloric acid by fusing them with potassium cyanide, and observing whether they deflagrate, etc. To attain the former object, the perfectly dry mixture of the substance and the deflagrating agent is projected in small portions at a time into a red-hot crucible. Experiments of the latter description are invariably made with minute quantities, preferably on a piece of thin platinum foil, or in a small spoon. 15. 14. THE USE OF THE BLOWPIPE.' This operation is of paramount importance in many analytical processes. We have to examine here the apparatus required,. the mode of its application, and the results of the operation. The blowpipe, Fig. 9, is a small instrument, usually made of brass or German silver. It consists of three parts; viz., 1st, a tube, a b, fitted, for greater convenience, with a horn or ivory mouthpiece, through which air is blown from the mouth; 2d, a small cylindrical - vessel, c d, into which a b is screwed air- ~ a 7 tight, and which serves as an air-chamber and to retain the moisture of the air blown into the tube; and 3d, a smaller tube,f g, I also fitted into c d. This small tube, which forms a right angle with the larger one, is fitted at its aperture either simply with a finely perforated platinum plate, or more conveniently with a finely perforated platinum cap (h). The construction of the cap is shown in Fig. 10. It is, indeed, a little dearer than a simple plate, but it is also much more durable. If thke opening of the cap gets stopped up, the obstruction may generally be removed by heating it to redness before the blowpipe. The proper length of the blowpipe de-' pends upon the distance to which the FIG. 9. * For fuller details of the use of the Blowpipe, see BRUSH'S Determinative Mineralogy. 2

Page  18 18 OPERATIONS. [~ 15. operator can see with distin tness: it is usually from eight to ten inches. The form of the mouthpiece varies. Some enlemists like it of a shape to be encircled by the lips; others prefer' the form of a trumpet mouthpiece, which is only pressed against the lips. The latter requires less exertion on the part of the operator, and is accordingly generally chosen by those who have a great deal of blowpipe work.;l"'i 9Ni~ The blowpipe serves to conduct a continuous fine current of air into a gas-flame, or into the flame of a candle or lamp. The flame of a candle or lamp, burning under ordinary circumstances, is seen to consist of three principal parts, as sllown in Fig. 11, viz., 1st, a dark nucleus in the centre (c); 2d, a lumi[I' V nous cone surrounding this nncleus (ef g); and 3d, FIG. 11. a feebly luminous mantle encircling the whole flame (b c d). The dark nucleus contains the gases which the heat evolves from the wax or fat, and which cannot burn hlere for want of oxygen. In the luminous cone these gases comne in contact with a certain amount of air insufficient for their complete combustion. In this part, therefore, it is principally the hvdroogen of the htydrocarbons evolved which burns, whilst the carbonl separates in a state of intense ignition, which imparts to the flame the luminous appearance observed in this cone. In the outer coat the access of air is no longer limited, and all the matter not yet burned is consumed here. This part of the flame is the hottest, and the extreme apex is the hottest point of it. Oxidizable bodies oxidize, therefore. with the greatest possible rapidity when placed in it, since all tile conditions of oxidation are here united, viz., high temperature and an unlimited supply of oxygen. This outer part of the flame is therefore called the oxidizzniyflame. On the other hand, oxides having a tendency to yield up their oxygen suffer redztction when placed within the luminous part of the flame, the oxygen being withdrawn from them by the carbon and the still unconsumed hydrocarbons there present. The luminous part of the flame is therefore called the r-ec[tcing The effect of blowing a fine stream of air across a flame is, first, to alter the shiap3 of the flame, as, froml tending upward, it is nowv driven sidewVays in the direction of the blast, being alt the samne time lengthened and narrowed; and, in the second plac, to cxtend the sphere of combustion from the outer to the innor part. As the latter circumstance causes an extraordlillary increase in the heat of the flame, and tile former a concentration of that heat within narrower limits, it is easy to understand the exceedingly energetic action of the blowpipe flame. The way of holding the blowpipe and the nature of the blast will depend upon whether the operator wants a re.

Page  19 ~ 15.] THE'USE OF THE BLOWPIPE. 1 ducing or an oxidizing flame. The easiest way oPf producing most efficient flames of both kinds is by means of coal-gas delivered from a jet, shaped as in Fig. 12, the slit being 1 FIG. 12. centimetre long, and 11 to 2 millimetres wide; as with the use of gas the operator is enabled to regulate not only the current of air, but that of the gas also. The task of keeping the blowpipe steadily in the proper position may be greatly facilitated by firmly resting that instrument upon some movable metallic support, such as, for instance, the ring of BUNSEN'S gaslamp intended for supporting dishes, &c. Fig. 12 shows the flame for reducing; Fig. 13 the flame for oxidizing. The luminous parts are shaded. FIG. 13. The reducinTg-fame is produced by keeping the jet of the blowpipe just on the border of a tolerably strong gas flame, and driving a moderate blast across it. The resulting mixture of the air with the gas is only imperfect, and there remains between the inner bluish part of the flame and the outer barely visible part a luminous and reducing zone, of which the hottest point lies somewhat beyond the apex of the inner cone. To

Page  20 20 OPERATIONS. [~ 15. produce the oxii,7zinqgfname, the gas is lowered, the jet, of the blowpipe pushed a little farther into the flame, and the strength of the current somewhat increased. This serves to effect an intimate mixture of the air and gas, and an inner pointed, bluish cone, slightly luminous towards the apex is formed, and surroundecld by a thin, pointed, light-bluish, barely visible mantle. The hottest part of the flame is at the apex of the inner cone. Difficultly fusible bodies are exposed to this part to effect their fusion; but bodies to be oxidized are held a little beyond the apex, that there may be no want of air for their combustion. An oil-lamp with broad wickl of proper thickness may be used instead of gas; a thick wax-candle also will do. For an oxidizing flame a small spirit-lamp will in most cases answer the purpose. The current is produced with the cheek muscles alone, and not with the lungs. The way of doing this may be easily acquired by practising for some time to breathe quietly with distended cheeks and with the blowpipe between the lips; with practice and patience the student will soon be able to produce an even and uninterrupted current. The sztpports on which substances are exposed to the blow pipe flame are generally either wood charcoal, or platinum wire or foil. Charcoal supports are used principally in the reduction of metallic oxides, etc., or in trying the fusibility of bodies. The substances to be operated upon are put into small cavities, scooped out with a penknife or with a little tin tube. Metals that are volatile at the heat of the reducing flame evaporate wholly or in part upon the reduction of their oxides; in passing through the outer flame the metallic fumes are re-oxidized, and the oxide formed is deposited around the portion of matter upon the support. Such deposits are called incrustations. Mlany of these exhibit characteristic colors, leading to the detection of the metals. The charcoal of pine, linden, or willow is greatly preferable to that of harder woods. Saw the thoroughlyburnt charcoal of well-seasoned and straight-split pine-wood into rectangular pieces, and brush off the dust; they may then be handled without soiling the hands. Those sides alone are used on which the annual rings are visible on the edge, as on the other sides the fused matters are apt to spread over the surface of the charcoal. Small charcoal supports are sometimes sold, which have been made from powdered charcoal, mixed with rice or starch paste, and stamped into convenient shapes-they are very handy and clean. Charcoal is so valuable a material for supports in blowpipe experiments, because of —st, its infusibility; 2d, its low conducting power for heat, which permits substances being heated more strongly upon a charcoal than upon any other support; 3d, its porosity, which makes it imbibe readily fusible substances, such as borax, sodium carbonate, etc., whilst infusible

Page  21 ~ 16.] THE USE OF LAMPS. 21 bodies remain on the surface'; 4th, its reducing powner, which greatly contributes to the reduction of oxides in the inner blowpipe flame. We use platinJum wire, and occasionally also platinum fo[l, in all oxidizing processes before the blowpipe, and also when fusing substances with fluxes, with a view to try their solubility in them, and to watch the phenomena attending the solution, and mark the color of the bead; lastly, also to introduce substances into the flame, to see whether they will color it. The wire is cut into lengths of 8 centimetres, and each length twisted FIG. 14. at both ends into a small loop (Fig. 14). When required for use, the loop is moistened with a drop of water, then dipped into the powdered flux (where a flux is used), and the portion adhering fused in the flame of a gas or spirit lamp. When the bead produced, which sticks to the loop, is cold, it is moistened again, and a small portion of the substance to be examined put on and made to adhere to it by the action of a gentle heat. The loop is then finally exposed, according to circumstances, to the inner or the outer blowpipe flame. What renders the application of the blowpipe particularly useful is the great expedition with which results are attained. These results are of a two-fold kind, viz., either they afford us simply an insight into the general properties of the body, and enable us accordingly only to determine whether it is fixed, volatile, fusible, etc.; or the phenomena which we observe enable us at once to recognize the particular body which we have before us. We shall have occasion to describe these phenomena when treating of the deportment of the different substances with reagents. Chemists have devised various forms of self-acting blowpipe apparatus, in some of which the air-current is produced by means of a gasometer, in others by means of a caoutchouc balloon, in others again by a species of hydrostatic blast, etc. Bu: the simplest self-acting apparatus, by which most of the objects attainable with the blowpipe may be conveniently accomplishled, is the Bunsen gas-lainp, provided with a chimney, which burns without luminosity and without soot. A description of this lamp follows in the next paragraph. ~ 16. 15. THE USE OF LAMPS, PARTICO1LARLY OF GAS-LAMPS. As we have to deal mostly with small quantities of matter, we commonly use in processes of qualitative analysis requiring

Page  22 22 OPERATIONS. [~ 16 the application of heat, such as evaporation, ignition, etc., either spirit-lamps or gas-lamps. Of spirit-lamps there are two kinds in use, viz., the simple spirit-lamp, as shown in Fig. 17, and the Berzelius lamp with double draught (Fig. 15). In the construction of the latter lamnp it should be borne in mind that the part containining the wickl and the vessel with the spirit must be in separate pieces connected only by means of a narrow tube; otherwise troublec somne explosions are apt to occur in lighting the lamp. Nor should the chimney be too narrow, or the stopper fit air-tight on the mouth through which the spirit is poured in. A lamp should be selected that may be readily moved up and down the pillar of the stand, which must be fitted with a movable brass ring to support dishes and flasks in processes of ebullition, and a ring of moderately stout iron wire to support the triangle for holding the crucibles in the processes of ignition and fusion. Of the various forms of lamps in use, the one shown in Fig. 15 is the most suitable. Fig. 16 shows a triangle of platinum wire fixed within an iron wire triangle: this serves to support the crucible in processes of ignition. Glass vessels, more particularly FIG. 16. FIG. 15. FIG. 17. bealers, which it is intended to heat over the lamp, are most conveniently rested on a piece of gauze made of fine iron wire such as is used in making sieves of medium fineness. Of the many gas-lcamjps proposed, BUNSEN'S, as shown in its simplest form in Figs. 18 and 19, is the most convenient. a b is a foot of cast-iron. In the centre of this is fixed a brass box, e d, which has a cylindrical cavity of 12 mm. deep, and 10 mnm. in diameter. Each side of the box has, 4 mm. from the upper

Page  23 ~ 1 6.] THE USE OF LAMPS, 2.3 rim, a circular aperture of 8 mm. diameter, leading to the inner cavity. One of the sides has fitted into it, 1 mm. below tilhe circular aperture, a brass tube, which serves for the attachment of the India-rubber supply tube. This brass tube is turned in the shape shown in Fig. 18; it has a bore of 4 mm. The gas conveyed into it re-issues from a tube in the centre of the cavity of the box. This tube, which is 4 mm. thick at the top, thicker at the lower end, projects 3 mm. above the rim of the box; the gas.issues from a narrow opening which appears formed of 3 radii of a circle, inclined to each other at an angle of 120~. The length of each radius is 1 mm.; the opening of the slit is i mmn. wide; e f is a brass tube 95 min. long, open at both ends, with a bore of 9 mm.; the screw at the lower end of this tube fits into the upper part of the cavity of the box. With this tube screwed in, the lamp is completed. On opening the h. 8.. FIG. 18. FIG. 19. stop-cock, the gas rushes into the tube e f, where it mixes with the air coming in through the circular apertures. When this mixture is kindl.d at f, it burns with a straight, upright, bluish flame, entirely free from soot, which may be regulaated at will by opening the stop-cock more or less; a partial opening of the cock suffices to give a flame fully answering the purpose of

Page  24 24 OPERATIONS. [~ 16. the common spirit-lamp; whilst with the full- stream of gas turned on, the flame, which will now rise up to 2 decimetres in heirt, affords a most excellent substitute for the Berzelius lam p. If the flame is mInde to burn very low, it will often occur that it recedes; in other words, that instead of the Imixture of gas and air burnilng at the mouth of the tube, e J; the gas takes fire on issuing from the slit, and burns below in the tube. This defect may be perfectly obviated by covering the tube, e f, at the top with a little wire-gauze cap. Flasks, etc., which it is intended to heat over the gas-lamp, are most conveniently supported on a gacmuselate-a square piece of thin iron plate to which o a piece of wire-gauze of equal size is riveted, as shown in Fig. 20. Simple wire-gauize rapidly burns through in the middle, and does not offer the same protection against the cracking of beakers or flasks. For blowpipe operations, the tube g h must be inserted into ef; this tube terminates in a slanting flattened top, and having an opening in it 1 cm. long, and 11 to 2 mm. wide. The insertion of g h h:'.'m into ef serves to close the air-holes in the.-.-...-... ii". box, and pure gas, burning with a luminous flame, issues from the top of the tube.. Fig. 19 shows the apparatus complete, fixed in the fork of an iron stand; this arrangement permits the lamp being moved backward and forward between the prongs of the fork, and up and down the pillar of FIa. 20. the stand. The movable ring on the same pillar serves to support the objects to be operated upon. The 6 radii round the tube of the lamp serve to support an iron-plate chimney (see Fig. 24), or a porcelain plate used in quantitative analyses. To heat crucibles to the brightest red..... heat, or to a white heat, the bellows Iblowpipe is resorted to. But even without this the action of the gas-lamp may be considerably heightened by heating the crucible within a small clay furnace, as recommended by ERD3MANN. Fig. 21 shows the simple contrivance -I__ - - by which this is effected. The fur_i _ naces are 115 mm. high, and measure ___ _-_ z70 min. diameter in the clear. The —'- i — kthickness of material is 8 mm. If the FIG. 21. ordinary ]Bunsen burner is not sufficiently strong for any purpose, the three-Bunsen burner (Fig. 22) may be used. BUNsz}EN has devised a more perfect form of this lamp" tc * Annal. d. Chem. u. Pharm., 111, 257 and 138, 257. Also Zeitschr. f, anal. Chem., 5, 351.

Page  25 ~ 16.] THE USE OF LAMPS. 25 render the flame a more complete substitute for the blowpipe flame, namely, for reducing, oxidizing, fusing, and volatilizing, and for the observation of the coloration of fame (~ 17). This improved form of the lamp is shown in Fig. 23. a is a sheatll, which can be turned round for regulating the flow of air. When in use the conical chimney, d d d cld (Fig. 24), is placed on e e; it is of such dimensions that the flame may burn tranquilly. Fig. 24 shows the flame half its natural size. In this three parts are at once apparent, namely, 1. a a a a, the dark cone, Which contains th6 cold gas mixed with about 62 per cent. of air; 2. a c a b, the mantle formed by the burning mixture of gas and air; 3. a b a, the luminous tip of the dark cone, which does not appear unless the air-holes are somewhat closed. The latter is useful for reductions Such are the three principal parts of the flame, but BUNSEN disti nguishes no less than six parts, which he names as follows: FIG. 22. a. \z FIG. 23. FIG. 24. 1. Zhe base at a, which has a relatively low temperature, be. cause the burning gas is here cooled by the constant current of fresh air, and also because the lamp itself conducts the heat away. This part of the flame serves for discovering the colors produced by readily volatile bodies when less volatile bodies which color the flame are also present. At the relatively low

Page  26 26 OPERATIONS. [~ 16. temperature of this part of the flame the former volatilize alone instantaneously, and the resulting color imparted to the flame is for a moment visible unmixed with other colors. 2. The fusinzg zone. This lies at 13, at a distance from tle bottom of somewhat more than one-third of the height of the flame, equidistant from the outside and the inside of the mantle, which is broadest at this part. This is the hottest part in the flame, namely, about 2300, and it therefore serves for testing substances as to their fusibility, volatility, emission of light, and for all processes of fusion at a high temperature. 3. T7he lower oxidizingflacme lies in the outer border of t'he fusing zone at y, and is especially suitable for the oxidation of oxides dissolved in vitreous fluxes. 4. liLe upper oxidizing zone at e consists of the non-luminous tip of the flame. Its action is strongest when the air-holes of the lamp are fully open. It is used for the roasting away of volatile products of oxidation, and generally for all processes oi oxidation where the very highest temperature is not required. 5. Tlhe lower reducing zone lies at d in the inner border of the fusing zone next to the dark cone. The reducing gases are here mixed with oxygen, and therefore do not possess their full power; hence they are without action on many substances which are deoxidized in the upper reducing flame. This part of the flame is especially suited for reduction on charcoal or in vitreous fluxes. 6. The u pper redclcingflame lies at 7 in the luminous tip of the dark inner cone, which, as I have already explained, may be produced by dimrinishing the supply of air. This part of the flame must not be allowed to get large enough to blacken a test-tube filled with water and held in it. It contains no free oxygen, is rich in separated incandescent carbon, and therefore has a much stronger action than the lower reducing zone. It is used more particularly for the reduction of metals collected in the form of incrustations. With the help of a gas flame of this description we can obtain as high a temperature as with the blowpipe, and even higher if the radiating surface of the substance is made as small as possible; and by the use of the different parts of the flame processes of reduction and of oxidation may be carried out with the greatest convenience. In order to study the deportment of bodies at a higqh temperature, namely, their emission of light, fusibility, volatility, and power of coloring flame, they are introduced into the flame in the loop of a platinum wire, which should be barely thicker than a horse-hair. Should the substance attack platinum, a little bundle of asbestos is used, which should be about one-fourth the thickness of a match. Decrepitating substances are first very finely powdered, then placed on a strip of moistened filterpaper about a square centimetre in surface, and this is cautiously burnt between two rings of fine platinum wire. The

Page  27 ~ 16.] Tni USE OF LAMPS. 27 substance now presents the appearance of a coherent crust and may be held in the flame without difficulty. For testing fluids to see whether they contain a substance which colors flame, the round loop of the fine platinum wire is flattened on an anvil to the form of a small ring. This is dipped into the fluid, and then withdrawn, when a drop will be found attached to the rilng. This drop is held near the flame and allowed to evaporate without boiling, after which the residue may be conveniently tested. If bodies are to be exposed for a considerable tinme to the action of the flame, the stand, Fig. 25, is used. A and B are provided with springs, and can be easilymoved up and down. On A is the arm, a, intended for the support of the platinum wire fixed in a glass tube (Fig. 26); also another little arrangement to hold the glass tube, o, with its bundle of asbestos fibres, d. B bears a clip for the reception of a test-tube, which in certain cases has to be heated for a considerable time in a definite part of the flame. C serves to hold t h e various platinum wires fixed in glass tubes. Ex per'irents of reduction are I Dperformed either with the aid of a suitable reducing agent in a small glass tube, or with the aid of a little stick of charcoal. In order to prepare the latter, BUNSEN recommends to hold an uneffloreseed crystal of sodium carbonate near the flame, and then E0I- having taken off the head of a match to smear three-fourths of its X A * ^ > length with the wet mass produced by warming the crystal..~:[ X aThe match-stick is then slowly aBoij- -3 rotated on its axis in the flame, when a crust of solid sodium carbonate will form on the carbonized wood, and on heating in the fusing zone of the flame this crust will be melted and absorbed by the charcoal. The little stick of charcoal will now in a measure be protected from combustion. iii The substance to be tested is i made into a paste, with a drop i...... —-= — - H of melted crystallized sodium -- carbonate, and a mass about FIG FIG. 25. the size of a millet-seed is 26.

Page  28 28 OPERATIONS. [~ 16. taken up on the point of the carbonized-match; it is then first melted in the lower oxidizing flame, and afterwards moved through a portion of the dark cone into the opposite hottest part of the lower reducing zone. The reduction will be rendered evident by the effervescence of the sodium carbonate. After a few moments the action is stopped by allowing the substance to cool in the darkl cone of the flame. If, finally, the point of the carbonized match is cut off and triturated with a few drops of water in a small agate mortar, the reduced metal will be obtained in the form of sparkling fragments which may be purified by elutriation, and, if necessary, more minutely examined. Volatile elements which are reducible by hydrogen and carbon may be separated as such or as oxides from their combinations and deposited on porcelain. These deposits are called incrustations; they are thicker in the middle, and become thin towards the edges. They may be converted into iodides, sulphides, and other combinations, and may thus be further identified. These reactions are so delicate that in many cases a quantity of from 1-% to 1 mrmn. is sufficient to exhibit them. Ek7e metallic incrustatwon is obtained by holding in one hand a small portion of the substance on asbestos in the upper reducing-flame, and in the other hand a glazed porcelain dish, from 1 to 1.2 decimetres in diameter, filled with water, close over the asbestos in the upper reducing-flame. The metals separate as sooty or mirror-like incrustations. If the substance is held as just directed, and the porcelain dish is held in the upper oxidizing flame, then an incrustation qf oxide is obtained. In order to be sure of getting it, the flame must be comparatively small if the portion of substance is minute. To turn the incrustation of oxide into an incrustation of iodide, let the dish covered with the oxide cool, breathe on it, and Ir ~"'. _ place it on the wide-mouthed bot-_____; Il~1ff Ijtie, Fig. 27. This bottle contains phosphorus tri-iodide, which has - been allowed to deliquesce and become converted into fumting hydriFig. 27. odic acid and phosphorous acid; it should have an air-tight glass stopper. If the hydriodic acid has become so moist that it has ceased to fume, it may be restored to its proper condition by the addition of phosphoric pentoxide. To turn the incrustation of iodide into an incrustation of sullpide, direct a current of air containing ammonium sulphide upon it, breathing upon the dish occasionally; then drive off the excess of ammonium sulphide by gentle warming If more considerable qunatities of the metallic incrustation

Page  29 ~ 17.] SPECTRUM ANALYSIS. 29 are required for further experiments, the porcelain dish is replaced by a test-tube half filled with water, D (Fig. 25), in which a few pieces of marble should be placed to prevent bumping when the water subsequently boils. In this case the asbestos, d, with the substance on it, is fixed at'he Maime height as the middle of the upper reducing-flame, the test-tube is fixed with its bottom close over the asbestos, as shown in the figure, and then the lamp is moved just under the test-tube. The substance thus comes within the reducing-flame, and the metallic incrustation forms on the bottom of the test-tube. The incrustation may be obtained as thick as is wished by renewal of the substance. ~ 17. 16. OBSERVATION OF THE COLORATION OF FLAME AND SPECTRUMi ANALYSIS. Many substances give characteristic tints to a colorless flame, which afford excellent means for their identification. Thus, for instance, salts of sodium impart to flame a yellow, salts e of potassium a violet, salts of lithium a carmine tint, and may thus be easily distinguished from each other. d The flame of BUNSEN'S gas- _ lamp with chimney, described in ~ 16, and shown in Fig. 23, is more particularly suited for observations of this kind. The substances to be examined are put on the small luop of a ine platinum wire, and thus, by means of the holder shown in Fig. 25, or the more simple one, Fig. 28, placed in the fusing-zone of the gas-flame. A particularly striking coloration is imparted to the flame by the volatile salts of the alkali and alkali-earth metals. If different salts of one and the same base are compared in this way, it is found that - every one of them, if at all volatile at high temperatures, or permitting at least the FIG. 29.

Page  30 30 OPERATIONS. [~ 17. volatilization of the base, imparts the same color to the flame, only with different degrees of intensity, the most volatile of the salts producing also the most intense coloration; thus, for instance, potassium chlloride gives a more intense coloration than.potassium carbonate, and this latter again a more intense one than potassium silicate. In the case of difficultly volatile compounds, the coloration of the flame may often be developed by adding some other body which has the power of decomposing the compound under examination. Thus, for instance, in silicates containing only a few per cent. of potassium, the latter body cannot be directly detected by coloration of flame; but this detection may be accomplished by adding a little pure gypsum, as this will cause formation of calcium silicate and potassium sulphate, a salt which is sufficiently volatile. But however decisive a test the mere coloration of flame affords for the detection of certain metallic compounds, when present unmixed with others, this test becomes apparently quite useless in the case of mixtures of compounds of several metals. Thus, for instance, mixtures of salts of potassium and sodium show only the sodium-flame; mixtures of salts of barium and strontium, only the barium-flame, etc. This defect may be remedied, however, in two ways. The first way, introduced by CARTMELL,* and perfected afterwards by BUNSEN t and by MERZ,4 consists in looking at the colored flame through some colored medium (colored glasses, indigo solution, etc). Such colored media, in effacing the flamne coloration of the one metal, bring out that of the other metal mixed with it. For instance, if a mixture of a salt of potassiumn and a salt of sodium is exposed to the flame, the latter will only show the yellow sodium coloration; but if the flame be now looked at through a deep-blue cobalt glass, or through solution of indigo, the yellow sodiumn coloration will disappear and will be replaced by the violet potassium tint. A simple apparatus suffices for all observations and experiments of the kind; all that is required for the purpose beingFIG. 29. 1. A hollow prism (Fig. 29) composed of mirror-plates, the chief section of which forms a triangle with two sides of 150 * Phil. Mag., 16, 328. t Annal. d. Chem. u. Pharm., 111, 257. t Journ. f. Prakt. Chem., 80, 487.

Page  31 ~ 17.] SPECTRUM ANALYSIS. 31 mm., and one side of 35 mm. length. The indigo solution required to fill this prism is prepared by dissolving 1 part of indigo in 8 parts of fuming sulphuric acid, adding to the solution 1500-20)0 parts of water, and filtering. When using this apparatus the prism is moved in a horizontal direction ciose before the eyes, in such a way that the rays of the flame are made to penetrate successively thicker and thicker layers of the effacing medium. 2. A blue, a violet, a red, and a green glass. The blue glass is tinted with cobalt monoxide; the violet glass with manganese sesquioxide; the red glass (white glass colored red superficially) with cuprous oxide; and the green glass with iron oxide and cupric oxide. The colored glass of commerce will generally be found to answer the purpose. As regards the tints imparted to the flame by the different bodies, when viewed through the aforesaid media, and the combinations by which these bodies are severally identified, the information required will be found in Section III., in the paragraphs treating of the several bases and acids. The second way, which is called S2pectrznm Analysis, was introduced by KIRCHII FF and BUNSEN. It consists in letting the rays of the colored flame pass first through a narrow slit, then through a prism, and observing the so refracted rays throulgh a telescope. A distinct spectrum is thus obtained for every flame-coloring metal; this spectrum consists either, as in FIG. 30 b. FIG. 30 a. the case of barium, of a number of colored lines lying side by side; or, as in the case of lithium, cf two separate, differently

Page  32 32 OPERATIONS. [~ 17. colored lines; or, as in the case of thallium, of a single green line. These spectra are characteristic in a double sense —viz., the spectrum lines have a distinct color, and they occupy also a fixed position. It is this latter circumstance which enables us to identify without difficulty, in the spectrum observation of mixtures of flame-coloring metals, every individual metal. Thus, for instance, a flamle in which a mixture of potassium, sodium, and lithium salts is evaporated, will give, side by side, the spectra of the several metals in the most perfect purity. A spectroscope which suffices for all common purposes is shown in Fig. 30 a. A is an iron disk, in the centre of which a prism, with circular refracting-faces of about 25 mm. diameter, is fastened by a clamp and screw. The same disk has also fastened to it the three tubes B, C, and D. Each of these tubes is soldered to a metal block (Fig. 30 b), by which they may be adjusted in the proper position. B is the observation-telescope; it has a magnifying power of about six. The tube C is closed at one end by a brass disk, into which the perpendicular slit is cut through which the light is admitted. The tube D) carries a.photographic copy of a millimetre-scale, reduced on a glass plate to about one-tifteenth the original dimensions. This scale is covered with tin-foil, with the exception of the narrow strip upon which the divisional lines and the numbers are engraved. It is lighted by a gas or candle flame placed before it. The axes of the tubes B and D are directed, at the same inclination, to the centre of one face of the prism, whilst the axis of the tube C is directed to the centre of the other face. This arrangement makes the spectra produced by the light passing throughl C, and the image of the scale in D produced by total reflection, appear in one and the same spot, so that the positions occupied by the spectrum-lines may be read off on the scale. The prism is placed in about that position in which there is a minimum divergence of the rays of the sodium-line; and the telescope is set in that direction in which the red and the violet potassium lines are about equidistant from the middle of the field of view. The colorless flame into which the flane-coloring bodies are to be introduced is placed 10 cm. from the slit. BUNSEN'S lamp, shown in Fig. 23, gives the best flame. The lamp is adjusted so as to place the upper border of the chimney about 2'0 min. below the loswer end of the slit. When this lamp has been lighted, and a bead of substance-say of potassium slilpllate —introduced into the fusinc-zone by means of the holder shown in Fig. 28, the iron disk of the spectrum apparatus, which, with all it carries, is movable round its vertical axis, is turned until the point is reached where the himinesity of the spectrum is the mnost intense.

Page  33 ~ 18.1 APPARATUS. 33 To cut off foreign light in all spectrum observations, the centre part of the apparatus is covered with a black cloth or box. The spectra which are the most serviceable for analytical purposes are mapped on plate I. The scale employed is that of KIirchhoff and Bunsen's instrument, in which the degree 50 coincides with the yellow sodium line. The topmost scale gives the positions of some of the more important dark lines (Fraunhofer's) of the solar spectrum, which are distinguished by the letters A, B, C, etc., and a and b. The limits of the seven colors are indicated with sufficient accuracy by the vertical lines drawn below each spectrum. The long dashes of black drawn at the upper edge of the spectra of potassium, rubidium, cmesium, and sodium, represent broad, continuous bands of color. The proper spectral lines are shown at the lower edge of each scale. The width of each line is seen from the number of degrees it covers. Its brightness is indicated by its vertical depth in the engraving. The most characteristic or important lines are designated by the Greek numerals. Special notice of them is given in Section III. In using the spectroscope it is. not always sufficient to perceive a line with its appropriate color; its position with relation to known standards ilust be likewise ascertained. This is done by making for each spectroscope a diagraml of the spectra, similar to plate I. For most purposes it is, however, only needful to map the more important lines. Any arbitrary scale being drawn, the lines are placed against degrees corresponding to those seen in the spectroscope, when beads of the purest accessible compounds of the various alkali and alkali-earth metals are placed in the flame. To insure uniformity the left edge of the sodium line, which is rarely absent even in specially prepared salts, is brought to coincide with the degree 500 or 1000 of the scale of the instrument. To the position once adopted the scale must always be brought before taking observations, if by any means it has been disturbed. With aid of the spectroscope we are able to detect quantities. of substances that are not recognizable in any other manner. The results possess the utmost certainty. and are arrived at in a few momnents. APPENDIX TO SECTION I. ~ 18. APPARATUS. The following list includes the articles actually required for the performance of simple experiments and investigations: 1. A BERZELIUS SPIRIT-LAMP (S~16, Fig. 15). 8

Page  34 34 OPERATIONS. [~ 18 2. A GLASS SPIRIT-LAMIP ( 16, Fig. 17). Or, instead of these two, where coal-gas is procurable, a IBUNSEN'S Gas-lamp —best one with chimney (~ 16, Figs. 18, 19, and 23). 3. A BLOWPIPE (see ~ 15). 4. A PLATINUM CRUCIBLE Which Will contain about a quarter of an ounce of water, with a cover shaped like a shallow dish. 5. PLATINUM FOIL, as smooth and clean as possible, and not too thin; length about 40 mm.; width about 25 mm. 6. PLATINUAI WIRE3 (see pp. 21 and 27). Three stronger wires and three finer wires are amply suffcient. They are kept most conveniently in a glass half filled with diluted acid; the wires may thus be kept clean. 7. A STAND WITH TWELVE OR MORE TEST-TUBES. 16 to 18 cm. is the proper length of the tubes; from 1 to 2 cm. the proper width. The tubes must be made of thin white glass, and well annealed. The rim must be quite round, and slightly flared. The stand shown in Fig. 31 will ________________ _______=_ be found most suitable. 8. SEVERAL NESTS OF BEAEERS AND A DOZEN SMIALL FIG. 31. FLASKS of thin, well-annealed glass. 9. SEVERAL NESTS OF PORCELAIN EVAPORATING DISHES, AND A DOZEN SrMALL PORCELAIN CRUCIBLES. Those of the royal manufacture of Berlin are unexceptionable, both in shape and durability. 10. SEVERAL GLASS FUNNELS Of various sizes. They must be inclined at an angle of 60~, and merge into the neck at a definite angle. 11. A WASHING-BOTTLE of a capacity of from 500 to 800 c.c. (see ~ 7). 12. A FEW POUNDS OF GLASS TUBES AND SOME GLASS RODS. The former may be bent, drawn out, etc., over a Berzelius lamp or gas-lamp; the latter are rounded at the ends by fusion. 13. A selection of WATCH-GLASSES. 14t. A small AGATE MORTAR. 15. A STEEL OR BRASS PINCERS about four or five inches long. 16. A WOODEN FILTER-STAND (see ~ 5). 17. A TRIPOD Of thin iron, to support the dishes, etc., which it is intended to heat over the small spirit or gas lamp. 18. The COLORED GLASSES described in ~ 17, especially blue and green.

Page  35 ~ 19.] REAGENTS. 31 SECTION II. REAGENTS. ~ 19. A VARIETY of phenomena may manifest themselves upon tile decomposition or combination of bodies. In some cases liquids change their color; in others precipitates are formed; sometimes effervescence takes place, and sometimes deflagration, etc.'Now, if these phenomena are very striking, and attend only upon the action of two definite bodies upon one another, it is obvious that the presence of one of these bodies may be detected by means of the other. If we know, for instance, that a white precipitate of certain definite properties is formed upon mixing baryta with sulphuric acid, it is clear that, if upon adding baryta to any liquid we obtain a precipitate exhibiting these properties, we may conclude that this liquid contains sulphuric acid. Those substances which indicate the presence of others by any striking phenomena are called reagents. Accordins, to the different objects attained by the application of these bodies, we make a distinction between general and specia reagents. By general reagents we understand those which serve to determine the class or group to which a substance belongs; and by special reayents those which serve to detect bodies individually. That the line between the two divisions cannot be drawn with any degree of precision, and that one and the same substance is often made to serve bothl as a general and a special reagent, cannot well be held a valid objection to this classification, which is simply intended to induce a habit of employing reagents always for a settled purposeviz., either simply to find out the groutp to which the substance belongs, or to determine the latter individually. Whilst the usefulness of general reagents depends principally upon their efficiency in strictly characterizing groups of bodies, and often effecting a complete separation of the bodies belonging to one group from those belonging to another, that of special reagents depends upon their being characteristic and sensitive. We call a reagent characteristic if the alteration produced by it, in the event of the body tested for being present, is so distinctly marked as to admit of no mistake. Thus iron is a characteristic reagent for copper, stannous chloride for mercury, because the phenomena produced by these reagentsviz., the separation of metallic copper and of globules of mercury-admit of no mistake. We call a reagent sensitive or delicate if its action is distinctly perceptible, even though a very

Page  36 36 REAGENTS. [~ 19. minute quantity only of the substance tested for be present; sulch is, for instance, the action of starch upon iodine. Very many reagents are both characteristic and de];Tate; thus, for instance, anrie chloride for stannous salts, potassiumn ferrocyanide for ferric and cupric salts, etc. I need hardly mention that, as a general rule, reagents must be chemically pure-i-.e., they must consist purely and simply of their essential constituents, and must contain no admixture of foreign substances. We must therefore make it an invariable rule to test the purity of our reagents before we use them, no matter whether they be articles of our own production or purchased. Although the necessity of this is fully admitted on all hands, yet we find that in practice it is too often neglected; thus it is by no means uncommon to see aluminium entered among the substances detected in an analysis, simply because the solution of sodium hydroxide used as one of the reagents happened to contain that element; or iron, because the ammonium chloride used was not free from that metal. The directions given in this section for testing the purity of the several reagents refer, of course, only to the presence of foreign matter resulting from the mode of their preparation, and not to mere accidental admixtures. One of the most common sources of error in qualitative analysis proceeds from missing the proper measure-the right quantity-in the application of reagents. Such terms as "'addition in. excess," " supersaturation," etc., often induce novices to suppose that they cannot add too much of the reagent, and thus solme willfill a test tube with acid, simply to supersaturate a few drops of an alkaline fluid, whereas every drop of acid added, after the neutralization point has once been reached, is to be looked upon as an excess of acid. On the other hand, the addition of an insufficient amount is to be equally avoided, since a reagent added in insufficient quantity often produces phenomena quite different fronm those which will appear if the same reagent be added in excess: e.g., a solution of mercuric chloride yields a white precipitate if tested with a small quantity of hydrogen sulphide; but if treated with the same reagent in excess, the precipitate is black. Experience has, however, proved that the most common mistake beginners make, is to add the reagents too copiously. One reason why this over-addition must impair the accuracy of the results is obvious; we need simply bear in mind that the changes effected by reagents are perceptible within certain limits only, and that therefore they may be the more readily overlooked the nearer we approach these limits Sby diluting the fluid. Another reason is in the fact that a large excess of a reagent will often have a solvent or modifying action upon a precipitate or color, and will entirely prevent the exhibition of phenomena which a suitable quantity would without difficulty produce.

Page  37 ~ 19.] SIMPLE SOLVENTS. 37 No special and definite rules can be given for avoiding this source of error; a general rule may, however, be laid down, which will be found to answer the purpose, if not in all, at least in the great majority of cases. It is simply this: let the studen t always reflect before the addition of a reaygentfor what purpose he applies it, whlat are the phenomena he intends to produce, and what are the results of the addition of excess. We divide reagents into two classes, according to whether the fluiditv which is indispensable for the action of reagents upon the various bodies, is brought about by the application of heat, or by means of liquid solvents; we have consequently, 1, Reagents in the wet way; and 2, Reagents in the dry way. For greater clearness we subdivide these two principal classes as follows: A. REAGENTS IN THE WET WAY. I. SIIPLE SOLVENTS. II. COLORING MATTERS AND INDIFFERENT VEGETABLE SUBSTANCES. III. AcIDs and HALOGENS. a. Oxygen acids. b. Hydrogen acids and halogens. c. Sulphur acids. IV. BASES, AMETALS, and SULPHIDES. a. Oxygen bases and metals. b. Sulphides. V. SALTS. a. Of the alkali-metals. b. Of the alkali-earth metals. c. Of the heavy metals. B. REAGENTS IN THE DRY WAY. I. FLUXES. II. BLOWPIPE REAGENTS. A. REAGENTS IN THE WET WAY.' I. SIMPLE SOLVENTS. Simple solvents are fluids which do not enter into chemical combination with the bodies dissolved in them; they will accordingly dissolve any quantity of matter up to a certain limit, which is called the point of saturation, and is in a measure dependent upon the temperature of the solvent. The essentali

Page  38 38 REAGENTS. [~~ 20, 21. and characteristic properties of the dissolved substances (taste reaction, color, etc.) are not destroyed by the solvent. (See ~ 2.) ~ 20. 1. WATER, H20. Preparation.-Pure water is obtained by distilling spring Cwater from a copper still with head and condenser made of pure tin. The distillation is carried to about three-fourths of the quantity operated upon. If it is desired to have the distilled water perfectly free from carbonic acid and ammonium c.,arbonate, the portions passing over first must be rejected. In the larger chemical laboratories, distilled water is obtained from the steam apparatus which serves for drying, etc. Rain watei collected in the open air may in many cases be substituted for distilled water.* Tests.-It must be colorless, odorless, and tasteless, and should not leave the smallest residue when evaporated in a platinum,-essel.t It should not be changed by ammonium sulphide (copper, lead, iron), nor rendered turbid by barvta water (cirblonic acid). No cloudiness should be caused even after long standing by the addition of ammonium oxalate, of barium chloride and hydrochloric acid (sulphuric acid), of silver nitrate and nitric acid (chlorides), or of mercuric chloride and sodium carbonate (ammonia). Uses.-We use water: principally as a simple solvent for a lgreat variety of substances; the most convenient way of using it is with the washing-bottle (see ~ 7, Fig. 4), by which means a stronger or finer stream may be obtained. It serves also to effect the conversion of several neutral metallic salts (more particularly antimony trichloride and the salts of bismuth) into soluble acid and insoluble basic compounds. ~ 21. 2. ETHYL ALCOHOL, C2E15.OH. Preparation.-Two sorts of alcohol are used in chemical analyses: viz., 1st. Commercial " 95 per cent. alcohol," whic re:ally contains 93 to 94 per cent. of alcohol by weight; and 2d, absolute alcohol. The latter may be prepared most con* As regards the preparation of water absolutely free from organic matter, see STAS, Zeitschrift f. anal. Chem. 6, 417. t Ordinary distilled water rarely fails to leave some slig7tt residue on evaporation; but this does not interfere with its ordinary uses in chemical analysis. -ED.: In analytical expernrients we use only distilled water; whenever, there. fore, the term water occurs in the present work, distilled water is meant.

Page  39 ~ 22.] CARBON DISULPUIDE. 39 veniently by placing in a flask or tin call 800 grinms of g'ood quick-lime in coarse powder or small lumps, adding 1 liter of "95 per cent, alcohol," connecting the vessel with the lower end of a condenser like Fig. 8, and keeping its contents boiling on a water bath for an hour. The can is then connected to the upper end of the condenser, and the dehydrated alcohol distilled off into a bottle for USe.-ERLENMEYER; J. LAWRENCE SAIITIH. Tests.-Pure alcohol must completely volatilize, and ought not to leave a smell of fusel-oil when rubbed between the hands; nor should it alter the color of moist blue or red litmus paper. When kindled,it must burn with a faint bluish, barely perceptible flame. Uses.-Alcohol serves (a) to effect the separation of bodies soluble in this fluid from others which do not dissolve in it, e.g., of strontium chloride from barium chloride; (b) to precipitate from aqueous solutions many substances which are insoluble ill dilute alcohol, e.g., gypsum, calcium malate; (e) to produce various kinds of ether, e.g., ethyl acetate, which is characterized by its peculiar and agreeable smell; (d) to reduce, mostly with the co-operation of an acid, certain peroxides and metallic acids, e.g., lead dioxide, chromic acid, etc.; (e) to detect certain substances which impart a characteristic tint to its flame, especially borit acid, strontium, potassium, sodium, and lithium. g 22. 3. ETHYL ETHER, (C,2Hl O. 4. CHLOROFORMn, CiHC1,. 5. CARBON DISULPHIDE, CS2. These solvents find but limited application in the qualitative analysis of inorganic bodies. They serve indeed almost exclu sively to detect and isolate bromine and iodine. Chloroform and carbon disulphide are preferable to ether in this respect. The latter is used for the detection of chromic acid by means of hydrogen dioxide. These preparations are best procured by purchase. Tests.-Ether must have a specific gravity of.713 at 20~, and require 9 parts of water for solution. The solution n-must not alter the color of test papers. Ether must, even at the common temperature, rapidly and completely evaporate on a watchglass. Chloroform, must be colorless and transparent and have a specific gravity of 1.48. It must have no acid reaction, nor impair the transparency of solution of nitrate of silver. lMixed with 2 vols. of water, and shaken, its volume must not appear perceptibly diminished. It must even at the common temperLa

Page  40 40 REAGENTS. [~ 23. ture readily and completely evaporate on a watch-glass, Carbon diszlpAidec should be colorless, completely volatile even at the common temperature, and exercise no action upon lead carbonate. If yellow, it may be purified by agitating with, and distilling from mercury. II. COLORING MATTERS AND INDIFFERENT VEGETABLE SUBSTANCES. ~ 23. 1. TEST PAPERS. a. BLUE LITMUS PAPER. Prevaratioln.-IDigest 1 part of litmus of commerce with 6 parts of water, and filter the solution; divide the intensely blue filtrate into 2 equal parts; saturate the free alkali in the one part, by repeatedly stirring with a glass rod dipped in very dilute sulphuric acid, until the color of the fluid just appears red; add now the other part of the blue filtrate, pour the whole fluid into a dish, and draw strips of filter paper through it; suspend these slips over threads and leave them to dry. The color of litmus paper must be uniform, and neither too light nor too dark. Uses. —Litmus paper serves to detect the presence of free acids which change its blue color to red. It must be borne in mind, however, that many metallic salts produce the same effect. }3. REDDENED LITMUS PAPER. Preparation.-Stir blue solution of litmus with a glass rod dipped in dilute sulphuric acid, and repeat this process until the fluid has just turned distinctly red. Steep slips of paper in the solution, and dry them as in a. The dried slips must look distinctly red. Uses. —Pure alkalies and alkaline earths, and also the sulphides of their metals, give a blue color to red litmus paper; alkali-carbonates and the soluble salts of several other weak acids, especially of boric acid, possess the same property. This reagent serves therefore for the detection of these bodies in general. y. TURME.RIC PAPER. P'reparatio.-Digest and heat 1 part of bruised turmeric root with four parts of alcohol, and two of water, filter the tincture obtained, and steep slips of fine paper in the filtrate. The dried slips must exhibit a fine yellow tint.

Page  41 ~ 24, 25.] ACIDS AND HALOGENS. 41 Uses. —Turmeric. paper serves for the detection of free alkalies, which change its yellow color to brown. It is not so delicate a test as the other reagent papers; but the change of color is highly characteristic, and is very distinctly perceptible in many colored fluids; we cannot well dispense, therefore, with this paper. When testing with turmeric paper, it is to be borne in mind that, besides the substances enumerated in 13, several other bodies (boric acid, for instance) possess the property of turning its yellow color to brown-red. It affords an excellent means for the detection of the latter substance. All test papers are cut into slips, which must be kept in wellclosed boxes, or in black bottles away from light and fumes. ~ 24. 2. SOLUTION OF INDIGO. Preparation.-Take from 4 to 6 parts of fuming sulphuric acid, add slowly, and in small portions at a time, 1 part of finely pulverized indigo, taking care to keep the mixture well stirred. The acid has at first imparted to it a brownish tint by the matter which the indigo contains in admixture, but it subsequently turns deep blue. Elevation of temperature to any considerable extent must be avoided, as part of the indigo is thereby destroyed; it is therefore advisable, when dissolving larger quantities of the substance, to place the vessel in cold water. When the whole of the indigo has been added to the acid, cover the vessel, let it stand forty-eight hours, then pour its contents into 20 times the quantity of water, mix, filter, and keep the filtrate for use. UTses.-Indigo is decomposed by boiling with nitric acid, yellow-colored oxidation products being formed. It serves, therefore, for the detection of nitric acid. Solution of indigo is also well adapted to effect the detection of chloric acid and of free chlorine. III. ACIDS AND HALOGENS. ~ 25. The acids which are used as reagents are soluble in water. The solutions taste acid and redden blue litmus paper, and are commonly designated by-the simple name of the free acid, as the accession of water does not destroy their acid properties. Acids are divided into oxygen acids, sulphur acids, and hydrogen acids. [Oxygen acids (or oxacids) consist of acid or negative radicals united to hydrogen by ineans of oxygen. In other words, they

Page  42 42 REAGENTS. [~ 25. are compounds of negative radicals with hydroxyl (01I), They are acid hydroxides. Oxygen bases, are compounds of basic (positive) radicals with hydroxyl. In most cases the oxygen acids may be formed by the reaction of an oxide of an electro-negative element (anhydride) upon water. N205 + HI0 - 2 (N2011). Nitric pentoxide. Water. Nitric acid. SO, + 1IO -SO <oi Sulphur Water. Sulphuric trioxide. acid. The oxygen bases, or basic hydroxides, may also result from the action of an oxide of an electro-positive element upon water. KO + 1120 = 2K11OEI. Potassium Potassium monoxide. hydroxide. Oxygen acids are mono, cli, and tri, or more basic, and oxygen bases are mon, di, tri, and more acid according as they contain one, two, three, or more hydroxyls united respectively to univalent, bivalent, or trivalent radicals. When oxygen acids act upon metallic oxides or hydroxides, the metal of the latter takes the place of hydrogen, and an oxyyen salt is formed, while at the same time water is produced. NO20H + IKOIH = N02,0K + H2,0. Nitric acid. Potassium Potassium. Water. hydroxide. nitrate. SO,(OH)2 + I(20 = SO,(OK), + I1O, and Sulphuric Potassium Potassium acid. monoxide. sulphate. SO2(0o), + KOH = SO2< O + H20 Potassium Hydrogen hydroxide. potassium sulphate. SO2<OH + Zn< < >n + 2HO Zinc hydroxide. Zinc sulphate (normal.) OIH SO, < OH + 2(n< Zn < O>SO, — +- 2 io Zinc sulphate (basic.) By the mutual action of acids or negative oxides, and bases or positive oxides, three classes of salts are produced, viz., normal, acid, and basic. Aormal salts are those in which the acid and base saturate each other, in which, therefore, all the hydroxyls:

Page  43 ~ 26.] SULPHURIC ACID. 43 whether of acid or base, are eliminated (in the form of water) and the acid radical remains united to metal by means of oxygen, e.g., potassium nitrate and potassium and zinc sulphates (see above). Acid salts are those which retain a part of the acid hydroxyl. e.g. hydrogen potassium sulphate. Basic salts are those in which a part of the hydroxyl of the base, or of the oxygen of the positive oxide, remains in the combination e.g. basic zinc sulphate. (See previous page.) The reaction towardes test papers of soluble salts is either acid, neutral, or alkaline, according as the salt is acid, normal, or basic, or according to the more or less pronounced acidity or basicity of the acid and basic radicals. —ED.] The hy/drogen acids are formed by the combination of the, halogens with hydrogen. Most of these possess the characteristic properties oE acids in a high degree. They neutralize oxygell bases with formation of haloid salts and water; 2 I1 C1 and Na,0 --- 2 Na C1 and 1-2 O; — 6 I Cl and Fe. 0, Fe2 C1, ana 3 H2 O. The haloid salts produced by the action of powerful hydrogen acids upon strong bases have a neutral reaction; whilst the solutions of those haloid salts that contain wearily basic elements (such as aluminium and iron) have an acid reaction. [The sulp1hur acids may be regarded as compounds of negative radicals with hydrosulphuryl (S 11) e.g. sulphocarbonic acid C S(S 11)2 and hydrosulphuric acid (hydrogen sulphide) 1- (S I-I). Slylphur bases are K (S H), Ca (S H1)2 etc. Sulphur salts result from the reaction of sulphur acids upon sulphur bases. Most sulphur salts, however, are produced by the action of negative anhydrosulphides on sulphur bases, or on positive aniihydrosulphides, e.g: As2 S5 + 6 (KI S II) = 2 [As S (S K)] + 3 112 S. Arsenic Potassium Potassium Hydrogen sulphide. hydrosulphide. sulpharsenate. sulphide.-ED, ~ 26. 1. SULPHURIo AcID, H, S,04 or S 0, (O H)2 We usea. Concentrated sulphuric acid of commerce. b. Con centrated pure stlphuric acid. The following methods may be recommended for preparing chemically pure sulphuric acid: a. Put 1000 grm. of ordinary concentrated sulphuric acid in a porcelain dish, add 3 grm. of sulphate of ammonium, and heat till copious fumes of sulphuric acid begin to escape in order to destroy the oxides of nitrogen which are present. Aftei' coolinl,, add 4 or 5 grin. of powdered manganese dioxide, and heat to boiling with stirring, in order to convert any arsenious acid

Page  44 44 REAGENTS. [@ 26. into arsenic acid. When cool pour off the cleat fluid by means of a long funnel tube into a retort coated with clay. The retort should not be more than half full, and is to be heated directly over charcoal. To prevent bumping, rest the retort on an inverted crucible cover, so that the sides may be more heated than the bottom. The neck of the retort must reach so far into the receiver that the acid distilling over drops directly into the body.'To cool the receiver by means of water is unnecessary and even dangerous. To prevent the receiver coming into actual contact with the hot neck of the retort, somle asbestos in large fibres is placed between them. When about 10 or 15 grin. has been drawn over, change the receiver and slowly distil off three-fourths of the contents of the retort. This method depends on th3 fact discovered by B-ussy and B3IGNET, that on distilling sulphuric acid which contains arsenic in the form of arsenic acid an arsenic-free distillate is obtained. fJ. Pour into 4 parts of water 1 part of concentrated sulphuric acid, and conduct into the mixture for some time a slow stream of hydrogen sulphide, keeping the fluid heated to 70~. Let the mixture stand at rest for several days, then decant the clear supernatant fluid from the precipitate, which consists of sulphur, lead sulphide, perhaps also arsenic sulphide, and heat the decanted fluid in a tubulated retort with upturned neck and open tubulature until sulphuric acid fumes escape with the aqueous vapor. The acid so purified is fit for many purposes of chemical analysis; if it is wished, however, to free it also from non-volatile substances, it may be distilled from a coated retort as in a. As soon as the drops in the neck of the retort become oily, the receiver is changed, and the concentrated acid which then passes over is kept in a separate vessel. c. Commonn dilute sulphuric acid.-Add to 5 parts of water in a thin glass or porcelain dish gradually, and whilst stirring, 1 part of concentrated sulphuric acid. The lead sulphate which separates is allowed to subside, and the clear fluid finally decanted. Tests.-Pure sulphuric acid must be colorless; when colorless solution of ferrous sulphate is poured upon it in a test tube, no brown tint must mark the plane of contact of the two fluids (nitric acid,:nitrous acid); when diluted with twenty parts of water it must not impart a blue tint to a solution of potassium iodide (see ~ 158) mixed with starch paste (nitrous acid). Mlixed withl pure zinc and water, it must yield hydrogen gas, which, on being passed through a red-hot tube, must not deposit the slightest trace of arsenic. It must leave no residue upon evaporation on platinum, and must remain perfectly clear upon dilution with four or five parts of alcohol (lead, iron, calcium). The presence of small quantities of lead is detected most easily by adding some hydrochloric acid to the sulphuric acid in a test tube. If the plane of contact is marked by turbidity (lead chloride), lead

Page  45 ~ 27.] NITRIC CID. 45 is present. Sulphurous acid is discovered by the odor after shaking the acid in a half-filled bottle. Uses.-Sulphuric acid has for most bases a greater affinity than almost any other acid; it is therefore used principally for the liberation and expulsion of other acids, especially phosphoric, boric, hydrochloric, nitric, and acetic acids. Oxalic acid and many other substances are decomposed when brought into contact with concentrated sulphuric acid. The nature of the decomposed body may in such cases be inferred from the pro.lucts of decomposition. Sulphuric acid is also used for the evolution of certain gases, more particularly of hydrogen and hydrogen sulphide. It serves also as a special reagent for the detection and precipitation of barium, strontium, and lead. ~ 27. 2. Nrrmic Acrm, H N Oor N O2. O H. Preyar.ttor.-a. Iheat crude nitric acid of commerce, as free as possible from chlorine, and of a specific gravity of at least 1.31,e in a glass retort to boiling, with addition of some potassium nitrate; let the distillate run into a receiver kept cool, and try from time to time whether after dilution it still continues to precipitate or cloud solution of silver nitrate. As soon as this ceases to be the case, change the receiver, and distil until a trifling quantity only remains in the retort. Dilute the distillate with water until the specific gravity is 1.2. b. Dilute crude nitric acid of commerce of about 1.38 specific gravity with two-fifths of its weight of water, and add solution of silver nitrate as long as a precipitate of silver chloride continues to form; then add a further slight excess of solution of silver nitrate, let the precipitate subside, decant the perfectly Kiear supernatant acid into a retort or an alembic with ground head; add some potassium nitrate free from chlorine, and distil until only a small quantity remains, taking care to attend to the proper cooling of the fumes distilling over. Dilute the distillate, if necessary, with water until it has a specific gravity of 1.2. Tests.-Pure nitric acid must be colorless and leave no residue upon evaporation on platinum foil. Solution of silver nitrate or of barium nitrate must not cause the slightest turbidity in it. Dilute the acid with water before adding these reagents, as otherwise nitrates will precipitate. Silver should be tested for by hydrochloric acid. Uses. —Nitric acid serves as a chemical solvent for metals, oxides, sulphides, oxygen salts, etc. With metals and sul* A weaker acid will not answer the purpose. The " parting acid " used in Assay Offices, of sp. gr. 1. 4 commonly contains no impurities but a trace of chlorine, and answers for most analytical uses.

Page  46 46 REAGENTS. [~~ 28, 29. phides of metals the acid first oxidizes the metal present, at the expense of part of its own oxygen, and dissolves it as nitrate. Mlost oxides are dissolved by nitric acid at once as nitrates; and so are also most of the insoluble salts with weaker acids, the latter being expelled in the process by the nitric acid. Nitric acid dissolves also salts with soluble non-volatile acids, as, e.y., calcium phosphate, with which it forms calcium nitrate and acid calcium phosphate. Nitric acid is used also as an oxidizing agent: for instance, to convert ferrous oxide into ferric oxide stannous oxide into stannic oxide, etc. ~ 28. 3. ACETIC ACID,,2 14 02 or CH3. C 0 0H. The No. 8 acetic acid of commerce which contains 30 per cent. of C, H,4 02 and has a specific gravity of 1.04, answers most purposes of analysis. Tests.-Pure acetic acid must leave no residue upon evaporation, and-after saturation with sodium carbonate -emit no empyreunatic odor. Hydrosulphuric acid, solution of silver nitrate, and solution of barium nitrate must not color or cloud the dilute acid, nor must ammonium sulpllide after neutralization of the acid by ammonia. Solution of indigo must not lose its color when heated with the acid. Empyreumatic matter is best detected by neutralizing the acid with sodium carbonate, and adding solution of potassium permanganate. If the solution loses its color and afterwards deposits a brown precipitate, empyreumatic matter is present. If the acid is not pure, add some sodium acetate and redistil from a glass retort not quite to dryness; if it contains sulphur dioxide (in which case hydrogen sulphide will produce a white turbidity in it), digest it first with lead dioxide or finely pulverized manganese dioxide, and then distil with sodium acetate. Uses.-Acetic acid possesses a greater solvent power for some substances than for others; it is used therefore to distinguish the former from the latter; thus it serves to distinguish calcium oxalate from calcium phosphate. Acetic acid is used also to acidulate fluids where it is wished to avoid the employment of mineral acids. ~ 29. 4. TARTARIc Acrm,,4 H6 0o.* The tartaric acid of commerce is sufficiently pure. It is kept C H (O H)-COO H *Or i C H (OH) - COO E

Page  47 ~ 30.] HYDROCHILORIC ACID. 47 in powder, as its solution suffers decomposition after a time. For use it is dissolved in a little water with the aid of heat. Uses.-The addition of tartaric acid to solutions of salts of various metals, especially of iron and aluminimn, prevents the usual precipitation of these metals by an alkali; this non-precipitation is owing to the formation of double tartrates, which are not decomposed by alkalies. Tartaric acid may therefore be employed to effect the separation of these metals from others the precipitation of which it does not prevent. Tartaric acid forms a difficultly soluble salt with potassium, but not so with sodium; it is therefore one ol our best reagents to distinguish between the two metals. Acia sodiurn tartrate answers this latter purpose still better than the free acid. This reagent is prepared by dissolving one of two equal portions of tartaric acid in water, neutralizing with sodium carbonate, then adding the other portion of the acid, and evaporating the solution to the crystallization point. For use, 1 part of the salt is dissolved in 10 parts of water. b. HYDROGEN ACIDS AND HIALOGENS. ~ 30. 1. HYDROC- LORIC ACID or fHydrogen Chloride, I: C1. Preparation.-Pour a cooled mixture of seven parts of concentrated sulphuric acid and two parts of water over four parts of sodium chloride in a retort; expose the retort, with slightly raised neck, to the heat of a sand-bath until the evolution of gas ceases; conduct the evolved gas, by means of a bent tube, into a flask containing six parts of water, and take care to keep this vessel constantly cool. To prevent the gas from receding the tube ought to dip but about one line into the water of the flask. When the operation is terminated, try the specific gravity of the acid produced, and dilute with water until it marks from 1.11 to 1.12. If you wish to ensure the absolute purity of the acid, and its perfect freedom from every trace of arsenic and chlorine, you must take care to free the sulphluric acid intended to be used in the process from arsenic and the oxygen compounds of nitrogen, according to the directions of ~ 26. A pure acid may also be prepared cheaply from the crude hydrochloric acid of commerce by diluting the latter to a specific gravity of 1.12, and distilling the fluid, with addition of some chloride of sodurnm. Or you may put the acid into the retort in the concentrated form, placing 60 parts of water into the receiver for every 100 parts of concentrated acid, and not luting the receiver to the retort. If the crude acid contains chlorine this should be removed first by cautious addition of solution of

Page  48 48 REAGENTS. [~ 31. sulphur dioxide, before proceeding to the distillation; if, on the other hand, it contains sulphur dioxide, this is removed in the same way by cautious addition of some chlorine water. Hydrochloric acid not unfrequently contains arsenious chloride. owing to the presence of arsenic in the sulphuric acid employed, To free it from this impurity, the acid is mixed with twice its volume of water, hydrogen sulphide is conducted into it, the mixture allowed to stand at rest for some time, the clear fluid then decanted from the sulphur and arsenious sulphide, and heated, to expel the hydrogen sulphide. c~sts.-Hydrochloric acid must be perfectly colorless and leave no residue upon evaporation. If it turns yellow on evaporation, ferric chloride is present. It must not impart a blue tint to a solution of potassium iodide mixed with starch paste (chlorine or ferric chloride), nor discolor a fluid made faintly blue with iodized starch (sulphur dioxide). Barium chloride ought not to produce a precipitate in the highly diluted acid (sulphuric acid). Hydrogen sulphide must leave the diluted acid unaltered (arsenic). After neutralization with ammonia, ammonium sulphide must produce no change in it (iron, thallium). Uses.-Hydrochloric acid serves as a solvent for many substances. It dissolves many metals and sulphides of metals as chlorides, with evolution of hydrogen or of hydrogen sulphide. It dissolves metallic oxides and peroxides in the form of chlorides, in the latter case mostly with liberation of chlorine. Salts with insoluble or volatile acids are also converted by hydrochloric acid into chlorides, with separation of the original acid; thus calcium carbonate is converted into calcium chloride, with liberation. of carbon dioxide. Hydrochloric acid dissolves salts with non-volatile and soluble acids apparently without decomposing them (e. g. calcium phosphate); but the fact is that in cases of this kind a metallic chloride and a soluble acid salt of the acid of the dissolved compound are formed; thus, for instance, in the case of calcium phosphate, calcium chloride and acid calcium phosphate are formed. With salts of acids forming no soluble acid compound with the base present, hydrochloric acid forms metallic chlorides, the liberated acids remaining free in solution (calcium borate). Hydrochloric acid is also applied as a special reagent for the detection and separation of silver, mercury, and lead, and likewise for the detection of free ammonia, with which it produces in the air dense white fumes of ammoniumn chloride. ~ 31. 2. CHLORINE, (CI) AND CHLORINE WATER. Preajratiom.-_ Mix 18 parts of common salt in lumps with

Page  49 ~ 32.] NITRO-HYDROCHLORIC ACID. 49 15 parts of finely pulverized good manganese dioxide, free from calcium carbonate; put the mixture in a flask, pour a co0wpletely cooled mixture of 45 parts of concentrated sulphuric acid and 21 parts of water upon it, and shake the flask: a uniform and continuous evolution of chlorine gas will soon begin, which, when slackening may be easily increased again by the application of a gentle heat. This method of WVIGGERS is excellent, and can be highly recommended. Conduct the chlorine gas evolved first through a flask containing a little water, then into a bottle filled with cold water, and continue the process until the fluid is saturated. Where it is desired to obtain chlorine water quite free from bromine, the washing flask is changed after about one-half of the chlorine has been expelled, and the gas which now passes over is conducted into a fresh bottle filled with water. If the chlorine water is to be quite free from llydrochloric acid, the gas must be passed through a U tube containing manganese dioxide. The chlorine water must be protectedl from the action of light; since, if this precaution is neglected, it speedily suffers complete decomposition, being converted into dilute hydrochloric acid, with evolution of oxygen (resulting from the decomposition of water). Smaller quantities, intendedl for use in the laboratory, are best kept in a stoppered bottle protected by a case of pasteboard. Chlorine water which has lost its strong peculiar odor is unfit for use. Uses.-Chlorine has a greater affinity than iodine and bromine for metals and for hydrogen. Chlorine water is therefore an efficient agent to effect the expulsion of iodine and bromine from their compounds. Chlorine serves moreover to effect the solution of certain metals (gold, platinum), to decompose metallic sulphides, to convert sulphurous acid into sulphuric acid, ferrous into ferric oxide, etc.; and also to effect the destruction of organic substances, as in presence of these it withdraws hydrogen from the water, enabling thus the liberated oxygen to combine with the vegetable matters, and to effect their decomposition. For this latter purpose it is often advisable to evolve the chlorine in the fluid which contains the organ ic substances; this is effected by adding hydrochloric acid to the fluid, heating the mixture, and then adding potassium chlorate. This gives rise to the formation of potassium chloride, water, free chlorine, and chlorine tetroxide, which acts in a similar manner to chlorine. ~ 32. 3. KITRO-HYDROCHLORIa AcmD. Aqua regia. Prapcaration.-Mix 1 part of pure nitric acid with from 3 to 4 parts of pure hydrochloric acid. Uses. —Nitric acid and hydrochloric acid decompose each other, 4

Page  50 50 REAGENTS. [~ 33 the decomposition mostly resulting, as GAY-LUssAC has shown, in the formation of two compounds which alre gaseous at the ordinlary temperature, N 0 Ci, and N 0 C1, and of free chlorine and awater. Thus, 2 (N 0O2. O I) + 6 (11 C1) - 4 (, 0) + N 0 Cl + N 0 C12 + 3 C1). This decomposition ceases as soon as the fluid is saturated with the gas; but it recommences the instant this state of saturation is disturbed by the application of heat or by decomposition of the acid. The presence of the free chlorine, and' also, but in a subordinate degree, that of the acids named, imakes aqua regia our most powerful solvent for metals (iwith the exception of those which form insoluble compounds with chlorine). Nitro-hydrochloric acid serves principally to effect the solution of gold and platinum, which metals are insoluble both in hydrochloric and in nitric acid; and also to decompose various metallic sulphides, e. g. cinnabar, pyrites, etc. ~ 33. 4. HYDROFLoUOSILICIc AcID, IH Si F6. Prejparationr.-Take 11 part of powdered glass, or 1 part of powdered ignited flint, or 1 part of quartz sand. Whichever is used, it must have been washed from every particle of dust, and then ignited. Mlix intimately with one part of perfectly dry fluor spar in powder; pour nine parts of concentrated sulphuric acid over the mixture in a non-tubulated retort, which it is ad-isable to coat with clay, and mix carefully by shaking the vessel. As the mixture swells up when getting warm, it must at first fill the retort only to one-third. The neck of the retort is connected air-tight with a small tubulated receiver, and the tubulus of the latter again, by means of India-rubber, with a awide glass tube twice bent at right angles. To the descending limb of the glass tube a funnel is attached by means of Indiar1ubber; this funnel is lowered into a beaker containing four parts of water. Promote the disengagement of gaseous silicon fluoride, which commences even in the cold, by moderately heating the retort over charcoal. Towards the end of the process a pretty strong heat should be applied. Every gas bubble produces in the water a precipitate of silicic acid, with simultaneous formation of hydrofluosilicic acid, 3 Si F4 -- 2 H O -2 H2 Si Fe + Si 02. The precipitated silicic acid renders the liquid gelatinous, and it is for this reason that the aperture of the descending limb of the tube cannot be allowed to dip direct into the water, since it would in that case speedily be choked. It sometimes happens in the course, and especially towards the end of the operation, that complete channels of silicic acid are formed in the gelatinous liquid, through which the gas gains the surface without undergoing decomposition if the liquid is not

Page  51 ~ 34.] HYDROGEN SULPHIDE. 51 occasionally stirred. When the evolution of gas has C( mpletely' ceased, throw the gelatinous paste upon a linen cloth, squeeze the fluid through, and filter it afterwards. Keep the filtrate for use. Yests.-Htydrofluosilicic acid must produce no precipitate in solutions of salts of strontium (strontium sulphate). Uses. —eBases decompose with hydrofluosilicic acid, forming water and metallic silicofluorides. Mlany of these are insoluble, whilst others are soluble; the latter may therefore by means of this reagent be distinguished from the former. In the course of analysis hydrofluosilicic acid is applied simply for the detection and separation of barium. C. SULPHUR ACIDs. ~ 34. 1. HYDROGEN SULPHIDE. HydrosulpAuric -Acid. Suljphuretted Hydrogen, I1.,S. Preparation,-H'ydrogen sulphide is usually evolved from iron sulphide, which is broken into small lumps and then treated with dilute sulphuric or hydrochloric acid. Fused iron sulphide may be purchased cheaply, or may be made by'heating iron turnings, or 1 to 11 inch iron nails, in a covered HIessian crucible to a white heat, and then adding small lumps of roll-sulphur until the entire contents of the crucible are in fusion. As soon as this is the case, pour the fused mass upon sand, or into an old Hessian crucible. Or make a hole in the bottom of the crucible, when the iron sulphide will run through as fast as it forms, i and may be received in a shovel placed in the ash-pit. 7 Or introduce an intimate mixture of thirty parts of iron filings and twenty-one parts of flowers of sulphur, in small portions into a redhot crucible, awaiting always -I' the incandescence of the portion last introduced be- i tore proceeding to the ad- dition of a fresh one. When i - you have thus put the whole P'"'; mixture into the crucible, FIG. 32. cover the latter closely, and expose it to a more intense heat, sufficient to make the iron sulphide fuse more or less.

Page  52 52 RBEAGENTS. [~ 34. The evolution of the gas may be effected in the apparatus illustrated by Fig. 32. Pour water over the iron sulphide in c, add concentrated hydrochloric or sulphuric acid, and shake tile mixture; the evolved gas is washed in c. When a sufficient quanLtity of gas is evolved, pour the fluid off the still undecoinpos'd iron sulphide, rinse the bottle repeatedly with water, then till it p:artly with that fluid, and keep it for the next operation. For larger laboratories, or for chelnists having to operate often and largely witll hydrogen sulphide, a gasometer may be used, or thle following apparatus, devised by BrIUGNTrELLI, and modified as shown in Fig. 33. The flask, B, is provided with a i q ii FIG. 33 Atubulure at a' its neck is filled with broken glass, its body with iron sulphide in small pieces. The India-rubber stopper in the neck contains two tubes-s (which may sometimes be omitted, see below), and the short tube, c, which must have a ~ Flasks with a lateral tubulure, such as are generally used for receivers, are also app'icable.

Page  53 ~ 34.] HYDROGEN SULPHIDE 53 bore of 1 cm. at least; the latter is connected with the tube, d, of the same size by means of India-rubber. The tube, e, extends almnost to the bottom of A, and is connected on the other side with the bottle, M; by means of the India-rubber tube, f. M is closed with a cork or India-rubber stopper, containing a small tube open at both ends. The stopper in the tubulure, CD, of the flask, b, contains a glass tube, which is in connection with a leaden pipe. The latter conducts the gas, and is supplied with the brass cocks, A, b, i i. To set the apparatus going, open A, and fill M with a mixture of 1 volume common hydrochloric acid and 2 volumes water The fluid will pass into A, fill the bottle, and rise through d and c into the flask, A. As soon as the neck of the latter is nearly full, close the cock, A, and take care that ar is not more than half full. If now b is opened, and also i, the acid rises up to the sulphide, the evolution of gas commences and proceeds wvith great regularity, since the wide tubes c and d allow the constant descent of the solution of ferrous chloride and ascent of fresh acid. If the acid does not rise in n as high as is wished, place one or two blocks of wood under M. The current of (gas n1iay be entirely regulated by raising or lowering ir, as BIuUGNATELLI recommends, but the cocks will be found necessary in large laboratories where the gas has to be passed into several differenlt fluids at the same time. If the apparatus is not required for some time, MI should be placed lower; the fluid will thus sink in B, and to be in contact with the iron sulphide, the evolution of gas will cease. In this case, if the evolution of gas in B is not rapid enough to fill- the space vacated by the Huid, air will enter through the tube, s. If the tube, s, is present at all, it should be sufficiently long to prevent the exit of fluid when there is a pressure of gas. After the acid has flowed from B, the still moist iron sulphide may continue evolving gas, but this will merely occasion more acid to pass from A to tM. The tube, s, may be left out when the cocks are used. Under these circumstances the fluid in B will descend more slowly on lowering M, sir.r,e the space filled by the descending acid has to be occupied by sulphuretted hydrogen. When there are no cocks, however, s is essential; otherwise on lowering M, the fluid through which the gas is passing might recede into the apparatus. This inconvenience may be easily prevented where cocks are provided, simply by closing b before lowering im. The gas from i i is conducted through wash-bottles, or in winter through U tubes filled with cotton before beinz used. When the acid is finally exhausted, M is placed lower than A, and the air-cock, A, is opened, if the tube, s, is not present. All the fluid then passes into M, and can be poured away. The apparatus (Fig. 34) devised by FR. MIour depends upon the same principle as the above. A is a cylinder used for drying gases; at b is a perforated disk of lead, and above are lumps

Page  54 54 REAGENTS. [~ 34. of iron sulphide. To the end of d is fixed, by means of Indiarubber, a, a small piece of wide glass tube, which is filled with cotton, and is intended to stop any particles of liquid which may be spirted up. c is a glass cock with a long wooden handle, which may be replaced by a rubber tube wnd clamp;, I FIG. 34. e contains a solution of sodium carbonate, to prevent the escape of the sulphuretted hydrogen from the solution of ferrous chloride, and to protect the latter from the action of the air. The acid used is a mixture of commuon hydrochloric acid with one or two measures of water. [If A is of large size-18 inches high and 3 inches wide-this form of HS generator suffices for a large laboratory. It is only necessary to provide one such apparatus for every 6 to 8 operators. The tube e may be omit-ted. Pure hydrogen sulphide may also be procured cheaply and abundantly by heating together in a flask a mixture of equal parts of sulphur and paraffine. On cooling the mixture the gas ceases to be formed, but escapes again on renewed application of heat. -GALLETLY. A very cheap and effective self-regulating apparatus is shown in Fig. 35. It is made from a two-quart fruit-bottle, in whose neck the chimney of a student lamp is suspended by means of a wide cork; a disk of perforated lead plate, or a perforated cork, rests on the constriction in the chimney; the latter is then nearly

Page  55 ~ 34.] HIYDROGEN SULPHIDE. 55 fillod with lumps of fused ferrous sulphide; above this a wad of moist sponge to wash the gas is placed, and to the chimney is fitted a rubber stopper, bent tubes joined by rubber, and screw-clamp, as in the figure. A rubber band stretched over the lower rim of the chimney may avert fracture in disjointing the apparatus. The bottle being nearly filled i'! l, a -with a mixture of equal vols. i commercial hydrochloric acid and water, is ready for use.-ED.] Su&phuretted hydrogen water 11i V,i (hydrogen slphidle solzlution) is _____usually prepared by conducting, the gas into very cold water, which has been previously freed FIG. 35. from air by boiling. The operation is continued until the water is saturated with the gas, which may be readily ascertained by closing the mouth of the flask with the thumb, and shaking it a little: if upon this a pressure is felt from within, the operation may be considered at an end. Sulphuretted hydrogen water must be kept in wellclosed vessels, otherwise it will soon suffer decomposition, the hydrogen being oxidized to water, and a small portion of the sulphur to sulphuric acid, the rest of the sulphur separating. [A solution of hydrogen sulphide, made and preserved under aP pressure of two atmospheres as described by CooKE, is the most convenient form of this reagent. For description and figure of apparatus see the Amnerican Cheminst, Vol. 4, p. 1 3.-ED.] Pure sulphuretted hydrogen water must be perfectly clear and strongly emit the odor of the gas; when treated with ferric chloride, it must yield a copious precipitate of sulphur. Addition of ammonia must not impart a blackish appearance to it. It must leave no residue upon evaporation on platinuml. Uses.- I-ydrogen sulphide has a strong tendency to undertro decomposition with metallic oxides, forming water and metallic sulphides, which latter being mlostly insoluble in water are usually precipitated in the process. By modifying the conditions of precipitation we may divide the whole of the precipitable metals into groups, as will be found explained in Section III. Some of the precipitated sulphides exhibit characteristic colors indicative of the individual metals which they contain. The great facility with which hydrogen sulphide is decomposed renders this substance also a useful reducing agent for many compounds; thus it serves, for instance, to reduce ferric salts to ferrous salts, chromic acid to chromic oxide, etc. In these

Page  56 56r REEAGENTS. I~ 35, 36. reductions the sulphur separates in the form of a fine white powder. NV hether the hydrogen sulphide had better be applied in the gaseous form or in aqueous solution depends upon circumstances. ~ 35. IV. BASES, METALS, AND SULPHIDES. Bases are divided into oxygen bases and sulphur bases (see ~ 25). The oxygen bases and the corresponding oxides are classified into alkalies, alkali-earths, earths proper, and oxides or hydroxides of the heavy metals. The alkalies are readily soluble in Mwater; the alkali-earths dissolve with greater difficulty in that menstrum; and magnesia, the last mnenmber of the class, is only very sparingly soluble in it. The earths proper and the oxides and hydroxides of the heavy metals are insoluble in water or nearly so (except thallious hydroxide). The solutions of the alkalies and alkali-earths are caustic when sufficiently concentrated; they have an alkaline taste, change the yellow color of turmeric paper to brown, and restore the blue tint of reddened litmus paper; they saturate acids completely, so that even the salts which they form with strong acids do not change vegetable colors, whilst those with weak acids generally have an alkaline reaction. The earths proper and the hydroxides and oxides of the heavy metals combine likewise with acids to form salts, but, as a rule, they do not entirely take away the acid reaction of the latter. The sulphur bases containing the metals of the alkalies and alkali-earths are soluble in water. The solutions have a strong alkaline reaction. The other sulphur bases do not dissolve in water. a. OXYGEN BASES. a. ALKALIES. ~ 36. 1. POTASSIrM HYDROXIDE, OR POTASSA, K O H, AND SODIFM HYDROXIDE, OR SODA, Na 0 H.* The preparation of perfectly pure potassa or soda is a difficult operation. It is advisable, therefore, to provide, besides perfectly pure caustic alkali, also some which is not quite pure, *Also termed potassium hydrate and sodium hydrate.

Page  57 ~ 36.] POTASSA AND SODA. 57 and some which, being free from certain impurities, may in many cases be safely substituted for the pure substance. a. Common solution of socda.-Put into a clean cast-iron pan provided with a lid, 3 parts of crystallized sodium carbonate of commerce and 15 parts of water, heat to boiling,'and add, in small portions at a time, thick milk of lime prepared by pouring 3 parts of warm water over 1 part of fresh-burned quicklimne, and letting the mixture stand in a covered vessel until the lime is reduced to a uniform pulpy mass. Keep the liquid in the pan boiling whilst adding the milk of lime, and for a quarter of an hour longer; then filter off a small portion, and try whether the filtrate still causes effervescence in hydrochloric acid. If this is the case, the boiling must be continued, and if necessary some more milk of lime must be added to the fluid. When the solution is perfectly free from carbonic acid, cover the pan, allow the fluid to cool a little, and then draw off the nearly clear solution from the residuary sediment, by means of a siphon filled with water, and transfer it to a glass flask. Boil the residue a second and a third time with water, and draw off the fluid in the same way. Cover the flask close with a glass plate, and allow the lime suspended in the fluid to subside completely. Scour the iron pan clean, pour the clear solution back into it, and evaporate it to 6 or 7 parts. The solution so prepared contains from 9 to 10 per cent. of soda, and has a specific gravity of from 1.13 to 1.15. If it is wished to filter a solution of soda which is not quite clear, a covered funnel should be used, which has been charged first with lumps of white marble and then with powder of the same, the fine dust being rinsed out with water before the filter is used (GRAEGER). Solution of soda must be clear, colorless, and as free as possible from carbonic acid; ammonium sulphide must not impart a black color to it. Traces of silicic acid, alumina, and phosphoric acid are usually found in a solution of soda prepared in this:manner; on which account it is unfit for use in accurate experimnents. Solution of soda is kept best in bottles closed with ground glass caps. In default of capped bottles, common ones With well-ground stoppers may be used, in which case the neck nmust be wiped perfectly dry and clean inside and the stopper coated with paraffine; since, if this precaution is neglected, it will be found impossible after a time to remove the stopper, particularly if the bottle is only rarely opened. b. Potassa purified with alcohol. —Dissolve some caustic potassa of commerce in alcohol, in a stoppered bottle, by digestion and shaking; let the fluid stand, decant it, or filter it if necessary, and evaporate the clear fluid in a silver dish over the gas or spirit lamp until no more vapors escape; adding from time to time, during the evaporation, some water to pre vent blackening of the mass. Place the silver dish in cold water until it has sufficiently cooled; remove the cake of

Page  58 58 REAGENTs. L~ 36, potassa from the dish, break it into coarse lumps in a hot mortar, and keep in a well-closed glass bottle. When required for use, dissolve a small lump in water. The potassa so prepared is sufficiently pure for most purposes; it contains, indeed, a minute trace of alumina, but is usually free from phosphoric, sulphuric, and silicic acids. The solution must remain clear upon addition of amrmonium sulphide; hydrochloric acid must only produce a barely perceptible effervescence in it. The solution acidified with hydrochloric acid must, upon evaporation to dryness, leave a residue which dissolves in water to a clear fluid. The solution acidified with hydrochloric acid, and then mixed with ammonia in the least possible excess, must not show any flocks of aloumina, at le'ast until it has stood in a warm place for several hours. The solution acidified with nitric acid must not give any precipitate with a nitric acid solution of ammonium molybdate. e. Potassa prepared with baryta.-Dissolve pure crystals of baryta (~ 38) by heating with water, and add to the solution pure potassium sulphate'until a portion of the filtered fluid, acidified with hydrochloric acid and diluted, no longer gives a precipitate on addition of a further quantity of the sulphate (16 parts of crystals of baryta require 9 parts of potassium sulphate). Let the turbid fluid clear, decant, and evaporate in a silver dish as in b. The potassa so prepared is perfectly pure, except that it contains a trifling admixture of potassium sulphate, which is left behind upon dissolving in a little water. It is but rarely raequired, its use being in fact exclusively confined to the detection of minute traces of aluminium. [d. Absolutely pure soda is best prepared by dissolving sodium in pure water in a silver dish and evaporating until a drop of the liquid solidifies on cooling. This preparation is now to be had in commerce.-ED.] Uses.-The great affinity which the fixed alkalies possess for acids renders these substances powerful agents to effect the decomposition of the salts of most bases, and consequently the precipitation of those bases or oxides which are insoluble in water. 3Many of the so precipitated hydroxides redissolve in an excess of the precipitant, as, for instance, those of alumniniumn, chrominnum, and lead; whilst others remain undissolved, as those of iron, bismuth, etc. The fixed alkalies serve therefore also as a means to separate the former from the latter. Potassa and soda dissolve also many salts (e.g., lead chromate, sullphur comnpounds, etc.), and contribute thus to separate and distinguish thlemn from other substances. Many of the hydroxides and oxides precipitated by the action of potassa or soda exhibit peculiar colors, or possess other characteristic properties that may serve to lead to the detection of the individual metal which they respectively contain; such are, for instance, the precipitates of mnainganous hydroxide, ferrous hydroxide, mer

Page  59 ~ 37.1 A.IMONIA. 5I curous oxide, etc. The fixed alkalies expel ammonih from its salts, and enable us thus to detect that body by its smell, its action on vegetable colors, etc. ~ 37. 2. AMMONIA N I,.3. AMMONIUM HYDROXIDE N H4 0 H. Preparation.-Ammonia is obtainable in commerce in a very pure state.* For preparing, it on a small scale the following method answers well. Introduce into a flask 4 parts of amlnonium chloride, either crystallized or in coarse powder, and ti e dry slacked lime prepared from 5 parts of quicklime, mix jy shaking, and cautiously add enough water to make the powder agglomerate into lumps. Set the flask in a sand bath and connect it with a rather large wash-bottle and delivery tube. Put a small quantity of water in the wash-bottle, and about 10 parts of water in the flask destined to absorb the gas. Place the latter in cold water, and then begin to apply heat. Evolution of gas speedily sets in. Continue to heat until no more bubbles appear. Open the cork of the flask to prevent the receding of the fluid. The solution of alnlnonia contained in the washing bottle is impure, but that contained in the receiver is pure; dilute it with water until the specific gravity is about.96 = 10 per cent. of ammonia. KSeep the fluid in bottles closed with ground stoppers. Tests.-Solution of ammonia must be colorless, and ought not to leave the least residue when evaporated in a platinumn dish. When heated with an equal volume of lime water, it should cause no turbidity, at least not to a very marked extent (carbonic acid). [ Concentratecd ammonia precipitates lime water and must be diluted before applying this test for carbonic acid. —ED.] When supersaturated with nitric acid, neither solution of barium nitrate nor of silver nitrate must render it turbid, nor must hydrogen sulphide impart to it the slightest color. lUses.-Solution of ammonia, although formed by conducting ammoniacal gas (Nil,) into water and suffering escape of that gas upon exposure to the air, and much quicker when heated, may be regarded as a solution of hydroxide of ammonium (N FI 0 II) in water, the first acceding molecule of water 1H20 beingo assumed to form N H140 1 with N H3. Upon this assumption solution of ammonia may be looked upon as an analogous fluid to solution of potassa and solution of soda, which greatly simplifies the explanation of all its reactions, the salts resulting from the neutralization of oxygen acids by sclution of ammonia being assumed to contain ammonium N t., * Of Bela Clapp, Pawtucket, R. I.

Page  60 6 () REAGENTS. [~ 38. instead of N H,. Ammonia is one of the i lost frequently used reagents. It is especially applied for the saturation of acid fluids, and also to effect the precipitation of a great many metallic hydroxides; many of these precipitates redissolve in an excess of arnmonia, as, for instance, the hydroxides of zinc, cadminurn, silver, copper, etc., whilst others are insoluble in free ainmocnia. This reagent may therefore serve also to separate and distinguish the former from the latter. Some of these precipitates, as well as their solutions in ammonia, exhibit peculiar colors, which may at once lead to the detection of the metal which they contain. MIany of the hydroxides which are precipitated by ammonia fron neutral solutions are not precipitated by this reagent from acid solutions, their precipitation from the latter being prevented by the ammonium salt formed in the process. Compare ~ 56. i. ALKALI EARTHS. ~ 38. 1. BARIUM IHIYDnROIDE, OR BARYTA, Ba (0 H)2. Preparation.-There are many -ways of preparing baryta; but as witherite (barium carbonate) is now cheaply procurable, I prefer the following: Mix intimately together 100 parts of finely pulverized witherite, 10 parts of charcoal in powder, and 5 parts of rosin, put the mixture in an earthenware crucible, lute on the lid with clay, and expose the crucible so prepared to the heat of a brick-kiln. Break and triturate the baked mass, boil repeatedly with water in an iron pot, filter into bottles, stopper, and let them stand in the cold, when large quantities of crystals of barium hydroxide Ba (O H), + 8 I-I, 0 will make their appearance. Let the crystals drain in covered funnels, dry rapidly between sheets of blotting paper, and keep them in well closed bottles. For use dissolve 1 part of the crystals in 20 parts of water, with the aid of heat, and filter the solution. The baryta water so prepared is purer than the mother liquor running off from the crystals. The residue, which is insoluble in water and consists of undecomposecl witherite and charcoal, may be turned to account in the pre. paration of barium chloride. Tests. —Baryta water must, after precipitation of the barium by pure sulphuric acid, give a filtrate remaining clear when mixed with alcohol, and leaving no fixed residue upon evaporation in a platinum crucible. Ulses. —Barium hydroxide being, a strong base, precipitates the metallic hydroxides insoluble in water from the solutions of their salts. In the course of analysis we use it simply to

Page  61 ~~ 39, 40.] HEAVY METALS AND THEIR OXIDES. 61 precipitate magnesia. Baryta water may also be used to pre cipitate those acids which form insoluble barium compounds; it is applied with this view to effect the detection of carbonic acid. the removal of sulphuric acid, phosDhoric acid, etc. ~ 39. 2. CALCIUMI HYDROXIDE, OR LIME, Ca (0 H)2. Calciunm hydroxide is obtained by slacking lumps of pure calcined lime in a porcelain dish, with half their weight of water. The heat which accompanies the combination of the lime and the water is sutficient to evaporate the excess of water. Slacked lirne must be kept in a well-stoppered bottle. To prepare lime water, digest slacked lime for some time \with cold distilled water, shakilng the mixture occasionally; let the undissolved portion of lime subside, decant, and keep the clear fluid in a well-stoppered bottle. If it is wished to have the lime water quite free from all traces of alkalies, baryta and strontia, which are almost invariably present in slacked lime prepared from calcined limlestone, the liquids of the first two or three decantations must be removed, and the fluid decanted afterwards alone made use of. Tests.-Lirne water must impart a strongly-marked brown tint to turmeric paper, and give a not too inconsiderable precipitate with sodium carbonate. It speedily loses these properties upon exposure to the air, and is thereby rendered totally unfit for analytical purposes. Uses.-Lime forms with many acids insoluble, with others soluble salts. Lime water may therefore serve to distinguish the forimer acids, which it precipitates from their solutions, from the latter, which it will of course fail to precipitate. Manly of the precipitable acids are thrown down only under certain conditions, e. y., on boiling (citric acid), which affords a ready means of distinguishing between them by altering these conditions. We use lime water in analysis principally to effect the detection of carbonic acid, and also to distinguish between citric acid and tartaric acid. Slacked lime is chiefly used to liberate amrnonia from ammoniuam salts. 7. HEAVY METALS AND THEIR OXIDES AND HYDROXIDES ~ 40. 1. ZINc, Zn. Select zinc of good quality and, above all, perfectly free from arsenic. The method described ~ 132, 10 will serve to

Page  62 62 REAGENTS. [~ 41 detect the presence of the slightest trace of this substance. Fuse the metal and pour it in a thin stream into a large vessel with water. Zinc which contains arsenic must be rejected, for no practicable process of purification is known (ELIOT alnd STORER).* Uses.-Zinc serves in qualitative analysis for the evolution of hydrogen, and also of arsenetted and antimonetted hydrogenl gases (compare ~ 131, 10, and ~ 132, 10); it is occasionally used also to precipitate some metals from their solutions; in which process the zinc simply displaces the other metal (Cu SO4 + Zn- Zn SO, + Cu). Zinc is also sometimes used for the detection of sulphurous acid and phosphorous acid; it must then be tested for zinc sulphide or zinc phosphide, as the case may be, see ~~ 139 and 148. 2. IRON, Fe. Iron reduces many metals and precipitates them from their solutions in the metallic state. We use it especially for th6 detection of copper, which precipitates upon it with its characteristic color. Any clean surface of iron, such as a knife-blade, a needle, a piece of wire, etc., will serve for this purpose. 3. COPPER, CU. We use copper exclusively to effect the reduction of mercury, which precipitates upon it as a white coating shining with silvery lustre when rubbed. A copper coin scoured with fine sand, or in fact any clean surface of copper, may be employed for this purpose. ~41. 4. LEAD DIOXIDE, Pb O_. PJ'epa?'ation.-Dissolve separately 4 parts of crystallized lead acetate and 3 parts of crystallized sodium carbonate in hot water, and filter if needful; mix the solutions, and pass wellwashed chlorine gas through the mixture until it has become dark-brown and all effervescence from escape of carbon dioxide has ceased. Throw on a filter and wash with hot water until silver nitrate no longer causes any turbidity in the washings. The contents of the filter are dried for use. —W6HLER. 1'ests.-Lead dioxide, when boiled with thrice its bulk of pure nitric acid for several minutes and allowed to settle, must * According to GUNNING (Scheikundige Bijdragen, Deel I. Nr. I, p. 113), the purification may be effected by repeated fusion with a mixture of sodiurm carbonate and sulphur.

Page  63 ~~ 42, 43.] AMMONIUM SULPHIDE. 63 not communicate the faintest red color to the acid (absence of manganese). tUes. —This reagent serves to oxidize chromic oxide when in alkaline solution, to chromic acid. It also is a most delicate and characteristic test for manganese. ~ 42. 5. B3ISMUTHOUS HYDROXIDE, Bi 0. 0 HIt. Pr'eparatioon.-Dissolve bismuth, freed from arsenic by fusion with hejpar smuphuris, in dilute nitric acid; dilute the solution till a slight permanent precipitate is produced; filter and evaporate the filtrate to crystallization. Wash the crystals with water containing nitric acid, triturate them with water, add ammonia in excess, and let the mixture digest for some time; then filter, wash, and dry the white precipitate, and keep it for use. Tests.-The bismuth hydroxide is dissolved in dilute nitric acid and precipitated with sulphuretted hydrogen. Part of the precipitated sulphide is treated with ammonia and filtered, part is treated with ammonium sulphide and filtered. The filtrates are then mixed with hydrochloric acid in excess; the first should give no precipitate, the second only a white precipitate of sulphur. Uses.-Bismuth hydroxide when boiled with alkaline solutions of metallic sulphides decomposes with the latter, giving rise to the formation of metallic oxides and bismuth sulphide. It is better adapted to effect decompositions of this kind than cupric oxide, since it enables the operator to judge immediately upon the addition of a fresh portion whether the decomposition is complete or not. It has still another advantage over cupric oxide, viz., it does not, like the latter, dissolve in the alkaline fluid iIn presence of organic substances; nor does it act as a rednc.ilig agent upon reducible oxygen compounds. We use it prinlcipally to convert arsenious sulphide and arsenic sulphide into arsenious and arsenic acids, for which purpose cupric oxide is altogether inapplicable, since'it converts the arsenious acid immediately into arsenic acid, being itself reduced to the state of cuprous oxide. b. SULPHIDES. ~ 43. 1. AMMONIUM SIJLPHIDE. We use in analysisa. Colorless ammoniurn monosulphide. (N 14)2,S. t The basic nitrate of bismuth of commerce, if perfectly free from arseni and antimony, may also be used instead of the hydroxide.

Page  64 64 REAGENTS. [~ 43 b. Yellow amrnmowznium polysulpiclde. (N H4)2Sx. Preparation.-a. Transmit hydrogen suilphide through 3 parts of ammonia solution until no further absorption takes place; then add 2 parts more of the same ammlnonia solution. The action of hydrogen sulphide upon ammonia gives rise to the formation, first, of (N H4)2S, [2N,4 0 1O ) and It,S - (N H,;)S and 2(II,0)], then of N -14S 1H; upon addition of the same quantity of solution of ammolnia as has been saturated, the ammollia decomrnposes with the aimnoniumn hydrosulphide and ainmonium mnonosulphide is formed, thus: NIH,S H + N 11O 11 - (N HI,)2 S + 1120. The rule, however, is to add only two-thirds of the quantity of solution of ammonia, as it is better the pre)aration should contailn a little anmmonini hydrosulphide than that free ammonia should be present. To employ ammonium hydrosulphide ilstead of the sinmple monosulphide is unnecessary, and telnds to increase the slnell of sulphuretted hydrogen in the laboratory, as the prelparation allows that gas to escape when ill contact with mnetallic acid sulphides. Ammoninum sulphide should be kept in well-corked phials. It is colorless at first, and deposits no sulphur upon addition of acids. Upon exposure to the air, however, it acquires a yellow tint, owing to the forlmation of ammonium disulphide, which is attended also with foi'mation of almnonia and water, thus: 2(N H14)2S + 0 (N HI)42S2 + 2N IH, + 112O. Continued action of the oxy gen of the air upon the ammnninum sulphide tends at first to the formation of still higher snlphides; but afterwards the fluid deposits sulphurl, and finally all the ammonium sulphide is decomposed and the solution conltains nothingr lbut ammonia and ammnonium thiosulphate. The formation of thiosulphate proceeds.thus: (N H-I4)S2 + O, (N IT4)2S2 03. b. The amlnoniim sulphide which has turned yellow by lnoderate exposure to the air may be used for all purposes requiring the employment of yellow amrnmonium sulphide. Tile yellow sulphide may also be expeditiously prepared by digesting the monosulphide with some sulphur. All kinds of yellow anmmoll unm sulphide deposit sulphur and look turbid and nilly on being mixed with acids. Te'ts. —-Amnmonium sulphide must strongly emit the odor peculiar to it; with acids it must evolve abundance of sulphuretted hydrogen; the evolution of gas may be attended by the separation of a pure white precipitate, but no other precipitate must be formed. Upon evaporation and exposure to a red heat in a platinum dish it must leave no residue. It must not, even on Leating, precipitate or render turbid solution of magnesium sulphate or solution of calcium chloride (free aminonia, ammuonium carbonate). Uses.-Ammoniumn sulphide is one of the most frequently employed reagents. It serves (a) to effect the precipitation of those metals which hydrogen sulphide fails to throw down from

Page  65 ~ 44.] SALTS. 60 acid solutions, e.g. of iron, cobalt, etc., (N II,)3S + Fe S 04Fe S + (N I14,)S 04; (b) to separate the metallic sulphides thrown down from acid solutions by hydrogenl sulphide, since it dissolves some of them to sulphur salts, as for instance, the sulphides of arsenic and antimony, etc. (N I-I4)3As S,, etc.), whilst leaving others undissolved-for instance, lead sulphide, cadmium sulphide, etc. The amnionium sulphide used for this purpose must contain an excess of sulplhur if the metallic sulphides to be dissolved will dissolve only as higher sulphides, as, for instance Sn S, which dissolves with ease only as Sn S2. From solutions of alumilliun and chromium salts ammonium sulphide precipitates hydroxides, with escape of sulphuretted hydrogen, as the sulphur compounds corresponding to these hydroxides cannot form in the wet way. [Al, (S 04)3 + 3 (N,4)2S + 6 II20 -Al, (O I)6 + 3 (N H4)2 S 04 + 3 2,S]. Salts insoluble in water are thrown down by ammonium sulphide unaltered from their solutions in acids; thus, for instance, calcium phosphate is precipitated unaltered from its solution in hydrochloric acid. ~ 44. 2. SODIUM SULPHIDE ia2S. P_'efpar'ation.-Same as ammonium sulphide, except that solution of soda is substituted for solution of ammonia. Filter, if necessary, and keep the fluid obtained in well-stoppered bottles. If required to contain some higher sulphide of sodium digest it with powdered sulphur.'7Ses. —Soditum sulphide must be substituted for ammonium sulphide to effect the separation of cupric sulphide from sulphur compounds soluble in alkaline sulphides, e.g. from stanllnous sulphide, as cuprous sulphide is not quite insoluble in ammonium sulphide. V. SALTS. Of the many salts employed as reagents those of potassium, sodium, and ammonium are used principally on account of their acids; salts of sodium may therefore often be substituted for the corresponding potassium salts, etc. Thus it is almost always a matter of perfect indifference whether we use sodium carbonate or potassium carbonate, potassium ferrocyanide or sod lurm ferrocyanide, etc. I have therefore here classified the salts of the alkali metals by their acids. With the salts of the alkali-earth metals and those of the heavy metals the case is

Page  66 66 REAF(ENTS. [~ 45, 46. different; these are not used for their acid, but for their base; we may therefore often substitute for one salt of a base another similar one, as e.g. barium nitrate or acetate for barium chloride, etc. For this reason I have classified the salts of the alkali, earth metals and of the heavy metals by their bases. a. SALTS OF THE ALKALI METALS. ~ 45. 1. POTASSIUM S3ULPHIATE, K2S O,. Preparation. —Purify potassium sulphate of commerce by recrystallization, and dissolve 1 part of the pure salt in 12 parts of water. Uses.-Potassinm sulphate serves to detect and separate barium and strontiaum. It is in many cases used in preference to dilute sulphuric acid, which is employed for the same purpose, as it does not, like the latter reagent, disturb the neutrality of the solution. ~ 46. 2. HYDROGEN DISODIUM PHOSPHATE, OR SODIUI PHOSPHATE. Na H P 04. 12 120. t Preparation.-Purify " phosphate of soda " of commerce by recrystallization, and dissolve 1 part of the pure salt in 10 parts of water for use. Tests.-Solution of sodium phosphate must not become turbid when.heated with ammonia. The precipitates which solution of barium nitrate and solution of silver nitrate producee in it must completely, and without effervescence, redissolve upon addition of dilute nitric acid. Uses.-Sodium phosphate precipitates the alkali-earth metals and all the heavy metals from solutions of their salts. It serves in the course of analysis, after the separation of the heavy metals, as a test for alkali-earth metals in general; and, after the separation of barium, strontium, and calcium, as a special test for the detection of magnesium; for which latter purpose it is used'in conjunction with ammonia, the magnesium precipitating as magnesium ammonium phosphate. * Or, OK ONa ~Or K S OK t Or, Po-o Na + 12 H20 7 \' OK __1 ~~0It

Page  67 ~ 47, 48.] SODIUM ACETATE. 67 ~ 47. 3. AMMONIUM OXALATE. (Ni H4)2 C24O. 2 aq.* ]'reparation.-Dissolve commercial oxalic acid to saturation in hot hydrochloric acid of 10 to 12 per cent., cool rapidly with constant agitation, wash the crystals (best with help of a filter pulnp) with cold water to remove most of the hydrochloric acid, redissolve in hot water, filter hot to separate dirt, cool again with stirring, and wash the crystals with cold water until chlorine is mostly removed.-STOLBA. Dissolve the pure oxalic acid in 2 parts of distilled water, with the aid of heat, add solution of aininonia until the reaction is distinctly alkaline, and put the vessel in a cold place. Let the crystals drain. The mother liquor will, upon proper evaporation, give another crop of crystals. Dissolve 1 part of the pure salt in 24 parts of water for use. Test8s.-The solution of ammlonium oxalate must not be precipitated nor rendered turbid by hydrogen sulphide, nor by amnmonium sulphide. Ignited on platinum, the salt must volatilize without leaving a residue. Uses. —Oxalic acid forms with calciumn, strontimn, barium, lead, and other metals, insoluble or very diflicultly soluble compounds; ammonium oxalate produces therefore in the aqueous solutions of the salts of these bases, precipitates of the corresponding oxalates. In analysis it serves principally for the detection and separation of calcium. ~ 48. 4. SoDIvu ACETATE Na C,11,0,. 3 aq.t Preparation.-Dissolve crystallized sodium carbonate in a little water, add to the solution acetic acid to slight excess, evaporate to crystallization, and purify the salt by recrystallization. This salt is now to be had very pure in commerce. For use dissolve 1 part of the salt in 10 parts of water. Tests.-Sodiumrn acetate must be colorless and free from ermpyreumatic matter and inorganic acids. U1ses.-The stronger acids in the free state decompose sodium acetate, combining with the base and setting the acetic acid free. In the course of analysis sodium acetate is used p)rincipally to preci,)itate ferric phosphate (which is insoluble iL COONI4 C H3 * Or, i + 2 HO t Or, d + 3 120. U U UN H4 C 00 Na

Page  68 63 8REAGENTS. [~ 49 acetic acid) from its solution in hydrochloric acid. It serves also to effect the separation of ferric oxide and alumina, which it precipitates on boiling from the solutions of their salts. ~ 49. 5. SODIUUM CARBONATE (Na, C03. 10 aq.*) Prvparation. —It is best to provide this salt in several grades of purity, as follows: a. For orclinary use as soluttion select clear, colorless crystals of "'; sal soda," and dissolve theln in twice their weight of water. The solution is likely to contain a little sulphate, chloride, and silicate, and if these are present it must not be used in processes for the detection of the corresponding acids. As sodium carbonate attacks glass, the salt should be kept in the dry state, and dissolved shortly before use. b. Free fromn sulphur and chlorine. Finely pulverize " bicarbonate of soda" of commerce, put the powder into a funnel stopped loosely with some cotton, mlake the surface even, cover it with a disk of thick filter paper with turned-up edges, and wash by pouring small quantities of water on the paper disk until the filtrate, when acidified with nitric acid, is not rendered turbid by solution of silver nitrate, nor by solution of barium chloride. Let the salt dry, and then convert it by gentle ignition into the simple carbonate. This is effected best in a vessel of silver or platinum; but it may be done also in a perfectly clean iron, or, on a small scale, in a porcelain dish. Dissolve 1 part of the anhydrous salt in 5 parts of water. [c. Free from silica. The salt as prepared in b, is liable to conltain silica as well as sand and dirt. To purify it further, dissolve in twice its weight of water, or dissolve" sal soda" crystals in their own weight of water, filter, and pass into the cold solution washed and pure carbon dioxide, but not to complete saturation. The crystals of hydrogen sodium carbonate that separate are drained in a funnel, washed with cold water, dried, and Vently ignited, as above directed, as long as water is given off. Prepared in glass vessels by this method, sodium carbonate may be readily procured containing but — 10 — of silica.-EDITOR. d. To a clear and cold solution of 145 grins. of sal soda crSstals in 100 cc. of water, add gradually with vigorous stirring, a solution of 60 pasts of purified oxalic acid (see ~ 47) in 100cc. of warm water. When sodium oxalate ceases to separate, break up the crystals, and transfer them to a 6-inch filter connected *Or, C o~ Na + 10 ao.

Page  69 ~ 50.] AMMONIUM CARBONATE. 6 with the Bunsen filter pump, wash with 500cc. of water and dry. Heat to full redness in a platinumn dish until the oxalate is fully decomposed, dissolve, filter, and evaporate to dryness. -J. LAWRENCE SMITH, prlivate communication.] ]Tests.-Sodiuin carbonate must be perfectly white. Several gralmies of the salt must dissolve in water without turbidity, and if the salt is to be used in a flux (see ~ 78), without leaving grains of sand. Its solution, after supersaturation with nitric acid, must not be rendered turbid by barium chloride or silver nitrate; nor nmust addition of potassiumn sulphocyanate impart a red, or warminlg with ammoniumn molybdate and nitric acid a yellow tint to it, or give a yellow precipitate; the residue which remains upon evaporating its solution to dryness, after previous supersaturation with hydrochloric acid, must leave no residue (silica) when redissolved in water. When fused in a glass tube with potassium cyanide for a long time in a current of carbon dioxide, it should give no trace of a dark saulimate (arsenic). See ~ 132, 12. Uses. —With the exception of the alkali metals, sodium carblonate precipitates all the metals in the form of normal or basic carbonates. Those metals which form soluble acid carbollates require boiling for their complete precipitation from acid solutions. MBany of the precipitates produced by the action of sodium carbonate exhibit a characteristic color, which may lead to the detectioni of the individual metals which they respectively contain. Solution of sodiumn carbonate serves also for the decomposition of many insoluble salts, more particularly of those with organic acids. Upon boiling with sodium carbollate these salts are converted into insoluble carbonates, whilst the acids combine with the sodium, and are thus obtained in solution. Sodium carbonate is often used also to saturate free acids. ~ 50. 6. A.m3m0uNIUM CARBONATE (N H,)2 C O,.* Preparation.-Take commercial "carbonate of ammonia entirely free from any smell of animal oil, such as is prepared by subllimation, carefully scrape off the outer and inner surface of the mass, and dissolve one part of the salt by digestion with 4 parts of water to which one part of ammonia solution has been added. Tests. —Pure ammonium carbonate must completely volatilize. Neither solution of barium nitrate nor of silver nitrate, nor hydrogen sulphide, must color or precipitate it, after supersaturation;vith nitric acid * Or, C 0, o N H

Page  70 70 REAGENTS. [~ 51 Uses.-Ammoninm carbonate precipitates, like sodium carbonate, most metals; it is generally employed inl preference to the latter reagent, because it introduces no non-volatile body into the solution. Complete precipitation of many of the metals takes place also only on boiling. Several of the precil)itates redissolve again in an excess of the precipitant. In like manaler ammonium carbonate dissolves many hydroxides and sulphides, and thus enables us to distinguish and separate them fromn others wlhich are insoluble in this reagent. Ammonium carbonate, like ammonia solution, and for the same reason, fails to precipitate from acid solutions many metals which it precipitates from neutral solutions. (Compare ~ 53.) We use amrnmonium carbonate in analysis principally to effect the precipitation of barium, strontium and calcium, and the separation of these substances from magnesium; also to separate arsenious sulphide, which is soluble in it, from antimnonious sulphide, which is insoluble. ~ 51. 7. HYDROGEN SODIUM SULPHITE, I ha SO,*. Preparation.-IIeat 5 parts of copper tacks or clippings with 20 parts of concentrated sulphuric acid in a flask, and conduct the sulphur dioxide gas evolved, first through a washing bottle containing some water, then into a flask containing 7 p.arts of clean crystallized sal-soda, and from 20 to 30 parts of water, and which is not much more than half full; continue the transmission of the gas until the evolution of carbon dioxide ceases. Keep the solution, which smells strongly of sulphurous acid, in a well-stoppered bottle. Tests.-Acid sodium sulphite, when evaporated to dryness with pure sulphuric acid, must leave a residue,t the aqueous solution of which is not altered by hydrogen sulphide, nor precipitated yellow by heating with a solution of ammonium mol-vbdate mixed with nitrict acid. Uses. —Sulphurous acid has a great tendency to pass to the state of sulphuric acid by absorbing oxygen. It is therefore one of our most powerful reducing agents. Acid sulphite of; sodium, which has the advantage of being less readily decoinmposed than sulphurous acid, acts in an analogous manner upon addition of acid. We use it principally to reduce arsenic acid to arsenious acid, chromnic acid to chromic oxide, and ferric oxide to ferrous oxide. It will serve also to effect the separation of * Or, S 0<0 Na f The evaporation is attended with copious evolution of s:dlphur dioxide,

Page  71 ~ 52-54.] POTASSIUM PYROANTIMONATE. 71 arsenious sulphide, which is soluble in it, from the sulphides of antimony and tin, which are insoluble in this reagent. ~ 52. 8. POTASSIUM NITRITE, KiN.* Prepatration.-In an iron pan fuse 1 part of nitre, add 2 )arts of lead, and keep stirred with an iron rod. Even at a low red heat the lead blecomes for the most part oxidized and converted into a yellow powder. To oxidize the remainder, the heat is increased to visible redness and maintained at that point for half an hour. Allow to cool, treat with cold water, filter and pass carbon dioxide through the filtrate. This precipitates almost the whole of the lead in solution, the remainder is removed with a little hydrogen sulphide. Evaporate the clear fluid to dryness, finally with stirring, and fuse in order to destroy ally potassium thiosulphate (AuG. STROMEYER). When required, dissolve 1 part in 2 parts of water, neutralize cautiously with acetic acid, and filter. Tests. —Potassiuinm itrite must, upon addition of dilute sul phuric acid, copiously evolve nitrogen dioxide gas. Uses.-Potassiumn nitrite is an excellent means to effeUt the detection and separation of cobalt, in the solutions of which metal it produces a precipitate of potassium cobaltic nitrite. It serves also in presence of free acid to liberate iodine from its compounds. ~ 53. 9. POTASSIUM DICHROMATE, KI, Cr2 O,7. Preparation. — Purify "biehrolmate of potash " by recrystallization, and dissolve one part in 10 parts of water for use. lUses.-Potassium dichromate decomposes most of the soluHle metallic salts. MIost of the precipitated chromnates are very sparinlgly soluble, and many of them exhibit cllarateristic colors which lead readily to the detection of the particular netal which they respectively contain. We use potassium dichromate principally as a test for lead. ~54. 10. POTASSIUM PYIROANTIMONATEt I2 K2 Sb2 07.61T0.0 Preyparation.-Project a mixture of equal parts of pulverized tartar-emetic and potassium nitrate in small portions at a /O K Cr ~2-~}'E Sb O-OH Or, NO - OK. * Or, >O Or, >O + GH20. Cr 02-0 K. Sb 0-0 H t Metantimonate of former editions. O0 K

Page  72 72 REAGENTS. L~ time into a red-hot crucible. After the mass has deflagrated, keep it at a moderate red heat for a quarter of an hour; it froths at first, but after some time it will be in a state of calm fusion. Remove the crucible from the fire, let the mass get nea ly cold, and extract it with warm water. Transfer to a suitable vessel, by rinsing-, and decant the clear fluid from the heavy white powder deposited. Concentrate the decanted fluid by evaporation. After one or two days a doughy mass will separate. Treat this mass with three times its volumne of cold water, working it at the same time with a spatula. This operation will serve to convert it into a fine granular powder, to which add the powder from which the fluid was decanted, wash well with boiling water, till the washings cease to be alkaline, and dry on blotting paper. 100 parts of tartar-emetic give about 36 parts of the pyroantimonate (BRUNNER). Tests and CUses. —Granular potassium antimonate is very sparingly soluble in water, requiring 90 parts of boiling and 250 parts of cold water for solution. The solution is best prepared immediately before use, by boiling the salt with water, and filtering from the undissolved portion. The solution must be clear and of neutral reactionl; it must give no precipitate with solution of potassium chloride, nor with solution of ammlloniun chloride; but solution of sodium chloride must produce a crystalline precipitate in it. Potassium pyroantimonate is a valuable reagent for soda, but its employment requires great caution, see ~ 90. ~ 55. 11. AMMONIUM MOLYBDATE (N HI,)Mo 0,, DISSOLVED IN NITRIC ACID.-M OLYBDIO SOLUTION. Prelparati;on.-Triturate molybdenum sulphide with about an equal bulk of coarse quartz sand washed with hydrochloric acid, until it is reduced to a moderately fine powder; heat to faint redness, with repeated stirring, until the mass has acquired a lemnon-yellow color (which after cooling turns whitish). With small quantities this operation may be conducted in a flat platinum dish, with large quantities in a muffle. Extract with solution of ammonia, filter, evaporate the filtrate, heat the residue to faint redness until it appears yellow or white, and then digest for several days with nitric acid in the water bath, in order to convert any phosphoric acid present to the tribasic state. Whenl the nitric acid is evaporated dissolve the residue in 4 parts of solution of ammlonia, filter rapidly, and pour the filtrate into 15 parts by weight of nitric acid of 1'20 specific gravity. Keep the mixture standing several days in a moderately warm place, which will cause the separation of any remnainiu~ traoces of phosphoric acid as amnonium phosph(o

Page  73 ~ 6.] AxIMONIUM CHLORIDE. 73 inolybdate. Decant the colorless fluid from the precipitate. anlld keel) it for use. IHeated to 40~ no white precipitate (Ino lybdie acid or an acid salt of the same) will separate; buf above that poinlt precipitation -x11l take place unless more nitric acid be added (EGGERTZ). U'es.-Phosphoric acid and arsenic acid form with molybdic acid and ammonia peculiar Ayellow compounds which are almost absolutely insoluble in the nitric acid solution of amimoi;uin molybdate. The phosphoric acid compound is formed in the cold, the arsenic acid compound requires heat. Annlmonium mlolybdate affords therefore an excellent means to detect these acids, and more especially very minute quantities of phsophoric acid inl acid solutions containing aluminium and alkali-earth metals. ~ 56. 12. AMAiONIUM CHLORIDE, N H, CI. Prepcaration. —Select sublimed white sal ammoniac of coinmerce. If it contains iron it must be purified by slowly passillg chlorine gas i:nto the nearly saturated solution for a short time, or until potassiumn ferricyanide gives no blue color with a few drops of the liquid. Ammonia is then added in slight excess, the whole is warmed, filtered from the separated ferric oxide, and evaporated to crystallization. Dissolve 1 part of the salt in 8 parts of water for use. Tests.-Solution of ammnoniumn chloride must leave no fixed residue upon evaporation on platinum. Ammonium sulphide lniust have no action upon it. Its reaction must be perfectly neutral. Uqes.-Ammlnonium chloride serves principally to retain in solution certain oxides (e.g., manganese and magnesium monoxides), or salts (e. g., calcium tartrate) upon the precipitation of other oxides or salts by ammonia or some other reagent. This application of ammonium chloride is based upon the tendency of the ammonium salts to formn double compounds with other salts. Annnoniumn chloride serves also to distinguish between precipitates possessed of similar properties; for instance, to distinguish the mnagnesium-anmmonium phosphate, which is insoluble in ammnonium chloride from other magnlesian precipitates. It is used also to precipitate from their solutioins in potassa variOls substances which are soluble in that alkali, but insoluble in ammollia; e.g., alumina, chromic oxide, etc. In this process the elements of the ammonium chloride transpose with those of the potassa, and potassium chloride, water, and ammonia are forlned. Amlnoniumn chloride is applied also as a special reagent to effect the precipitation of platinum as ammonium platinic, chlo ide.

Page  74 74 REAGENTS. [~ 57 ~ 57. 13. POTASSIUM CYANIDE, K Cy, or K C N. ]repcaration. —Heat potassium ferrocyanide of commerce (perfectly free from potassium sulphate) gently, with stirring, until the crystallization water is completely expelled; triturate the anhydrous mass, and mix 8 parts of the dry powder with 3 parts of perfectly dry potassium carbonate; fuse the mixture in a covered Hessian or, better still, in a covered iron crucible, until the mass is in a faint glow, appears clear, and a sample of it, taken out with a heated glass or iron rod, looks perfectly white. Remove the crucible now from the fire, tap it gently, and let it cool a little until the evolution of gas has ceased; pour the fused potassium cyanide into a heated, tall, crucible-shaped vessel of clean iron or silver, or into a mnoderately hot Hessian crucible, with proper care, to prevent the running out of any of the minute particles of iron which have separated in the process of fusion and have subsided to the bottom of the crucible. Let the mass now slowly cool in a somlewhat warm place. The potassiuln ceanide so prepared is exceedingly well adapted for analytical purposes, although it contains potassium carbonate aid cyanate, which latter is upoll solution in water transformed into ammonlimn carblonate and potassium carbonate [0C O IK + 4 I1 O = -K2 C 03 + (N 114)2C 03]. Keep it in the solid form in a well-stoppe ied bottle, and dissolve 1 part of it in 4 parts of water, without application of heat, when required for use. Tests. —Potassium cyanide lmust be of a milk-white color and quite free from particles of iron or charcoal. It must completely dissolve in water to a clear fluid. It must contain neither silica nor potassium sulphide; the precipitate which lead salts produce in its solution must accordingly be of a white color, and the residue which its solution leaves upon evaporation, after previous supersaturation with hydrochloric acid,* must completely dissolve in water to a clear fluid. Uses. —Potassium cyanide prepared in the manner described, produces in the solutions of most metallic salts precipitates of cyanides of metals or of hydroxides or carbonates which are insoluble in water. The precipitated cyanides are soluble in potassium cyanide, and may therefore by further addition of the reagent be separated fromn the hydroxides or carbonates which are insoluble in potassium cyanide. Some of the metallic cyanides redissolve invariably in the potassium cyanide as double cyranides, even in the presence of free hydrocyallic acid and upon boiling; whilst others combine with cyanogen to * This supersaturation with hydrochloric acid is attended with disengage ment of hydrocyanic acid.

Page  75 ~~ 58, 59.] POTASSIUMr FERRICYANIDE. - 75 new radicals, which remain in solution in combination with the potassium. The most common compounds of this nature are potassium cobalticyanide and potassium ferro- and ferricyanide. These differ from the double cyanides of the other kind particularly in this, that dilute acids fail to precipitate the metallic cyanides which they contain. Potassium cyanide may accordingly serve also to separate the metals which form compounds of the latter description from others the cyanides of which are precipitated by acids from their solution in potassium cyanide. In the course of analysis this reagent is of great importance, as it serves to effect the separation of cobalt from nickel; also that of copper, the sulphide of which metal is soluble in it, from cadmium, whose sulphide is insoluble. ~ 58. 14. POTASSIUM FEROCOYANIDE, K, Fe Cy, + 3 aq. Pfreparation.-The potassium ferrocyanide found in commerce is sufficiently pure. 1 part of the salt is dissolved in 12 parts of water for use. Uses.-Ferrocyanogen forms with most metals compounds insoluble in water, some of which exhibit highly characteristic colors. These ferrocyanides are formed when potassium ferrocyanide is brought into contact with soluble metallic salts, the potassium changing places \vith the metals. The cupric and ferric ferrocyanides exhibit the most characteristic colors of all; potassium ferrocyanide serves therefore particularly as a test for cupric and ferric compound. ~ 59. 15. POTASSIUM FERRICYANIDE, K8 Fe2 Cy,1. Pfreparation.-Conduct chlorine gas slowly into a solution uf 1 part of potassium ferrocyanide in 10 parts of water, with frequent stirring, until the solution exhibits a fine deep red color by transmitted light (the light of a candle answers best), and a portion of the fluid produces no longer a blue precipitate in a solution Of ferric chloride, but imparts a brownish tint to it. Evaporate the fluid now in a dish to ~ of its weight, and let crystallize. The mother liquor will upon further evaporation yield a second crop of crystals equally fit for use as the first. Dissolve the whole of the crystals obtained in 3 parts of water, filter if necessary; evaporate the solution briskly to half its volume, and let crystallize again. The commercial salt may also be employed. The solution, as already remarked,

Page  76 76 REAGENTS. [~~ 60, 61 must produce neither a blue precipitate nor a blue color in a solution of ferric chloride. As this salt decomposes when long kept in solution, it is best preserved and applied in the state of powder. Uses. —Potassium ferricyanide decomposes with solutions of metals in the same manner as potassium ferrocyanide. Of the metallic ferricvanides the ferrous ferricyanide is more particu. larly characterized by its color, and we apply potassium ferricyanide therefore principally as a test for ferrous compounds. ~ 60. 16. PoTAssIUM SULPHOCYANATE, K C N S. Prepcaration.-Mix together 46 parts of anhydrous potassium ferrocyanide, 17 parts of potassium carbonate, and 32 parts of sulphur; introduce the mixture inlto an iron pan provided with a lid, and fuse over a gentle fire; maintain the same temperature until the swellinol of the mass which ensues at first has completely subsided and given place to a state of tranquil and clear fusion; increase the temperature now, towards the end of the operation, to faint redness, in order to decompose the otassium thiosulphate which has been formed in the process. Remove the half refrigerated and still soft mass from the pan, crush it, and boil repeatedly with alcohol of from 80 to 90 per cent. Upon cooling, part of the potassium sulphocyanate will separate in colorless crystals; to obtain the remainder, distil the alcohol from the mother liquor. Dissolve 1 part of the salt in 10 parts of water for use. Tests. —Solution of potassium sulphocyanate must remain perfectly colorless when mixed with perfectly pure dilute hydrochloric acid.;.ses.-Potassium sulphoevanate serves for the detection of ferric compounds, for which it is at once the most characteristic and the most delicate test. b. SALTS OF THE ALKALI-EARTH METALS. ~ 61. 1. BARIUM CHLORIDE, Ba C1, + 2 H, O. The commercial salt may be used after purification by recrystallizing, if need be. Preparation.-a. From heavy spar. Mix together 8 parts of pulverized barium sulphate, 2 parts of charcoal in powder. and 1 part of common rosin. Put the mixture in a crucible,

Page  77 ~ 62.] BARIIUYI NITRATE. 77 and expose it in a wind furnace to a longc-continued red heat. Triturate the crude barium sulphide obtained, boil aLout -9%- of the powder with 4 times its quantity of water. and add hydrochloric acid until all effervescence of hydrogen sulphide has ceased, and the fluid manifests a slight acid reaction. A dd now the remaining -I part of the barium sulphide, boil some time longer, then filter, and let the alkaline fluid crystallize. Drain the crystals, redissolve them in water, and crystallize again. b. From witherite. Pour 10 parts of water upon 1 part of pulverized witherite, and gradually add crude hvdrochloric acid until the witherite is almost completely dissolved. Add now a little more finely pulverized witherite, and heat, with frequent stirring, until the fluid has entirely or very nearly lost its acid reaction; add solution of barium sulphide as long as a precipitate forms; then filter, evaporate the filtrate to crystallization, and purify by crystallizing again. For use, dissolve 1 part of the barium chloride in 10 parts of water. Tests.-Pure barium chloride must not alter vegetable colors; its solution must not be colored or precipitated by hydrogen sulphide, nor by amlnonium sulphide. Pure sulphuric acid must precipitate every fixed particle from it, so that the fluid filtered from the precipitate formed upon the addition of that reagent leaves not the slightest residue when evaporated on platinum foil. Lses. —Barium forms with many acids soluble, with others insoluble compounds. This property of barium affords us therefore a means of distinguishing the former acids, which are not barium chloride from the latter, in the solution of the salts of which this reagent produces a precipitate. The precipitated barium salts severally show with acids a different deportment. By subjecting these salts to the action af acids we are therefore enabled to subdivide the group of plecipitable acids and even to detect certain individual acids. This makes barium chloride one of our most important reagents to distinguish between certain groups of acids, and more especially also to effect the detection of sulphuric acid. ~ 62. 2. BARIUM NITRATE, Ba (N 0,)2*. Preparation.-Treat barium carbonate, no matter whether witherite or that precipitated by sodium carbonate from solulion of barium sulphide, with dilute nitric acid free from chlox NOr N2 > Ba. *Or, N 0. 0 ~ a

Page  78 s 8 ~REAGENTS. [~ ~ 63, 64 rine, and proceed exactly as directed in the preparation of barium chloride from witherite, or else recrystallize the commercial salt. For use, dissolve 1 part of the salt in 15 parts of water. Tests.-Solution of barium nitrate lmust not be made turbid by solution of silver nitrate. Other tests the same as for balium chloride. Uses.-Bariumn nitrate is used instead of barium chloride in cases where it is desirable to avoid the presence of a metallic chloride in the fluid. ~ 63. 3. BARIUM CARBONATE, Ba Co*. Preparation.-Dissolve crystallized barium chloride in water, heat to boiling, and add a solution of ammoniumn carbonate mixed with some caustic ammonia, or of pure sodium carbonate, as long as a precipitate forms; let the precipitate subside, decant five or six times, transfer the precipitate to a filter, and wash ulntil the washing water is no longer rendered turbid by solution of silver nitrate. Stir the precipitate with water to the consistence of thick milk, and keep this mixture in a stoppered bottle. It must of course be shaken every time it is required for use. Tests.-Pure sulphuric acid must precipitate every fixed particle from a solution of barium carbonate in hjydrochloric acid (compare ~ 38). Uses. —Barium carbonate completely decomposes the solutions of certain metallic salts, precipitating from them the whole of the metal as hydroxide and basic salt, whilst some other metallic salts are not precipitated by it. It serves therefore to separate the former from the latter, and affords an excellent means of effecting the separation of ferric okide, and alumina from the monoxides of manganese, zinc, calcium, magnesium, etc. It must be borne in mind, however, that the salts must not be sulphates, as barium carbonate equally precipitates the latter bases from these compounds. ~ 64. 4. CALCIUM SULPHATE, Ca S 04t, crystallized + 2 I-I2 0. Preparation.-Digest and shake powdered crystallized gypsum (selenite) for some time with water; let the undissolved portion subside, decant, and keep the clear fluid for use. Ues. —Calcium sulphate, being difficulty soluble, is a con. *CO <O>Ba. t so2 <> Ca.

Page  79 ~~ 65, 66.] MAGNESIUM SULPIHATE. 79 venient agent in cases where it is wished to apply a solution of a calcium salt or of a sulphate of a definite degree of dilution. As dilute solution of a calcium salt it is used for the detection of oxalic acid; whilst as dilute solution of a sulphate it affords an excellent means of distinguishing between barium, strontium, and calcium. ~ 65. 5. CALCIUM CHLORIE, Ca CI2, crystallized + 6H, 0. Preparation.-Dilute 1 part of crude hydrochloric acid with 6 parts of water, and hdd thereto marble or chalk until the last portion added remains undissolved; add now some slacked lime, then hydrogen sulphide until a filtered portion of the mixture is no longer altered by ammonium sulphide. Then let the mixture stand covered for 12 hours at a gentle heat; filter, exactly neutralize the filtrate, concentrate by evaporation, and crystallize. Let the crystals drain, and dissolve 1 part of the salt in 5 parts of water for use. Tests.-Solution of calcium chloride must be perfectly neutral, and neither be colored nor precipitated by amminoniumn sulphide; nor ought it to evolve ammonia when mixed with potassa or lime. Uses.-Calcium chloride is in its action and application analogoous to barium chloride. For as the latter reagent is used to separate the inorganic acids into groups, so calcium chloride serves in the same manner to effect the separation of the organic acids into groups, since it precipitates some of them, whilst it forms soluble compounds with others. And, as is the case with the barium precipitates, the different conditions under which the various insoluble calcium salts are thrown down enable us to subdivide the group of precipitable acids. ~ 66. 6. MAGNESIUM SULPHATE, iMg S 04, crystallized + 7HI2 O. Preparation.-Dissolve 1 part of magnesium sulphate of commerce in 10 parts of water; if the salt is not perfectly pure, subject it to recrystallization. Tests.-lfagonesiurm sulphate must have a neutral reaction. Its solution, when mixed with a sufficient quantity of amlmonium chloride, must, after the lapse of half an hour, not appear clouded or tinged by ammonia, or by ammonium carbonate or oxalate, or sulphide. Uses.-Magnesium sulphate serves almost exclusively for the detection of phosphoric acid and arsenic acid, which it

Page  80 80 REAGENTS. [~ 67 precipitates from aqueolls solutions of phosphates and arsen ates, in presence of ammonia and amrnoniuml chloride, in the form of almost absolutely illsoluble highly characteristic salts (ammonium inagnesium phosphate or arsenate). [lagnesiuml sulphate is also employed to test amlnonium sulphide (see ~ 43). C. SALTS OF THE IEAVY -METALS. ~ 67 1. FERROUS SULPHATE, Fe S 04,,* crystallized+ 71,O.?P'reparation.-Heat an excess of iron nails free from rust. or of clean iron wire, with dilute sulphuric acid until the evolu: tion of hydrogen ceases; filter the sufliciently concentrated solution, add a few drops of dilute sulphuric acid to the filtrate, and allow it to cool. Wash the crystals with water very slighltly acidulated with sulphuric acid, dry, and keep for use. The commercial " protosulphate of iron"' sold for photographic use answers every purpose of analytical chemistry. Tests. —The crystals of ferrous sulphate must have a fine pale green color. Crystals that have been more or less oxidized by the action of the air, and give a brownish-yellow solution when treated with water, leaving undissolved ferric sulphate behind, must be altogether rejected. I-Iydrogen sulphide must not precipitate solution of ferrous sulphate after addition of some hydrochloric acid, nor even impart a blackish tint to it. U'ses.-Ferrous sulphate has a great disposition to absorb oxygen, and to be converted into ferric sulphate. It acts therefore as a powerful reducing agent. We employ it principally for the reduction of nitric acid, from whicht it separates nitrogen dioxide by withdrawing three atoms of oxygen from it. The decomposition of the nitric acid being attended in this case with the formation of a very peculiar brownish-black cornpounid of nitrogen dioxide with an undecomposed portion of the ferrous salt, this reaction affords a particularly characteristic and delicate test for the detection of nitric acid. Ferrous sulphate serves also for the detection of ferricyanides, with which it produces a kind of Prussian blue, and also to effect the pre. cipitation of metallic gold from solutions of that metal. * Or, SO2 <o> Fe. t Considered as N, O. See ~ 159, 6.

Page  81 ~E 68, 69.] SILVER NTITRATE. 81 ~ 68. 2. FERRIC CHLORIDE, Fe. C10.' Preparation.-Iieat in a flask a mixture of 10 parts of water and 1 part of pure hydrochloric acid with smnall iron nails until no further evolution of hydrogen is observed, even after adding the nails in excess; filter the solution into another flask, and conduct into it chlorine gas, with frequent shaking, until the fluid nolonger produces a blue precipitate in solutionl of potassium ferricyanide. }Heat until the excess of chlorine is expelled. Dilute until the fluid is twenty times the weight of the iron dissolved, and keep for use. Tests.-Solution of ferric chloride must not contain an excess of acid; this may be readily ascertained by stirring a diluted sample of it with a glass rod dipped in amlmollia, when the absence of any excess of acid will be proved by the formation of a precipitate which shakling the -vessel or agcitatingT the fluid fails to redissolve. Potassium ferricyanide must not impart a blue color to it. Uses. — erric chloride serves to subdivide the group of organic acids which calcium chloride fails to precipitate, as it produces precipitates in solutions of benzoates and seccinates, but nlot il cold solutions of acetates and formates. The aqueous solutions of normal ferric acetate and forinate exhibit an intensely red color; ferric chloride is therefore a useful agent for detecting acetic acid and formic acid. Ferric chloride is exceedingly well adapted to effect the decomposition of phosphates of the alkali-earth metals (see ~ 142). It serves also for the detection. of ferrocyanides, with which it produces Prussian blue. ~ 69. 3. SILVER 1NITRATE, Ag N O3.t Preparation.-Dissolve 1 part of the pure crystallized salt in 20 parts of water. Tcsts.-Dilute hydrochloric acid must completely precipitate all fixed particles from solution of silver nitrate, which should have a neutral reaction; the fluid filtered from the precipitated tilver chloride must accordingly leave no residue when evap-C1 Fe' C1 \C1 *or I6C fOr,NO. -0 Ag. -C1

Page  82 82 REAGENTS. [~~ 70, 71. orated on a watch-glass, and must be neither precipitated nor colored by hydrogen sulphide. Uses.-Silver forms with many acids soluble, with others insoluble compounds. Silver nitrate may therefore serve, like barium. chloride, to effect the separation and arrangement of acids into groups. nMost of the insoluble compounds of silver dissolve in dilute nitric acid; chloride, bromide, iodide, and cyanide, ferrocyanide, ferricyanide, and sulphide of silver are insoluble in that mnenstruum. Silver nitrate is therefore a most excellent agent to distinguish and separate from all other acids the acids correspondling to the last enumerated compounds of silver. Many of the insoluble salts of silverl exhibit a peculiar color (silver chromate, silver arsenate) or manifest a characteristic deportment with other reagents or upoln the application of heat (silver formate); silver nitrate is therefore an important agent for the positive detection of certain acids. ~ 70. 4. LEAD ACETATE, Pb (C1HO,302), crystallized + 3H2 0. The best lead acetate of commerce is sufficiently pure; for use dissolve I part of the salt in 10 parts of water. Tests.-Lead acetate must completely dissolve in water acidified with one or tnwo drops of acetic acid; the solution must be quite clear and colorless; hydrogen sulphide must throw down all fixed particles from it. On mixing the solution with amrnonium carbonate in excess, and filtering, the filtrate must no+ show a bluish tint (copper). UCes.-Lead forms with a great many acids compounds insoluble in water, which are marked either by peculiarity of color or characteristic deportment. Lead acetate therefore produces precipitates in the solutions of these acids or of their salts, anld serves for the detection of several of them. Thus lead chromate is characterized by its yellow color, lead phosphate by its peculiar deportment before the blowpipe, and lead malate by its ready fusibility. ~ 71. 5. Mi-eRCuROus NITRATE, Hg, (N 0O)2t, crystallized + 2I, 0. Preparation.-Pour 1 part of pure nitric acid of 1'2 spec. gr. on 1 part of pure mercury in a porcelain dish, and let the *Or HS3C -COO N 0> O2-OHg Or > Pb. t Or, I H3 TC —COOpN N02 -O Hg.

Page  83 ~ 72,0 73.] COPPER SULPHATE. 83 vessel stand twenty-four hours in a cool place; separate the crystals formed from the undissolved mercury and the mnother liquor-, and dissolve them in water mixed with one-sixteenth part of nitric acid, by trituration in a mortar. Filter the solution, and keep the filtrate in a bottle with some metallic nercurry covering the bottom of the vessel. Tests.-The solution of mercurous nitrate must give with dilute hydrochloric acid a copious white precipitate of inercurons chloride; hydrogen sulphide must produce no precipitate in the fluid filtered fromn this, or at all events only a trifling black precipitate (mercuric sulphide). Ues. —Mercurous nitrate acts in an analo+gous manner to the corresponding silver salt. In the first place, it precipitates many acids, and, in the second place, it serves for the detection of several readily oxidizable bodies, e.g., of formic acid, as the oxidation of such bodies, which takes place at the expense of the oxygen of the mercurous salt, is attended with the highly characteristic separation of metallic mercury. ~ 7T2. 6. MIERCIURI CHLORIDE, IHg C12. The corrosive sublimate of colnmerce is sufficiently pure. For use dissolve 1 part of salt in 16 parts of water. Uses. —lIercuric chloride gives with several acids, e.g., with hydriodic acid, peculiarly colored precipitates, and may accordingly be used for the detection of these acids. It is an important agent for the detection of tin, where that metal is in solution in the state of stannous chloride; if only the smallest quantity of that compound is present the addition of mercuric chloride in excess to the solution is followed by separation of merenrons chloride insoluble in water. In a similar Inanner mercuric chloride serves also for the detection of formic acid. ~ 73. 7. COPPER SULPHATE, OR CUPRIC SULPHATE, Cu S 04O, crystallized + 511, 0. Preparation.-This reagent may be obtained in a state of great purity from the residue remaining in the flask in the )recess of preparing hydrogen sodium sulphite (~ 51), by treat. ing with water, a-pplying heat, filtering, adding a few drops of *Or, S 02<0>Cu. 0 u

Page  84 84 REAGENTS. [~ 74, nitric acid, boiling for some time, allowing to crystallize, and purifying the salt by recrystallization. For use dissolve 1 part in 10 parts of water. Tests.-After precipitation by hydrogen sulphide, ammonia and ammonium sulphide must leave the filtrate unaltered. Uses. —Copper sulphate is employed in qualitative analysis to effect the precipitation of hydriodic acid in the form of cuprous iodide. For this purpose it is necessary to mix the solution of of one part of copper sulphate with 29- parts of ferrous sulphate, otherwise half of the iodine will separate in the free state. The ferrous salt changes in this process to ferric salt, at tlhe expense of the cupric sulphate, Awhich latter is thus reduced to cuprous salt;* copper sulphate is used also for the detection of arsenious and arsenic acids; it serves likewise as a test for the soluble ferrocyanides. ~ 74. S. STANNOUS CHLORIDE, Sn Cl2, crystallized + 211 0. Preparation.- Reduce grain tin to powder bv means of a file, or by fusing it in a small porcelain dish, removing from the fire, and triturating with a pestle until it has passed againl to the solid state. Boil the powder for some time with concentrated hydrochloric acid and a few drops of platinic chloride in a flask (taking care always to have an excess of tin in the vessel) until hydrogen gas is scarcely evolved; dilute the solution with 4 times the quantity of water slightly acidulated with hydrochloric acid, and filter. Keep the filtrate for use in a wellstoppered bottle containing small pieces of metallic tin, or some pure tin-foil. If these precautions are neglected the stannous chloride will soon change to staLnic chloride, with separation of white oxychloride, which will render the reagent unfit for use.!Tests.-Solution of stannons chloride must, when added to excess of solution of mercuric chloride, immediately produce a white precipitate of mnerclrous chloride; when treated with hydrogen sulphide it must give a dark brown precipitate; it must not be precipitated nor rendered turbid by sulphuric acid. Uses.-The great tendency of stannous chloride to absorb oxygen, and thus to form stannic oxide, or rather stannic chloride, as the stannic oxide at the moment of its formation decomposes with the free hyrJrochloric acid present-makes this substance one of our most powerful reducing agents. It is more particularly suited to withdraw part or the whole of the chlorine from chlorides. We employ it in the course of analysis as a test for mercury; also to effect the detection of gold. * (Fe S 04)2 + (Cu S 04)2 = Fe2 (S 04)a + Cu2 S 04.

Page  85 ~~ 75, 76, 77. AURIC CHLORIDE. S5 ~ 75. 9. PLATINIC CHLORIDE, Pt C14, cpystallized + 10HO20. Preparation. —I-eat in a clay cruc'ble 5 parts of zinc to fu sion. with sufficient common salt to cover the surface and prevent its oxidation, then introduce 1 part of platinum scraps in small quantities at a time into the fused metal. An alloy is formed from which the zinc is to be removed by digesting ill somewhat dilute common hydrochloric acid, until all effervescence ceases, and subsequent boiling for a time with fresh hvdrochloric acid. The residual platinum is completely washed with water and boiled with nitric acid. It is again washed,. anld finally dissolved by warming with concentrated hydrochloric acid and some nitric acid. Evaporate the solution on the water-bath, with addition of hydrochloric acid, and dissolve the semifluid residue in 10 parts of water for use. Tests. —lPlatillic chloride must, upon evaporation to dryness in the water-bath, leave a residue which dissolves completely in alcohol. Uses.-Platinic chlorlide forms very sparingly soluble double salts with potassium chloride and amnnonium chloride (also with ctesiumn and rubidium chlorides), but a very soluble double salt with sodiumln chloride; it serves therefore for discriminating the alkali metals. ~ 76. 10. SODIUM PALLADIO-CHrLORIDE Pd C1,. 2Na C1. Dissolve 5 parts of palladium in nitrohydrochloric acid, add 6 parts of pure sodium chloride, evaporate inl the water-bath to dryness, and dissolve 1 part of the residuary double salt in 12 parts of water for use. The brownish solution affords an excellent means for detecting and separating iodine. ~ 77. 11. AURIo CtHLORIDE, OR GOLD TRICHLORIDE, Au Cl,. Prepacration.-Take fine shreds of gold, which may be alloyed with silver or copper, treat them in a flask with nitrohydrochloric acid in excess, and apply a gentle heat unlltil no more of the metal dissolves. then dilute the solution with 10 parts of water. If the gold was alloyed with copper-which is known by the brownish-red precipitate produced by potassium ferlocyanide in a portion of the solution diluted with water-mix it

Page  86 86 REAGEN TS. [ 78, witlh solution of ferrous sulphate in excess. This will reducc the auric chloride to metallic gold, which will separate in the forml of a fine blrownisll-blalck powder; wash the powder ill a smlnall flask, and redissolve it in nitrohydrochlloric acid; evaporate the solution on the water-bath, and dissolve the residue in 30 parts of water. If the gold was alloyed with silver, the latter metal remains as chloride upon treating the alloy witll nitrohydrochloric acid. In that case evaporate the solution at once% and dissolve the residue in water for use. Uses.-Gold' trichloride has a great tendency to yield up its chlorine; it therefore readily converts lower chlorides into higher chlorides, and lower oxides,with the co-operation of water, into higher oxides. These chloridations or oxidations are usually indicated'by the precipitation of pure metallic gold in the form of a brownish-black powder. In the course of analysis this reagent is used only for the detection of stannous salts, in the solutions of which it produces a brownish-red or purple color or precipitate. B. REAGENTS IN THE DRY WAY. I. FLUXES AND DECOMPOSING AGENTS. ~ 78. 1. SODIU`M CARBONATE, Na, C O,. Preparation and tests as in ~ 49, b, c, and d. Uses.-If silicic oxide or a silicate is fused with about 4 parts (consequently with an excess) of sodiumr carbonate, carbonic gas escapes with effervescence, a.nd a basic alkali-silicate is formed, which, being soluble in water, may be readily separated from such metallic oxides as it may contain in adclmixture; from this basic alkali-silicate hydrochloric acid separates the silicic acid. For this fusion, if traces of silica are to be looked for, the flux nmust be prepared as given ~ 46, c, or d. If sodiuml carbonate is fused together with sulphlates of barium, strontium, or calcium, there are formed carbonates of the alkaliearth metals and sodium sulphate, in which new colnponnlld both the base and the acid of the originally insoluble salt may now be readily detected. For this fusion use the sodirum car bonate, made as directed ~ 46 6. The fusion with alkali carbonates is invariably effected in a platinum crucible, provided n. reducible metallic compound be present.

Page  87 ~ 79, 80.1 AMMONIUM CHLORIDE. 79. 2. CALcIuM CARBONATE, Ca C Oa.* Preparation.-Solution of pure calcium chloride, ~ 65, is neated to boiling and precipitated by a slight excess of solution of ainmonium carbonate with addition of some aremionia, ~ 50. Tlhe precipitate is washed 5 or 6 times with hot water by decaltation, then is brought upon a filter and further edulcorated until the washings give no turbidity with silver nitrate. The contents of the filter are then dried and bottled. Te-sts.-Calciumm carbonate for use as a flux, must be free from salts of the fixed alkalies. When washed with hot water the washing must yield no residue when evaporated to dryness. For uses, see ammonium chloride, ~ SO. 80so. 3. AMMONIIuM CIILOIDE, N 14 Cl. Preparation.-Crystals of ammonimn chloride, prepared as described in ~ 56, are dried and preserved in a wide-nmouthed bottle. Tests.-Ammonium chloride must be free from salts of the alkali metals. A considerable quantity, when ignited in a platinum vessel, must leave no residue. Uses.-When a silicate, containing alkali metals, that is insoluble in acids, is intimately mixed in a state of fine powder with ammonium chloride and calcimn carbonate ill suitable proportions, and heated for some time in a platinumn crucible, a mass results, from which hot water extracts, besides caustic liime and calcium chloride, the alkalies of the silicate in the form of chlorides; while the silica and other bases remain behind undissolved. Ammonium carbonate (or oxalate) may be used to remove the lime from the solution, and the filtrate, on evaporation to dryness and ignition yields the alkali metals as pure chlorides (or carbonates). In this operation the larger share of the calcium carbonate, at a red heat, loses carbonic gas and is converted into caustic lime. A smaller portion, by the action of ammllonium chloride, is converted into calcium chloride, which, readily fusing, allows the lime and silicate to come into intimate contact, whereby insoluble basic calcium silicate and soluble alkali chlorides result. —(,. Lawrence Smith.) This is incomparably the best method of fluxing silicates for the separation of the alkali metals. See ~ 210, 2. c. * Or, CO<~> Ca.

Page  88 88 REAGENTS. r 81. 82 81. 4. SoDmur NITRATE, Na N O or NaO. N 02. Perparation. —Neutralize pure nitric acid with pure sodiumlr carbonate exactly, and evaporate to crystallization. Dry the crystals thoroughly, triturate, and keep the powder for use. Tests.-A solution of sodilum nitrate must not be made turbid by solution of silver nitrate or barium nitrate, nor precipitated by sodium carbonate. Uses. —Sodium nitrate serves as a very powerful oxidizing agent, by yielding oxygen to combustible substances when heated with them. We use this reagent principally to convert several metallic sulphides, and more particularly the sulphides of tin, antimony, and arsenic into oxides or acids; also to effect the rapid and complete combustion of organic substances. For the latter purpose, however, ammonium nitrate is sometimes preferable; it is prepared by saturating nitric acid with ammonium carbonate. 82. 5. SODIUM DISULPHATE, K, S, 0O,. Preparation,.-Mfix 7 parts of pure sodium sulphate (obtained by recrystallizationl of clean Glauber's salts, and drying away the water of crystallization at a genltle heat) with 5 parts of pure concentrated sulphurlic acid, in a platinum dish or large platinum crucible, heat to low redness till the mass is in a state of calmn fusion, then pour out into a platinum dish placed in cold water, or upon a piece of porcelain, break the cake into smaller pieces and keep for use. Tests.-The sodiuml disulphate must dissolve in water with ease to a clear fluid with a strong acid reaction. The solution must not be rendered turbid or precipitated by hydrogen sulphide or by ammonia and alnmoniuml sulphide. Uses.-The sodium disulphate at the telllperature of fusion dissolves and decomposes manlly bodies, which cannot be dissolved and decomposed by acids in the wet way without considelable difficulty, such as ignited alumina, titanic oxide, chrome ironstonle, &c. This reagent, therefore, is of service in effecting the solution or decomposition of such bodies. The fusion is preferably effected in platinum vessels. 0 KOS O2 Or S >0.

Page  89 ~ 83, 84.J POTASSIIT3 CYANIDE. 89 II. BLOWPIPE REAGENTS. ~ 83. 1. SoDIUM CArBONATE, Na2 CO3 or Na O-CO-ONa. P'reparation.-See ~ 49. UMes.-Sodium carbonate serves, in the first place, to pro mote the reduction of oxidized substances in the inner flame of the blowpipe. In fusing it brilngs the oxides into the most intimate contact with the charcoal support, and enables the flame to embrace every part of the substance under examination. With salts of the heavy metals the reduction is precedecd by separation of the base. It co-operates in this process also chemi cally by the transposition of its constituents (according to R. WAGNER, in consequence of the formation of sodium cyanide) Where the quantity operated upon was very minute, the rednced metal is often found in the pores of the charcoal. In such cases the parts surrounding the cavity which contained the substance are dug out with a knife, and triturated in a small mortar; the charcoal is then washed off from the metallic particles, which now become visible either in the form of powder or as smnall spangles, as the case may be. Sodium carbonate serves, in the second place, as a solvent. Platinum wire is the most convenient support for testing the solubility of substances in fusinlg sodium carbonate. A few only of the bases dissolve in fusingl sodium carbonate, but acids dissolve in it with facility. Sodiumn carbonate is also applied as a decomposing agent and flux, and mnore,)articularly to effect the decomposition of the insoluble simlphates, with which it exchanges acids, the newly-formed sodiuln sulphate being reduced at the same tine to sodiumn sulphide; and to effect the decomnposition of arsenious sulphide -with which it forms a double arsenious and sodium stllphide, and sodium arsenite or arsenate, thus converting it to a state which permits its subsequent reduction by hydrogen. Sodium carbonate also is the most sensitive reagtent in the dry way for the detection of manganese, as it produces when fused in the outer flaile with a substance contmimlling manganese a green opaque bead, owing to the forma-',~on of sodium manganate. ~84. 2. POTASSIUM CYANIDE, K Cy. Preparation.-See ~ 57. Uses.-Potassium cyanide is an exceedingly powerful reducing agent in the dry way; indeed it excels in its action almost

Page  90 90 REAGENTS. [ Sa all other reagents of the same class, and separates the iletals not only froln most oxygen compounds, but also from many sulphur compounds. This reduction is attended in the forlme case with formation of potassium cyanate, by the absorption of oxygen, and in the latter case with formation of potassiuln sul phocyanate, by the taking up of sulphur. By means of this reagent we may effect the reduction of metals from their compounds with the greatest possible facility; thus we may, for in stance, produce metallic antimony from antimonious acid om from antimony sulphides, metallic iron from ferric oxide, etc. The readiness with which potassium cyanide enters into fusion facilitates the reduction of the metals greatly; the process may usually be conducted even in a porcelain crucible over a spirit or gas lamp. Potassium cyanide is a most valuable and important agent to effect the reduction of stannic-oxide, antimonic oxide, and more particularly of arsenious sulphide. Potassium cyanide is equally important as a blowpipe reagent. Its action is exceedingly energetic; substances like stanniie oxide, the reduetion of which by means of sodiuml carbonate requires a tolerably strong flame, are reduced by potassiunl cyanide with the greatest facility. In blowpipe experiments we invariabl) use a mixture of equal parts of sodium carbonate and potassium cyanide; the admixture of the former is intended here to check in some mneasure the excessive fusibility of the potassium cyanide. This mixture, besides being a far more powerful reducing agent than the simple sodium carbonate, has, noreover, this great advantage over the latter, that it is absorbed by thie pores of the charcoal with extreme facility, and thus permlits the production of the metallic globules in a state of the greatest purity. 85. 3. SODIUM TETRBmORATE. Borazx. (Na, B, O,*), crystallized +101, 0. The purity of commercial borax may be tested by adding to its solution sodium carbonate, or, after previous addition of nitrie acid, solution of barium nitrate or of silver nitrate. The borax may ble considered pure if these reagents fail to produce any alteration in the solution; but if either of them causes the formlation of a precipitate, or renders the fluid turbid, recrystallization is necessary. The pure crystallized borax is exposed to O-B-O-B <O N;.

Page  91 ~ 85.] HYDROGEN SODIUM AMMONIUM PHOSPHATE. 91 a gentle heat, in a platinum crucible, until it ceases to swell; it is then left to cool, and afterwards pulverized and kept fo' use. Borax in a state of fusion decomposes metallic salts and dis solves metallic oxides with formation of characteristically colored glasses, which makes it one of the most valuable of reagents. In the process of fusing with borax we usually select platinum wire for a support; the loop of the wire is moistened or heated to redness, then dipped into the powder, and exposed to the outel flame; a colorless bead of fused borax is thus produced. A small portion of the substance is then attached to the bead, by bringing the latter into contact with it whilst still hot or having previously moistened it. The bead with the substance adhering is now exposed to the gas or blowpipe flame, and the reactions are observed. The following points ought to be mlore particularly watched: —(1) Whether or not the substance dissolves to a transparent bead, and whether or not the bead retains its tra.nsparency on cooling; (2) whether the bead exhibits a distinct color, which in many cases at once clearly indicates the individual metal which the substance contains; as is the case, for instance, with cobalt; and' (3) whether the bead manifests the same or a different deportment in the outer and in the inner flame. lReactions of the latter kind arise from the ensuing reduction of higher to lower oxides, or even to the metallie state, and are for some substances particularly characteristic. 85 a. 4. HIYDROGEN SODIUM AMoIONI:uMI PHOSPHATE..i crocosmnwo Salt, Salt of Phosphorus. (HNa NI-,) PO,4, crystallized + 8IIO. and SODIU/M METAPHOSPHATE Na PO,. Preparation.-a. Heat to boiling 6 parts of hiydrogen disodium phosphate and 1 part of pure ammonium chloride with 2 parts of water, and let the solution cool. Free the crystals prodluced, from the sodium chloride which adheres to them, by recrystallization, with addition of some solution of anmonia. Dry the purified crystals, pulverize, and keep for use. b. Take 2 equal parts of pure tribasic phosphoric acid, and add solution of soda to the one, solution of amnmonia to the other, until both fluids have a distinct alkaline reaction; mix the two together, and let the mixture crystallize. /OH * Or, PO-O Na'O Nl,

Page  92 92 REAGENTS. [~ 85. Tests.-H-ydr,gen sodium ammoniruml phosphate dissulveE in water to a fluid with feebly alkaline reaction. The yellow precipitate produced in this fluid by silver nitrate must colmpletely dissolve in nitric acid. Upon fusion on a platinum -ilre, microcosmic salt must give a clear and colorless bead. LCses.-On heating two molecules of hydrogen sodium alnmonilum phosphate, a molecule of water and one of ammonia escape, together with the water of crystallization, leaving hydrogen sodium pyrophosphate II, Na, P, O,; * upon heating more strongly an additional molecule of water escapes, and two molecules of readily fusible sodium metapho~sjphate, Na P0,, t are left behind. The action of sodium metaphosphate is quite analogous to that of sodium tetraborate. We prefer it, however, in some cases to borax as a solvent or flux, the beads which it forms with many substances being more distinctly colored than those of borax. Platinlm wire is also used for a support in the process of fuxing with sodium metaphosphate; the loop must be made small and narrow, otherwise the head will not adhere to it. The operation is conducted as directed in the preceding paragraph. ~ 85 b. 5. COBALT NITRATE. Co (N 0,),t crystallized + 5 H, O. J)reparation.-Fuse. in a Hessian crucible 3 parts of potassiumn disulphate, and add to the fused mass, in small portions at a timne, 1 part of well-roasted cobalt ore (the plirest zaffre you can. procure) reduced to fine powder. The mass thickeins and acquires a pasty consistence. Heat now more strongly unltil it has becoume more fluid again, alld continue to apply heat until the excess of sulphuric acid is compldetly expelled, and the mass accordingly no longer emits white fumres. Vernove the fused mass now from the erucible with al iron spoon or spatula, let it cool, and reduce it to powder; boil this with water until the undissolved portion presents a soft nmass; then filter the rose-red solution, which is free from arsenic and nickel, and mostly also from iron. Add to the Altrate a small quantity of sodium carbonate, so as to throw down a little cobalt carbonate, boil, and filter. Precipitate the solution which is now free from iron, boiling with sodium carbonate, wash the precipitate well, and treat it still umoist with oxalic acid in excess. Wash the rose-red cobalt oxalate thoroughly, dry, and heat to redness in a glass tube, in a current of hydrogen gas. O H PO Na *r PO Or,a PO//,O t Or, N2 OO PO 0 Na N02O 01o

Page  93 ~ 86.] DEPORTMENT OF BODIES WITH REAGENTS. 93 This decompses the oxalate into carbonic gas, which escapes, and metallic cobalt which is left behind. Wash the metal, first with water containing acetic acid, then with pure water, dissolve in dilute nitric acid, treat, if necessary, with hydlogen sulphide, filter the fluid from the copper sulphide, &c., wlich may precipitate, evaporate the solution in the water-bath to dryness, and dissolve 1 part of the residue in 10 parts of water for use. Tests.-Solution of cobalt nitrate must be free from other metals, and especially also from salts of the alkali metals; when precipitated with ammonium sulphide and filtered, the filtrate must upon evaporation on platinum leave no fixed residue. Uses.-Cobalt monoxide forms upon ignition with certain infusible bodies (zinc oxide, alumina) peculiarly colored comrn poulds, and may accordingly serve for their detection. SECTION III. REACTIONS, OR DEPORTMENT OF BODIES WVITH REAGENTS. ~ S6. I STATED in my introductory remarks that the operations and experiments of qualitative analvsis have for their object the conversion of the unknown constituents of any given compound into forms of which we know the deportment, relations, and properties, and which will accordingly permit us to draw correct inferences re(arding the several constituents of which the inalyzed compound consists. The greater or less value of such analytical experiments, like that of all other inquiries and investigttions, depends upon the greater or less degree of certainty with which they lead to definite results, no matter whether of a positive or negative nature. [But as a question does not render us any the wiser if we do not know the language in which the answer is returned, so in like manner will analytical investigations prove unavailing if we do not understand the mode of expression in which the desired information is conveyed to us; in other words, if we do not know how to interpret the phenomena produced by the action of our reagents upon the substance examined. Before we can therefore proceed to enter upon the practical investigation of analytical chemistry, it is indispensable that we should really possess the most perfect knowledge of the deport. ment, relations, and properties of the new forms into which we

Page  94 c9V) 4 REACTIONS. [~ 87 intend to convert the substances we wish to analyze. Now this perfect knowledge consists, in the first place, in a clear conlception and comprehensioll of the conditions necessary for the formation of the new comnpounds and the manifestation of the various reactions; and in the second place, in a distinct ilnpression of the color, form, and physical properties which characterize the new compound. This section of the work demands therefore not only the most careful and attentive study, but requires, moreover, that the student should examine, and, as far aspossible, verijf by actual experiment everyfact asserted iln it. I have, in the present work, arranged those substances which are in mnany respects analogous, into groups, thus, by colnparillg their analogies with their differences, to place the latter in the clearest possible light. A..-DEPORTMENT OF TIIE METALLIC MOSTLY BIASIC RADICALS ~ 87. Before proceeding to the special study of the several metals, [ give here a general view of the whole of them classified in groups, showing which belong to each group. The grounds upon which the classification has been arranged will appear fromn the special consideration of the several groups. First groupPotassium, sodium, ammonium (cresilm, rubidium, lithium). Second groupBarium, strontium, calcium, magnesium. Third groupAluminnium, chromium (glucinum, or beryllium, thorium, zirconiulm, yttriumn, erbium, cerium, lanthanium, didymium, titanium, tantalium, niobium). Fourth groupZinc, manganese, nickel, cobalt, iron (uranium, thallium, indiumn, vanadium). Fifth groupSilver, mercury, lead, bismuth, copper, cadmium (palladium, rhodiuln, osmium, ruthenium). Sixth groupGold, platinum, tin, antimony, arsenic (iridium, molybdenumn, tellurium, tungsten, selenium). Of these metals only those printed in italics are found distributed extensively and in large quantities in that portion of the earth's crust which is accessible to our investigations; these are thlerefome most important to chemistry, arts and manufactures, agriculture, pharmacy, &c.; and we shall therefore

Page  95 ~ 88, 89.1 GROUP I. POTASSIUM. 95 dwell upon them at greater length. The remainder are more briefly considered in paragraphs printed in smaller type, which may be passed over by the Nyoun ger class of students of analytical chemistry. The less important reactions of the common elements are also printed in smaller type. The properties and reactions of the metals themselves 1 have given only in the case of those that are more frequently met with in the metallie state. ~ 88s. FIRST GROUP. More common metals:-POTASSIUM, SODIUM, AMMONIUMI. Rarer metals: —CESIUM, RUBIDIUM, LITHIUM. Properties of the gro'up.-The metals of the first groupalkali metals-are lighter than water, and decompose it, are highly oxidizable alld inflammable, and have a silveryv brilliant metallic lulstre. The metals of the first goroup are generally regarded as univcalent or molnd elements. The hydroxides of the metals of the first group —the alkalies-are readily soluble in water, as are also the sulphides, carbonates, and phosphates of these metals. (Lithiumn carbonate and phosphate, however, dissolve with difficulty.) Accordingly the alkalies do not precipitate one another, nor do the alkali carbonates or phosphates (in the case of lithium, however, a high degree of dilution of the solutions is presupposed), nor are they precipitated by hydrogen sulphide under any conditions whatever. The solutions of the pure alkalies, as well as of the sulphides and carbonates of this group, restore the blue color of reddened litmus-paper, and impart an intensely brown tint to turmeric paper. Special Reactions of the more common 2Metals of the Rirst Group..~ 89. a. POTASSIUM, K. 39.1. 1. POTASSIUM iS soft as wax at common temperatures, melts at 62.50 and at a low red-heat rises in green vapor. It instantlv tarnishes on exposure to air, and must be kept in naphtha. Thrown on water, it burns with evolution of hydrogen, and with a purple flame, and dissolves to a bitter; caustic, alkaline solution of hydroxide, H2 0 + K = 11 + K O H. 2. POTASSIUM HYDROXIDE and POTASSIUM SALTS are not volatile at a faint red-heat. The hydroxide deliquesces in the air; the oily liquid formed absorbs carbon dioxide rapidly from the air, but without solidifying.

Page  96 96 REACTIONS. GROUP I. [ 8 9 3. NTearly the whole of the POTASSIUM SALTS are soluble ir water. Those with colorless acids are colorless. The norma. salts with strong acids do not alter vegetable colors. Potassium carbonate crystallizes (in combination with 2 molecules of water) with difficulty, and deliquesces in the air. Potassium sulphate is anhydrous and suffers no alteration in the air. Use K C1 for the following reactions. 4. Platinic chloride produces in the neutral and acid soltttions of potassium salts a yellow crystalline heavy precipitate Of POTASSIUM PLATINIC CIJLORIDE (Pt Cl4. 2K Ci). In concentrated solutions this precipitate separates immediately uponl the addition of the reagent: in dilute solutions it forlms only after sonme time, often after a considerable time. Very dilute solutions are not precipitated by the reagent. The precipitate consists of octahedrons discernible under the microscope. Alkaline solutions must be acidified with hldrochloric acid before the platinic chloride is added. The precipitate is difficultly soluble in water; the presence of free acids does not greatly increase its solubility; it is insoluble in alcohol. Plaftinic chloride is therefore a particularly delicate test. for potass-i lml salts dissolved in alcohol. The best method of applying t!lis reagent is to evaporate the aqueous solution of the potassinln salt with platinic chloride nearly to dryness on the water-bath, and to pourl a little water over the residue (or, better still, some alcohol), provided no substances insoluble in that menstlrnumn be present), when the potassium platinic chloride will be left undissolved. Care must be taken not to confound this double salt with ammbnium platinic chloride which greatly resembles it (see ~ 91, 5). 5. Tartctric acid produces in neutral or alkaline * solutions-a white, quickly subsiding, granular crystalline pIrecipitate of HYDROGEN POTASSIUI.I TARTRATE (C4 H5 K OO)t. In concentrated solutions this precipitate separates immediately; in dilute solutions often only after the lapse of a considerable time. Vigorous shaking or stirring of the fluid greatly promotes its formation. Very dilute solutions are not precipitated by this reagent. Free alkalies and free mineral acids dissolve the precipitate; it is sparingly soluble in cold, but pretty readily soluble in hot water. In acid solutions the free acid must, if pIracticable, first be exl)elled by evaporation and ignition, or the solution must be neutralized with sodium hydroxide or carbonate. Hydrogen sodium tartrate answers still better as a test for potassium than free tartaric acid. The reaction is the same in kind, but different in degree, being much more delicate with the salt than with the free acid, since where the former is used the sodium salt of the acid that was combined with the potassium is formed. whllereas where free tartaric acid is the test applied, the acid originally combined with the is liberatecl which tends to increase tile dissolving action of the water present upon the * To alkaline solutions the reagent must be adde I until the fluid shows a strongly acid reaction. C H (O H)-C 00 H Or, -C ClH (O 1)-C 00 K.

Page  97 ~ 90.] SODIUM. 97 hydrogen potassium tartrate, and thus to checlk the separation of the latter. 6. If a potassic salt which is volatile at anl intense red heat is held on the loop of a fine platinum wire inL the fusingr zone of the Bunsen gas-lagcnT (p. 26), the salt volatilizes, and imnpalrts a BLUE VIOLET tint to the part of the flame above the sample. Potassium chloride and potassimun nitrate volatilize rapiclyv, the carbonate and sulphate less rapidly, and the phosplhate still more slowly; but they all of them distinctly show the reaction, though decreasing in degree. If it is wished to obtain a mrrore, uniform manifestationll of the reaction, i.e., a manifestation independent of the nature of the acid that may chance to be combined with the potassium, the sample need simply be nmoistened with sulphuric acid, dried at the border of thle flame, and then introduced into the fusinl zone. With silicates, and other p:)tassium comnpounds of difficult volatility, the reaction may be insured by fusing the sample first nwith pure gypsum, as this serves to formn calcium silicate and potassium sulphate, which latter salt then readily colors the flame. Decrepitating salts are ignited in a platinum spoon before they are attached to the loop. The sample of the potassium salt may also be held lefore the apex of the inner blowpipefaneme produced with a spirit-lamp. Presence of a sodilum salt coin. pletely obscures the potassium coloration of the flame. The spectrum of the potassium flamle produced by the spectroscope (p. 31) is mapped on Plate I. It contains two characteristic lines, the red line a and the indigo blue line /. If potassium flame is observed throlgh the indigo prism (p. 30) the coloration appears sky-blue, violet, and at last intensely erimsol:, even through the thickest layers of the solutioln. Admixtures of cal(cic, sodic, and lithic compounds do not alter this reaction, as the yellow rays cannot penetrate the indigo solution, and the rays of the lithium flame also are only able to pass through the thinner layvers of that solution, but not througrh the thicker layers; the exact spot where the penetrating power of the rays of the lithium flame ceases has to be marked by the operator on his indigo prism. BJut organic substances which impart lmninosity to the flame might lead to mistakes, and must therefore, if present, first be destroyed by heat. Instead of the indigo prism a bluo glass may be used: if lithium is presemlt the glass must be sufficiently thick tt keep out the red lithium rays. ~ 90. b. SODIUM, Na. 23. 1. SoDIUM closely resembles potassium, melts, however, at a higher temperature, viz. 97.6~. Thrown on hot w.lter it buins 7

Page  98 98 REACTIONS. GROUP I. [~ 90. with intense yellow flame, leaving its hydroxide in solution. TI O +N a =-Na 0H II+l. 2. SODIuIM HYDROXIDE and SODIU:T SALTS present in general the same properties and reactions as potassium and its correspendingll compounds. The oily'fluid which sodium hydroxide forlns by deliquescing in the air resolidifies speedily by absorption of carbon dioxide. Sodiumn carbonate crystallizes readily; the crystals (Na, C 0, + 1011, O) effloresce rapidly wbhel exposed to the air. The same applies to the crystals of sodium sulphate, NTa, S 04 + 10H, 0. 3. I-f a sufficiently concentrated solution of a sodium salt with neutral or alkaline reaction is mixed, for greater convenience, in a watch-glass, with a solution of granular ootassiumn pyroanctimonate prepared according to tle directions of ~ 54, the mixture -remains clear at first, or appears only slightly turbid; but' upon rubbling the part of the glass wetted by the fluid with a glass rod, a crystalline precipitate of SODIUM PYROANTIMONATE (Sb2 O, H, Na + 611H2 0) speedily separates, which makes its appearance first along the lines rubbed with the rod, and subsicdes from the fluid as a heavy sandy precipitate. From dilute solutions of sodiuln salts the precipitate separates only after some time, occasionally as much as twelve lIOurs. Froim very dilute solutions it does not separate at all. The preeipitated sodium pyrloantimonate is invar'iably crystalline. Where it has sieparated slowly it occasionally consists of wvell-formed microscopic cublic octalhedrons, but more frequently of four-sided columns taperilig pyramid fashion; where it has searatecd promptly, it appears in the form of small boat-shaped crystals. Presence of large quantities of potassium salts interferes very considerably with the reaction. Acid solutions cannot be tested with potassiulm pyroantimonate, as free acids will sepalrate from the latter substance metantimonic acid. It is indispensable, therefore, before adding the reagent, to remove, if possible, the free acid by evaporation or ignition, or where this is not practicable, by neutralizing the acid solution with a little potassium carbonate until the reaction is feebly alkaline. It shlould also be borne in mind that only those solutions can be tested with potassium pyroantimonllate which contain no other salts besides those of sodium and potassium. 4. If sodium salts are held in the fusing zone of the Bunsen.gas-[am p, or in the inner blowpipe flame, they show. with regard to their relative volatility and the action of decomposing agents uponl them, a similar deportment to the salts of potas siluln; the sodinm salts are, however, a little less volatile than the corresponding potassium salts. But the most chlaracteristic sion1 of the presence of sodium salts is the INTENSE YiELLOW COLORATION which tlmy impart to the flame. This reaction will effect the detection of even tile ninutest quantities of sodium,.and is not obscured by the presence of large quantities of potassiuln salts. The spectrum (Plate I.) shows only a single yellow line a in an ordinary spectrg.scop)e, but with a very powerful apparatus two lines wvill be visible distinctly, altllhougll they are exceedingly close to each other. The reaction is so delicate that the sodiumll chloride contained inl atmospheric dust generally suffices to give a sodium spectrum, althouighl a faint one.

Page  99 ~'91.] AMMONOIU)M. 9S It is characteristic cf the sodium flame that a crystal of potassium dichromate appears colorless in its light, and that a slip of paper coated with mercuric iodide appears whlite, with a faint shade of yellow (BUNSEN); also that it looks orange yellow when observed through a green glass (MAERZ). These reactions are not obscured by presence of salts of potassium, lithium, and calcium. 5. Platinic chloride produces no precipitate in neutral or acid solutions of sodium salts. Sodium platinic chloride dissolves readily both in water and in sp)irit of wine; it crystallizes in long yellow prisms. 6.'Tartaric accidl and hyd/loyeen soldiinm tar'trate fail to precipitate even concentrated neutral solutions of sodium salts. ~ 91. o. AimroNIuAr, N H4. 1 S. 1. AmnronIT does not exist as such, but in the ammoniumn salts the group N 114 4aCts as a univalenlt basic radical, analogous to KI and Na. It probably exists in comiiluation with imercury in the'' aminonium amalgam," but if so it qluickly breaks up into N HI, anlld II. 2. AMMroNxi (N HI,) is gaseous at the commlzon temperature; but we have most frequently to deal with it in its aqueous solution, in which it betrays its presence at once by its penetrating odor. It is expelled from this solution by the application of heat. It may- be assumed that the solution contains it as ammonium hydrcoxide (N 1140 II) (see ~ 37). 3. All the AAMIMoNIUM SALTS are volatile at a low heat, either with or without decomposition. MBIost of them are readily soluble in water. The solutions are colorless. The norinal comnpounds of amlmolniuml with strong acids do not alter vegetable colors. 4. If AIIONIUMv SALTS are triturated together with slce7ecd line, best with the addition of a few drops of water, or are, either in the solid state or in solution, heated with solution of.p)otassa or1 of so(ca, ammnonia is liberated in the gaseous state, and betrays its presence-1, by its characteristic odor; 2, by its REACTION on moistened -test-papers; and 3, by givingl rise to the formation of VHITE FUAMES when ally object (e. g., a glass rod) moistened with hydrochloric acid, nitric acid, acetic acid, or any of the volatile acids, is brought in contact with it. These fumes arise from the formation of solid ammoninmn salts produced by the contact of the gases in the air. Hydrochllloric acid is the most delicate test in this respect; acetic acid, however, admits less readily of a mistake. If the expulsion of the ammonia is effected in a slnall beaker, best wvith slacked lilne, with addition of a very little water, and the beaker is covered

Page  100 100 SEPARATIONS. GROUP I. [~ 92. wvith a watch-glass having a slip of moistened turmeric or red dened litmus paper attached to the centre of the convex side, the reaction will show the presence of evenl very minute quantities of ammonia; only it is not immediate in such eases, but requires some time for its manifestation. It is promoted and accelerated by application of a gentle heat. 5. Platinzic ciloride shows the same deportment with ammonic salts as witlh salts of potassium; the yellow precipitate of AMtMOIMUM PLATINIC CIILorIDE (Pt C14. 2N 1-1 C1) consists, like thle corresponding potassium componnd, of octahedrons discernible under the microscope. 6. Tartariic acid throws down after some time from most highly concentlated solutions with neutral reaction, part of the ammonium as IIYDROGEN AINIMONIUMI TARTRATE C4 Hs (N H4) Oe. Less concentrated solutions are not precipitated. HIydrogen sodium tartrate precipitates concentrated solutions niore, completely, and produces a precipitate even in more dilute solutions. The precipitate is white and crystalline. Its separation may be promoted by shaking the glass, or rubbing it inside with a glass rod. By solvents it is acted upon like the corresponding potassium salt, only that it is a little more readily soluble in water and in acids. ~ 92. Recapitulation agnd remarks.-Thle potassium and sodium salts are not volatile at a mnoderate red-heat, whilst the alrmmonliiiin salts volatilize readily; the latter may therefore be easily separated fromn the former by ignition. The expulsion of ammnomiat, by slacked lime affords the surest means of ascertaining the presence of am-nmonliuin salts. Salts of potassium can ble detected in the wet way only after the removal of tlle ammloniacal salts which. may be present, since both classes of salts manifest the same or a similar deportment with platinic chloride and tartaric acid. After the removal of the ammrnonium compounds potassiqn is clearly and positively characterized by eitlelr of these two reagents. The reactions will only show in concentrated fluids; dilute solutions must therefore first be concenltrated. A single drop of a conwcentrcated solution will give a positiye result, which cannot be obtained with a large quantity of a dilute fluid. The most simple way of detecting potassium in the two sparingly soluble compounds that have come under our consideration here-viz., the potassiull platinic chloride and the hydrogen potassium tartrate-is to decompose these salts by gentle ignition; the former thereupon yields potassium chloride, the latter, potassium carbonate. For the direct detection of potassium in potassium iodide, tartaric acid is better suited than platinic chloride, since where the latter reagent is used the separation of the potassium platinic chloride is interfered -with in consequence of the formation of a dark red fluid containing platinum diniodide and iodide and free iodine. Sodium may be detected with positive certainty in the wet way by potAssiusl yroantimonate, provided the reagent be properly prepared

Page  101 ~ 92.] SEPARATIONS. GROUP 1. 101 and freshly dissolved, and the sodium salt solution be concentrated, neu tral, or feebly alkaline, andc free from other bases, and that it he borne in mind that sodium pyroantimonate invariably separates in the crystall line form, and never in a flocculent state. To detect in this way very nlinute quantities of sodium in presenice of a large proportion of potassium, precipitate the latter with platinic chloride, filter, remove the platinuml from the filtrate by hydrogen sulphide (~ 127), filter, evaporate the filtrate to dryness, ignite gently, dissolve the residue in a very little water, and then test the solution finally with potassium pyroantimonate. Potassium and sodiumn may be detected much more readily ndcl speedily than in the wet way, and also with far greater delicacy, by the flame colo:ration. We have seen, indeed, that the sodiumn coloration completely obscures the potassium. coloration, even though the potassium salt containls only a trifling admixture of sodium salt. But with the aid of the spectroscope the spectra of the two are obtained so distinct and beautiful that a mistake is altogetller impossible. And even without a spectr(oscope tle potassiullm coloration can alnways be distinctly recognllized through the inldico prism, or throiugh a blue glass, evell in a flame colored strollngly yellow by sodium, and tle sodinlll coloration again may be placed beyond doubt, if lecessary, Nwith the aid of merecuric iodide paper, or green glass, in the manmer already described. LThe followill, simple method, due to J. Lawrence Smith, serves for the direct detection of both sodiumn and potassium in absence of lithium when existing' as chlorides and free from. orgallic acids and other bases. A small fragment of the solid snbstance, which need not exceed I-th of an inch in diameter, or a drop of its concentrated aqueous solution, is placed on a slip of glass, and to it is added a sinllle drop of solution of platinic chloride. The plate is genitly warmled; if potassium be present a yellow deposit soon forms, which, nuder a magiiifier, is seen to consist of octahedral crystals of potassium platinic chloride; the warrningl is continued until the liquid begins to dry on the edges; if it then be examined with the magnifier the characteristic yellow prisms or needles of sodium platinic chloride will be seen, or they will appear on further slow evaporation. —ED.] The following methods serve for the detection of ammoniumn in ezceedi gly vmimnte6 quaztities, as for instance in natural waters; they depend upon the sep)ara,tion of certain mercury compounds which are insoluble in water, and which contain the nitrogen or the nitrogen and part of the hydrogen of the ammonia. a. If water containing a trace of ammonia (u-j-~-e) or ammonium carbonate is mixed with a few drops of solution of mercuric chloride, a white precilitate is formed, even in very dilute solution; the precipitate consists of mercurammonium chloride (N H2Hg" C1): 2NH3 + Hg"C12 = N H2Hg" C1 + Ni H4C1. If the solution is extraordinarily dilute no turbidity occurs, but on thle addition of a few drops of solution of sodium carbonate, thle fluid will become turbid or opalescent after a few minutes. This reaction takes place when water containing a trace of a normal ammonium salt is

Page  102 102 RARE METALS. GROUP I. [t 93. mixed with a few drops of solution of mercuric chloride and a few drops of solution of sodium carbonate. The precil)itate which separates on tihe addition of sodium carbonate consists of one molecule of the previously mentioned precipitate with two molecules of mercuric oxide, - 113 + 2HIg" Cl2 + 2K2 C 03 = (N H2Ig'" C1 + Hg" O) + 3K Cl + K TH CO, +C 02. Too much mercuric chloride and sodium carbonate must not bie added, etherwise a yellow precipitate of mercuric oxychloride would be formed (BOHLIG, SCH6iYEN). h. Upon adding to a solution of potassium mercuric iodide containing potassa * a little of a fluid containing ammonia, or an ammonium salt, a reddish-brown lpreciditate is formed if the ammonia is present in solme quantity; but there is, at any rate, always a yellow coloration plroduced, even if only most minute traces of ammonia are present. The precipitate consists of dimelcuramnmonium iodide (N Hg2" I. H20): the reaction is thus: 2 (2KI, Hg" I2) + NH3 + 3KSHO = NTlH"2 I. HO + 7KI + 2 H20. Application of heat promotes the separation of the precipitate. Presence of chlorides of the alkali metals, or of salts of the alkalies with oxygen acids, does not interfere with the reaction; but presence of l)otassium cyanide, and of potassium sulphide, will prevent it (J. NESSLE). ~ 93. Special Reactions of the rarer Ifetals of the First Group. 1. CmSIuAI, Cs. 133, and 2. RUBIDIUMI, Rb. 85.4. The cmsium and rubidiumn compounds are, it would appear, found pretty widely disseminated in nature, but in very minute quantities only. Tllhey have hitherto been found chiefly in the mother liquors of mineral waters, and in a few minerals (lepidolite, melaphyr, carnallite). Cmesium has been found in considerable quantities in pollux, and traces of rubidium have been found in the ashes of plants. The c'esium and rubidium compIounds bear in general great resemblance to the potassium comnlounds, more particularly in this, that their concentrated aqueous solutions are precipitated by tartaric acid and by platinic chlor'ide, and also that those of them that are volatile at a red llheat tinge theflarne violet. The most notable characteristic differences, on the other hand, are that the precipitates produced by platinic chloride are far more insoluble in water than the pIotassium platinic chloride; 100 grll. water will, at 10~ dissolve 900 mngrim. plotassium platinic chloride, but only 154 mgrm. of the rubidium platinic chloride, and as little as 50 mgrml. of the cmsium platinic chloride. Agoain, the alums show rreat differences as regards their solubility in cold -walter; thus 100 parts of water at 17~ dissolve 13'5 l)arts of potassium alum, 2"27 upafts of rubidium alum, and'619 parts of cuesium alum. But above all, the flames colored by c'esiuml and rubidium compounds give spectra quite different froml the potassium spectrum (see Piate I.). Thlle cisium spectrum is especially characterized by the two blue lines a andcl 3, which are remarkable for their wonderful intensity and sharp outline; also by tile line y, which, however, is less strongly marked. Amongst the lines in tlhe rubidium spectrum, the splendid indigo-blue lines marked a and,3 strike the eye by their extreme brilliancy. Less brilliant, but still -verv * Prepared as follows. Dissolve 2 grm. potassium iodide in 5 c.c. water, heat the solution, and add mercuric iodide till the last portion remains undis. solved. Let the mixture cool, then dilute with 20 c.c. water. Let the fluid stand some time, filter, and mix 20 c.c. of the filtrate with 30 c.c. of a concentrated solution of potassa; should the fluid turn turbid, filter it once more.

Page  103 ~ 93.j RARE METALS. GROUTP I. 103 characteristic, are the lines 1 and y. To detect )both alkalies in presence of each other. by the spectroscope, the chlorides should be taken and not the carbonates, since with the lat.ter salts the rulbidium. spectrum is not always distinct in the presence of the cresitmu spectruml (ALLE-N, HEINTZ). We have still to mention that cesium carbonate is soluble in absolute alco1hol, whilst rubidium carbonate is insoluble in that mnenstruuml. Still, a seplaration of the two mletals is effected only with difficulty by this imeans, as they seem to form a double salt which is not absolutely insoluble in aicohol. It is more easy to separate them when they are in the forml of acid taltrates; the hydrogen rubidium tartrate dissolres in 8-5 parts of boilingr water, and 84,57 parts of water at 25~, while the corresponding salt of cresiuImn dissolves in 102 p)arts of boiling water, and 10382 parts of water at 25~ (ALLEN). (The hydrogen l)otassiulll tartrate requires 15 parts of bloiling water, and 89 parts of water at 25~.) [Stannic chloride does not affect dilute neutral solutions of c-esium chloride, but on addition of an equal volume of strong hydrochloric acid, a dense crystalline lprecipitate of nearly )pure cresiumn stannic chloride Sn Cs2 C16, is thrown clown which is but slightly soluble in hydrochloric acid (SIrAPLar:ss). Amloniumlll salts give a similar reaction, and must be removed by ignition. To purify the cesiuml precipitate, wash it with strong HC1, dissolve in boiling' water containing some HC1, and throw down again with strong HC1 (STOLRE). —ED.] 3. LITHIUNr, Li. 7. Lithium is also found pretty widely disseminated in nature, but in minute quantities only. It is often met with in the analysis of mineral waters and aslhes of plants, less frequently in the analysis of minerals, and only rarely in that of technical and l)llalrmaceutical products. Lithium fornls the transition from the first to the second group. Its hydroxide dissolves with difficulty in water; it does not attract moisture from the air. Most of its salts are soluble in water; some of them are deliquescent (lithium chloride). Lithium carbonate is difficultly soluble, particularly in cold water. H. drogen sodium plwosphate procducs in not over-dilute solutions of salts of lithium upon boiling, a white crystalline precipitate of lithium phosphate (Li3 PO4 + iH20) which quickly subsides to the bottom of the precipitating vessel. This reaction, which is characteristic of lithium, is rendleed much more delicate by adding with the sodium l)hosphate a little solution of soda, just sufficicnt to leave the reaction alkaline, evaporating the mixture to dryn.ess, treating the residue with vwater, and adding an equal volume of liquid ammllonia. By th-is course of proceeding even very minute quantities of lithium will be separated as Li3 P04 + ~H20. The p)recipitate fuses before the blowpipe, andc gives upon fusion with sodium. carbonate a clear bead; when fused upon charcoal it is absorbed by the pores of the latter body. It dissolves in hydrochloric acid to a fluid which, when diluted and sulpersaturated with ammonia, remnains clear in the cold, but upon b)oiling gives a heavy crystalline precipitate of Li3 PO0 + ~H20. (Reactions by which the lithium phosphate differs fromn the hllosphates of the alkali earth mLietals.) [ra.rt aic acigd and cllaotilic chloridle fail to precipitate even concentrated solutions of lithllic salts. If salts of lithium are exposed to the gas or blowopipe Jlame, in the manner described ~ 89, 5, they tinge the flames carmine-red. Silicates containing lithium require addition of gypsum. to l)roduce this reaction. Lithium phoslhllate will tinge the flamle carmlinc-red if the fused bead is moistened with ihydrochloric acid. The sodium coloration conceals the lithium coloration; in presence of sodium, therefore, the lithium tint must be viewed through a blue glass, or through a thin layer of indigo solution. Presence of a small proportion of p)otassium will not conceal the lithium coloration. In presence of a large proportion of potassium, the lithium may be identified by plac

Page  104 104 REACTIONS. GROUP II. [ t4 ing the substance in the fusing zone, viewing the colored flame througlh the indigo prism and comparing it with a pure potassium flamne produced in the opposite part of the fusing zone. Viewed through thin lavel s, the lithium colored flame appears now redder than the pure potassium flame; viewed through somewhat thicker layecrs, the flames appearl at last equally red, if the prol)ortion of the lithium to the potassium is only trifling; liut when lithium predominates in the examined saml)le the intensity of the red col()ration imparted })y lithiuln decreases percel)tibly when vie-wed through thicker layers, whilst the purepotassium flame is scarcely impaired thereby. By this means lithium may be detected in potassium salts, even though present only in the proportion of one part in several thousand parts of the latter. Sodium, unless present in over-large quantities, interifercs but little with these reactions (CARTMELL, BUNSEN). The lithi/tim spectrumn (Plate I.) is most brilliantly characterized by the splendid carmine-red line a, and the orange-yellow very faint line 3. The flame of a Bunlsen burner yields only these two lines, but if lithium chloride is introduced into a lvydrogen flame, a dull blue line is perceptible whiclh becomes brilliant if the oxyhydrogen flame is used. Its position almost coincides -with the weaker of the two blue lines of cvesiuim (TYvDAL,L, F.CANKLAND). If alcohol be poured over lithium chloride, and then ignited, tile flame shows also a carmine-red tint. Presence of sodium salts will mask this reaction' To detect small quantities of carsium, rubidium, and lithium in presence of very large quantities of sodium or potassium, extract the dry chlorides, with addition of a few drops of hydrochloric acid, with alcohol of 90 per cent., which leaves behind the far larger portion of the sodium chloride and potassium chloride. Evaporate the solution to dryness, dissolve the residue in a little water, and precipitate with platinic chloride. Filter the fluid off, boil the precipitate repeatedly with small quantities of water, to remove the potassium platinic chloride present, and examine in the course of this process repeatedly by the spectroscope. The potassium spectrum will now be found to grow fainter and fainter, whilst the spectra of rubidiuln and cvesiuml will become visible, if these metals are present. Evaporate the fluid filtered off from the platinum, precipitate to dryness, heat thle residue to slight redness in a current of hydrocen, to decomlpose the sodium platinic chloride and the excess of platinic chloride, moisten with lhydrochloric acid, drive off the vcid again, and extract the lithium chloride finally -with a miixture of al)solute alcohol and ether. The evaporation of the solution obtained leaves the lithium chloride behind in a state of almost perfect purity; it may then be further examined and tested. Before drawino from the simple coloration of tile flame the conclusion that lithium is present, it is advisable. in orlder to guard against the chance of error, to test a portion of the residue, dissolved in water, with sulphuric acid and.alcohol, to make quite sure that strontium or calcium is not I)resent. The addition of hydrochloric acid, which is repeatedly plrescribcd in the above process to precede the extraction of the lithium chlloride with alcohol, is necessary for this reason, that lithium chloride is, even at a noclderate redheat, converted by tile action of aqueous vapor into lithium hydroxide, which then attracts carbonic acid, forming lithium carbonate, which is insoluble in alcohol. ~ 94. SECOND GROUP.. IBAPRIUM, STRONTIUM, CALCIUMS, nIAGNESIUM. -,rovperties of the groaup.-The alkali-earth metals have a brilliant lustre. Their color is white (barinrlm anld magnesium)

Page  105 ~ 95.] BARIUM. 103 or yellow (strontium and calcium). They are heavier than water anld decompose water (magnesium slowly) at coinlllno temperatures. They are reg-arded as bivalent or dyad elements. The monoxides and corresponding hydroxides of the metals of the second group are termled the alkali-earths, the monoxides whenl put in contact with water unite with it to forml hydroxides, which dissolve il additional water. Magnesia, however dissolves but very sparillgly in water. The solutions manifest alkaline reaction; the alkaline reaction of magnesia is most clearly apparellt when that earth is laid upon lmoistellned testpaper. The neutral carbonates and phosphates of the alkaliearthl metals are insoluble in Nwater; the solutions of their salts are therefore precipitated by carbonates and phosphates of the alkali metals. This reaction distinguishes the mnetals of the second groulp from those of the first. From the metals of the other groups they are distillg'ised by the solutions beinlg neither precipitated by hydrogen sulphide, nor by ammoiniln snilphide. The alkali earths and the salts of their metals are wllite or colorless, and not volatile at a moderate red-heat. The solutions of the nitrates and chlorides of this group are not precipitated by barium carbonate. Special Reactions. ~ 95. a. BARIUM, Ba. 137. 1. BARIUM IHYDROXIDE, Ba (O II)2, is pretty readily soluble in hot water, but rather sparingly so in cold water; it dissolves freely in dilute hydrochloric or nitric acid. It fuses at a red heat without losinll water. 2. Mo;t of tile BARIUM SALTS are insoluble in water. The solnlble salts do llot affect vegetable colors, and are decomposed upon ignitioll in a glass tube, with the exception of chloride, bromlide, and iodide of blariurn. The insoluble salts dissolve in dilute hydrochloric acid, except bariumn sulphate and barium silico-fluoride. Bari iiiii iitrate aiid chloride are insolublle in alcohol, and do not deliquesce in the air. Concentrated solutions of bariunm salts are precipitated by hydrochloric or nitric acid added ill large proportions, as barium chloride and nitrate are not soluble in the aqueous solutions of the said acids. 3. A mnoiii(a produces no precipitate in aqueous solutions of bariumn salts; potassa or so&a (free from carbonic acid) only in highly concentrated solutionls. Water redissolves the bulky precipitate of hydroxide or CRYS'rALS OF BARYTA (Ba 120,, Saq.) produced by potassa or soda. 4. Soluble c,'bonates (of t/he alkali-rnetals) throw down

Page  106 106 REACTIONS. GROUP II. E[ 95. BARIUM CARBONATE (Ba C 0O) in the form of a white precipitate. If the solution was previously acid, complete precipitation tal;es place only lupon heating the fluid. In ainionium chloride thle precipitate is soluble to a trifling yet clearly perceptible extent; aininoniuin carbonate therefore produces 1no precipitate in very dilute b)aric solutions containiing much amlnOllinumn chloride. 5. Sui>p/trric acid and all the soluble szuLjAcates, more particularly also solution of calciwnm sz/jc/ate, produce, evenl in very dilute solutions, a heavy, finely pnlverulellt, white precipitate of BIARIUMa SULPHATE (Ba S 0,4), which is insoluble in alkalies, nearly so in dilute acids, bnut perceptibly soluble in boiling concentrated hydrochloric and Ilitrie acids, as wvell as ill concentrated solutions of ammonium salts; however, in these latter only if thiere is no excess of sulphuric acid or a sulphate present. Thlis precipitate is generally formed immlediately upon the addition of the reaelnt; fr(om highly dilute solutions, however, especially when strongly acid, it separates only after some time. 6. Hydcroqfaosilicic acid throws down BARIUMr sILICO-FLUOtIioD (Ba F,. Si F4) ill the forin of a colorless crystalline quickly subsiding precipitate. In dilute solutions this precipitate is forimed only after the lapse of somle time; it is perceptibly solluble in hydrochloric and nitric acids. Addition of an equal volume of alcohol hastens the precipitation and mnakes it so colplete that the filtrate remains clear upon addition of sillphl iec acid. 7. Socliumn.hospAcate produces in neutral or alkalile solutions a white precipitate of BA.RIUM IIYDROGLN I'IIOSPIITE (Ba 111 P 0), which is soluble in free acids. Additionl of almmoia onlvy slighltly increases the quantity of this lprecipitate, a portioll of which is in thlis process con verted into lbariin plllospllate, Ba3(P 04)2. Amlnmoium. chloride dissolves the precipitate to a clearly perceptil)le extent. 8. Amnoniaum oxalate produces in moderately dilute solutions a white pulverulent precipitate of BARIUMr OXALA.TE (C04,13a.HO), which is soluble il hydrochloric anld nlitric acids. When recently thrown down, thlis precipitate dissolves also in oxalic and acetic acids; but the solutions speedily deposit barium binoxalate ((C,0411I),Ba. 4-110) in the forll of a crystalline powder. 9. Potassium chromate and dichromate produce a bright yellow precipitate of barium chrornate (13a Cr0) even in very dilute solutions of barie salts. The precipitate dissolves readily in hydrochloric or nitric acid to a yellowish red solution, from which it is thrown down again by ammonia. 10. If baric salts are held on the loop of a platinum wire in the fusing zone of tile _Bunsen gasflacflc, the part of the flame above the sample is colored YELLOWISH GREEN; or if the baric salts are held in the iinner blowyipe,flame, the samne coloration is imparted to the part of the flane beyond the samnple.

Page  107 ~ 96.] STRONTIUM. 107 With the soluble baric salts, and also with the barium carbonate and sulphate, the reaction is immediate or very soon. but the phosphate requires previous moistening of the sample with sulphurlic acid or hydrochloric acid, by which means the barilln mnay be detected by the flame colo)ration also in silicates decollposal)le by acids. Silicates which hydrochloric acid failsto decompose must be fused with soditum carbonate, when the barium calrl)blate produced will show the reaction. It is characteristic of the yellowish-green bariunlu coloration of the flame that it applears bluish-green when viewed through the green glass. If the sulphates are selected for the experilent, presence of calcium and strontium will not interfere with the reaction. The barium spectrm is shown in Plate I. The green lines a andll are the most intense; y is less marked, but still characteristic. The platinum wire sometimes contains barium (KrAUT), hence it is well to see first whether it will give a barium spectrum by itself. 11. Cold solutions of hydrogeln carbonates of the al7calz metals or of anmon201iu2 carbonate, fail to decompose bariun sulpllate, or, to speak mnore correctly, they decompose that salt onlly to a scarcely perceptil)le extent; the same applies to a bIoiling: solution of 1 part of potCassimi cCrbonate cland 3 parts of p)otassiuit?, stulphcate. Repeated action of boilinol solution of sodiuln or potassium carbonate upon barium sulphate succeeds in the end completely in decomposillg that salt. It is readily decomposed also by fusion with sodium carbonate, which results in the for-nation of sodium sulphate, soluble in water, and of barium carbonate, insoluble in that menstrutnm. ~ 96. b. STRONTIUIM Sr. 87'6. 1. STRONTIUsM HYDR1OXIDE and the STRONTIUM SALTrS have nearly the same general properties and reactions as the corresponding ~barirnn colnpounds. Strontium hydroxide is more sparingly soluble in water than barium hydroxide. Strolltium clloriicle diss-olves in ablsolute alcohol alld deliquesces in mnoist air. Strontiiumn nitrate is insoluble in absolute alcohol and does not dleliqiesce in the air. 2. The salts of strontium show with acmmoniac, potaCss.a, and solca, and also with the carbonates of the al/cali metgls, ald with soditmr pho1,sphate, nearly the same reactions as the barilln salts. Strontium carbonate dissolves somewhat more difficultly in alnlmoniuni chloride than barium carbonate. 3. Stlphuric acid and su~lophates throw down STRON'TIrUM SULriAT'rE (Sr S 04) in the forrn of a white precil)itate. Thrown downl by dilute sulphuric acid from concentrated solutions, it is at first flocculent and amorphous, afterwards pulverulent and

Page  108 108 REACTIOXS. GROUP I. [~'6. crystalline; thrown down by diltute sulphuric acid from dilute solutions, or produced by solutions of sulphates, it is immediately pulverluleilt and crystalline. Application of heat greatly proinotes the precipitation. Strontium sulphate is fair:ore soluble ill water than barium sulphate; owing to this readier solulility, the precipitated strontium sulphate separates from rather dilute solutions only after the lapse of some tine; and this is invariably the case (even in concenltrated solutions) if solution of calciuvtz s8?hpAhte is used as precipitant. Strontium sulphate is insoluble in spirit of wine; addition of alcohol will therefore l)rolmote the separation of the precipitate. In hydrochloric acid and in nitric acid, strontium sulpliate dissolves perceptibly. Preselnce of lalrge quantities of these acids will aceordinly most seriously impair the delicacy of the reaction. Solutioll of strontiumn sulphate in hydrochloric acid is, after dilutionl with water, relndered turbid by barium chloride. StrolltiLum sulphate does not dissolve on boiling in a collcenltrated solutionl of ammonium sulphate. 4. HIyddrqf/laosilicic acid fails to produce a, precipitate even in concentrated solutiolns; evenl upon addition of an equal volume of alcohol no precipitation takes place, except in very highly concentrated solutions. 5. Ammooniln oxcdlate precipitates even from rather dilute solutionll STRONTIUM OXALATE, in the form of a white powder, which dissolves readily in h-ydrochloric and nlitlice acid, and perceptibly in ammonium salts, but is only sparingly soluble in oxalic and acetic acid. 6. Jotassiumb dciclromzate does not precipitate solutions of salts of strontium, even when they are concentrated. Potassgqm chrzomzte at first produces no precipitate, but on long standing, if the solution is not very dilute, light yellow stl'rontinm chlomate separates inl the crystalline form. The crystals are but slightly soluble in water, but readily soluble in }hydrochloric, nitric, and chromic acids. 7. If a strontium salt is held in the fusing zone of the Bunsen yas j lame, or in the inner blowppie flmze, all ITESELY RED COLOR is imparted to the flame. The reactioll is tile llost distinct with strontium chloride, less clear with hydroxide aild carbonate, fainter still with sulphate, and scarcely appears with strontium salts of fixed acids. The sample is therefore, after its first exposure to the flame, moistened with hydrochloric acid, and then again exposed to the flamle. If strontium sulphate is likely to be present, the sample is first exposed a short time to the reducing flame (to produce strontium sulphide), before it is moistened with hydrochloric acid. Viewed through the blue glass, the strontium flame appears purple or rose (difference between strontium and calcium, which latter body shows a faint greenish gray color when treated in this manner); this reaction is the most clearly apparent, if the sample is moistened with

Page  109 ~ 97.] CALCIUIr. 109 hydrochloric acid when broughllt into the flame. In presence of barium, the strontium reaction shows only upon the first introduction of the sample moistened with hlidrochloric acid into tlhe flame. The strontium spectrrum is shfown in Plate.1. It contains a number of characteristic lines, more especially the orange line a, the red lines, and y, and the' blne lille 6, which latter is more particularly suited for the detection of strontium, in presence of barium and calcium. S. Strontium sulphate is completely decomposed by continued di;gestion with solutions of aminoniutn ccarbonate or of hydrogen alclali cacrbonates, but much more rapidly by boiling with a solution of 1 part of potassiumn carbonate and 3 cparts of potassium sulphate (essential difference between strontium sulphate and barium sulphate). ~ 97. c. CALCITxM. Ca. 40. 1. CALCIUM OXIDE (quicklime), CALCIUM HIYDROXIDE (slacked lime) and CALCIUM SALTS present in their genleral properties and reactions, a great similarity to the corresp6ndinll bariuln and strontimnn comupounds. Calcium hydroxide is far more dificultly soluble in water than the barium and strontium hydroxides; it dissolves also more sparingly in hot than in cold water. Calcilnum hydroxide loses its water upon ignition. Calcilum chloride and nitrate are soluble in absolute alcohol and deliquesce in the air. 2. Ammonia, potassca, carbonates of the alkali mnetals and sodiurn phospha/te show nearly the same reactions' with calciumn as with bariunm salts. Recently precipitated CALCIUMR CARBONATE (Ca C 0,) is bulky and amnorphous —after a time, and iml1mediately upon application of heat, it shrinks and assumes a crystalline form. Receltly precipitated calcium carbonate dissolves pretty readily in solution of ammoninm chloride; but the solution speedily becomes turbid, and deposits the greater part of the dissolved salt in forum of crystals. 3. Sulphuric acid and sodium sulphate prodnce imlmediately in highly concentrated solutions, white precipitates of CALCIUM11 SULPHATE (Ca S 0,. 21120), which redissolve completely in a large proportion of water, and are still far more soluble in acids. Calcium sulphate dissolves readily on boiling in a concentrated solution of ammonium sulphate. In less concentrated solutions the precipitates are formed only after the lapse of some time; and no precipitation whatever takes place in dilute solu-,ions. Solutions of calcium sulphate, of course, cannot produce a precipitate in calcium salts; but even a cold saturated solution of potassium sulphate, mixed with 3 parts of water, produ

Page  110 11]0 REACTIONS. GROUP II. [r 97 ces a precipitate only after standing from twelve to twenty. foulr hours. In solutions of calcium salts, which are so very dilute tlhat snlplhric acid has no apparent action on them, a precipitate will form upon addition of two volumes of alcohol either imnlnediately, or after the lapse of some limne. 4. JIZyi'j(laosilicic accdl does not precipitate calcium salts, even when anl equal volume of alcohol is added. 0. Agizmnoznii a ox:r(late produces a white pulverulent precipitate of C.ALCIUM OXALATE. If the fluids are in any degree coleeltrated or hot, the precipitate (C, Ca 04. 2 aq.) forlms at once; but if they are very dilute and cold, it forms only after soiie timle, in which latter case it is imore distinctly crystalline and colnsists of a llixture of the above salt Awith C2 Ca 0)4. 6 aq. Calciuml oxalate dissolves readily in lhydro(lloric and 1nitric ac ids; but acetic and oxalic acids fail to dissolve it to aly perceptible extent. 6. Xeither potassium cromcate nor clichromate precipitate solutions of salts of calcium. 7 If calcium salts are held in the fusing zone of the Bunsen gas flarme, or in the illler blowpe),e Zan2e, they impart to the flame a YELLOwIsI-IIED color. This reaction is the nmost distinct with calciuml chloride; calciull sulphate shows it onily after its incipient decomposition, and calcium carbonate also most distinctly after the escape of the carbonic acid. Compounds of calciunm with fixed acids do not color flame; those of them which are decomposed by hydrochloric acid will, however, show the reaction after -noistenino wTith that acid. The reaction1 is in such cases pronmoted by flattellillg the loop of the platinl llwTire, plaeing a small portion of tle calcic colmpoul uponl it, lettillng it frit, adding a drop of hydrochloric acid, which remains hangino to the loop, and then lholding the latter in the fusingl zone. The reaction shows now the most distinct light illlmnediately upon the disappeariance of the drop, which in this process, aasill LEIDENFnOST'S,henomnenon, evaporates without boilillg (L3uNsN). Viewed througll the gqree l gclass the calcium coloration of the flame appeals finch-green colored on brillnrg the sample moistened witli hydrochloric acid iito the flame (difference between calciumrn and strontium, which latter substance under similar circumlstances shows a very faillt yellow. (1MFIz). In presence of Iarium the calcium reaction shows only upon the first introduction' of the sample into the. flame. Thle ca(lcium spectrmtyc'n is shown in Plate I. The intensely green line, is more partictilarly characteristic, also the intensely orange line a. It requires a very good apparatus to show the indigo-blue line to the right of 6 in the solar spectrum, as this is much less luminous thlan the otlher lines. S. WVith carbonates and hydrogen carbonates of the alkali metals, also with a solution of potassium carbonate and sulphate, calciumr sulpllhate shows the salne reactions as strontiumn sulphlate.

Page  111 ~ 98.] MAGNESIUM. 111 ~ 9s. d. MAGESIrUM. Mg. 24. 1. MI-AGNESIUM iS silver white, hald, ductile, of 1'74 sp. gr it melts at a moderate red heat, and volatilizes at a white heat. When igrnited in the air it burns with a dazzlinog white flame to maglesium oxide It preserves its lustre inl dry air, bnt it gradually becomnes coated with hydroxide when exposed to moist air. Pure water is not decomposed by magnlesium at the ordinary temperature, but in water aciclulated with hycrochloric or sulphuric acid, magnesiumn dissolves rapidly with evolution of hydrogen. 2. MAGNESIUMI OXIDE and HYDROXIDE are white powders of far greater bulk than the other oxides and hydroxides of this group, and are nearly insoluble both in cold and hot water. The hydroxide loses water upon ignition. 3. Some of the SALTS OF MArGN~EsIUM- are soluble in water, others are insoluble in that fluid. The soluble salts have a nauseous bitter taste: the normal salts do not alter vegetable colors; with the exception of the sulphate, they undelrgo decolmposition when gently ignited, and the greater pairt of them even upoll simple evaporation of their solutions. Malausium sullhate loses its acid at a white heat. 5Nearlv all the magnesitum salts which are insoluble in water dissolve readily in hydrochloric acid. 4. Amnonizia throws down from the solutions of normal salts part of the magnesiumn as HYDROXIDE (NIg (O 11),) in the form of a white bulky precipitate. The rest of the ihagllesium remains in solution as a double salt, viz., in combination with the ammoninll salt which forms upon the decomposition of the magnesium salts. These double salts are not decomposed by a small excess of ammnonia. It is owing to this tendency of inagnesium salts to forml such double salts with amnmonic compounds that ammonia fails to precipitate them in presence of a sufficient proportion of an amnlmoniuln salt with neutral reaction; or what comes to the same, that ammonia produces no precipitate in solutions of magnesium containling a sufficient qtanltity of free acid, and that precipitates produced by ammlonia in neutral solutions of magnesium are redissolved upon the addition of ammonium chloride. It should be borne in mind that in solutionls containing only 1 mnolecule of an ammonlium salt [(N 1-4)2S O, or N 114Clj to 1 molecule of magllesiLmn salt, although no precipitate is produced by thle addition of a slight excess of ammonia, a portion of the magnesiunm is, however, thrown down on the addition of a large excess of ammlonia. 5. Potassca, soda, bacaryta, and limte throw down M.ArGNESIUM -IYDROXIDE. The separation of this precipitate is greatly pro

Page  112 112 REACTIONS. GROUP 11. L~ 98. moted by boiling the mixture. Amninonium chloride and other similar ammonium salts redissolve the washed precipitated hydroxide. If the ammonium salts are added in sufficient quantity to the mnagnesium solution before the addition of the precipitant, small quantities of the latter fail altogether to produce a precipitate. However, upon boiling the solution afterwards with an excess of potassa, the precipitate will of course make its appearance, since this process causes the decomposition of the ammoniumn salt, removing thus the agent which retains the magnesium hyvdeoxide in solution. It should be remembered that magnesium hydroxide is more soluble in solutions of potassium chloride, sodium chloride, potassiumn sul.phate, and sodium sulphate than ill water, and that (on1 this accoult its precipitation is less complete when these salts are present in large quantities. From such solutiolls the magneSium is, however, thrown down, for the most part, by an excess of solution of potassa or solution of soda. 6. Potassium carbonate and sodiumr carbonate produce in neutral solutions a white precipitate of BASIC MAGNESIUM CARBONATE, Mg1 (O H)2. 4 MBg C 03+ 10 aq. One-fifth of the carbonic acid of the decomposed alkali carbonate is liberated in the process, and combines with a portion of the magnesium carbonate to bicarbonate, which remains in solution. This carbonic acid is decomposed bly boiling, and an additional precipitate formed (Mg C 03 + 3 aq.) while carbon dioxide escapes. Application of heat therefore promotes the separation and increases the quantity of the precipitate. Ammoniunl chloride and other similar ammonium salts, when present in sufficient quantity, prevent this precipitation also, and readily recdissolve the precipitates after they have been washed. 7. If Inagnesitum solutions are mixed with avnrnonitm carbonate, the fluid always remains clear at first; but after standing some time, it deposits, more or less quickly according to the concentration of the solution, a crystalline precipitate. When the almmoniumn carbonate is in slight excess, the precipitate consists of magnesium carbonate (Mg C O0 + 3 aq.), when the amlnonium carbonate is in large excess, it consists of oMAGNESIUM AMMONIUM CARBONATE (Mg (N 114)2 (C O3)2 + 4 aq.). In rather highly dilute solutions this precipitate will not form. Addition of ammonia and of excess of ammoniumn carbonate plomotes its separation. Ammoniuln chloride counteracts it, but it cannot prevent the formation of the precipitate in rather highly concentrated solutions. S. Sodium phophate precipitates from magnesium solutions, if they are not too dilute, MAGNESIUMI HYDROGEN PHOSPtHATE (Mg H P 0, + 7 aq.) as a white powder. Upon boiling, magnesium phosphate (Mg3, (P O,)3 + 7 aq.) separates, even froml rather dilute solutions. But if the addition of the precipitant is preceded by that of ammonium chloride and azmmonica a white crystalline precipitate of AMMONIUIM MAtGNESIUMI PHTOSPITATE (N H MIg P 0, + 6 aq.) will separate even from very dilute solutions of magnesium; its separation may be greatly pro

Page  113 ~ 99.1 SEPARTATIONS. GRCOUP I. 113 moted and accelerated by stirring with a glass rod; even slhould the solution be so extremely dilute as to forbid the formation of a precipitate, yet the lines of direction in which the glass rod has moved along the inside of the vessel will after the la~pse of some time appear distinctly as white streaks (soluble ill hydrochloric acid). Water and solutions of arnmonium salts dissolv-e the precipitate but very slightly; but it is readily soluble in acids, even in acetic acid. In water!lontaining aommonlia it may be considered insoluble. 9. Ammonium oxalcfte produces no precipitate in highly dilute solutions of magnesium; in less dilute solutions no precipitate is formed at first, but after standing some time crystalline crusts of various double oxalates of ammonium and mar. nesium make their appearance. In highly concentrated solutions ammoniuml oxalate very speedily produces precipitates of magnesium oxalate (Mgcr CO,. 2 aq.), which contain small quan. tities of the above-namned double salts. Ammnonium chloride, especially in presence of free ammonia, interferes with the formation of these precipitates, but will not in general absolutely prevent it. 10. 8Sulphuric acid, hydroftuosilicic acid, and potassirnm chron ate do not precipitate salts of magnesium. 11. Salts of magnesium do not color flame. ~ 99. liecapitztation and remarks.-The difficult solubility of the magnesium hydroxide, the ready solubility of the sulphate (unless it is present in the natural form, either anhydrous or combined with 1 molecule of water), and the disposition of mnagnesium salts to form double salts with ammonium compounds, are the three principal points in which magnesium differs from the other alkali-earth metals. To detect magnesium in solutions containing all the alkali-earth metals, Awe always first remove the bariumn, strontium, and calcium. This is effected most conveniently by means of ammonium carbonate, with addition of some ammonia and of ammonium chloride, and application of heat; since by this process the barium, strontium,. and calcium are obl-tained in a form of combination suited for further examination. If the solutions are somewhat dilute, and; the precipitated fluid is quickly filtered, the carbonates of bariurn, strontium, and calcium are obtained on the filter, whilst the whole of the magnesium is found in the filtrate. But as ammonium chloride dissolves a little barium carbonate, and also a little calcium carbonate, though much less of the latter than of the former, trifling quantities of these bases are fonlld in the filtrate; nay, where only traces of them are present, they may altogether remain in solution. 8

Page  114 114 SEPARATIONS. GROUP II. [~ 99 In accurate experiments, therefore, the separation is effected in the following way: Divide the filtrate ilto three portions, test one portion with dilute sulphulric acid for the trace of barium which it may contain ill solution, and anlother portion with ammonium oxalate for the minute trace of calcium which may have remained in solution. If the two reagents produce no turbidity even after solne time, test the tllird portion withll sodium phosphate for Mr.GNESIUM. B]at if one of the reagents causes turbidity, filter the fluid from the gradually subsiding precipitate, and test the filtrate for magnlesiuin. Should both reagents produce precipitates, mix the two first portions together, filter after some time, allnd then test the filtrate. To Inake sure that the precipitate thrown down by amnluonium oxalate is actually calcium; oxalate, and not, as it lmay be, oxalate of lnagnesiurn and ammonium, dissolve it in very little hydrochloric acid, and add dilute sulphuric acid, and then alcohol. To show the presence of barium, strontium, and calcium in the precipitate produced by ammonium carbonate, dissolve the'precipitate in some dilute hydrochloric acid; add solutioll of gypsum to a small portionl of this solution, when the immediate formation of a precipitate will prove the presence of BAnIrrnu. Evaporate the remainder of the hydrochloric acid solution on the water-bath to dlvyness, and treat the residue with absolute alcohol, which will dissolve the stroltium chloride and the calcium chloride, leaving the greater part of the barium chloride undissolved. Mix the alcoholic solution with anl equal volume of water and a few drops of hvdrofluosilicic acid, alld let the mixture stand several hourls, when the last traces of thle barium present will be foulnd precipitated as barium silicofluoride. Filter, and add sulphuric acid to the alcoholic filtrate. This will throw down the strontium and the calcium. Filter the fluid from the precipitate, wash with weak alcohol, and boil the sulphates for some tile with a sufficient quantity of alrmoniumll sulphate in strong solution, -ellewilng the water as it evaporates and adding amm-aonia, so as to keep the fluid slightlv alkaline. STRONTIUM sulphate remains unldissolved, while the calciumn sulphate dissolves. After the solution has beell much diluted the cALCIuM may be thrown down by ammon umoi oxalate. The mixture of strontiumn and calcium sulphates may also be treated as follows: Boil with solutionl of sodium1 calrbonate. By this means the sulphates are (converted into carlbonates. ~Wash these, dissolve them in nitric acid, evaporate the solution to dryness, ]?ulvcrize the residue and digest it for a considerable time.with absolute alcohol to which a little ether has been added, when the calcilmn nitrate will dissolve, leavinlg thle strontiumn nitrate ulldissolved. The latter may be readily examined, by dissolving in a small quantity of water and adding solution of calcium sulphate; the calcium in the alcoholic solution of

Page  115 ~ 100.] GR rP III. 113 calcium nitrate may be detected by the addition of silllrlic acid. Tile precipitate of calcilum sulphate thui-s produced, when treated Nwith water, should yield a solution which gives an immnediate and considerable precipitate wvith airnmoniiuml oxalate. The best and most convenient way of detecting the alkali-earth metals in their phosphates, is to decompose these latter by means of ferric chloride with addition of sodium acetate (~ 142). The ozalates of this group are converted into carbonates by ignition, preparatory to the detection of the several metals which they may contain. The followiing method will serve to analyze mixtures of the sulp7hates of the alkali-earthl metals: Extract the mixture under examination with small portions of boiling water. The solution contains the whole of the magnesiuml sulphate unless it is present in the native anhydrous state, besides a trifling quantity of calcium sulphate. Digest the residue, according to H. ROSE's direction, in the cold for 12 hours, with a solution of amloniunl carbonate, or boil it 10 minutes with a solution of 1 part of carbonate and 3 parts of sulphate of potassium, filter, wash, then treat w.ith dilute hydrochloric acid, which will dissolve the carbonates of strontium and calcium formed, and if the anhydrous native magnesium sulphate was present the magnesium carbonate or the ammonium magnesium carbonate, but alwavs also a minute trace of barium (FRESENrUS), leaving behind the undecomposed barium sulphate. The latter may then be decomposed by fusion with alkali carbonates. The solutions obtained are to be examined further according to the above directions. The detection of barium, strontium and calcium in the moist way is very instructive, but also very laborious and tedious. By means of the spectroscope these metals are much more readily detected even when present all three together. According to the nature of the acid, the sample is either introduced into the flame directly, or after previous ignition or moistening with hydrochloric acid. To detect very minute quantities of bariuml and strontium in presence of large quantities of calcium, ignite a few grammes of the mixed carbonates a few minutes in a platinum crucible strongly over the blast,* extract the ignited mass by boiling with a little distilled water, evaporate with hydrochloric acid to dryness, and examine the residue by spectrum analysis (ENGELRBACH). ~ 100. THIRD GROUP. More common metals: —ALUMINIUM, CHROIIUM. Rarer mIetals:-GLUCINUM, TInoRITM, ZIRCONIUM, YTTRIUM, ERBIUM, CERIUMI, LANTHANIM, DI)IDYMIUIM, TITANIUM, TANTALIIUM, iNrIOBI UM. Properties of the grou2p.-The oxides and hydroxides of the third group are insoluble in water. Their sulphides cannot be produced in the moist way. Hydrogen sulphide, therefore, fails to precipitate the solutions of their salts. Atmmoninin sulphide throws down from the solutions of the salts in wllich * The carbonates of barium and strontium are much more readily reduced to the caustic state in this process than would be the case in the absence oi:alcium carbonate.

Page  116 116 IREACTIONS. GROUP III. [p l(l the metals of the third group constitute the base,* the hydroxides in the same way as ammonia. The reaction with amilnoiiiu-m sulphide distinguishes the metals of the third from those of the two preceding groups. Special Reactions of the more common ifetals of the third gro2T. ~ 101.a. ALoUINIUM, Al 27'4. f 1. ALUMINIUM is nearly white. It is not oxidized by the action of the air, in compact masses not even upon ignition. It may be filed, and is very malleable; its specific gravity is only 2'67. It is fusible at a bright red heat. It does not decompose water at a boiling heat. Aluminium dissolves readily in hydrochloric acid, as well as in hot solution of potassa, with evolution of hydrogen. Nitric acid dissolves it only slowly, even withl the aid of heat. 2. ALUMINIUM OXIDE (Al2 0,) or ALUMINA is non-volatile and colorless; the HYDROXIDES are also colorless. Alumina dissolves in dilute acids slowly and with very great difficulty, but more readily in concentrated hot hydrochloric acid. In fusing sodium disulphate, it dissolves readily to a mass soluble in water. The trihydroxide in the amorphous condition is readily soluble in acids; in the crystalline state it dissolves in them with very great difficulty. By ignition with alkalies, an aluminate is formed which readily dissolves in acids. 3. The ALUMINIUM SALTS are colorless and non-volatile; some of them are soluble, others insoluble. The anhydrous chloride is solid, pale yellow, crystalline, volatile. The soluble salts have a sweetish, astringent taste, redden litmus-paper, and lose their acid upon ignition. The insoluble salts are dissolved by hydrochloric acid, with the exception of certain native comnIounds; the aluminium compounds which are insoluble in * While the metals of the third group act as bases towards strong acids, they also deport themselves as acids towards strong bases. Aluminium, its oxide and its hydroxide, dissolve in sulphuric acid to form aluminium sulphate A1,2 (S 04)3 and in potassa, yielding potassium aluminate Al2 (K O)G, or Al (K 0)3. t Aluminium in all its known compounds is apparently a triad. It is, however possible, that two tetrad atoms of this element are always associated as a sexivalent group, e.g. — /C1 A=23 = 0 Cl Ai0.9O = I >0 andAl, C16 - C A C1 A1 =0~N

Page  117 101.] ALUIINIUM. 117 hlydrochlolric acid are mlade soluble by ignition with sodium callrbliate, or sodium disulphate. Their decomposition and sulultion illay be effected also by lcatill thle, reduced to a fine powder, with llydrochloric acid of 25 per cellt,, or with a mixttre of 3 p)arts by weight of sulphuric acid, and 1 part by weigllt of water, ill sealed glass tubes, to 200~-210~ for two hIours (A. Mlr'ScIIEIILICII). 4. P'otassa and so&Ca throw down froml solutions of alunininum salts a bulky precipitate of ALUM3INIUMI HYDIOXIDE, Al (O II)3, lwhich contains alkali and genierally also al admlixture of basic salt; this precipitate redissolves readily and completely in an excess of the precipl)itlt, but from this solution it is reprecipitated by addition of allmnolilll chloride, even in the cold, but lore coplllPletely uIpomn application of heat (comlpare, 56). The lpecipitate does inot dissolve in excess'of ammonium chloride. Th'lle prosece of amumlloillmn salts does not prevent the precipitation by potassa or soda. 5. AlwniZbict also produllces a precipitate of ALUMINIUM fHYmI)OXII)c, which conltains ainmomia and anl admixture of basic salt; this precipitate also redissolves in a very considercable excess of tile precipitant, but with clifficulty onl'y, which is' the (recater thle larger thle quantity of anlinolnlilu salts contained in tile solutionl. Boilillg promotes precipitation, as it drives off the excess of ammonia. It is this deportmlelnt which accounts for the colnplete precipitatiol of alumliiuml hydroxide from solution in potassa by an excess of ammoniumn chloride. 6. Sbdiltm carbonate precipitates BASIC ALUMtNINIUM CARBONATE, which is somlewhat soluble in excess of fixed alkali carbonate, and still less soluble in excess of anlllloniun carbonate. Boiling promotes precipitation by the latter. 7. If thle solution of an aluminium salt is digested with finelv divided bariu) a carboalte, the greater part of the acid of the alltmillilnum salt combines with the bariumn, the liberated car'bollic acid escapes, and the aluliniiulm precipitates completely as IIYDIiOXII)E MIXED W'ITH BASIC SALT; even digestion ill the cold stuffices to produce this reaction. N.1B. to 4, 5, 6 and 7. —Tartaric, citric, and other non-volatile organic acids completely prevent the precipitation of aluminium as hydroxide or besic salt, when they are present in any notable quantity. The presence of sugar and similar organic substances interferes with the completeness of thile preci pitation. 8. SoGilam phosp)hate precipitates ALUMINIUM PROSPHATE (Al P04) from solutions of alumliniulm salts. The bulky white precipitate is readily solubIle in potassa or soda solution, but not in amllllonia; amnllonium chloride therefore prlecipitates it from its solution in potassa. or soda. The precipitate is readily soluble in hydrochloric or nitric acid, but not in acetic acid (difference from aluminium hydroxide); sodium acetate, therefore, precipitates it from its solution in hydrochloric acid, if the latter is not too predominant. Tartaric acid, sugar, etc., do not prevent the precipitation of aluminium phosphate, but citric acid does prevent it (GROTHE). 9. Oxa'ic acid and its salts do not precipitate solutions of aluminium

Page  118 118 REACTIONS. GROUP m. [~ 1i0 10. Potassium sulphate, added to very concentrated solutions of salts of alumninium, occasions the gradual separation, in the form of crystals, or a crystalline powder, of aluminium potassium sulphate.* 11. If aluminium hydroxide or other compound is ignlited upon charcoal before the blowpipe, and afterwards moistened Nwith a solution of cobalt nitrate, and then again stronglly ignited, anl unfused mass of a deep SITY-BLUE color is produceeid, whllich consists of a compound of the two oxides. The b)lue color becomes distinct only upon cooling. By candlelight it appears violet. This reaction is to be relied on in a measure olllv in the case of infusible or diflicultlv fusible compounds of aluminium pretty free from other metals; it is never quite decisive, since cobalt solution gives a blue color nnder similar circumstances not only with readily fusible compounds, but also with certain infusible compounds free from aluminliun, such as the normal phosphates of the alkali-earth mretals. ~ 102. 6. CHROMIUMVJ Cn. 52'2 A-ND CIEROnIC COMIPOUNDS.t 1. CItROMIc OXIDE Cr, 03 is a green, CIJmoMIc HYDROXIDE, a bluish gray-green powder. Chromic hydroxide dissolves readily il acids. The non-ignited chromic oxide dissolves more diflicultlv, and the ignited chromnic oxide is allllost altogether insoluble. 2. The cHRoNIC ScALTS have a green or violet color. Manv of themn are soluble in water. AMost of them dissolve in hydrochloric acid. The solutions exhibit a fine green or a dark violet color, which latter, however, changes to green Iupon heating. The chromic salts with volatile acids are decomposed upon ignitionll, the acids being expelled. The chromnic salts which are soluble in water redden litmllus. Anhydrous chromic chloride is crystalline, violet-colored, insoluble in water and in acids, and volatilizes with difficulty. 3. Potassca and sodca produce in the green as well as in the violet solutions a bluish-green precipitate of cImnormc HYDROXIDE which dissolves readily and completely in an excess of the preK > SO4 Al:SO4 A12 K, (SO4)4 + 24 H20. or, SO + 24 H20. Al-SO, K >SO, t In the chromic compounds, Cr. is apparently trivalent, but is really quadrivalent, Cr, being sexivalent, thus: Cr C1 Cr-~ ->0 Cr -C1l Cl

Page  119 ~ 102.] CHROMIUM. 119 cipitant, imparting to the fluid an emerald-green tillt. Ulpoll lo2ng-continued ebullition of this solution, thle whole of the blydroxide separates againl, and the supernatant fluid appears perfectly colorless. The same reprecipitation takes place if ammnonlium chloride is added to the alkaline solution. Application of heat promotes the separation of the precipitate. 4. Amwoniac produces in green solutions a grayish-(green, in violet solutions a grayish-blue precipitate of cimRomiic I-nDRoxIn)i,. The former precipitate dissolves in acids to a green fluid, the latter to a violet fluid. Other circumstances (ollcelltration, way of adding the ammonia, etc.) exercise also some inlfluelce upon the composition and color of these hydroxides. A slnall portion of the hydroxide redissolves inl an excess of the precipitant in the cold, imparting to the fluid a peach-blossom red tint; but if, after the addition of ammonia in excess, heat is applied to the mixture the precipitation is comlilete. 5. Alkali carbonates precipitate BASIC CHROMIC CARBONATE, which redissolves with difficulty in excess of the precipitant. 6. Barium2 carbonate precipitates the whole of the chromlinmn as a GREENISH HYDROXIDE MIXED WVI''I BASIC SALT. The precipitation talces place in the cold, but is complete only after lolg-contillnued digestion. N. 13. to 3, 4, 5, and 6-Tartaric and citric acids, sugar, and oxalic acid interfere mnore or less with the precipitation of violet or green solutions of chromic hydroxide by ammonia, the first fornmed precipitates frequently redissolving entirely to red fluids after long standing. The above-named acids generally prevelnt altogether the precipitation by sodium carbonate. In the presence of these acids also the precipitation by barium carbonate is incomplete. 7. If a solution of cliromic hydroxide in solution of potassa or soda is mixed with some lead dioxlide in excess, and the mixture is b)oiled a short time, the chromic hydroxide is oxidized to cliromic acid. A yellow fluid is therefore ol)tained on filtering, which consists of a solution of LEAD cmmioMATE in solution of potassa or soda. Upon acidifying this fluid with acetic acid, the lead chromate separates as a yellow precil)itate (CHANCETL). Very mlinute traces of chromic, acid ma1y be detected in this fluid with still greater certainty by acidifying with hydrocllloric acid, and bringing it in contact with hydrogen dioxide and ether. (Compare ~ 138.) S. Tle fusion of chromnic oxide or of any chromic compound with sodliuz, nitrcate and carbonate, or still better, witl potassizuin cidorate Cand sodium carbonate, gives rise to the formlatio11 of yellow ALIKLI-CHIROMATE, which dissolves in water to an intensely yellow fluid. For the reactions of chromic acid see ~ 138. 9. Sodiugm metcahospatcten* dissolves chromic oxide and chromic salts, both in the oxidizinlg and reducing flame of the blowpipe, to clear beads of a faint yellowislkgreenl tint, which upon * Obtained by fusing, on platinlm wire, hydrogen sodium phosphate. See. 85a.

Page  120 120 REACTIONS. GROUP IIL [~~ 103, 104. cooling changes to EMIERALD-GREEN. Chromic oxide and chronie salts show a similar reaction with sodiamn tetraborate The Bunsen gas flame is used for the experiment, or the blowpipe flame. ~ 103. lecapiitulation and remarks.-Tile solubility of aluminium hydroxide ir solutions of potassa and soda, and its reprecipitation from the alkaline solutions by ammonium chloride, afford a safe means of detecting alumilniulm in the absence of chromic salts. But if the latter are present, whlich is seen either by the color of the solution, or by the reaction with sodium mletaphosphate, they llust be removed before aluminium can be tested for. The separation of chromium from aluminilumn is effected the most completely by fusing 1 part of the mixed oxides with 2 p:arts of sodium carbonate and 2 parts of potassium chlorate, wvhicli may be doile ill a platillumn crucible. The yellow mass obtained is boiled with water; by this process the whole of the clhrolnium is dissolved as potassitum chromate, alld part of tle alluminium as potassium alulminate, the rest of the alluminliul remainling undissolved. If the solution is acidified witlh nitric abid, it acquires a reddisli-yellow tilit; if ammnonia is thern added to feebly alkaline reaction, the dissolved portion of the aliluinium separates. The precipitation of chromic hydroxide, effected by boiling its solution in solution of potassa or soda is also sufficiently exact if the ebullition is continued long enouglh; still it is often liable to mnislead in cases where only little chromic salt is present, or where the solution contains organic matter, even though in small proportion only. I have to call attention here to the fact thlait the solubility of chromic hydroxide in an excess of cold solution of potassa or soda is considerably impaired by the presence of other hydroxides (manganous, nickelous and cobaltous hydroxides, and more particularly ferric hydroxide). If these hydroxides haplpen to be present in large excess they may even altogether prevent the solution of the chromic hydroxide in pIotassa or soda solution. Lastly, the influence of non-volatile organic acids, sugar, etc., upon the precipitation of alumniniuml and chromium hydroxides by ammllonia, etc., must be remembered. If organic substances are present therefore, ignite, fuse the residue with sodium carbonate and potassium chlorate, and proceed as directed before. In respect to the' detection of traces of aluminiumiu by an alcoholic solution of morin, compare GOPPELSREODE..* Special Reactions of the rarer Metals of the Third Group. ~ 104. 1. BERYLLIUM or GLUCINUAX, G1. 9,4. Beryllium is a rare metal found in the form of a silicate in p)henacite, and, with other silicates, in beryl, euclase, and some other rare mlinerals. Berylliutm oxide, (berylla or glucina) is a white, tasteless powder insoluble in water. The ignited earth dissolves slowly but completely in acids: it is readily soluble after fusion with sodiuml disulphate. The hydroxide dissolves readily in acids. The compounds of beryllium very much reselmble the aluminium compounds. The soluble beryllium salts have a sweet astringent taste; their reaction is alkaline. The native silicates of * Zeitschr. f. anal. Chema., 7, 208.

Page  121 ~ 104.] THORIUM. 121 berylliuln ar/oml — 5Ib-teW decomposed by fusing with 4 parts of sodium carbona:te. bo Z s,ammonia, and ammnonium sulphide throw down froll solutio ni y bery1fiim salts white flocculent hydroxide, which is insol ible in ammonia, but dissolves readily in solution of potassa or sodla, froml which solution it is precipitated again by ammoniunl chloride; the concentrated alkaline solutions remain clear on boiling, but from more dilute alkaline solutions almost the whole of the beryllium separates upon continued ebullition (difference between beryllium and aluminiuml). Upon continue(l ebullition with ammonium chloride, the freshly precipitated hydroxide dissolves as beryllium chloride, with expulsion of ammonia (difference between beryllium and alulinium). Alkali carbonates precipitate white beryllium carbonate, which redissolves in a great excess of sodium or potassium carbonate, and in a much less considerable excess of ammlionilum carbonate (most characteristic difference between beryllium and alullinium, but they cannot be completely separated in this way, as in the presence of beryllium a certain quantity of aluminiume dissolves in almmlonium carbonate, JoY). Upon boiling these solutions basic beryllium carbonate separates, readily and completely from the solution in ammonium carbonate, but only upon dilution and imperfectly from the solutions in sodium and l)otassium carbonate. Bari'inm caObate piecipitates bery-ulm completely upon coldie(on. Oxalic acid and oxalates do not precipitate beryllium (diffelence between beryllium and thorium, zirconium, yttrium, erbium, cerium, (in cerous salts) lanthanium, didymiuml). Berylliuml, when fused with 2 parts of ltydrogenz potassiumzfluoride, dissolves in water acidified with hydrofluoric acid. (This reaction serves as a means of separating beryllium froml aluminiium, for when aluminium is similarly treated it remains insoluble as aluminium potassium fluoride.) MIoistened with solution of cobalt nitrate, the beryllium compounds give gray masses upon ignition. 2. THORIUM or THonINum, Th. 231. Thorium is a very rare metal found in thorite and monazite. Thorium oxide. (thloria or thorina) is white, while hot, yellow. Ignited thoria is soluble only upon heating with a mixture of 1 part of concentrated sulphuriC acid and 1 part of water; but it is not soluble in other acids, not even after fusion with alkalies. When evaporated with hydrochloric or nitric acid, the corresponding salts are left in a varnish-like form, which dissolves at once in water completely. Hydrochloric and nitric acids precipitate from such solutions the chloride or nitrate; even sulphuric acid may produce a precipitate in the solutions (BAHI). The moist hydroxide dissolves readily in acids, the (dried hydroxide only with difficulty. Tllorium chloride is not volatile. Thorite (thorium silicate) is decomposed by moderately concentrated sulphuric acid, and also by concentrated hydrochloric acid. Potassa, ammnonia, and ammoniutn sulphide precipitate from solutions of thorium salts white hydroxide, which is insoluble in an excess of the precipitant, even of potassa (difference between thorium, and aluminiuml, and beryllium). Potassium carbonate, and ammoWiumb cacbonate precipitate basic thorium carbonate, which readily dissolves in an excess of the precipitant in concentrated solutions, with diffieulty in dilute solutions (difference between thorium and aluliniulll). From the solution in ammonium carbonate basic salt separates again even at 50~. Bariulvm carbonate precipitates thorium completely. Hydrofluoric acid precipitates the fluoride which at first appears gelatinous, but after a little while pulverulent. The precipitate is insoluble in water and hydrofluoric acid. (Here thorium differs from alumillium, beryllium, zirconiulm, and titaniunm). Oxalic acid produces a white precipitate (here'thoriumln differs from beryllium and aluminium). Tlhe precipitate does not dissolve in oxalic acid nor in dilute mineral acids, but it does dissolve in a solution of am

Page  122 122 REACTIONS. GROUP III. [| 104. monium acetate containing free acetic acid. (Here thoriit: differs from yttrium and cerium in cerous salts). The precilpitate is insoluble in excess of ammnioium oxalate (difference letween tloriumn and zirconium). ]Dotossiumn sulp7/hate in concentrated solution lprecipitates thorium slowly lit coni pletely (here thorium differs from aluminiuml and beryllium). Thle recipitate consists of thorium sulphate; it is insoluble in conccntlirat(,d solution of potassium sull)hate. it dissolves with difficulty in cold and al1,, in hot water, but readily on addition of some hydrochloric acid. On heating the neutral solution of thorium sulphate in cold water, it separates in the form of a heavy white curdy precipitate (difference between thorium, and aluminium, and beryllium). This precipitate recdissolves in cold water (in which it differs from titaniumll). Sodiumz thiosulpchate precipitates from neutral or slightly acid solutions on boiling thoriuml thiosulphate mixed with sulphur; the precipitation, however, is not quite complete (difference between thorium and yttrium, erbium and didymiuml). 3. Zimcoxiui~, Zr. 89.6. Found in zircon andc some other rare minerals. Zirconium oxide or zirconia (Zr 02) is a white p'owder insoluble in hydrochloric acid, soluble upon addition of water, after continued heating with,.tuure of 2 parts of hydrated sulphuric acid and 1 part of water...e hydroxl e resembles alulninium hydroxide, dissolving readily in hydroc rkori- d when precipitated cold, and still moist, but with difficulty when precipitated hot, or after drying. The zirconium salts soluble in water redden litmus. The native zirconiumr silicates may be decomposed by fusion with sodium carl)onate. The finely elutriated silicate is fused at a high templerature, to-,gether with 4 parts of sodium carbonate. The fused lmass gives to water lsodiulm silicate, a sandy sodium zirconate being left behind, iNhich is vaslied, and dissolves in hydrochloric acid. Zircon nlay easily be leclmlposed bly fusion with hydrogen potassium fluoride at a red heat, potassium silicofluoricle and zirconium p)otassium fluoride being-produced. l'ott.s.a soda, amCmonia, and an7monium su.lphide prlecipitate from solutions of zilC()nium salts a flocculent hydroxide, which is, insoluble in an excess of tlle precipitant, even of soda and potassa (difference between zirconiuml and aluminiunim, and beryllium), and is not dissolv:d even by boiling solution of alnlmonium chloride (difference between zirconium and beryllium). C(abeonates of potassium, 8odium and ammnonium, throw down zirconiulll carlonate gs a flocculent precipitate, which redissolves in a large excess of potassium carbonate, more readily in potassium bicarbonate, and miost readily in anlnionium carbonate (difference between zirconiumo and aluminiuri), from wvhich solution it precipitates again on boiling. Oxalic acid plroducecs a bulky precipitate of zirconium oxalate (difference between zirconium and aluminium and beryllium), which is soluble in oxalic acid, soluble in hydrochloric acid, soluble in excess of ammonium oxalate (difference between zirconium and thorium). A concentrated solution of potassiumz s1lphate speedily produces a white precil)itate of zirconium potassium sulphate, insoluble in excess of the precipitant (difference between zirconiuml and aluminium and beryllium), which-if precipitated coldl-dissolves readily in a large proportion of hydrochloric acid, but is almost absolutely insoluble in water and in hydrochloric acid if lirecipitated hot (difference between zirconium and thorium and cerium in cerous salts). Zirconium sulphate is difficultly soluble in cold water, readily soluble in hot water (difference between zirconium and thorium). Bariivm carboliate does not precipitate zirconium salts completely, even upon boiling. Hydr ofluoric acid does not precipitate zirconium salts (difference between zirconium and thorium and yttriun). Sodiumn thiosulphate precipitates zirconium salts (difference between zirconium and yttrium, erbium and didymiunmn). The separation of the zirconiumr thiosulphate takes place on boiling even

Page  123 ~ 104.] ITTRIUM. 123 in the presence of 100 parts of water to I part of the metal (difference between zirconium and cerium and lant'laniuln). Turmeric paper dipped into solutions of zirconium slightly acidified with hydrochloric or sulphuric acid, acquires a brownish red color after drying (difference between zirconiuml and thoriul). In the presence of titanic acid, which also lias the effect of turning turmleric paper brown, treat the acid solution -with zinc first, to reduce the titanic acid to titanous oxide, the solution of which does not affect turmeric paper (PISANI). 4. YTTRIUM, Y 61-7. Yttrium is a rare metal found in gadolinite, orthite, yttro-tantalite. Yttria (Y O ) when pure is pale yellowish-white, when ignited in the oxidizing flame it emits a white light (difference between yttrium and erbium) without fusing or volatilizing. In nitric, hydrochloric, and dilute sulphuric acid it is difficulty soluble in the cold, but on warming it dissolves completely after some time. The solutions, and likewise the salts of yttrium are colorless; they have an acid reaction and a sweetish astringent taste. Yttria does not combine directly with water. Yttrium under no circumstances yields a spectrum, nor do the solutions of its salts show any absorption bands (BAIIrl and BUNSEN). Anhydrous yttrium ch.laride is not volatile (difference between yttrium and aluminium, beryllium and zirconiull). Potassa precipitates white hydroxide, which is insoluble in an excess of the precipitant (difference between yttrium and aluminium and beryllium). Ammonzi(a and ammo-nium sulphide produce the same reaction. Presence of a small quantity of ammonium chloride will not prevent the precipitation by ammonium sulphide; but in presence of a large excess of ammlonium chloride, ammonium sulphide fails to precipitate solutions of yttrium salts. Alkali carboCnates produce a white precipitate, which dissolves with difficulty in potassium carbonate, but more readily in hydrogen potassium carbonate anct in ammonium carbonate, though by no means so readily as the corresponding beryllium precipitate. The solution of the pure hydroxide in ammonium carbonate deposits on boiling the whole of the yttrium; if ammonium chloride is present at the same time, this is decomposed upon continued hcating, with separation of ammonia, and the precip)itate redissolves as yttrium chloride. Saturated solutions of yttrium carbonate in ammonium carbonate have a tendency to deposit yttrium carbonate, which should be borne in mind. Oxalic acid produces a white precipitate (difference between yttrium and aluminium and bleryllium). The l)lecipitate does not dissolve in oxalic acid, but it dissolves with difliculty in dilute hydrochloric acid, and it is partially dissolved by boiling with ammoniuml oxalate. Yttrium potassium sulphate dissolves readily in water and in a solution of potassium sulphate (difference between yttrium and thoriumll, zirconium and the metals of cerite). Barium carbonate produces no precipitate in the cold (difference between yttrium and aluminium, lberyllium, thorium, cerium, and didymium), on boiling even the precipitation is incomplete. Turmeric paper is not altered by acidified solutions of yttriurn salts (difference between yttrium and zirconium). Tartaric acid does not interfere with the precipitation of yttriul by alkalies (characteristic difference between yttrium and aluminium, bleryllium, thorium and zirconium). The precipitate is yttriumtartrate. The p)recipitation ensues only after some time, but it is complete. Sodium thiosilphate does not precipitate yttrium (difference between yttrium and aluminium, thorium, zirconium and titanium). Hydrofluoric acid produces a precipitate (here yttrium differs from aluminium, beryllium, zirconiuml and titanium); the precipitate is gelatinous, insoluble in water and hydrofluoric acid; before ignition it will dissolve in mineral acids, after ignition it is decomposed only by strong sulphuric acid. A cold saturated solution of the sulphate becomes turbid when heated to between 30~ and 400; on boiling

Page  124 124 IREACTIONS. GROUP III. [n 104. almost tle whole of the salt separates. Yttrliuim gives clear colorless beads with borax and sodium metaphosphate in both the outer and inner flame (difference between yttrium and cerium and didymium). 5. ERBIUM, Er. 112'6. Erblium accompanies yttrium in gadolinite.* Erbiumn oxide is distinguished by its fine rose color, it does not alter on ignition in hydrogen, and does not fuse in the hlighest white heat. When strongly heated in the form of a spongy lmass, it glows with an intense green light. In nitric, 71ydrochloric, and sullpAhuric acid it dissolves with difficulty, but on warming completely. The erbium salts have a more or less bright rose tint, which is stronger generally with the hydrated than with the anhydrous salts; they have an acid reaction and a sweetish astringent taste. Erbium oxide does not comline directly with water. The sullphate when hydrated dissolves in iwater with difficulty, when anhydrous it dissolves readily. The basic nitrate (N 0O. Er. O H + 112 0) forms bright rose-colored, needle-shaped crystals whlich are difficultly soluble in nitric acid, decomposed by water into nitric acid and gelatinous hyperbasic salt, and yield the oxide on ignition. The oxalate is a rose-colored, heavy sandy powder. Finally the erbiunm oxide is most decisively characterized by the absorptio1n-.sect'rum which is given by the solutions of its salts. Of the absorption bands a lies between 71 and 74, 3 )between 64'5 and 65'5, y between 32'6 and 38'0, betwvee'n 85 and 91 on the spectrum table. If the ignited oxide is saturated with not too concentrated phosplhoic acid and reignited, a direct sp)ectrum is obtained, the bright lines of which coincide with the dark ones of the absorption-spectruml. With borax and sodium gmetaphosphate erbium gives beads which are clear and colorless when hot and also after cooling (difference between erbium and cerium and didymium). In the separation of erbiuml from yttrium, wlhich show a great likeness to each other in their deportment to reagents, BAIIn and BUNISEiN make use of the different behavior of the nitrates when heated. The separation is, "however, not complete unless the process is repeated ever and over again. Compare op. cit., p. 3. 6. CERrIJM, Ce. 92. Cerium is found in cerite, orthite, etc. It forms two oxides, cerous oxide (Ce 0) and eerie oxide (Ce3 04). The cerous hydroxide is white, but turns yellow upon exposure to the air, by absorption of oxygen. By ignition in the air it is converted into orange-red or red eerie oxide (difference between it and the preceding elements of the 3d group). Cerous flydroxide dissolves readily in acids. Ignited eeric oxide, containing lantlhanium and didymlium monoxides, dissolves readily in hydrochloric acid, -with cvolution of chlorine; in the pure state it dissolves very slightly in boiling hydrochloric acid; upon addition of alcohol it passes into solution (difference b)etween cerium and thorium and zirconiuml); the solution contains cerous chloride. Ceric oxide dissolves in concentrated sulphuric acid, although with difficulty; it is hardly attacked by nitric acid. The eerie oxide obtained from the oxalate when evaporated with nitric acid yields a basic salt, which gives an emulsion with water, and is not completely solulble in very considerable quantities of water (difference from thorium). The cerous salts are colorless, occasionally with a slig'ht shade of amethystred; the soluble cerous salts redden litmus. Cerous chloride is not vola* MOSANDER imagined that he had separated also another element, namely, terbium PoPP considered both erbium and terbium to be mixtures of yttrium with cerium and didymium. DELAFONTAINE defended MOSANDER'S view. However, BAIII and BuNsaEN'found in gadolinite, besides yttrium, only erbium (Annal. d. Chem. u. Pharm. 137, 1).

Page  125 ~ 410.] LANTHANIJu3M. 125 tile (difference from aluminium, beryllium, and zirconium). The sulphate does not dissolve entirely in boiling water. Ce:rite does not dissolve in aqua regia, but is decomposed by fusion with sodium carbonate, and also by concentrated sulphuric acid. Potassa precipitates white hydroxide, wVhich turns yellow in the air, and does not dissolve in an excess of the precipitant (difference from aluminiuml and beryllium). Ammonia precipitates basic salt, which is insoluble in an excess of the precipitant. Alkali carbonates produce a whlte precipitate, which dissolves sparingly in an excess of potassium carbonate, somewhat more readily in ammonium carbonate. Oxalic acid produces a white precipitate; the precipitation is complete even in moderately acid solutions (difference from alullliniunl and beryllium). The precipitate is not dissolved by oxalic acid, but it dissolves in a large proportion of hydrochloric acid. A saturated solution of potassium sulphate precipitates, even from somewhat acid solutions, white cerous potassium sulphate (difference from aluminium and beryllium), which is difficultly soluble in cold water, readily soluble in hot water and altogether insoluble in a saturated solution of potassium sulphate (differences from yttrium). The precipitate may be dissolved by boiling with a large quantity of water, to which some hydrochloric acid has been cdedcl Barium carbonate precipitates solutions of cerium salts slowly, but completely upon long-continued action. 7krtaric acid prevents precipitaltion by ammonia (difference from yttrium) but not by potassa. Sodium thiosulphate does not precipitate cerium, even on boiling with very concentrated solutions. The precipitated sulphur only carries down traces of the salt with it. If we conduct chlorine through a not too acid solution of a cerous salt mixed with sodium acetate, or if we add sodium hypochlorite to such a solution, all the cerium is precipitated as a light yellow eerie hydroxide (free from didyinmium and lanthanium. Popp.). If a cerous salt be dissolved in nitric acid, with addition of an equal volume of water, and if a small quantity of lead dioxide be added, and the liquid be boiled for some minutes, the solution turns yellow, even if only small quantities of cerium be present. On evaporating this solution to dryness, heating the residue till a portion of the acid escapes, and treating it with water acidified with nitric acid, no cerium will be dissolved, ibut any didymium and lanthanium present will be dissolved (GIBBS). Solutions of ceric salts are precipitated in the cold by barium carbonate. Sodium thiosulplhate precipitates a solution of ceric nitrate. Borax and sodium metaphosphate dissolve cerium oxides in the outer flame to yellowish red beads (difference from the preceding metals); the coloration gets fainter on cooling, and often disappears altogether. In the inner flame colorless beads are obtained. 7. LANTHANIUM. La., 93'6. This element is generally found associated with cerium. Lanthanium oxide is white and remains unaltered by ignition in the air (difference from cerous oxide). In contact with cold water it is slowly converted into a milk-white hydroxide;'i;thi To- water the conversion is rapid. The oxide and hydroxide change the color of reddened litmus-paper to blue; they dissolve in boiling solution of ammonium chloride, also in dilute acids. Lanthanium oxide in this resembles magnesia. The salts of lanthanium are colorless; the saturated solution of lanthanium sulphate in cold water deposits a portion of the salt already at 30~ (difference from cerium). Potassium sulphate, oxalic acid, and barium carbonate give the same reactions as with cerous salts. Potassa precipitates hydroxide, which is insoluble in an excess of the precipitant, and does not turn brown in the air. Ammonia precipitates basic salts, which pass milky through the filter on washing. The precipitate produced by ammonium carbonate is insoluble in an excess of the precipitant (difference from cerous salts). If a cold dilute solution of lanthanium acetate is supersaturated with ammonia, the

Page  126 12;' 6 REACTIONS. GROUP III. [~ 104 slimy precipitate repeatedly washed with cold water, and a little iodine ix powder added, a blue coloration makes its appearance, which gradually pervades the entire mixture (characteristic difference between lanthanium alnd the other earth-metals). 8. DIDYMIUM, D, 95. This element, like lanthanium and in conjunction with it, is found associated with cerium. Didymium oxide after intense ignition appears white, moistened with nitric acid and feebly ignited dark brown, after intense ignition again white. In contact with water it is slowly converted into hydroxide; it rapidly attracts carblon dioxide; its reaction is not alkaline: it dissolves readily in acids. The concentrated solutions have a reddish or a faint violet color. The nitrate on heating is first converted into a basic salt (difference from lanthanium) which is gray when hot and also Whellcn cold (difference from erbiuln). The chloride is not volatile. The saturated solution of the sulphate deposits salt, not at 300, but upon boiling. Potassa precipitates hydroxide, which is insoluble in an excess of the precipitant, and does not alter in the air. Ammonia precipitates basic salt, which is insoluble in ammonia, but slightly soluble in ammoniumn chloride. Alkali carbonates produce a copious precipitate, which is insoluble in an excess of the precipitant, even in an excess of ammonium carbonate (difference from cerous salts), but dissolves slightly in concentrated solution of ammonium chloride. Oxalic acid precil)itates salts of didymiunm almost completely; the precipitate is difficultly soluble in cold hydrochloric acid, but dissolves in that menstruuln upon application of heat. Barium carbonate precipitates didymium solutioIns slowly (more slowly than cerous and lanthanium solutions), and never completely. A concentrated solution of potassium sulphate precipitates didymium solutions more slowly andless completely than cerous solutions. The precipi-,tate is insoluble in'solution of potassium sulphate and in water (DELAFONTATNE), but it dissolves in hot hydrochloric acid with difficulty. Sodium thiosulphate does not precipitate solutions of didymiulm. Didymium gives with borax in both flames a nearly colorless bead, which in the presence of large quantities has a faint amethyst-red tinge. Sodium metaphosphate dissolves the oxide in the reducing flame to an amethyst-red lbead inclining to violet. With sodium carbonate in the outer flame a grayish-white mass is obtained (difference from manganese). The absorl)tionspectrum given by the solutions of the salts is peculiarly characteristic for didymium. This was first described by GLADSTONE, and afterwards by O. L. ERDMANN and DELAFONTAINE. BARR and BUNSEN have laid down the exact position of the bands (Zeitschr. f. anal. Chem. 5, 110). A direct spectrum mnay also be obtained from didymium as from erbium, but it is by no means well marked. For the separation of cerium from lanthanium and didymium, one of the following methods may be used:-a. Nearly neutralize the solution of the three metals, if acid, without allowing any permanent precipitate to form, add a sufficient quantity of sodium acetate and an excess of sodium hypochlorite, and boil for some time; the cerium will fall as eerie oxide, whllile lanthaniumn and didymium remain in solution. (Popp, Ann. d. Cliem. u. Pharm., 131, 360.) b. Precipitate the metals with potassa, wash, suspend the precipitate in potassa, and pass chlorine. Lanthanium and didymium dissolve; eerie oxide remains behind. (DAMOUR and ST. CLAIRE DEVILLE, Compt. Rend., 59, 272). c. Dissolve in a largo excess of nitric acid; boil with lead dioxide; evaporate the orange colored solution to dryness, and heat the residue till a portion of the acid escapes; treat with water acidulated with nitric acid, and separate the insoluble basic celic nitrate from the solution which contains all the lanthanium and

Page  127 ~ 104.] TITANIUM. 127 didymium. (GIBBS, Zeitschr. f. anal. Chem., 3, 396.) In using the last method, before proceeding with the residue or solution, the lead must be first separated by hydrogen sulphide. d. Heat the chromates to 110~, and treat with hot water to extract the undecomposed compounds of lanthaninum and didymiulll. The cerium remains behind as insoluble ceric oxide (PATTINSON and CLARK, Chem. News, 16. 259). Froml the solutior of lanthanium and didymium obtained by one or other of the above methods, the b)ases are precipitated with ammonium oxalate, the oxalates are ignited, and the oxides thus obtained are treated with dilute nitric acid. If the separation of cerium was incomlllete, the remainder of the cerium will here remain behind. The solution is evaporated in a dish with a flat bottom to dryness and heated to 4000-500~. The salts fuse; nitrous fumes escal)e. The residue is treated with hot water, which dissolves the lmnthanlitum, leaving behind gray basic didymium nitrate. By a repetition of thle evaporation, etc., the two bases mlay be satisfactorily separated. (DAMIOUil and ST. CLAIRE DEVILLE.) Another method of separation, whicL is however less complete, consists in converting the didymium and lanthllanlli into sulphates, making a saturated solution of the dry salts in water at 50 or (0, and heating the solution to 300, when the lantlhanium sulplate is for the most part thrown down and the didycl ium sulphate is for tile most pIart held in solution. For another method of separating lantllanium and didynium, which requires the presence of a considerable quantity of cerium, compare CL. WINILER (Zeitschr. f. anal. Chem., 4, 417). 9. TITANIUM, Ti. 50. Titanium forms two oxides, titanious oxide (Ti20) and titanic oxide (Ti O,), and the hydroxides, titanic and metatitanic acids. Tile latter are lnore frequently met with in analysis. Titanic oxide is found in the free state in rutile and anatase, in combination with bases in titanite, titaniferous iron, etc. It is found in small proportions in many iron ores, in clays, and generally in silicates, consequently also in blast furnace slags. The small copper-colored cubes which are occasionally found in such slags consists of a combination of titanium cyanide with titanium nitride. Feebly ignited titanic oxide is white; it transiently acquires a lemon tint when heated; very intense ignition gives a yellowish or b1rownish tint to it. It is infusible, insoluble in water, and its specific gravity is 3-9 to 4'25. The titanic chloride (Ti Cl4) is a colorless volatile fluid, funming strongly in the air. a. Deportmrenzt with acids, and reactions of acid solutions qof titanzic oxide. -Ignited titanic oxide is insoluble in acids, except in hydrofluoric acid and in concentrated sulphuric acid. If the solution in hydrofluoric acid is evaporated with sulphuric acid, no titanic fluoride Will volatilize (difference from silicic oxide). With sodiumr sulphate it gives upon sufficiently long continued fusion a clear mass, which is completely soluble in a large proportion of cold water. Titanic oxide is very easily brought into a clear solution, by fusing with hydrogen potassium fluoride and dissolving the fujion in dilute hydrochloric acid. The titanium potassium fluoride is difficultly soluble in water, 1 part requiring 96 parts at 14~. Normal titanic hydroxide, Ti (OH)4, or titanic acid, dissolves, both moist and when dried without the aid of heat, in dilute acids, especially in hydrochloric and sullphuric acids. All the solutions of titanic acid in hydrochloric or sulphuric acid, but more particularly the latter, when subjected in a higlhly dilute state to long-continued boiling, deposit mectatitanic acid as a white powder insoluble in dilute acids. Presence of much free acids retards the separation and diminishes the quantity of the precipitate. The precipitate which separates from the hydrochloric acid solution emay, indeed, be filtered, but it will pass milky through the filter on washing, except an acid or ammoniu n chloride be added to the washing water. Sc.u.

Page  128 128 REACTIONS. GROUP ITT. [~ 104. Ntio of potassa throws down from solutions of titanic acid in hydroclhloric or sulphuric acid, titanic acid as a bulky white precipitate, which is insoluble in an excess of the precipitant; ammonia, ammonium sulphide, and barium carbonate act in the same way. The precipitate, thrown down cold and washed with cold water, is soluble in hydrochloric acid and in dilate sulphuric acid; presence of tartaric acid prevents its formation. Potassium ferrocyanide produces in acid solutions of titanic acid a dark brown precipitate; infusion of galls a brownish precipitate, which speedlily turns orange-red. On boiling a solution of titanic acid with soditum thiosulphate, the whole of the titanic acid is thrown down. Soditmn phosplhate throws down the titanic acid almost completely as phospho-titanic acid even from solutions containing much hydrochloric acid. The washed precipitate consists of P2Ti2O7 (AIERz). Zinc or tin boiled in acid titanic solutions produces after some time a pale violet or blue coloration; subsequently a blue precipitate, which gradually becomes white. The coloration is caused by the reduction of the titanic acid to titanous hydroxide. If to the blue but still clear solution potassa or ammonia is added, blue titanous hydroxide separates, which is gradually converted into white titanic acid with decomposition of water. The reduction of titanic acid in hydrochloric solution takes place also in the presence of potassium fluoride (difference from niobic acid), the fluid becoming b}right green. The solutions of titanium chloride in water have properties which vary according to their preparation with hot or cold water. The solution prepared with cold water is not precipitated by sulphuric acid, nor by hydrochloric, nor by nitric, it is precipitated by phosphoric acid, arsenic acid, or iodic acid; but if the solution be boiled only for a few seconds it becomes slightly opalescent, and so far modified that hydrochloric and nitric acids produce white precipitates in it which are insoluble in excess of the acids, sulphuric acid also precipitates it, but an excess redissolves the precipitate. The solution prep)ared in the cold contains titanic acid, the boiled solution contains metatitanic acid. (R. WEBEER, Pogg. Ann., 120, 287.) b. eacrtion with alkalies.-Recently precipitated titanic acid is almost absolutely insoluble in solution of potassa. If titanic oxide or acid is fused with hydrate o fpotassa, and the fused mass treated with water, the solution contains a little more titanic acid. By fusion with alkali carbonates normal alkali titanates are formed, with expulsion of carbon dioxide. Water extracts from the fused mass alkali and alkali carbonate, leaving behind acid titanate of the alkali-metal, soluble in hydrochloric acid. Titanic oxide mixed with charcoal gives upon ignition in a stream of chlorinze titanium chloride as a volatile liquid, which emits copious fumes in the air. Sodium metaphosplhate dissolves titanic oxide at the point of the outer blow-pipe flame to a colorless bead but with difficulty, in the outer flame but near the point of the inner flame it dissolves readily and in considerable quantity. If the clear and colorless bead is again held in the point of the outer flame, It becomls opaque if sufficiently saturated, and by continued action of the flame titanic oxide will separate in microscopic crystals of the form of anatase (G. RosE). If the bead is held in a good reducing flame for some time, it will appear yellow while hot, red while cooling, and violet when cold. The reduction is promoted by the addition of a little tin. If some ferrous sulphate is added, the bead obtained in the reducing flame will appear blood-red. 10. TANTALUM, Ta., 182.* Tantalum forms with oxygen tantalic oxide, Ta2 O0. There is also a tantalous oxide, Ta 02. Tantalum occurs in columbite and tantalite (tl* The results of the recent investigations on tantalium and niobium by M[ARIGNAC, BLOMSTIRAND, DEVILLE, and TROOST, and HER.IANN will be found in Zeitschr. f. anal. Chem., 5, 384 et seq. and 7, 104 et seq.

Page  129 104.] NIOB3IUi. 129 most always in conjunction with niobium). Tantalic oxide is white, pale yellowish when hot (difference from Ti 02). It has a specific gravity of 7-'68'01. Tantalic oxide is not reduced by ignition in a current of hyilrogen. It combines with acids as well as with bases. a. Acid solutions. —When tantalic oxide is intilately mixed with charcoal ancd ignit,,cl in a current of dry chlorine, tantalum chloride (Ta Cl5) is formed. The latter is yellow, solid, fusible, and can be sul)limed; it is decomposed by water, with separation of tantalic acid (hydroxide); it is entirely soluble in sulphuric acid, nearly so in hydrochloric acid, and partially soluble in potassa solution. If titanium is present, on treating the lllixtures of oxides and charcoal with a current of chlorine, titanium chlorlide will be formed and will fume strongly in tlle alir. Tantalic acid dissolves inl hydrotloric acid, the solution, when mixed with potassium fluoride, yields a very characteristic salt in line needles (2 K F. Ta F5), which is distinguished by its difficult solubility in water acidified with hydrofluoric acid (1 of the acid to 150 or 200 of -water). Hydrochloric and concentrated sulphuric acid do not dissolve ignited tantalic oxide. With sodium disulphate it fuses to a colorless mass; if this is treated with water, tantalic acid combined with sulphuric acid remains undissolveci (difference between tantalic acid and titanic acid, but cannot be made the trounld of a method of separation). When ignited in an atmosphelre of ammlonium carbonate the tantalic sulphate is converted into tantalic oxidc. If a solution of alkali tint:tlate is mixed with hydrochloric acid in excess, tlh fi-st-formned precipitate redissolves to an opalescent fluid. Amnmzonia and oamnzoonoit sulphiale precipitate from this fluid tantalic acid or an acid alnnlmonium tantalate, but tartaric acid prieventts the p)recipitLation. Salpl/)/ric'acid precipitates tantalic sulplhate from the opalesccnt fluid. WhVlen acid solutions of tantalic acid are broullht into contact with zinc, no blue coloration is observed (difference between tantalic acid and niobic acid). b. B-haviior to al1X;aies. —By continued fusion with pgtassibio hydroxilde potassium tantalate is formed; the fused mass dissolves in water. By fusion with sodiurm hydroxide a turbid mass is obtained; a little water l)oured on this mass will dissolve out the excess of sodium hydroxide, leavinc the whole of the sodium tantalate undissolved, as this latter salt is insoluble in solution of soda- but the sodium tantalate will dissolve in water after the removal of the excess of soda. Solution of soda throws down from this solution the sodium tantalate; if the precipitant be added slowly, the form of the precipitate is crystalline. Carbon dioxide throws down froml solutions of alkali tantalates acid salts, not soluble in boilincg solution of sodium calrbonate. SulpAhuric acid throws down tantalic sulphate even from. the dilute solutions of alkali tantalates; potassiumn tfrrocyanzide and infusion of galls produce precipitates only in acidified solutions; the precipitate produced by the former is yellow, by the latter light brown. Soditon metlphosphate dissolves tantalic acid and oxide to a colorless bead, which is colorless also when hot, remains colorless even in the inner flame, and does not acquire a blood-red tint by addition of ferrous sulphiate (difference between tantalum and titanium). 11. NIOBIUM, Nb., 94. Niobium combines with oxygen in several proportions, viz., Nb O, Nb O2, and Nbl20. It is occasionally found in columbite, samarskite, etc., and it is usually accompanied by tantalum. Niobic oxide (Nb2 O) is white, but turns transiently yellow when ignited (difference between niobic oxide and tantalic oxide). Its specific gravity lies between 4-37 to 4'53 (difference between niobic oxide and tantalic oxide). By strong ignition in hydrogen the niobic oxide is converted into black Nb O2. Niobic oxide combines both with bases and acids. Niobic acid (hydroxide) is a white, bulky, insoluble p)recipitate. 9

Page  130 130 REACTIONS. GROUP IV. [~ 105. a. Acid solutions of niobium.-Concentrated sulphuric acid dissolves the acid on heating, unless it las been strongly ignited and thus converted into oxide. On the addition of much cold water, a clear solution is obtained. On fusing with sodium or potassium disuIphate, both acid and oxide dissolve readily to a colorless mass, and on treating the fusion with boiling water niobic acid containing sulphuric acid remains undissolved, which however is readily soluble in hydrofluoric acid (see below). By mixing niobic oxide intimately with charcoal and treating with a current of chlorine, a mixture is obtained of white infusible difficultly volatile niobic oxychloride (Nb O Cl3) and yellow more volatile niobic cllolnide (Nb Cl5). Treated with water both compounds give turbid fluids, in wMhich a portion of the niobium is separated as niobic acid, but the larger portion remains dissolved. By boiling with hydrochloric acid and afterwards adding water the compounds give clear solutions, which are not precipitated by boiling or by sulphuric acid in the cold (difference f'romn tantalum chloride). By igniting niobic oxide in the vapor of nio-' biu cllloride the oxychllloride is formed (difference fromn tantalic oxide).' From the acid solutions of niobium, agmmonia and ammnonium sulphide tllrow down niobic acid containing- ammonia; this dissolves in hydrofluoric acid. The hydrofluoric solution when mixed with potassium fluoride gives potassium niobium fluoride (2 K F. Nb F5) when hydrofluoric acid is in exces3, otherwise it gives potassium niobium oxyfluoride (2 K F. N1b 0 F3). The latter salt is also obtained when potassium niobate is dissolved in hydrofluoric acid; it is readily soluble in cold water, one part dissolving in 12'5 parts (difference from potassium titanium fluoride, which requires 96 parts of water, and from potassium tantalum fluoride which requires 200 parts of water). On digesting a hydrochloric or sulphuric acid solution of niobic acid with zinc or tin, it acquires a blue and generally also a brown color, in consequence of the reduction of the niobic acid to lower hydroxides. In the presence of alkali fluorides the reduction does not take place (difference between niobic acid and titanic acid). b. Alkaline solutions.-With potassiumn hydroxide niobic oxide or acid fuses to a clear mass, soluble in water. To sodium hydroxide niobic oxide or acid shows the same deportment as tantalic acid or oxide. From the solution of potassium niobate, solution of soda precipitates an almost insoluble sodium niobate. On boiling a solution of potassiulm niobate with potassilmn hydrogen carbonate an almost insoluble acid potassium niobate is thrown down. On fusing niobic acid or oxide with sodium carbo;iate and boiling the fusion with water, a crystalline acid sodium niobate remains undissolved. Carbon dioxide when passed into solution of sodium niol)ate precipitates all the niobic acid as an acid salt. Sodium metaphosphate dissolves niobic acid or oxide readily; the bead held in the outer flame appears colorless as long as it is hot; in the inner flame it has a violet, blue, or brown color, according to the quantity of the acid p)resent, and a red color on the addition of ferrous sulphate. For the best methods of detecting the whole of the members of the third group in presence of each other, see Part II., Section III. ~ 105. FOURTH GROUP. 3More common metals:-ZINC, MANGANESE, NICKEL, COBALT IRON. Rarer elements:-URANIubi, THALLIUM, INRIUM, VANADIUM.

Page  131 106.] ZINC. 131 Profperties of the Groycp.-The solutions of the metals of the fourth group, if containing a stronger free acid, are not precipitated by hydrogen sulphide; nor are neutral solutions, at least not completely. But alkaline solutions are completely precipitated by hydrogen sulphide; and so are other solutions if a sulphide of an alkali metal is used as the precipitant, instead of hydrogen sulphide.* The precipitated sulphides are insoluble in water; some of them are readily soluble in dilute acids; others (nickel sulphide and cobalt sulphide) dissolve only with very great difficulty in these mlenstrua. Some of themn are insoluble in sulphides of the alkali metals, others (nickel) are sparilngly soluble in them, under certain circumstances, whilst others again (vanadium) are completely soluble. The metals of the fourth group differ accordingly from those of the first and second group in this, that their solutions are precipitated by ammnoninln sulphide, and from those of the third grounp inasmnuch as the precil)itates produced by ammonium sutlphide are sulphides, ald not hydroxides, as is the case with aluminium, chromiunm, etc. Special Reactions of the more commn'on, netals of the fourth grou~p. ~ 106. a. ZINC, Zn., 65'2. 1. hMETALLIC ZINC iS bluish-white and very bright; when exposed to the air, a thin coating of basic zinc carbonate forms on its sulrface. It is of mediumn hardness, malleable at a temperature of between 100~ and 150~, but otherwise more or less brittle; it fuses readily on charcoal before the blowpipe, boils afterwards, and burns with a bluish-green flame, giving off white fumlnes, and coating the charcoal support with oxide. Zinc dissolves in dilute hydrochloric and sulphuric acids, with evolutionl of hydrogen gas; in dilute nitric acid, with evolution of nitrogen monoxide; in more concentrated nitric acid, with evoluntionl of nitrogen dioxide. 2. ZINC OXIDEn and Z[NC HYDROXIDE are white powders, \which are insoluble in water, but dissolve readily in hydrochloric, nlitric, and sulphuric acids. Zinc oxide acquires a lemon-yellow tint when heated, but it resumes its original white color upon cooling. When ignited before the blowpipe, it shines with considerable brilliancy. 3. The ZINC SALTS are colorless; part of them are soluble in water, the rest in acids. The normal salts of zinc which are soluble in water redden litmus-paper, and are readily decom-,-nadic acid behaves in a peculiar way to ammonium sulphide, see ~ 113, d,

Page  132 132 REACTIONS. GROUP IV. [~ 106 posed by heat, with the exception of zinc sulplate, which can bear a duill red heat without undergoinll deconnposition. Zinc chloride is volatile at a red heat. 4. II'/drlogen sulpjAirle precipitates from neutral solutions a portion of the metal as white hvdrated ZINC SULPI-IDE (Zll S.120), Ill acid solutions this reagenlt fails altogether to produce a precipitate if the free acid present is one of the stronger acids; but from a solution of zinc in acetic acid it throws down the whole of the zinc, eveIl if the acid is present in excess. 5. Ammzo7n~ium s'a)hide throws down from neutral and hyVdrogen sulphide froin alkaline solutions the whole of the metal as hydrated ZINC SULPIIIDE, ill the forlm of a white precipitate. Amnluiolim chloride greatly promotes the separation of the precipitate. From very dilute solutions the precipitate separates oiily after long; standing. This precipitate is not redissolved by an excess of alnlnollimln ssulphide, nor by potassa or amlnmollia; hut it dissolves readily ill hydrochloric acid, nitric acid, and dilute sulphuric acid. it is insoluble in acetic acid. 6. Potassa a;nd soda thrlow dowlv ZINC IYDROXIDE (Zn(0lI))), in the form of a white gelatinoius precipitate, which is readcily and completely redissolved by an excess of the precipitant. Upon boiling these alkaline solutions they remain, if concentrated, unaltered; but from dilute solutions nearly the whole of the zillc hydroxide separates as a white precipitate. Amnl olimln chloride added to alkalile solutions, not containing a large excess of potassa or soda, produces a white precipitate of ziue l-cdroxide, which, however, redissolves on addition of more ammuollinlun chloride (difference between zillc and alumliniuln). 7. Ammonia. also produces in solutions, if they do iiot contain a large excess of free acid, a precipitate of ZINC IIYDIROXIDE, which readily dissolves in an excess of the precipitant. Thle concentrated solution turnl'll turbid wvhen mixed with water. On- boiling the concentrated solution part of the zinc hydroxide separates immediately; on boiling the dilute solution all the zinc hydroxide precipitates. AmImonium salts interfere with these precipitations more or less. S. ASoliun carbonate produces a precipitate of 1BSIC ZINC CARiONBATE 2 (Zn CO,) + 3 Znl (O 11)2 + 4 HI20, which is insolul)le in an excess of the precipitant. Presence of ammonllunm salts in great excess prevents the formation of this precipitate. 9. Ammonium carbonate also produces a precipitate of BASIC ZINC CARBONATE; but this precipitate redissolves upon further addition of the precipitant. On boiling the dilute solution zinc hydroxide precipitates. Ammoniumr salts interfere with this precipitation more or less. N.B. Non-volatile org'anic acids more or less interfere with the precipitation of solutions of zinc, by the caustic and carbonated alkalies. Sugar does not prevenlt the precipitations. 10. Barium carbonate fails to precipitate solutions of zinc salts in the cold, with the exception of the sulphate.

Page  133 10 7.] MANGANESE. 1 3 11. Potassivntm ferrocyanide throws down zIaC FERROCYANIDE (Zn2 Fe Cy6) as a white slimy precipitate, somewhat soluble in excess of the precipitant, insoluble in hydrochloric acid. 12. Potassiuml frcricyanide throws down ZINC FLERRICYANIDE (ZnsFe2Cy, 2) as a brownish orange-yellow precipitate, soluble in hyclhochloric acid and in ammonia. 13. If a mixture of a zin compound with sodium carboznate is exposed to the rcducing Jcane of the blowpipe, the charcoal support becomes covered with a slight coating of ZINC OXIDE, which presents a yellow color whilst hot, and turns white u1pon coolinl(. This coating is produced by the reduced metallic zilc volatilizing at the moment of its reduction, alld being reoxidized in passing through the outer flame. The METALLIC INCERUST.TIOr obtained aecordir to p. 26 is black with a brown edge, tlhe INCRs'TATrON OF OXIDE is white, and therefore invisible upon porcelain. It may be dissolved in nitric acid and examined' according to 14. 14. If zinc oxide or one of the zinc salts is moistened with solution of cobcalt nitrate, and then heated before the blowpipe, an unfused mass is obtained of a beautiful GREEN color: this mass is a comlpound of zinc oxide with cobalt oxide. If therefore in the first experiment described ili 13 the charcoal is moisteled around the little cavity with cobalt solution, the eoating appeals green when cold. This test may be applied with great delicacy by mixing the solution to be tested with a very little of the cobalt solution (not enough to give a lbright red col)or), adding sodiuml carbonate inll slight excess, boiling', filtering off, washing, and igniting on platinum foil. On trituratincr the residue the green color may be distinctly and readily observed (BLOXAAI). ~ 107. 6. MANGANESE,~* Mn. 55. 1. MlETALLIc MANGANESE is whitish-gray, dull, very hard, britfte, and fuses with very great difficulty. It oxidizes rapidly in tlhe ail, and in water with evolution of hydrogen, and crumbles to a dark gray powder. It dissolves readily in acids, forminl nagananous salts. 2. MA'NGANOUS OXIDE (MnI 0) is light green; manganous hyvdiroxide (Mn (O II)N) is white. The former smoulders to brown mlanganic oxide (Mn)O,) when heated in the ail, the latter even at the ordinary temperature rapidly absorbs oxygen flomn the air and passes into brown manganic hydroxide (Mn(OtI),). They are readily soluble in hydrochloric, nitlic, and sulphuric * MIn is bivalent in the manganous compounds: Mn is quadrivalent or Mn, is sexivalent in the manganic oxides and salts: in the manganates and per manganates (?) Min is also a hexad.

Page  134 134 REACTIONS. GROUP IV. [~ 107. acids, All the HIGHnrR OXIDES OF MANGANESE without exception dissolve to manganons chloride, with evolution of chlorine, when heated with hydrochloric acid; to manganous sulphate, with evolultion of oxygen, when heated with concentrated sulphurie acid. 3. The MANGANOUS SALTS are colorless or pale red; part of tlhem are soluble in water, the rest in acids. The salts soluble ili water are readily decomposed by a red heat, w.ith the excelpti1,l of the sulphate. The solutions do not alter vegetable colors. 4. 1-ydr'ogen sulrJphide does not precipitate acid solutions; neutral solutions also it fails to precipitate, or precipitates them (lnly very imperfectly. 5. Amzmonium. sualphzice throws down from neutral, and lhydrogen sulphide from alkaline solutions the whole of the metal as hydrated MANGAKNOUS SULPIIIDE (lMn S.112O), in form of a light flesh-colored* precipitate, which acquires a dark-brown color in the air; this precipitate is insoluble in ammnoniium sulphide and in alkalies, but readily soluble in hydrochloric, nitric, anid acetic acids. The separation of the precipitate is iaterially promoted by addition of ammloniurn chloride. From very dilute soultions the precipitate separates only after standira some time inl a warm place. Aninolninin oxalate, tartrate, and especially citrate retard the precipitation, the latter salt also keeps up some of the manganese. Iin the presence of ammonia and ammonium sullphide in large excess, the flesh-colored hydrated precipitate occasionally passes into the green anhydrous sulphide even inl the cold, the change being greatly facilitated by boiling, and being hindered mnore or less by the presence of ammonionm chloride. Solutiolls containing much free ammlonia nmust first be nearly neutralized with hydrochloric acid. 6. Potassa, soda, and amm.noniac produce whitish precipitates of rMANGAN-OUS HYDROXIDE (MIn1 (O 11)), which upon exposure to the air speedily acquire a brownish and finally a deep blackishbrown color, owing to the conversion of the inanganoun hydroxiclde into manganic hydroxide by the absorption of oxygen from the air. Ammonia and amlmonilmn carb)onate do inot redissolve this precipitate; but presence of ammonium chloride pre v.elnts the precipitation by ammonia altogether, aind that b)y potassa partly. Of already formed precipitates solution of amllonium chloride redissolves ollly those parts which ha've not yet underlgone oxidation. The solution of the mnanganous hydroxide in anmmonium chloride is owing to the disposition of the manganous salts to form double salts with ammonllium salts. The ammnoniacal solutions of these double salts turn brown In the air, and deposit dark-brown mnanganic hydroxide. N. B. Non-volatile organic acids impede the precipitation of * If the quantity of the precipitate is only trifling, the color appears yellow ish white.

Page  135 ~ 108.] NICKEL. 135 manganese by alkali carbonates. Sugar impedes the precipi. tation by alkalies, but not that by alkali carbonates. 7. Potassium ferrocyanide throws down MANGANESE FERROCYANIDi (Mn2 Fe Cy6) as a reddish-white precipitate, soluble in hydrochloric acid. 8. Ptassinumfer'ricyanide precipitates brown MANGANESE FERRICYANIDE (M1n3 Fe, Cyi2) insoluble in hydrochloric acid and ammonia. 9. If a few drops of a fluid containing mlananous salt, and free from chloline, are sprinkled on lead dioxide, and nitric acid free from chlorine is added, the mixture boiled and allowed to settle, the fluid acquires a red color, from the formation of permanganic acid H Mln 04 (TIOPPE-SEYLER). 10. Bariumn carbonate does not precipitate aqueous solutions of mnanranous salts upon digestion in the cold, with the exception of manlganous sulphate. 11. If any compound of manganese, in a state of minute division, is fused'with 2 or 3 parts of sodium, carbonate on a platinumn wire, or on'a small strip of platinum foil (heated by directing the flalne upon the lower surface), in the outer flamne of the Bunsen lamp or blowpipe, SODIUM MANGANATE (]Na, Mn 04) is formed, which makles the fused mass appear GRZElEN while hot, and of a BLUISI1-GREEN tint after coolillg, the bead at the saine tiine losing its transparency. This reaction enables us to detect the smallest traces of mllallngese. 1. 2. ]Borax and soditim n etapiho.2)pkate dissolve manganese compounds in the outer gas or blowpipe flamle to clear VIOLETRED beads, which upon c(oolillg acquire an AMETHYST-RlED tillt: they lose their color in the innler flame, owing to a reduction of manganic borate, or phosphate to inanganous salts. The borax bead appears black when containing a considerable portion of manllranlic borate, but that formed by sodium metaphosphate never loses its transparency. The latter loses its color in the inner flame of the blowpipe far mnore readily than the former. ~ l08. c. NICKEL, Ni., 58'8.* 1. ~iETALLIC NICKEL in the fused state is yellowish white, inclining to gray; it is bright, hard, malleable, difficultly fusible; it does not oxidize in the air at the comnmorl temllperature, l)ut it oxidizes slowly upon ignition; it is attracted by the mlagnet and may itself become mnagnetic. It slowly dissolves in hydrochloric acid and dilute sulphuric acid upon the application of heat, with evolution of hydrogen gas. It disaoltes readily in nitric acid. The solutions contain nickelons salts. 2. NICKELOUS HYDROXIDE is light green, and remains unaltered in the air, but is converted by ignition into amorphous green * In the monoxide and all the salts Ni is bivalent, in the sesquioxide lNi2 is sexivalent.

Page  136 136 PEACTIONS. GROUP IV. [~ 108 NICKELOUS OXIDE. (Ni 0). Both nickelous oxide and the corre. sponding hydroxide are readily soluble in hydrochloric, nitric, and sulphuric acids. But the niekelous oxide which crystallizes in octahedrons is insoluble in acids; it dissolves, howo'er, in fusing sodiuln disulllphate. NICIslLIC OXIDE (N'i2 03) is black; it dissolves in hvdrochliborti acid to nickelous chloride witll evolutionll of chlorlihne. By gentle ignition of the nitrate, nickelons oxide colltaininog a little nickelic oxide of grayish-greell color is obtained. 3. Most of the NICKEL SALTS are yellow in the alllhdlrols, fgreen in the hydh'ated state; their solutions are lightS gleen. The soluble norlmal salts slightly redden litmus-paper, and are decomnposed at a red heat. 4. JL,(droye2n suly/ri4de does not precipitate solutions of nickel salts with strong acids in presence of free'acids; in the absenor of free acid a small portion of the nicklel gradually separates as black NICKIEL ULPInIDE (Ni S).-Nickel acetate is not precipitated, or scarcely at all, in presence of free acetic acid B3ut ill the absence of free acid the greater part of the nickel is thrown down by, long-continued action of hydrogen sulphide. 5. Amnonitn?, sulphide produces in neutral, and hydrogen sulphide in alkaline solutions, a black precipitate of NICKEEL SULPIDE (Ni S). -which is not altogether insoluble in aminonium sulphide, especially if the latter contain free am-nmonia; the fluid fromn which the precipitate has been thrown down exhibits therefore usually a brownish color. The presence of ammonium chloride, and still more of ammoniumn acetate, considerably pronotes the precipitation. Nickel sulphide dissolves scarcely at all in acetic acid, with great difficulty ill hydrochloric acid, but readily in nitro-hydrochloric acid upon application of heat. 6. Potassa alld sode produce a light green precipitate of NICKELOUS IIYDROXIDI)i (N'i(O II),), which is insoluble in an excess of the precipitants, and unalterable in the air, and on boiling (even in the presence of alcohol). Alnmonium carbonate dissolves this precipitate, when filtered and washed, to a greenish-blue fluid, froln which potassa or soda reprecipitates the nickel as apple-green hydroxide. 7. Ammrnoni added in small quantity produces a trifling greenish turbidity; upon further addition of the reaYgent this redissolves readily to a blue fluid containing a compound of NICKELOUS SALT AND AIMAIONIA. Potassa and soda precip)itate flroml this solution nickelous hydroxide. Solutions containing ai mnoniuln salts or free acid are not rendered turbid by ammnonia. N.B. The presence of non-volatile organic acids, and of sugar, impedes the precipitation by alkalies. S. Potassiumfevrocyanide precipitates greenish-white FERROCYANKJDE OF NICKEL, Ni2 Fe (C N)6, which is insoluble in hydrochloric acid. 9. Potassiumft.rricyanide precipitates yellowish-brown NICKEL FERRIICY, &nIDE (Ni3 CO2 (CN)12). which is insoluble in hydrochloric acid.

Page  137 ~ 108.] NICKEL. 13 7 10. Potassium cya.nzide produces a yellowish-green precipitate of NIcIuEr CYANIDE (Ni(C-N)2), which redissolves readily in an excess of the precipi taut as a double nickel potassiuml cyanide (Ni (C N)2. 2 K C N); the solution is brownish-yellow, and does not acquire a darker color on exposure to tile air. If sulplhuric acid or hydrochloric acidclis added to this solution, the potassium cyanide is decomposdc, and the nickel cyanide reprecipitated. From more highly dilute solutions the nickel cyanide separates only after some time; it is very difficultly soluble in an excess of the precipitating acids in the cold, but more readily upon boiling. If the solution of the double cyanide is rendered alkaline by solution of soda, being also kept so by a furtller addition of soda if necessary, and chlorine gas is passed into it without warninng, the whole of the nickel gradually separates as black nickelic hydroxide (Ni (OH)3). 11. On adding to solutions which are not too dilute and which have beenl rendered alkaline by ammonia, a solution of potassium sulphocarblonate,< a deep brownish-red fluid is obtained whllich is barely translucent, and appears almost black by reflected light. If the solution of nic.kel is extremely dilute, the addition of the reagent will produce a delicate pink color (C. D. 3iRAUN). The occurrence of this color in highly dilute solutions is chllaracteristic of nickel. 12. ZBariuam carbonzate, on digestion in the cold does not precipitate solutions of nickel salts, solution of sulphate alone excepted. 13. Potassium nitrite with acetic acid does not throw down nickel, even from concentrated solutions. In the presence of calcium, bariuml or strontium, however, a yellow crystalline double nitrite of nickel and. of the alkali earth metal is precipitated from not too dilute solutions. The precipitate is difficultly soluble in cold water, more readily in hot water to a green fluid (KU~NZEL, O. L. ERDMANN). 1.4. Borax and sodju2gn qnetphosphtate dissolve compounds of nickel in the outer flamne to clear beads. The borax bead is violet while hot, reddish-brownl when cold; the sodium metaplhosphate bead is reddish or brownish-red while hot, yellow or reddishl-yellow when cold. In the inner flame the sodiumn Inetaphosphate bead relnains unaltered, but the borax bead becolnes gray alnd cloudy from reduced metal. On continued heating the particles of nickel. collect together without fusing, and the bead loses its color. 15. By the reduction in the sticz qf chacrcoal, according to p. 27, the compounds of nickel yield after trituration white, shinillg, ductile spalgles, which will be deposited on the point of a magnetic knife ill the form of a brtush. With nitric acid they give a green solution, which can be further examined. * Prepared by taking a solution containing about 5 per cent. of K O H, saturating one-half with H2S, adding the other half and then -~ of the volum6 of CS2, digesting at a gentle heat, and finally separating the dark orange-red fluid from the undissolved CS2. The solution must be kept in a well-closed bottle.

Page  138 138 REACTIONS. GROUP IV. [~ 109 ~ 109. d. COBALT, Co. 58'8. * 1. METALLIC COBALT in the fused state is steel-gray, pretty hard, malleable, difficultly fusible, and magnetic; susceptible of polish; it does not oxidize in the air at the colnmon telnperature, but it oxidizes at a red heat; with acids it behaves like nickel. The solutions contain cobaltous salts. 2. COBALTOUS OXIDE (CO O) is light brown; cobaltous hydroxide is a lale red powder. Both dissolve readily in. hydrochloric, nitlic, and sulphuric acids. COBALTIC OXIDE, (CO, 03) is black; - it dissolves in cold hydrochloric acid to cobaltic chloride (Co2 Cl,), but oil heatingl this is converted into cobaltous chloride (Co C12), w-ith evolution of chlorine. 3. The con3Lrous SALTr colltailing water of crystallization are red, the anhydrons salts mostly blue. The moderately concentrated solutions appear of a light red color, \which they retain though considerably diluted. The soluble normal salts redden litmnus slightly, and are decomposed at a red heat; cobaltous sulphate alone canl bear a moderate red heat without sufferinlg decomposition. Whell a solution of coblaltous chloride is evaporated, the light red color changes towards the enld of the operatioll to blue; addition of water restores the red col(!'. 4. JIydro yen sulpwile does not precipitate solutions of salts with stlongl acids, if they contain free acid; from neutral solutions it gradually precipitates part of the cobalt as black cobaltous suilphide (Co S). Cobaltous acetate is nllt precipitated, or to a very slight extent, il presenlce of free acetic acid. But in the absence of free acid it is completely precipitated, or almost completely. 5. Ammonioitn sulphide precipitates from neutral, and hydrogen sulphide from alkaline solutions, the whole of the metal as black COBALTOUS SULPIIDF, (Co S). Ammoniumn chloride promotes the precipitation most materially. Cobaltous sulphide is insoluble in alkalies and ammoniumn sulphide, scarcely soluble in acetic acid, very difficultly soluble in hydrochloric acid, upon application of heat. 6. P'otassa and soda produce blue precipitates of BasIC COBALTOUS SALTS, insoluble in excess of the precipitants, which turn green upon exposure to the air, owing to the absorption of oxygen. Upon boiling they are converted into pale red COBALTOUS HYDROXIDE, which contains alkali, and generally appears rather discolored from cobaltic hydroxide formed in the process. If, before boiling, alcohol is added, the precipitate is rapidly * In the cobaltous compounds Co is bivalent; in the cobaltic salts Co is tuadrivalent and Co2 sexivalent. The cobaltic salts, save the double cyanides, -itrides and amides, are unstable.

Page  139 ~ 109.J COBALT. 135 converted into dark brown cobaltic hydroxide. Normal am monium carbonate dissolves the washed precipitates of cobaltous basic salt or cobaltous hydroxide completely to intensely violet-red fluids, in which a somewhat larger proportion of potassa or soda produces a blue precipitate, the fluid still retainincr its violet color. 7. Amnrnonia produces the same precipitate as potassa, but this redissolves in an excess of the ammonia to a reddish fluid, which turns brownish-red on exposure to the air, from whichl potassa or soda throws down a portion of the cobalt as blue basic salt. Amlnonia produces no precipitate in solutions containing ammonium salts or a free acid. N.B. The presence of non-volatile organic acids or sugar checks the precipitation by alkalies. 8. Potassiumferrocyanide throws down green COBALTOUS FERROCYANIDE Co2 Fs (CN)a, insoluble in hydrochloric acid. 9. Potassium ferricyazide throws down brownish-red COBALTOUS FERRICYANIDE Co3 Fe2 (CN)12, insoluble in hydrochloric acid. 10. Addition of potassium cyanide gives rise to the formation of a brownish-white precipitate of COBALTOUS CYANIDE Co(CN)2, which dissolves readily in excess of the precipitant as a double cobaltous potassium cyanide Co (CN)2. 4 (K C N). Acids precipitate from this solution cobaltous cyanide. But if the solution is boiled with potassium cyanide in excess, in presence of free hydrocyanic acid (liberated by addition of one or two drops of hydrochloric acid), or if the solution is mixed with potassa or soda and chlorine is passed through it without warmning, the double cyanide is converted into potassium cobalticyanide Ka Co0 (CN),2, and acids will now produce no precipitate (essential difference between cobalt and nickel). Potassium nitrite, and acetic acid added to the unaltered solution of the double cyanide produce a blood-red color in consequence of the formation of cobalt potassium nitrocyanide; when the liquid is very dilute the color is merely orange red. Solution of soda added to the double cyanide occasions a brown color when the fluid is shaken, oxygen being absorbed (essential differences between cobalt and nickel, C. D. BnAUN). 11. Potassium sulphocarbonate, added to solutions which have been rendered alkaline by ammonia, produces a dark brown, almost black color; if the solution is very dilute a pale straw color. 12. Addition of tartaric or citric acid, then of ammlonia in excess, aid lastly of potrssium,frrieyanide, produces a deep yellowisll-red color; with extremely dilute solutions a rose c(11or (SKEY). This is a very delicate reaction, well suited for the detection of cobalt in the presence of nickel. 13. cBariun?, carbonate behaves in the same way as to solutions of nickel. 14. If potassium nitrite is added in not too small proportion to the solution of a cobaltous salt, then acetic acid to strongly acid reaction, and the mixture put in a moderately warmn place, all the cobalt separates, from concentrated solutions very sooll, from dilute solutions after some time, in the form of a cr-stalline precipitate of a beautiful yellow color (FIscnER, STrnoMEYE'-R). This precipitate is TRIPOTASSIUM COBALTIC NITRITE'(KNO0). Co(N2)6 + Aq. + (SADTLER). The precipitate is very

Page  140 J40 REACTIONS. GIOUP IV. [~ 1lo. perceptibly soluble in water, scarcely soluble in concentrated solutions of potassium salts and ill alcohol, insoluble in presence of potassium nitrite. When boiled with water it dissolves, thotghl not copiously, to a red fluid, which remains clear upon coo0lillg, and from which alkalies throw down cobaltous hydroxide. This reaction serves well to distinguish and separate cobalt froln nickel. 15. Boraxr dissolves compounds of cobalt in the inner and outer flame to clear beads of a magnificent blue color, which appear violet by candle light, and are almost black in the presence of a large quantity of cobalt. This test is as delicate as it is characteristic. Sodiun inetaphosJpate gives the same reaction. but it is less delicate. 16. In the reduction witll the sticik of charcoal, according to p. 27, compounds of cobalt behave in the same way as coinpounds of nickel. The solution with nitric acid is red. ~ 110. e. IRON AND FERROUS Co:rMPouNDS,* Fe. 56. 1. METALLIC IRON in the pure state has a light whitish-gray color (iron containing carboll is more or less gray); the nletal is hard, lustrous, minalleable, ductile, exceedingly difficult to fuse, ald is attracted by the mangnet. In contact with air and moisture a coating of rust (ferric hydroxide) forms on its surface: upon ignition in the air a coating of black ferrous-ferrie oxide Fe30,,. Hydrochloric and dilute sulphuric acids dissolve iron, with evolution of hydrogen; if the iron contains carbide, the hydrogen is mixed with hydrocarbons. The solntiols contain ferrous salts. Dilute nitric acid dissolves iron in the cold to ferrous nitrate, with evolution of nitrogfen monoxide; at a high temperature to ferric nitrate, with evolution of nlitrogen dioxide; if the iron contains carbide, some carbon dioxide is also evolved, and there is left undissolved a brown substance resemblinlg humus, which is soluble in alkalies; when graphlite is present, it also is left behind. 2. FERROUS OXIDE is black; ferrous hydroxide is white, and in the moist state absorbs oxygen and speedily acquires a grayish green, and ultimately a brownish-red color. Both ferlous oxide and ferrous hydroxide are readily dissolved by hlydroc(hloric, sulphuric, and nitric acids. 3. The FERROUS SALTS have in the anhydrous state a white, in the hydrated state a greenish color; their solutions only look greenish when concentrated. The latter absorb oxygen * Fe is bivalent iii the ferrous compounds. Fe is quadrivalent atd Fe2 il sexivalent in the ferric salts.

Page  141 ~ 110. IRON AND FERROUS COMIPOUNDS. 143 when exposed to the air, with precipitation of basic ferric salts, Chlorine or nitric acid converts them by boiling into ferric salts. The soluble normal salts redden litmus-paper, and are decomposed at a red heat. 4. Solutions of ferrous salts made acid by strong acids are not precipitated by hycfrogqe sulphi/de; nor are neutral soln. tions nor solutions acidified with weak acids precipitated by this reag'ent, or at the most but very incompletely. 5. Arnrzonoitam suj,iclde precipitates from neutral, and hvdrocen snlphide from alkaline solutions, the whole of the imetal as l)laclk FERROUS SULLHRIDE (Fe S), which is insoluble in alkla. lies and sulphides of the alkali metals, but dissolves readily in hydrochloric and nitric acids; this blackl precipitate turllns reddish. brow') in the air by oxidation. To highly dilute solutionlls anmmoniium sulphide imparts a green color, and it is only after some time that the ferrouns sulphide separates as a black precipitate. Anmmioniln chloride promotes the precipitatioll most materially. 6. Potacssa alld ammolnia produce a precipitate of FERROUS HYDIROXIDE Fe (011)2, which in the first mnoment looks almost white, but acquires after a very short time a dirty green, and nitimnately a reddish-brown color, owing to absorption of oxygenl fron the air. Preselce of ammonium salts prevents the precipitation by potassa partly, and that by ammonia altogether. If alkaline ferrous solutions thus obtained by the agency of ammoniunm salts are exposed to the air, ferrouis-ferric and ferric hydrioxides precipitate. Non-volatile organic acids, sutgar, etc., check the precipitation by alkalies. 7. Potassiumrn frrocycanilde produces a bluish-white precipitate of POTASSIUM FERROUS FERROOCYANIDE KI 2Fe2(CLN), which by absorption of oxygen from the air, speedily acquires a blue color. Nitric acid or chlorine converts it immediately into Prulssian blue, 6 K2Fe2 (CN)6 + C1,0_ Fe, (CON) s + 31K4 e (CN)G + i'e2Cl. 8. Potassirum ferricyanide produces a magnificently blue precipitate of FEmBOUS FERRICYANIDE Fe, Cy,,. This precipitate does not differ in color from Prussian blue. It is insoluble in hydrochloric acid, but is readily decomposed by potassa. In highly dilute solutions the reagent produces simply a deep bliue-green coloration. 9. Potassium s3ulphocyanate does not alter solutions of fer. rous salts when free froml ferric salts. 10. Barium carboznate does not precipitate solutions of ferrous salts in the cold, with the exception of the sulphate. 11. Borax dissolves ferrous compounds in the oxidizing flame, giving beads varying in color from yellow to dark red; when cold the beads vary from colorless to dark yellow. In the inner flame the beads change to bottle-green, owing to the reduction of the newly formed ferric borate to ferrous-ferric

Page  142 142 RTEACTIONS. GROUP IV. [~ 111 borate. Sodiuum metaphophacte shows a similar reaction; the beads produced with this reagent lose their color uponl cooling still more completely than those produced with borax; the signs of the ensuing reduction in the reducing flaime are alsc less marked. 12. When reduced in the stick of charcoal (p. 27), ferrous compounds give a dull black powder, which is attracted lby a magnetic knife. The reduced metal, when dissolved in a few drops of aqua regia, gives a yellow fluid, which can be further tested according to ~ 111. ~ 111., IRON IN FERRIC COIMPOUNDS. Fe, 56. 1. Native crystallized FERRIC OXIDE (Fe203) is steel-gray; the native as well as the artificially prepared ferric oxide gives upon tliturlation a brownish-red powder; the color of the ferric hydroxides is more inclined to reddish-brown. B3oth ferric oxide and the ferric hydroxides dissolve in hydrochloric, nitric, and sulp)huric acids; the normal ferlic hydrloxide Fe (01-I)3 dissolves readily in these acids, but the basic ferric hydroxides, and ferric oxide dissolve with greater difficulty, and completely only after longl and hot digestion. FERnRO US-FERRIC OXIDE (Fe,,0) is black; it dissolves in hylldrochloric acid to ferrous chloride and ferric chloride, in aqua regia to ferric chloride. 2. The normal anhydrons FERRIC SALTs are learly white; the basic salts are vellow or reddish-brown. The color of the solutions is brownish-yelldw; anlcl becomes reddisll-yellow upon the application of heat. The soluble normal salts redden litmuspaper, and are decomposed by heat. 3. ]fydcroyen st//phicle pr(oduces in solutions made acid by stronger acids a milky white turbidity, proceeding from separated SULPHUR; the ferric salt being at the same time converted into ferrous salt: Fe, (SO4), + I-I>S - 2 Fe SO4 + 1,2 SO4 + S. If solution of hydrogen sulphide is rapidly added to neutral solutions, a transient blackening of the fluid also occurs. From solution of normal ferric acetate, hydrogen sullphide throws down the greater part of the iron; but in presence of a sufficient quantity of free acetic acid sulphur alone separates. 4. Anmnoniurm sulphide precipitates from neutral, and hydrogen sulphide from alkaline solutions, the whole of the metal as black FERROUS SULPIJIDE (Fe S) mixed with sulphur; Fe, C1, + 3 (N1T4)2S - 6 NH4 C1 + 2 Fe S + S. In very dilute solutionlls the reagent produces only a blackish-green coloration. Tihe minutely divided ferrous sulphide subsides in such cases 0nlv after lonll standing. Ammonium chloride most materially promlotes the prlecipitation. Ferrous sulphide, as already stated

Page  143 ~ 111.] IPRON IN FERRIC COMIPOUNDS. 143 (~ 110, 5), is insoluble in alkalies and alkali sulphides, but dissolves readily in hydrochloric and nitric acids. 5. Potassa and amtnoncia produce bulky reddish-brown precipitates of NORMAL FERRIC HYDROXIDE (Fe (01-1)3), which are illsoluble in an excess of the precipitant as well as inamlnmoniuln salts. 5Non-volatile organic acids and sugar, when present in sufficient quantity, entirely prevent the precipitation. 6. Potassiumn ferrocyanide produces even in highly dilute solutions a mragnificenltly blue precipitate of FERRIC FERROCYA-'NIDE, or Prussian blue, Fe, Cy,:-3 K4 Fe Cy6 + 2 Fe2 C1, = 12 K Cl +Fe, Cy,8. This precipitate is insoluble in hydrocllloric acid, but is decomposed by potassa, with separation of ferric hydroxide. 7. Potassium ferricyanide deepens the color of solutions of ferric salts to reddish-brown; but it fails to produce a precipitate. 8. Potassium sulplocyan.ate imparts to acid solutions a most intense blood-red color, arisillg from the formation of a soluble FERRIC SULPHIOCYANATE. This color does not disappear on tlle addition of a little alcohol and warllinll (difference from the analolaoous reaction of nitlroren tetroxide, ~ 158). Solutions of ferric salts, containing sodium acetate (whllich consequently are more or less red from ferric acetate), do not show the blood-red color of the sulphocyanate till after the addition of mnuch hydrochloric acid. The samne relnarkl applies to solutiolls contaillillg an alkali fluoride, phosphate or borate, or an oxalate, tartrate, racemate, malate, citrate, or succinate. This test will Iidicate the presence of iron even in fluids, which are so highly dilute that every other reagent fails to produce in them the slightest visible alteration. The red co)loratioll may in such cases be detected most distinctly by resting the test-tube upon a sheet of white paper, and looking through it from the top. The delicacy of the reaction may also be increased by shaking gently with ether after the addition of hydrochloric acid, and of excess of potassium sulphoevalnate solution freshly prepared from the crystals. The ferric sulphocyanate dissolves in the ether, and the layer of the latter acquires a more or less red color. 9. Barium carbonate precipitates even in the cold all the ir'Oil as FERRIC HYDROXIDE MIXED WITH A BASIC SALT. 10.'When a solution containing a ferric salt is rendered nearly neutral by sodium carbonate, and then heated to boiling with addition of excess of sodium acetate, all the iron is precipitated as brown BAsIO FERRIC ACETATE, and may be completely removed fr m the solution by filtering hot and washing with boiling water. If it is allowed to remain in the solution it may partially redissolve as the latter becomes cold. 11. The reactions before the blowpipe are the same as with the ferrous compounds.

Page  144 144 SEPARATIONS. GROuP IV. [~ 112 ~ 112. Recaapitulation and remarks.-On observing the reactions of the several metals of the fourth group with solution of potassa, it would appear that the separation of zinc, whose hydroxide is soluble in an excess of this reagent, might be readily effected by its means; but in the actual experiment we find that notable quantities of zinc are thrown down -with ferric hydroxide, cobaltous hydroxide, etc., to such art extent indeed that it is often impossible to demonstrate the presence of zinc in the alkaline filtrate. This method would be entirely inadmissible in the presence of chromlic oxide, as solutions of the latter and of zinc oxide in potassa mutually precipitate each other. Again, the reactions of the different metals with ammonium chloride and an excess of ammonia would lead to the conclusion that the separation of iron as ferric hydroxide from cobalt, nickel, manganese, and zinc mighllt be readily effected by these agents. But this mnethod also is inaccurate, since greater or smaller portions of tile other metals will alhways precilitate along with the ferric hydroxide; and it mnay therefore haplpen that small quantities of cobalt, manganese, etc., altogether escape detection in this process. It is far safer therefore to separate the other metals of the fourth group from ferric hydroxide by barium carbonate, as in that ease the IRON is precipitated f ree from zinc and manganese, and, if ainmmonium chloride is added previously to the additiol of the bariinum (arbonate, almost entirely free also from lickel and cobalt. Instead of usilg the barium carbonate for the separation of ferric hydroxide, we may proceed as follows: nearly neutralize any excess of acid with sodilum carbonate, add sodium acetate, and boil; or mix the sufficiently diluted solution with a rather large quantity of ammonium chloride, cautiously add amlmonlinl carbonnate till the fluid cominences to become cloudy, the reaction still remaining acid, and thenr boil. In each of these last two methods the basic ferric salt must be filtered off hot. Manganese may conveniently be separated from cobalt and nickel, as well as from zinc, by treating the washed preeipitated sulphides with moderately dilute acetic acid, which dissolves the manganese sulphide, leaving the other sulphides undissolved. If the acetic solution is now evaporated and mixed with solution of potassa, the least trace of a precipitate will be sufficient to recognize the MANGANESE before the blowpipe with sodium carbonate. If the sulphides left undissolved by acetic acid are now treated, after washing, with very dilute hydcllochloric acid, zinc sulphide dissolves, leaving almost the whole of the cobalt and nickel sulphides behind. If the fluid is thellc boiled, and strongly concentrated to expel the hydrogen sulphide, and afte-rwards treated with solution of potassa or soda in excess without warming, the zriN is sure to be detected in the filtrate by passing into it hydrogen sulphide. On drying the filter containing the nickel allnd cobalt sulphides, incinerating it inl a smal porcelain dish, and testing a por.

Page  145 ~ 112.] SEPARATIONS.-GROUP IV. 145 tion of the residue with borax in the inner blowpipe flame, the COBALT may generally be detected with certainty even in the presence of nickel. The detection of nickel in presence of cobalt is not quite so simple a matter. It is best done by warlming the rest of the residue with a little aqiua regria, diltillg, filtering, evaporating the solution to a small bulk, mixing with a sufficiency of potassium nitrite, adding acetic acid to strongly acid reaction, and setting aside in a Inoderately warm place for at least twelve hours. The cobalt then separates as tripotassiumn cobaltic nitrite; the NICKEL may be precipitated from the filtrate by solution of soda, and, to prevent mistakes, tested before the blowpipe, or according to ~ 108, 11, after considerable dilution. For the detection of small quantities of nickel in presence of large quantities of cobalt, it is still better to use the solution of the cyanides in potassium cyanide mixed with solution of soda. In this solution the presence of cobalt will be shown by a dark color on exposure to the air, the presence fi nickel by the separation of b) nickelic hydroxide on treat. ment wilth chlorine (~ 108, 10, and ~ 109, 10). In practical analysis we geunerallIy separate the whole of the metals of the fourth group as sulpilides 1)y precipitation with ammonium sulphide ill presence of amnmollium cllolride. It is therefore in most cases still more convenient to separate nickel and cobalt, or at least the far larger portion of these two metals, at the outset. To this end the moist precipitate of the stilphides is treated with water and some hydrochloric acid, with active stirring, but without application of heat. 1Nearly the vwhole of the nickel sulphide and cobalt sulphide is left behind undissolved, whilst all the other sulphides are dissolved, being converted into chlorides. The undissolved residue of cobalt sulphide and nickel sulphide is filtered and washed, and treated as directed above. By boiling the filtrate with nitric acid the iron passes from the state of ferrous chloride, as it existed in the solution of the sulphide, into that of ferric chloride. After the free acid has been nearly neutralized by sodium carbonlate, the iron may be thrown down as basic ferric salt either by barium carbonate in the cold, or by sodium acetate and boiling. Manganese and zinc alone remain in the filtrate; these Inetals are then also precipitated with ammonium sulphide and some ammonium chloride, the precipitate is filtered and washed, and the two metals are finally separated fromn each other by acetic acid as directed above, or after removal of the barium by sulphuric acid and great concentration, by solution of potassa or soda. The trifling quantities of cobalt and nickel, dissolved on the first treatment of the sulphide precipitate with dilute hydrochloric acid, remain with the zinc sulphide in the separation of the latter from the Ianganese sulphide by acetic acid-or with the manganous hydroxide if the separation is effected by solution of potassa or soda. The zinc sulphide mav be extracted: 10

Page  146 146 RARER METALS. GROUP IV. [~ 113 from the blackish precipitate by dilute hydrochloric acid, and the detection of the manganese in presence of the cobalt and nickel may be readily effected by means of sodium carbonate in the outer flame. In the presence of non-volatile organic bodies the whole of the metals must be precipitated as sulphides, since such organic stibstances would cheek the precipitation of ferric hydroxide by barium carbonate. Ferrous and ferric salts may be detected in presence of each other by testing for the former with potassium ferricyanide, foi thle latter with potassium ferrocyanide or sulphocyanate. Special Reactions of the rarer Metals of the Fourth Group. ~ 113. a. URANIU-M, U. 240. This metal is found in a few minerals, as pitchblende, nran-ochre, etc. Uranium forms two oxides, viz., uranous oxide (U 02), and uranic oxide (U03). Uranous oxide is brown; it dissolves in nitric acid to uranic nitrate. The uranic hydroxide is yellow; at about 300~ it loses its water and turns red; it is converted by ignition into the dark blackish-green uranous-uranic oxide (U308). The solutions of uranic oxide in acids are yellow. Hydrogenz sulphide does not alter them; anmlmnoniuln sulphide throws down from them, after neutralization of the free acid, a slowly subsiding precipitate, which is readily soluble in acids, even acetic acid. The precipitation is promllotecl by ammonium chloride. The -precipitate, when formed in the cold, is chocolate brown, and contains uranic oxysulphide, ammoniumi sulphiclde, and water. It is insoluble in yellow annmmonium sulphide; but,,when free from other sulphides, it dissolves to a notable extent in colorless ammonium sulphide, forming a black fluid. On being -washed, the pre-.cipitate is gradually converted into yellow uranic hydroxide. On warming or boilinc the mixture of uranium solution and ammonium sulphllide the oxvsulphlide at first thrown down splits into sulpl-lur and black uranous oxide, which last is insoluble in the excess of amnlonium sulphide (nEMELE). The uranic oxysulphide (but not the plecipitate which has been converted into uranous oxide and sulphur) dissolves readily in almmonium carblonalte. ('llis reaction may be used as a means of separating uranium from zinc, manganese, iron, etc.) If the oxysulphide remains longl in contact with the fluid which has turned black in consequence of plartial solution of the precipitate in excess of ammonium sulpllide, it ogradually turns bl)ood-red, probably from becoming crystalline (IREMEL). A ori.i(oia, plotassa, and soda produce yellow precipitates containiing uranic hydroxide and alkali, which are insoluble in excess of the precip)itants. Aqnnoaiinm carhonzate and hydrogen potassium carbonate produce yellow precipitates of ammlonium or potassium uranic carbonate, which readily redissolve in an~ excess of the precipitants. Potassa and soda throw down from such solutions the whole of the uranium. Barium carbonate completely precipitates solutions of uranic salts, even in the cold (essential difference from nickel, cobalt, manganese, and zinc, and means of separating uranium from these metals), Potassium ferrocyanide produces a reddish-brown precipitate (a mlost delicate test). Borax and sodium metaphosph7ate give with uranium compounds in the inner flame of the blowpipe green beads, in the:-ter flame yellow beads, which acquire a yellowish-green tint on cooling.

Page  147 113.] TIALLIUMI, 4 7 5. THALLIUM, T1. 204. Thallium occurs, in minute quantities, in many kinds of copper and iron pyrites, in many kinds of crude sulphur, and accuimulates in the fluedust of the lead chambers, where the furnaces are fed with thalliferous pyrites. It is occasionally found in commercial sulphuric and hydrochloric acids, and it has been discovered in lepidolite, preparations of cadmium and bismuth, in ores of zinc. mercury, and antimony, in the ashes of plants, and in some saline waters. Thallium is a metal resembling lead, of 11.86 spec. grav., soft, fuses at 290Q, volatile at a white heat, and in a current of hydrogen at a red heat, crackling like tin when bent; it does not decompose water, even on addition of acid. Dilute sulphuric and nitric acids readily dissolve it; hydrochloric acid dissolves it with difficulty. It forms two oxides. THrALrIous OXIDE (TI2O), is black, and fusible, when in the imelted state it attacks glass or porcelain. It dissolves in water to hydroxide; the solution is colorless, alkaline, caustic, and absorbs carbonic acid. From the solution THALLIOUS HYDROXIDE (T1 0 H) may be obtained in yellow crystals, which dissolve in alcohol. THAI.LIC OXIDE (T1203) is insoluble in water and dark violet, THALLIC IHYDROXIDE ('1 0. O H) is brown. Thallic oxide is hardly acted on by concentrated sulphuric acid in the cold, on heating they combine. On continued heating oxygen escapes and thallious sulphate is formed. Treated with hydrochloric acid, thallic oxide yields the corresponding chloride, as a white crystalline mass, which splits into chlorine and thallious chloride when heated. In solutions of TIHALLIC SALTS alkalies throw down thallic hydroxide, hydrogen sulphide produces thallious salts with separation of sulphur, potassium iodide yields thallious iodide and iodine, hydrochloric acid produces no change. Th-e TIALLIOUS SALTS are colorless, some are readily soluble in water (sulphate, nitrate, phosphate, tartrate, acetate), some are difficultly soluble (carbonate, chloride), some are almlost insoluble (iodide, etc.). On boiling solutions of thallious salts with nitric acid they are not converted into thallic salts, but they are so converted entirely by boiling and evaporating with aqua regia. Potassa, soda, and amnmonzic do not precipitate aqueous solutions of thallious salts, carbonated al:kalies throw down thallious carbonate, but only from very concentrated solutions (for 100 parts of water dissolve 5-23 parts at 18~). Hydrochloric acid throws down thallious chloride, if the solutions are not extremely dilute, in the form of a white readily subsiding precipitate, unalterable in the air, still less soluble in dilute hydrochloric acid than in water. Potassium iodide precipitates, even from the.lmost dilute solutions, the lioght yeTlow thallious iodide, which is almost insoluble in water, but somewhat more soluble in solution of potassium iodide. Platilnic chloride precipitates fromn solutions which are not extremely dilute the pale orange thallious platinic chloride (2 T1 C1. Pt C14), which is very difficultly soluble. Hydrogen sulphide does not precipitate solutions rendered strongly acid by mineral acids, unless arsenious acid is present, when a brownish-red precipitate is formed, which contains the whole of the arsenic and a part of the thalliull. Neutral or very slightly acid solutions are incompletely precipitated by this rea(ent; froml acetic acid solutions the whole of the thallium is thrown down as black thallious sulphide. Aminonium sulphide precipitates the whole of the thallium as black sulphide, which readily collects into lu1)ps, especially on warmingr; hydrogen sulphide added to alkaline solutions has the same effect. The sulphicle thrown down is insoluble in ammonia, alkali sulphnidles and potassium cyanide, it rapidly oxidizes in the air to thallious sulphate, it dlissolves readily in dilute hydrochloric, sulphuric, and nitric acids, but it is acted on only with difficulty by acetic acid. On heating it first fuses and then volatilizes. Zice throws down the metal in the form of black crystalline laminin e. Colorless fia2?es are tinged intensely green l)y comlpounds of thalliuml. The spectrumt of thallium exhibits only one line

Page  148 148 RARER METALS. GROUTP IV. [ 113. (compare the spectrum plate) of an emerald green color, extremely characteristic. If the quantity of metal is small, the line soon disappears. The spectroscope generally affords the best means of detecting thallium. Thaliiferous pyrites often give the green line at once. To look for thallium in crude sulphur, it is best to remove the greater part of the sulphur with carbon disulphide,' and then to test the residue. In the presence of much sodium with very small quantities of thallium the green line will not be seen, unless you moisten the substance and examine the spectrum which is first produced. For the detection of thallium in the wet way, potassium iodide is the most delicate reagent; if a ferric salt is present, it must previously be reduced by sodium sulphite. c. INDIUM, In. 758. Indium has hitherto been discovered only in the blende of Freiberg, in the zinc prepared from the same, and in wolfram. It is a white highly iustrous metal, and resembles platinum in color, it is very soft, ductile, makes a mark on paper, is capable of receiving a polish, and preserves its lustre in the air and in water even when boiling. It fuses about as easily as lead. On charcoal before the blowplil)e it melts with a shining metallic surface, colors the flame blue, and yields an incrustation which is dark yellow while hot, light yellow when cold, and cannot be easily dispersed by the blowpipe flame. Indiuml dissolves in dilute hydrochloric and sulphuric acids with evolution of hydrogen, slowly in the cold, more rapidly on heating; in concentrated sulphuric acid it dissolves with evolution of sulphur dioxide: in nitric acid it dissolves with ease even when the acid is cold and dilute. The oxide, In O, is brown when hot, straw-colored when cold, it does not color vitreous fluxes; when ignited in hydrogen or with charcoal, it is readily reduced, and if a flux be used metallic globules will be obtained. The ignited oxide dissolves slowly in acids in the cold, but readily and completely by the aid of lheat. The salts are colorless, the sulphate, nitrate and chloride dissolve readily in water. The chloride is volatile and hygroscopic. Alkalies throw down the hydroxide in the form of a white bulky precipitate, which is completely insoluble in potassa and ammonia; tartaric acid prevents the precipitation. Alkali carbodnates precipitate a white gelatinous carbonate. When recently thrown down the precipitate dissolves in ammonium carbonate, but not in potassium or sodium carbonate; if the solution in ammbnium carbonate is boiled, the indium carbonate separates again. Sodium phosphate throws down a white bulky precipitate. Alkali oxalates produce a crystalline precipitate. Sodium acetate added to the nearly neutral solution of the sullhate throws down on boiling a basic sulphate. Barium carbonate precipitates the whole of the indium, on digestion in the cold, in the form of basic salt. (Means of separating indium from zinc, manganese, cobalt, nickel, and ferrous compounds.) Jhydrogen sulphide produces no precipitate in the presence of a strong acid. From dilute and slightly acid solutions it throws down some of the indiunl, as in the case of zinc. From a solution acidified with acetic acid this reagent throws down indium sullphide in the form of a slimy precipitate of a fine yellow color. Ammonzium sulphide added to a solution mixed with tartaric acid and ammonia produces a white precipitate which probably consists of indium hydrosulphide, and which turns yellow on treatment with acetic acid. Indium sul1)hllide is insoluble in cold, but soluble in hot ammonium sulphide; on cooling it separates from the solution with a white color. Potassium ferrocyanide produces a white precipitate. Potassium ferricyanide, sulphocyanate and chromate produce no precipitate. Zinc precipitates the metal in the form of white shining laminae. Indium compounds produce a peculiar bluish violet tinge in a col2r7lessflame. The spectrum has a characteristic intensely blue line (at 111-112~ of the scale; see the spectrum plate), and a

Page  149 ~ 113.] VANADIUM. 149 fainter violet line whllich appears brightest with the chloride, but they are very transient. For obtaining more persistent lines the sulphide is the most suitable compound. d. VANADIUM, V = 51 2. Vanadium occurs in the form of vanadates, occasionallyin small quanr tities in iron and copper ores, and in the slags obtained from the sale, There are five oxides of vanadium, the monoxide V2 0, the dioxide V. O2, the trioxideV2 03, the tetroxide V2 04, and the pentoxide V2 06: RoeCOE. V2 02 is gray, ossesses metallic lustreis insoluble iwaer. and is soluble in wieoluion of hlvdy n~ to blue fluids which bleach 6rganic ioloring matters by reducing thei. V2 03 is black insoluble not reduced by ignition inll hdroenexosed to tlm air is rad ually converted iatO z4 icsutouions containingn 0.are reen. V2 04 is iark blue aci; solutions in which it is present are pure blue. All the lower oxides l)ass into V2 05 on heating with nitric acid or aqua regia, on fusing with p)otassimlllll nitrate, or on igniting in oxygen or air. V2 05 is non-volatile, fusible, solidifies to a crystalline mass, dark red to orange-red in color. Heated to redness ill a current of hydrogen it is converted to V2. 03. V2 05 is difficultly soluble in water, but the solution reddens litmlus-paper strongly. It dissolves in acids and combines with bases yielding vanadates. a. Acid solutions.-The stro rer acids dissolve V2 05 to red or yellow fluids, which are frequently deco oizedTU ybTiliog. Tole sui1Pulphicauidsai.ltion when much diluted treated with zinc and warmed gently turns first blue,En r-, and finally from livend ler to violet. The V 06 is thus reduecdl to yv 0._Oan_- o in a iion of ammlonia a biowrni hioxis cipitated, whic ieln ateabsor b s oxygen. Sit7u e, hJ/&reogelz su phzdl, nih organzc athsta ces reduce tle solutmios but only to V2 04, hence the color pro duced is only blue.A U-i2 /l'_p.I odu-es- O a5ro3i co lon acicTifying with hycfrochloric acid, or better wif uurcacid the bsuroI etii'1e fa,'i, whicih is soitble in excess of ammonium sulphide with a lbrowvnsl-ie color. Potassium fer-rocyanide throws down a geen fLculei preeCipitate which is insoluble in acids, Tincture of galls produces afte sonle ti in siTutions free from excess of acid a brownish-black precipitate. b. Vanadates.-V2 06 yields five series of vanadates, viz., tribasic, bibasic, monobasic, biacid, and triacid. The monobasic salts (metavanadates) are mostly yellow, those of the alkali metals are colorless. Some of them pass by warmling with water into colorless isomeric salts. The acid vanadates are yellow or yellowish-red. The vanadates sustain a red heat, most of them are soluble in water, all are soluble in nitric acid. The alkali vanadates are soluble in water in inverse proportion to the quantity of free alkali or alkali salt present. When mixed with acids, the solutionsuaqnire a yellow or red coloi * silver nitrate, mercurous nitrate, bariumn, chloride, and lecad acetate, prodijce white or yellow precipitates readily soluble in. acids. amooniRm,tSlphide reacts as in acid solutions, uotassium fe:cr ide 4mdLc allow pieciuitate, tincture oj'rgatlls produces a deep black color, esplecially in solutions of acid vanadates of alkali metals. If the solution of anll alkali vanadatte is saturated with am.mionziumchloride~ t he Whlen of thn i. aiid setL), rates a whllite ammonium metavanadate, insoluble in solution of amlllmninllm chl orie (most characteristic reaction). The precipitate gives by ignition V" oramixture of the same witl a lower oxide. If an acidified solution of alkali vanadates is shaken with hydrogen dioxide the fluid acquires a red tint; if ether is then added, and the mixture shaken, the solution retains its color, the ether remaining colorless (most delicate reaction). WVERTHEJ. Boraz dissolves vanadium compounds in the inner and outer flame to a clear bead; the bead produced in the outer flame is colorless, with large quantities of vanadium yellow; the bead produced in the in

Page  150 130 REACTIONS. GROUP V. [~ 114. ner flame has a beautiful green color; with larger quantities of valiadiun' it looks brownish whilst hot, and only turns green on cooling. ~ 114. FIFTH GROUP. More common imetals: — SILVER, MIERCURY, LEAD), BISISMUTIT. COPPER, CADMIUM. Rarer netals:-PALLADIUIM, Rn)ODIUM, OSinIIIUr, RUTHENIUMr. Properties cf the groi. —The sulphides are insoluble both in dilute acids and in alkali sulphides.* The solutions of these metals are therefore completely precipitated by hydrogenl sulphide, no matter whether they be neutral, or contain fr:ee acid or free alkali. The fact that the solutions of the metals of the fifth group are precipitated by hydrogen sulphide in presence of a free strong acid, distinguishes them from the nletals of the fourth group and generally from the metals of all the preceding groups. For the sake of greater clearness and simplicity, we divide the more common metals of this group into two classes, and distinguish, 1. _MIETALS PRECIPITABLE BY IHYDROCHLORIC ACID, ViZ., silver, mercury in mercurous salts, lead. 2. METALS NOT PRECIPITABLE BY HYDROCHLORIC ACID, ViZ., mercury in mercuric salts, copper, bismuth, cadmium. Lead nmust be considered in both classes, since the sparingo solubility of its chloride might lead to confounding it with silver and mercury in mnercurous salts, without affordillg us oil the other hand any means of effecting its perfect separation from the metals of the second division. Special Reactions of the more common nzetals of the.fft1l group. FIRST DIVISION; METALS WHICH ARE PRECIPITATED BY HYDROCHLORIC ACID. ~ 115. a. SILVErR,t Ag. 108. 1. M3ETALLIC SILVER is white, very lustrous, moderately hard, highly malleable, rather difficultly fusible. It is not oxidized * Consult, however, the paragraphs on copper and mercury, as the latter remark applies only partially to them. t In the ordinary or argentic compounds Ag is univalent. The nature of the argentous compounds is not sufficiently understood but Ag, appears to be univalent in them.

Page  151 ~ 115.] SILVER. 151 by fusion. in the air. Nitric acid dissolves silveri readily; thle metal is insoluble in dilute sulphuric acid and in hydrochlloric acid. 2. ARGENTIC OXIDE Ag, O is a grayish-brown powder; it is not altogether insoluble in water, and dissolves readily ill dilute nitric acid. There is no correspondinlg hydroxide. Ago 0 is decomposed by heat into metallic silver and oxygen gas. The black argentous oxide Ag4 0 and SILVER DIOXIDE A, O2 are likewise decomposed by heat inlto metallic silver and oxygen. 3. The ARGENTIC SALTS are non-volatile and colorless; nmany of them acquire a black tint upon exposure to light. The soluble nolrmal salts do not alter vegetable colors, and are decomposed at a red heat. 4. fHydroyen sulpTide and ammnonzint sldphide precipitate black sILVER SULPI-InDE (Ag2 S) which is illsoluble in dilute acids, alkalies, alkali sulphides, and potassium cyallide. Boiling nitric acid decomposes and dissolves this precipitate readily, with separation of sulphur. 5. Potassa and soda precipitate ARGENTIC OXIDE in the form of a grayish-brown powder, which is insoluble in an excess of the precipitants, but dissolves readily in ammonia. 6. Ammozia, if added in very small quantity to neutral solutions, throws down ARGETIC OXIDE as a brown precipitate, w-hich readily redissolves in an excess of ammonia. Acid solutions are not precipitated. 7. Iiydrochloric acid and soluble mnetallic chlorides produce a white curdy precipitate of ARGENTIC CHLORIDE (Ag C1). In very dilute solutions these reagents impart at first simplv a bluish-whlite opalescent appearance to the fluid; but after long standing in a warnm place the silver chloride collects at the bottom of the vessel. By the action of liglht the white silver chloride loses chlorine, first acquiring a violet tint, and ultimately turninll black (probably fromn fornation of aro'entous chloride Ag, Cl2); it is illsoluble in nitric acid, but dissolves readily it ain;ollia as anmmonio-silver chloride (2 Ag C1. 3 N I-1,), from which double compound the silver chloride is again separated by acids. Collcentrated hydrochloric acid and concentrated solutionls of chlorides of the alkali metals dissolve silver cilloride to a very perceptible amount, more particularly upon application of heat; but the dissolved chloride separates agailn upon dilution. Upon exposure to heat silver chloride fuses without decomposition, giving upon cooling a translucent horny mass. 8. If compounds of silver mixed with sodiutn cacrbonate are exposed on a charcoal support to the inner flame of the blowwz/pe, white brilliant malleable metallic globules are obtained, with or without a slight dark red incrustation of the charcoal. The metal is also readily reduced in the stck of charcoat (p. 27).

Page  152 152 REACTIONS. GROUP V. DIV. I. [~ 116 ~ 116. &. MIERCURY,4 Hg. 200; AND MERCUROUS CoMpouNDs. 1. METALIIC MERCURY is grayish-white, lustrous, fluid at the coIlnion temperature;e; it solidifies at -39~, and boils at 360~. It is ilsoluble in hydrochloric acid; in dilute cold nitric acid it dissolves to inercurous nitrate, in concentrated hot nitric acid to mnercuiric nitrate. 2. MERCUTROUS OXIDE Hig2 O is a black powder, readily soluble in nitric acid. It is decomlposed by the action of heat, the mnercury volatilizing in the metallic state. There is no eorrespollding hydroxide. 3. The MERcuIrovs SALTS volatilize upon ignition; most of them suffer decomposition in this process. Mereurous chloride and inercuro-us bromide volatilizes unaltered. Most of the merCeurous salts are colorless. The soluble normal salts redden litmunns-paper. Mercurous nitrate is decomposed by addition of mllch water into a light yellow insoluble basic and soluble acid salt. 4. Hydrogern smuplhide and amrnoniium su7lphide produce black precipitates, which are insoluble in dilute acids, amtnolium sulphide, and potassium cyanide. The precipitates, especially after warming, consist of MERCumIC SULPHIDE MIXED WITH MERCURY. Sodium inonosulphide, in presence of some caustic soda, dissolves this precipitate with separation of metallic imercurly; sodium disulphide dissolves it wvithout separation of metallic mercury; the solutions contain mercuric slphllide. TIe precipitate gives up mercury to boililg cocelntrated nitric acid with formation of a white double mercuric compound, namely, 2 HII S. II (N O)2,. The precipitate is readily dissolved by aqua regria. *5. Potassa, sodaa, and ammonia produce black precipitates, which are insoluble in an excess of the precipitants. The precipitates produced by the fixed alkalies conlsist of MERCUROUS OXIDE; whilst those produced by ammlonia consist of MERCUROSAMRIONIUM SALTS. 6. h~ydrochlor'ic accid and sola6Je 9meta'le c cb/dorides precipitate MERCUROUS CHLORIDE (HIcrC12) as a filue powder of dazzlilg whiteness. Cold hydrochloric acid aiid cold nitric acid fail to dissolve this precipitate; it dissolves, however, althoughll very difficultly and slowly, upon loll-eontined boilillng with these acids, being resolved by hydrochloric acid into nlercuric chloride and metallic mercury, which separates; and converted by Hg Hg-C1 * In mercurous compounds Hgs is bivalent, e.g., > 0 and Hg IIg- C In mercuric salts Hg is bivalent, e.. Hg <C and Hg O

Page  153 ~ i17.] LEAD. 153 nitric acid into inercuric chloride and mercuric nitrate. Nitrohydrochloric acid and chlorine water dissolve the Inercurous chloride readily, converting it into mnercuric chloride. Ammonia and potassa decompose inercurous chloride, separating from it, the former dimercurosaminonium chloride, N 1 Hg, Cl, the latter mnercurous oxide. 7. If a drop of a neutral or slightly acid solution is put on a clean Cr and snooth/ sutj/cfCe of copper, and washed off after some time, the spot will afterwards, on being gently rubbed with cloth, paper, etc., appeal white and lustrous like silver. The application of a gentle heat to the copper causes the metallic lnercury precipitated on its surface to volatilize, and thus remnoves the apparent silvering. 8. St<annous chloride produces a gray precipitate of RETXLLIC MERCUR-Y, which may be united into globules by boiling the metallic deposit, after decantino the fluid, with hydrochloric acid, to which a little stalllnnos chloride may also be added. 9. If an iltimate mixture of a ahylllldrclrous compound of meri cuary with anhydrous sodiut~m carbonacte is introduced into a sealed glass tube, and covered with a layer of sodiumn carbonate, andc the tube is thell strongly heated, the nmercurial compound invariably undergoes decomposition, and METALLIC MERCURY separates, forminig a coat of gray sul)limnate above the heated part of the tube. By means of a lenls the sublimate will be seen to consist of globules of metal. Larger globules may be obtained by rubbing the sublimate with a glass rod. ~ 117. C. LEAD, Pb. 207. 1. METALLIC LEAD is bluish-gray; its surface recently cut exhibits a metallic lustre; it is soft, malleable, readily fusible; it evaporates at a white heat. Fused upon charcoal before the bllowpipe it forms a coating of yellow oxide on the support. [Iydrochloric acid and moderately concentrated sulphuric acid act upon it but little, even with the aid of heat; but dilute litrio acid dissolves it readily, nmore particularly on heating. 2. LEAD MONOXIDE PbO is a yellow or reddish-yellow powder, looking brownish-red whilst hot, and fusible at a red heat. Lead hydroxide Pb (O 1), is white. Both the oxide and hydroxide dissolve readily in nitric and acetic acids. LEA.D SUBOXIDE (Pb,O) is black, MINIUM (2 Pb O. Pb O,) is red, the socalled SESQUIOXIDE iS light brown, the DIOXIDE is brown. They are all of them converted into the imonoxide by ignitionl in the air. The dioxide is not dissolved by heatinr with nitric acid, but it dissolves readily in that nmenstruum on addition of some alcohol. The solution contains lead litrate Pb (N 0)2,. 3. The LEAD SALTS are noll-volatile; most of them are color.

Page  154 1.54 REACTIONS. GROUP V. DIV. I. [ 117 less; the normal soluble salts redden litmnls-paper, and are decomposed at a red heat. If lead chloride is ignited in tile air part of it volatilizes, and leaves behild a mixture of lead oxide and lead chloride. In the lead salts Pb iJ bivalent. 4. Iy(drogen sulpidce and camimoniu?,, sqtphicde produce black pr1'ecipitates of LEAD SULPHIDE (Pb S), which are illsoluble ill cold dilute acids, in alkalies aind alkali sulphides, and c(yanlides. Lead sulphide is decomposed by hot nitric acid. If the acid was dilute, the -whole of the lead is obtained in solution as lead nitrate, and sulphur separates-if the acid was fuming, the sulphur is also completely oxidized, and insoluble lead sulphate alone is obtained;- if the acid was of medium concenltration, both processes take place, a portion of the lead being obtained in solution as nitrate, whilst the remainder separates as sulphate, to,gether with the ulnoxidized sulphur. In solutions of lead salts containing a large excess of a concentrated mineral acid, hydrogen sulphide produces a precipitate olly after the addition of water or after partial neutralization of the free acid by an alkali. If a lead solution is precipitated by hydrogen sulphide in presence of a large quanlltity of free hydrochloric acid, a red precipitate is occasionally formed, consisting of lead chloro-sulphide, which is however converted by an excess of hydrogen sulphide into black lead sulphide. 5. Potassa, soda, and ammonia throw down HYDRLOXrDE MIXED WIT'H SASIC SALTS in the form of white precipitates, which are insolublle in ammonia, but soluble in potassa and soda. In solutions of lead acetate ammonia (free from carbonate) does not immediately p)Ioduce a precipitate, owing to the formation of a soluble lead di- or triactate. - 6. Sodium carbonate thrlows down a white l)recii)italte of BASIC LEAD CAllRBONATE, e.g., 2Pb C 0O. Pb (O H)2, which is not quite insoluble in a large excess of the precipitant, especially on heating, but is insoluble ill potassium cyanide. 7. hlydrochloric acid and soluble chlorides produce in con. centrated solutions heavy white precipitates of LEAD CIHLORIDE (Pb C1), which' are soluble in a large amnount of water, especially upon application of heat. Lead chloride is converted by ammonia inlto lead oxychloride, Pb C12. 3 P1) 0, which is also a white powder, but almost absolutely insoluble in water. In dilute nitric and hydrochloric acids lead chloride is more difficultly soluble than in water. 8. Saphuric acid and sulTpAates produce white precipitates of LEAD SULPHATE (Pb S 04), which are nearly illsolublle in water and dilute acids. From dilute solutions, especially from such as contain much free acid, the lead sulphate precipitates only after some time, frequently only after a lonlg, time. It is advisable to add a considerable excess of dilute sulphuric acid, as this tends to increase the delicacy of the reaction, lead sulphate being more insoluble in dilute sulphuric acid than water. The separation of small quantities of lead sulphate is best effected by evaporating, after the addition of the sulphuric acid, as far

Page  155 ~ 118.] SEPARATIONS. 155 as practicable on the water-bath, and then the residue with water; or, if allowable, with alcohol. Lead su)llhate is slightly soluble in concentrated nitric acid; it dissolves witbt difficulty in boiling concentrated hydrochloric acid, but more readily in solution of potassa. It dissolves also pretty readily ill the solutions of some amnmonium salts, particularly in solution of alnmmonium acetate; dilute sulphuric acid precipitates it again from these solutions. 9. Potassium chromoate produces a yellow precipitate of LEAD COIROMIATE (Pb Cr 04), which is readily soluble in potassa, but difficultly so in dilute nitric acid. 10. If a mixture of a compound of lead with socdium carbonate is exposed on a charcoal support to the reducingfilane of the blowpipe, soft malleable MIETALLIC GLOBULES OF LEAD are readily produced, the charcoal becoming covered at the same time with a yellow incrustation of LEAD OXIDE. The reduction may be also readily effected by means of the stick of charcoal. 11. The metallic incrustation, obtained according to p. 28, is black with brown edge, the incrustcation qf oxide is light yellow ochre, the incru.station, qf iodide varies from the yellow of the letlon to that of the yolk of an egg, the incrustatbion qf sulphide varies from brownish-red to black, and is not dissolved by ammonium sulphide (BUNSEN). ~ 118. RecapituZation and remarkcs.-The metals of the first division of the fifth group are most distinctly characterized in their chlorides; since the different reactions of these chlorides with water and ammolnia afford us a simple mneans both of detecting them arnd of effecting their separation from one another. For;f the precipitate containling the three metallic chlorides is boiled with a somewhat large quantity of water, or boiling water is repeatedly poured over it on the filter, the lead chloride dissolves, whilst the silver chloride and the mnercnlrous chloride remnain undissolved. If these two chlorides are then treated with ammonia, the mercurous chloride is converted into the black mercnrous ammrnonium salt, insoluble in an excess of ammonia, described in ~ 116, 5, whilst the silver chloride dissolves readily in ammonia, and precipitates from this solution again upon addition of nitric acid. (When operating upon small quantities it is advisable first to expel the greater part of the ammonia by heat.) In the aqueous solution of lead chloride the metal may be readily detected by sulphuric acid.

Page  156 156 REACTIONS. GR'OUP V. DIV. II. [~ 119 SECOND DIVISION: METALS WIIICII ARE NOT PRECIPITATED BY HYDRuCIILORIC ACID. ~ 119. a. hMERCURY IN MIERCURIC COMPOUNDS. 1. MERCURIC OXIDE (Hg O) is generally crystalline, and has a bright red color, which upon reduction to powder changes to a dull yellowish red; the oxide precipit'ated from solutions of mercuric nitrate or chloride forms a yellow powder. It is not quite insoluble in water, it turns gray in the air. Upon exposurle to heat it trlasiently acquires a deeper tint; at a dull red heat it is resolved into lletallic inercury and oxygell. Both the crystalline and noll-cr-stalline oxide dissolve readily in hydrochloric acid anld ill nitric acid. 2. The MERCURIC SALTS volatilize upon ignition; they suffer decomposition in this process; mercuric chloride, bromide, and iodide volatilize unaltered. On boililing a solution of the chloride, some of the salt escapes with the steam. AMost of the mercuric salts are colorless. The soluble normal salts redden litmus-paper. The nitrate and sulphate are decomposed by a large quantity of water into soluble acid and insoluble basic salts. 3. Addition of a very small quantity of hydcroyen slp/thidle or amrnmonium slphicde produces, after shaking, a perfectly white precipitate. Addition of a somewhat larger quantity of these reagents causes the precipitate to acquire a yellow, orlale, or brownish-red color; an excess of the precipitant produces a black precipitate of MERCURIC SULPHIDE (tig S). This progressive variation of color from white to black, which dep)elnds on the proportion of the hydrogen sulphide or ammoniuin sulphide added, distinguishes tie mercuric salts from all other bodies. The white precipitate which forms at first consists ()f a double compound of mercuric sulphide with the still nldecomposed portion of the mercuric salt (in a solution of mllercurie chloride, for instance, I-g C12. 2 Hg S); the gradlually increasing admixture of black sulphide causes the precipitate to pass through the several gradations of color above mentionled. Ammnionium sulphide only dissolves the smallest traces of melcuric sulphide; the least amount of mercury is dissolved when the precipitate is digested hot with yellow ammoniumn sulphide. Potassa and potassium cyanide do not dissolve mercuric sulphide, and it is entirely insoluble in hydrochloric and in nitric acid, even on boiling. By the very protracted action of hot concentrated nitric acid the precipitate is converted into a white body, consisting of 2 Hg S. HIg (N O,),

Page  157 ~ 120.] COPPER. 157 Potassium sulphide and sodium sulphide in the presence of potash or soda dissolve the precipitate comnpletely, but it is insoluble in potassium hydrosulphide, and in sodiumnl hydrosulphide. Aqua regia decomposes the precipitate and dissolves it with ease. In mercuric solutions containing a large excess of concentrated mineral acid, hydrogen sulphide produces a precipitate only after the addition of water. 4. Potassa added in small quantity produces in neutral or sliglltl.y acid solutions a reddish-brown precipitate, which acquires a yellow tint if the reagent is added in excess. The reddish-brown precipitate is a BASIC SALT; the yellow precipitate consists of MERCURIC OXTDE (Hg O). An excess of the precipitant does not redissolve these precipitates. In very acid solutions this reaction does not take place at all, or at least the precipitation is very incomplete. In presence of ammonium salts potassa produces white preci)itates. The precipitate thrown down lby potassa from a solution of mercuric chloride containing an excess of ammonium chloride is of analogous composition to the precipitate produced bly ammonia (see 5). 5. Ammonia produces white precipitates quite analogous to those produced by potassa in presence of ammonium chloride; thus, for instance, ammonia precipitates from solutions of mercuric chloride a MERCURAMIMONIUMI CHLORIDE (N H2Hg C1). 6. Stannous chloride added in small quantity to solution of mercuric chloride, or to solutions of mercuric salts in presence of hydrochloric acid, throws down MERCUROUS CIIORIDE (2 ITg C12 + Sil C12 I-Hgt, C12 + Sn C1). By addition of a larger quantity of the reagent the precipitated mercurous chloride is reduced to TMETAL (iI2C12 + Sn C12= Hg, + Sn Cl4). The precipitate, which was white at first, acquires therefore now a gray tint, and may, after it has subsided, be readily united into globules of metallic mercury by boiling with hydrochloric acid and a little stannous chloride. 7. If a little galvanic element, made out of a slip of platinum foil and a slip of tinfoil, joined at one end with a wooden clamp, but otherwise apart from each other, is introduced into a mercuric solution acidified with hydrochloric acid, all the mercury will gradually be precipitated by preference upon the platinum. On removing the foils, drying and heating strongly in a glass tube, globules of mercury will be obtained, which may be more distinctly seen under the microscope. On heating this mercury with a fragment of iodine, it will be converted into red mercuric iodide (VAN DEN BROEK). 8. Mercuric salts show the same reaction as mercnrous salts with metallic copper and when heated with sodium carbonate in a glass tube.. 120. o. COPPER,* Cu., 63'4. 1. METALLIC COPPER has a peculiar red color, and a strong lustre; it is moderately hard, malleable, rather difficultly fusi* In the cuprous compounds Cu2: in the cupric salts Cu is bivalent.

Page  158 158 REACTIONS. GROUP V. DIV. I. [. 120 ble; in contact with water and air it becomes covered with a green crust of basic cupric carbonate; upon ignition in the air it becomes coated over with cuprous oxide and cupric oxide. In hydrochloric. acid and dilute sulphuric acid it is insoluble or' lnearly so, even upon boiling. Nitric acid dissolves the metal readily. Concentrated sulphuric acid converts it il'to cupric sulphate, with evolution of sulphur dioxide. 2. CurPnouS OXIDE (CuO) is red, curPOUs HYDPOXIDE (Cll,2(01I)2) is yellow; both change to cupric oxide upon ignition in the air. O) treating cuprous oxide with dilute sulphurlic acid metallic copper separates, whilst cupric sulphate dissolves; on treating c('up'ous oxide with hydrochloric acid white cuprous chloride is formed, which dissolves in an excess of the acid, but is reprecipitated from this solution by water. 3. CurnIc OXIDE is a black powder; CUPRIC HYDROXIDE (Cu (O II)2), is of a light blue color. Both dissolve readily in hydrochloric, sulphuric, and nitric acids. 4. MIost of the normal cuplIc SALTS are soluble in water; the soluble salts redden litmus, and suffer decomposition when hleated to gentle redness, with the exception of the sulphate, which can bear a somewhat higher temperature. They are usually white in the anhydrous state; the hydrated salts are usually of a blue or green color, which their solutions continue to exhibit even when much diluted. 5. Hydrogen 8sulphde and ammnoniqm sulphide produce in alkaline, neutral, and acid solutions brownish-black precipitates of currTc SULPHIDE, Cu S. This sulphide is insoluble in dilute acids and caustic alkalies. IIot solutions of potassium sulphide and sodium sulphide fail also to dissolve it or dissolve it only to a very trifling extent; but it is a little more soluble in ammonlini sulphide, especially when yellow and hot. [Yellow ammoniuml sulphide produces in the cold a red-brown or red precipitate, Cu2(N HI-,),S,, which dissolves completely in an excess of the reagent, but is almost perfectly precipitated as black sulphide when the solution is heated to boiling.] The latter reagent is therefore not well adapted to effect the perfect separation of cupric sulphide from other metallic sulphides. Cupric sulphide is readily decomposed and dissolved by boiling nitric acid, but it remains altogether unaffected by boiling dilute sulphuric acid. It dissolves completely in solution of potassium cyanide. In solutions of cupriC salts which contain a very large excess of a concentrated mineral acid, hydrogen snlphide produces a precipitate only after the addition of water. 6. Potassa or soda produces a light blue bulky precipitate of curRTc HYDIROX[DE (Cu (O H)2). If the solution is highllly concentrated, and the precilitant is added in excess, the precipitate turns black after the lapse of sonime tinlme, and loses its bulkiness, even in the cold, from conversion into cupric oxide, but the change takes place immlllediately if the precipitate

Page  159 ~ 120.] COPPER. 159 is boiled with the fluid in which it is suspended. Cu (0 H)2Cu () + H20 7. Sodium carbonate produces a greenish-blue precipitate of BxsIC cUPrIC CARBONATE (Cu C 03. Cu (O H)2), which upon boiling changes to cupric oxide, and dissolves in ammonia to an azure-blue, and in potassium cvan!idle to a colorless fluid. 8. Ammonia added in small quantity to solutions of normal cupric salts produces a greenish-blue precipitate, consisting of a BASIC CUPRIC SALT. This precipitate redissolves readily ponll further addition of ammonia to a perfectly clear fluid of a nagnificent azure-blue, which owes its color to the formation of a CUPRODIAMMONIUM SALT. Thus, for instance, in a solution of cuprle sulphate excess of ammonia produces (N2H6Cu) S 0,. In solutions containing a certain amount of free acid ammonia produces no precipitate, but this azure-blue coloration makes its appearance the instant the ammonia predominates. The blue color ceases to be perceptible only in very dilute solutions. Potassa produces in such blue solutions in the cold, after the lapse of some time, a precipitate of blue cupric hydroxide; but upon boiling the fluid this reagent precipitates the whole of the copper as black cupric oxide. Ammonium carbonate shows the samne reaction as ammonia. N.B. In the presence of non-volatile organic acids the cupric salts are not precipitated by caustic or carbonated allkalies, the resulting solutions having a deep blue color. In presence of sugar or similar organic substances caustic alkalies produce precipitates which are soluble in excess of the precipitants; sodium carbonate, however, produces a permanent precipitate. 9. Potassium,ferrocaycnide produces in moderately dilute solutions a reddish-brown precipitate of cupric FERROCYANIDE Cu2 Fe (C N)6, insoluble in dilute acids, but decomposed by potassa. In very highly dilute solutions the reagent merely produces a reddish coloration. 10. If the solution of a cuprlic salt is mixed with sulphurous acid or with hydrochloric acid and sodium sulphite, and potassium sulphocyanate is then added, CL-UPROU SULPHOCYANATE Cu2 (C N S)O is thrown down. The precipitate is white, and is practically insoluble in water and dilute acids. 11. lfetallic irono when brought into contact with concentrated solutions of salts of copper is almost immediately covered with a coating of METALLIC COPPER; very dilute solutions produce this coating only after some time. Presence of a little free acid accelerates the reaction. If a fluid containing copper and a little free hydrochloric acid is poured into a platinum capsule (the lid of a platinum crucible), and a small piece of zinc is introduced, the bright platinum surface speedily becomes covered with a COATING OF COPPER; even withl very dilute solutions this coating is clearly discernible. If a piece of iron wire is inserted into a spiral formned from a rather stout

Page  160 160 REACTIONS. GROUP V. DIV. II. [L 12 1. platinutm wire, and the whole is tllen placed in a slightly acidified solution of copper, the platinum wire will after some tille be found to be coated with COPPER. 12. If a mixture of a compound of copper with sodium ca-' bonate is exposed on a charcoal support to the jiuner flnae qf the blowfp~?2pe, ZIETALLIC COPPER is obtained, without incrustationll of the charcoal. The reduction may be also very conveniently effected in the stick of charcoal (p. 27). The best method of freeing the copper from the partic]es of charcoal is to triturate the fused mass in a small mnortar with water, and to cautiously wash off the charcoal powder, when the copper-red metallic particles will be left behind. 13. If copper, or some alloy containing, copper, or a trace of a salt of copper, or even silnply the loop of a platinum wire dipped in a highly dilute copper solution, is illtoduced into the fusing zone of the gas flace, or exposed to the inner blowpilpe lmnze, the upper or outer portion of tile flame shows a magnificent emerald-green tint. Addition of hydrochloric acid to the sample considerably heightens the beauty and delicacy of this reaction, The flame then has an azure color. 14. Bowrax readily dissolves oxides of copper in the outer gas or blowpipe-flame. The beads are greel while hot, blue when cold. In the inner flame the bead is colorless unless a very ]arge quantity of copper is present; when cold it is red and opaque. In the lower reducing flame of the Bunsen gas flame the bead does not become red-brown until the addition of stannic oxide, when this change rapidly takes place, owing to the production of cuprous oxide. If the bead is introduced alternately into the lower oxidizing zone and the lower reducing zone, it becomes ruby red and transparent. ~ 121. C. BISMUTR*, Bi., 210. 1. B3IsMuTH has a reddish tin-white color and moderate metallic lustre; it is of medium hardness, brittle, readily fusible; fused upon a charcoal support it forms an incrustation of yellow trioxide, Bi, 0,. It dissolves readily in nitric acid, but is nearly insoluble in hydrochloric acid and altogether so in dilute sulphuric acid. Concenltated sulphuric acid converts it into bismuth sulphate with evolution of sulphur dioxide. 2. BIISMUTII TRIOXIDE (Bismuthous oxide) is a yellow powder, which transiently acqulires a deeper tint when heated..It fuses * In all its common compounds bismuth is trivalent; in some it is appaBi = C12 rently bivalent, but in fact trivalent, e.g., Bi2 C14 or,i C1 In bismutb entoideBi uinuivaen. pentoxide it is quinquivalent.

Page  161 ~ 121.] BIStUTf. 161 at a red heat. Bismuth hydroxide, 13i O OIT, is white. Both the trioxide and hydroxide dissolve readily in hydrochloric, silphuric, and nitric acids, yielding the bisiluth salts. The grayish-black DIOXIDE, i3i, 0Bi, and tile red PENTOXID, 13i2, O5, are converted into trioxide by ignition ill the air. By heating with nitric acid they are converted into bismuth nitrate. 3. MIost of the B3ISaUTh SALTS are non-volatile anld are decomposed at a red heat. Bismuth triclloride is volatile. The bismuth salts are colorless or white; somle of them are soluble in water, others insoluble. The soluble salts redden litnmus-paper; they are decomposed by a large quantity of water into insoluble basic salts, which separate, whilst the greater portion of the acid remains in solution together with somle bismuth. 4. lydroyen guZphide and ammnqnoniuqm su7phidce produce in bismuth solutions black precipitates of 13IS-rUTII TmISULPI1mDE, Bio, S3, which is insoluble in dilute acids, alkalies, alkali sulphides, and potassium cyanide, blut is readily deconmposed alnd dissolved by boiling nitric acid. In solutiolns of salts of lis inmth which contain a very conlsiderable excess of lhydroclloric or nitric acid, hydrogen sulphlide produces a precipitate only after the additionl of water. 5. iPotassac anld amononia tlhrow down IISMJIslT IIYDIROXIDE, 1i O O 1I, as a white precipitate, wh\iich is insoluble in an excess of the precipitant. 6. Sodium car7o7znate and ammoniulm carbhownte throl down BASIC BISMUTII CARBONATE (Bi202 C 03) as a white bulky precipitate, which is insoluble in excess of the precipitant, and in potassium cyanide. Warlming assists the precipitation. 7. Potassium dickromate precipitates BISmruCTi CTHliOMATE,. Bi, (Cr 04), as a yellow powder. This substalnce differs from lead c(hrolate in being readily soluble in dilute nlitric acid and. insoluble in potassa. 8. D)ilute sulp/utric acid fails to precipitate moderately dilute solutions of bisumuth nitrate. O)1 evaporating with an excess of sulphuric acid on thle water-bath to drynless, a white salinle mass of bismuth trisulphate 13i,(SO,),* is left, which always dissolves readily to a clear fluid in water acidified with sulplhuric acid (characteristic difference between bislnntth and lead). After long standing (several days occasionally) l)isinuth disulpllate, Bi (Bi 0) 2 S 04 + 3 112 0t, separates froln this solution in white microscopic needle-shaped crystals, whllih dissolve in nitric acid. 9. The reaction which characterizes the bismlnth more particularly is the decomposition of its normal or triacid salts by water, which is attended with separation of insoluble basic salts. The addition of a large amount of water to solutions of * Bi=S04 PBi=S04 >SO04 >O Bi = S 04 Bi = S04 11

Page  162 162 REACTIONS. GROUP V. DIV. II. [L 122 bismuth salts causes the immnediate formation of a dcazzlin white precipitate, provided there be not too much free acid present. If the basic or disulphate above mentioned (8), be treated with much water, it is converted into the more basic monosulphate (Bi O)2 S 04 + H2 O 0. This reaction is the lmost sellsitive with bisnmuth trichloride. as the BASIC BISMUTrI CHLORIDE O1' oxychloride, Bi O C1 is almost absolutely insoluble in water. Where water fails to precipitate nitric acid solutions of bismuth, owing to the presence of too munch free acid, a precipitate will almost invariably make its appearance ilnliediately upon addition of solution of sodium chloride or ammlonimun chloride. Presence of tartaric acid does not interfere with the precipitation of bismuth by water. 10. On1 mixing a solution of bismuth with an excess of solution of stannous ciloride iz1 potassca or soda, a black precipitate of bismuth dioxide will fall. This is a very characteristic and delicate reaction. 11. If a mixture of a comnpound of bismuth with sodium carbonate is exposed on a charcoal support to the reducing flacme, brittle GIOBULES OF BISMUTH are obtained, which fly into pieces under the stroke of a hammer. The charcoal becomes covered at the same time with a slight incrustation of HISMUTH TRIOXIDE, which is orange-colored whilst hot, yellow when cold. The reduction may be also conveniently effected in the stick of charcoal (p. 27). On triturating the end of the charcoal stick containing the reduced metal, yellowish spangles will be obtained. 12. Bismuth compound, even in minute quantities, when heated on charcoal in the blowpipe flame, with a mixture of equal parts of sulphour and potassin?, iodide, yield a very volatile intensely scarlet sulblimate of BIS.IUTII IODIDE (V. KOBELL). 13. The metallic incrustation, obtained according to p. 28, is black with a brown edge. The incrustation of oxide is yellowish white; it is turned black by stanllnos chloride and soda, see 10 (difference from the lead incrustation). The incrustationz of iodide is bluish-brown with red edge. The incrustation (of sul2phide is umber-colored with coffee-colored edge, not dissolved by ammonium sulphide (BUNSEN). ~ 122. d. CADMrUM, Cd., 112. 1. METALLIC CADMIUM has a tin-white color; it is lustrous, not very hard, malleable; it fuses at a temperature below red * Bi = o > S04 Bi = O

Page  163 ~ 122.] CADMIUM. 163 heat, and volatilizes at a temperature somewhat above the boiling point of merelury, and may therefore easily be sublimed in a glass tube. Heated on charcoal before the blowpipe it takes fire and burns, emitting brown fumes of cadmium oxide, which form a coating on the charcoal. Hydrochloric acid and dilute sulphuric acid dissolve it, with evolution of hydrogen; but nitric acid dissolves it most readily. 2. CADMIUM OXIDE, Cd 0, is a brown, fixed powder; its nryDIOXImDE, Cd (O I-i)2, is white. Both dissolve readily in hydrochloric, nitric, and sulphuric acids. 3. The CAD:MIUM SALTS are colorless or white; some of them are soluble in water. The soluble normal salts redden litmuspaper, and are decomposed at a red heat. 4. Iiydrogen sulphida and ammonium suzphtide produce in alkaline, neutral, and acid solutions, bright yellow precipitates of CADMIUMr SULPHIDE (Cd S), which are insoluble in dilute acids, alkalies, alkali sulphides, and potassium cyanide (difference from copper). They are readily decomposed and dissolved by boiling nitric acid, as well as by boilingl hydrochloric acid and by boiling dilute sulphuric acid (difference from copper). In solutionls of cadmium containing a large excess of acid, hydrogen sulphide produces a precipitate only after dilution with water. 5. Potassa and soda, produce white precipitates of CAkDMfIUJM HYDROXIDEI Cd (O H)2; which are insoluble in an excess of the precipitants. 6. Ammonica likewise precipitates white CADxMIUM HYDROXIDE which, however, redissolves readily and completely to a colorless fluid in an excess of the precipitant. 7. Sodium carbonate and ammonziunei carbolate produce white precipitates of CADMINUM CAIBONATE (Cd C O0) which are insoluble in an excess of the precipitants. The presence of annmoniumu salts impedes the precipitation; free ammonia prevents it. The precipitate is readily soluble in potassium cyanide. It takes some time to separate fronl dilute solutions; warminug assists the separation greatly. 8. Potassium sulphocyan1at does not throw down solutions of cadmium, even after the addition of sulphurous acid (difference from copper). 9. If a mixture of a compound of cadmimn with sodium carbonate is exposed on a charcoal support to the reducing flame, the charcoal becomes covered with a brownish yellow coating of CADMIUM OXIDE, owing to the instant volatilization of the reduced metal and its subsequent reoxidation in passing through the oxidizing flame. The coating is seen Inost distinctly after cooling. 10. The metallic incrustation, obtained according to p. 28, is black with brown edge. The increuzstation of oxide is brownish black, the edge passing from brown to white. The incrustation of iodide is white. The incru.ttation of su~phide is lenon yellow, not dissolved by ammonium sulphide (BUNSEN.)

Page  164 164 SEPARATIONS. GROUP V. [r 123. ~ 123. Iecapitulation and remnar8ks.-' he perfect separation of the metals of the second division of the fifth group from silver and mercurous salts may, as already stated, be effected by means of hydrochloric acid; but this agent fails to separate them completely from lead. Traces of imercuric salt, which are at first retained by tile precipitated silver chloride by surface attraction, are dissolved out completely by washing (G. J. MIuLDER). MlERcuRIC compounds are distinguished from compounds of the other metals of this division by the insolubility of mercuric sulphide in boiling nitric acid. This property affords a convenient means for their separation. Care must always be taken to free the sllphides completely by washing from all traces of hydrochlloric acid or a chloride that mnay happen to be present, before proceeding to boil them with nitric acid. M[oreover, the reactions with stannons chloride or with metallic copper, as -well as those ill the dry way, will, after the previous removal of mercurous chloride, always readily indicate the presence of mercuric compounds. When the moist way is chosen, the mercuric sulphide is dissolved most conveniently by hleating with hydrochloric acid and a crystal of potassium chlorate. From the remaining metals LEAD iS separated by sulphuric acid. The separation is the most complete if the fluid, after addition of dilute sulphuric acid in excess, is evaporated on the water-bath, the residue diluted with water, slightly acidified with sulphuric acid, and the undissolved lead sulphate filtered off immediately. The lead sulphate may be further examined inl the dry way by the reaction described in ~ 117, 10, or also as follows: —Pour over a small portion of the lead sulphate a little of a solution of potassium chromate, and apply heat which will convert the white precipitate into yellow lead chromate. Wash this, add a little solution of potassa or soda, and heat; the precipitate will now dissolve to a clear fluid; by acidifying this fluid with acetic acid, a yellow precipitate of lead chrolnoste will again be produced. After the removal of mercury and lead, BISMrUTH may be separated from copper and cadmium by addition of ammonia in excess, as the hydroxides of the latter two metals are soluble in an excess of this agent. If the precipitate, after being filtered off, is dissolved in one or two drops of hydrochloric acid on a watch-glass, and water added, the appearance of a milky turbidity is a confirmation of the presence of bismuth. The presence of a notable quantity of COPPER is revealed by the blue color of the ammoniacal solution; smaller quantities are detected by evaporating the ammoniacal solution nearly to dryness, adding a little acetic acid, and then potassium ferrocyanide. The separation of copper froml CAD

Page  165 ~ 124.J PALLADIUM. 165 MITJM nmay be effected by evaporating the ammoniacal solution to a small bulk, acidifyillg with hyvdrochloric acid, adding a little sulphurous acid alnd potassium sulphocyanate, filtering off the cuprous sulphocyanate, and precipitating the cadmium inl tile filtrate by hydrogen sulphide (an ulnnecessarily large excess of sulphurous acid must of course be avoided). The separation of copper froml cadmium may also be effected by acting on. the sulphides with potassium -cyanide or with boiling dilute sulphuric acid (5 parts of water to 1 part of concentrated acid). In the two latter methods the solution of the copper and cadmium is precipitated by hydrogen sulphide, and the precipitate separated from the fluid by decantation or filtration. On treatinug the precipitate now with some water and a small lump of potassium cyanide, the cupric sulphide will dissolve, leaving the yellow cadmium sulphide undissolved. By boiling the precipitate of the mixed sulphides, on the other hand, with dilute sulphuric acid, tle cupric sulphide relnains undissolved, whilst the cadmium sulphide is obtained in solution. Hydroogen sulphide will therefore now throw down, from the filtrate yellow cadmium sulphide (A. W. IIOFMIANN). S Rpecial Reactions of the 7rarer M3etals of the Fifth Group. ~ 124. a. PALLADIUM, Pd., 106'6. PALLADIUM is found in the metallic state, occasionally alloyed with gold and silver, but more particularly in platinum ores. It greatly resembles platinum, but is somewhat darker in color. It fuses with great difficulty. Heated in the air to dull redness it becomes covered with a blue film; but it recovers its light color and metallic lustre upon more intense ignition. It is sparingly solul)le in pure nitric acid, but dissolves somewhat more readily in nitric acid containing nitrous acid; it dissolves very sparingly in boilingy concentrated sulphuric acid, blut it is soluble in fusing sodiumn disulphate, and readily soluble in nitrohydrocllloric acid. There are three oxides, the suboxide (Pd2O), the monoxide (PdO), and the dioxide (Pd 02)- PALLADIUNI MONOXIDE is black, the corresponding hydroxide dark brown; both are decomposed by intense ignition, leaving a residue of metallic palladium. PATLLADIUM DIOXIDE is black; by heating with dilute hydrochloric acid it is dissolved to palladious chloride (Pd C12), with evolution of chlorine. The PALLADIOUS SALTS are mostly soluble in water; they are brown or reddish-brown; their concentrated solutions are reddishbrown, their dilute solutions yellow. Water precipitates from a solution of palladious nitrate containing a slight excess of acid a b)rown basic salt. The oxys'alts, as well as palladious chloride, are decomposed by ignition, leaving metallic palladium behind. Hydrogen sulphide and amnmoniun.z sullphide throw down from acid or neutral solutions black palladious sulphllide, which does not dissolve in almmnoniuml sulphide, but is soluble in boiling hydrochloric acid, and readily soluble in nitrohydrochloric acid. Fromn the solution of palladious chloride potassa precipitates a brown basic salt, soluble in an excess of the precipitant; ammonnia, flesh-colored aommonio-palladium chloride (Pd C12. 2 N H3) soluble in excess of ammonia to a colorless fluid, from which hydrochloric acid throws down yellow

Page  166 I 66 11AILE.ME1'ALS. GROUP V. [~ 124 crystalline palladammonium chloride (N2Pd I116Cl2). Mer7uric cya1nidd lhrows down yellowish-white palladious cyanide as a gelatinous precipi. tate, slightly soluble in hydrochloric acid, readily soluble in almmiloniai (especially characteristic). Stannic chloride produces, in absence of free hydrochloric acid, a brlownish-black precipitate; in presence of free hlydrlochloric acid, a red-colored solution, which speedily turns brown and ultiinately green, and upon addition of water brownish-red. Ferroals sulplAhtc produces a deposit of l)alladium on the sides of the glass. Potassiuon iodide precipitates black palladious iodide (very characteristic). Potassium chlor'ide precipitates from highly concentrated solutions potassium pallaclious chloride (2K C1. Pd C12), in the form of golden-yellow needles, whlich dissolve readily in water to a dark red fluid, but are insoluble in absolute alcohol. Potassium nitrite plroduces in not too dilute solutions a yellowish, crystalline precipitate which becomes reddish on long standing and is soluble in much water. Potassium sulphocyanate does not precipitate palladiumr, even after the addition of salphurous acid (difference from copper, and best means of separating from the same). On treatment with sodium carbonate in the upper oxidizing flame (p. 26) all the compounds of palladium yield a gray metallic sponge. b. RHODIUM, Rh. 1044. RHODIUM is found in small quantity in platinum ores. It is almost silver white, very malleable, and difficultly fusible. When prepared in the wet way it is a gray powder. The powder when ignited in the air absorbs oxygen, which it gives up again upon stronger ignition. Rhodium is insoluble in all acids; it dissolves in aqua regia only when alloyed with platinum, copper, etc., and not when alloyed with gold or silver. Fusing metaphosphoric acid and fusing potassium disulphlate dissolve it, forming a rhodic salt. There are four oxides: the monoxide (RhO), rhodic oxide (Rh203) (base of the salts), dioxide (Rh 02), and trioxide (Rh O.) (a weak acid). RHODIC OXIDE is gray, it yields a yellow and a brownish-black hydroxide; it is insoluble in acids, but dissolves in fusing metaphosphoric acid and in fusing sodium disulphate. The solntions are rose-colored. Stphuretted hydrogen and ammonium sullhide precipitate in time, especially when assisted by heat, brown rhocdic sulphide, which is insoluble in ammonium sulphide, but dissolves in boiling nitric acid. Potassa, if added in not too larmge excess, throws down at once yellow Rh (O H)3HO, which is soluble in excess of the precipitant at the ordinary temperature; on boiling the solution, blackish-brown Rh (O H)s is precipitated. In a solution of rhodic chloride, plotassa at first produces no precipitates, but, on addition of alcohol, black Rh (O H)3 separates soon (CLAUs). Ammonia produces after some time a yellow precipitate, soluble in hydrochloric acid. Zinc precipitates I)lack metallic rhodium. On heating with potassium nitrite, rhodic chloride becomes yellow, and an orangeyellow precipitate is formed, which is slightly soluble in hydrochloric acid; at the same time another portion of the rhodium is converted into a yellow salt, which remains in solution and is precipitated by alcohol (GIn3sS). All solid compounds of rhodium, on ignition in hydrogen, or on ignition on' platinum wire with sodium carbonate in the upper oxidizing flamle, yield the metal, which is well characterized by its insolubility in aqua regia, it. solubility in fusing, potassium disulphate and the behavior of its solution to potassa and alcohol. c. OsMIUM. Os., 199'2. OsMIUM is found in platinum ores as a native alloy of osmium and ii. Cium. It is generally obtained as a black powder, or gray and with me.

Page  167 ~ 124.] RUT1IENIUtI. 167 tallic lustre; it is infusible. The metal, the IIYPo-oSMaIOUS OXIDE (Os O), and the OSMIC OXIDE (OS 02) oxidize readily when heated to redness ill the air, and give OSMIUM TETROXIDE (Os 04), which volatilizes and makes its presence speedily known by its peculiar exceedingly irritating and offensixe smell, resembling that of chlorine and iodine (highly characteristic). If a little oslllium on a strip of platinum foil is held in the outer mantle of a gas or alcoholflarme, at half height, the flame bl)comes most strikingly luminous. Even minute traces of osmiull may by this reaction be detected in alloys of iridium and osmium; but the reaction is in that case only momentary; it may however be reproduced by holding the sample first in the reducing flame, then again in the outer mantle. Nitric acid, more particularly red fullling nitric acid, and aqua regia dissolve osmium to tetroxide. Application of heat' promotes the solution, which is however attended in that case with volatilization of tetroxide. Very intensely ignited osmlium is insoluble in acids. On fusing with potassium nitrate and distilling the fused mass with nitric acid, osmium tetroxide is found in the distillate. By heating osmium in dry chlorine free from air, first bluish-black IIYPOOSMIOUS CHLORIDE (Os C12) is formed, but always only in small quantity, then the more volatile and rQd osMIC CHLORIDE (Os C14); if moist clllorine is used, a green mixture of both chlorides is formed. The hypo-osmious chloride dissolves with a blue color, the osmic chloride with a yellow color, and both together with a green color, which turns red. The' solutions are soon decomposed, osmium tetroxide, hydrochloric acid, and a mixture of hypo-osmious and osmic oxides being formed, the mixed oxides separating as a black powder. On heating a mixture of powder of osmllium, or of osmiumn sulphide and potassium chloride in chlorine, a double salt of POTASSIUM HYPO-OSAIIOJS CIILORIDE is produced ill the form of octahedra, which are slightly soluble in water and insolulble in alcohol. The solution of this double salt is more permallnent than that of the hypoosmious chloride.. Potassa decolorizes the solution; on boiling, bluishblack osMIC HYDROXIDE OS (O H)4 separates. On fusing the double cllloride with sodium carbonate, dark gray osMIC OXIDE separates. Osmlium tetroxide is white, crystalline, fusible at a gentle heat, and boils at about 1000~; the fumes attack the nose and eyes p)owerfully. Heated with water, it fuses and dissolves, but slowly. The solution has an irritating, unpleas.. ant smell. Alkalies color the solution yellow in consequence of the formnation of osmites, (e.g., K2 Os 04. 2 t12 0); on distilling, the greater part of the osmilum passes over as tetroxide (very characteristic), the remainder gives off oxygen, leaving an oslllite, or on boiling, splits into osmium tetroxide, osmlic oxide, and potassa. Osmium tetroxide decolorizes indigo solution, seIarates iodine from potassiumn iodide, converts alcohol into aldehyde and acetic acid. Potassium nitrite readily reduces it to Iotassium osmlite. Hlydrogen sulphide precipitates brownish-black sulphide, which only separates when a strong acid is present; the precipitate is insoluble in ammonium sulphide. Sodium sulphite produces a deep violet coloration, and dark-blue hypo-osmious sulphite gradually separates, especially on evaporating or warming with sodium sulphate or carbonate. Ferrous sulphate produces a black precipitate of osmic oxide. Stannous chloride produces a brown precipitate, soluble in hydrochloric acid to a brown fluid. Zinc and many metals in the presence of a strong acid precipitate metallic osmium. All the compounds of osmium yield the metal on ignition in a current of hydrogen. d. RUTIIENIUM. Ru., 104'4. RUTmINIIJM is found in small quantity in platinum ores. It is a grayish-white, brittle, and very difficultly fusible metal. It is barely acted upon by aqua regia; fusing sodium disulphate fails altogether to affect it. By ignition in the air it is converted into bluish-black ruthenious oxide,

Page  168 168 REACTIONS. GROUP VI. [~ 125 Ru2 02, insoluble in acids; by ignition with potassium chloride in a current of chlorine gas into potassium ruthenious chloride, by fusion with potassiuim nitrate, with potassa, or with potassium chlorate into potassium rutlhenate, K2 Ru 04. The fused mass obtained in the latter case is greenish-black, and dissolves to an orange-colored fluid, which tinges the skin black, from s3paration of black oxide. Acids throw down from the solution bhlCk IIUTILENIOUS OXIDE, which dissolves in hydrochloric acid to an oranlgl,-yellow fluid containing ItUTHIENIOUS CHLORIDE~, Ru2 C13. This solution is resolved by heat into hydrochloric acid and ruthenious oxide. In a concentrated state it gives with potassium chloride and ammllonium chloride crystalline glossy-violet precipitates (e.g., potassium rulthenious chloride, Ru2 C16. 4 K C1), which on boiling with water deposit a b)lack oxychlloicle. o'tassac precipitates black ruthenious hydroxide, Ru(O H)3, which is insoluble in alkalies, but dissolves in acids. Hydrogen sulphide causes at first no alteration; but after some time the fluid acquires an azure-blue tint, and deposits brown ruthenium sulipllide (very characteristic). Ananonium sulpAhide produces brownish-black precipitates, barely solul)le in an excess of thle plrecipitant. Potassiunm sliphocyanate produces -in tllh absence of other metals of the platinum ores-after some time a red coloration, which gradually changes to purple-red, and upon heating to a fine violet tint (very characteristic). Zinc produces at first an azureb)lue coloration, which subsequently disappears, ruthenium being deposited at the same time in the metallic state. Potassium nitrite colors the solution yellow, with the formation of a double salt, which is readily soluble in water and alcohol. The alkaline solution of this double salt, when mixed with a little colorless alnmonium sulphide turns crimson (characteristic); on the addition of more ammonium sulphide, ruthenium sulphide is precipitated. ~ 135. SIXTH GROUP. Mlore common elements: GOLD, PLATINUMII, TIN, ANTIIONY, ARSENIC. Rarer elemelntS.-IIIDIu-M, AIOLYBDENUM, TUNGSTEN, TELLURIUMI, SELENIUM. The higher hydroxides of the elements belonging to the sixth group have all of them mlore or less stronllly pronounced acid characters. But we class theln here, as they cannot well be separated from the lower oxides and hydroxides of the same elements, to which they are very closely allied il their reactions with hydrogen sulphide. Properties of the group.-The sulphides of the elements of the sixth group are insoluble in dilute acids. These sulphlids combine with alkali sulphides (either immediately, or with the aid of sulphur) to soluble sulphur salts, inl which they take the part of the acid. IHydrogen sulphide p)recipitates these eleieents therefore, like those of the fifth group, comnpletely fromir acidified solutions. The precipitated sulphides differ, however, fr:om those of the fifth group in this, that they dissolve ii ammonium sulphide, potassium sulphide, etc., anld are reprecipi. tated from these solutions by addition of acids.

Page  169 ~ 126.] GOLD. 169 We divide tile more common nletals of this gioup into twc classes, and distinguish, 1. AIETALS WVHOSE SULPHIDES ARE INSOLUBLE IN HYDROCIILORIC ACID AND IN NITRIC ACID, and are reduced to the metallic state upon fusion with sodium nitrate and carbonate, viz., GOLD and PLATINUMI. 2.-M IETAL!S WHIOSE SULPHIDES ARE SOLUBLE IN BOILING HYDROCIILORIC ACID OR NITRIC ACID, and are upon fusion with sodi1um nitrate and carbonate converted into sodium salts: viz., ANTIMIONY, TIN, and ARSENIC. FIRST DIVISION. Specia7l Rfcitions. ~ 126. a. GOLD, Au., 197. 1. METALLIC GOLD has a reddish-yellow color and a high metallic lustre: it is rather soft, exceedingly malleable, di cultly fusible: it does not oxidize upon ignition in the air, and is insoluble in hydrochloric, nitric, and sulphuric acids; but it dissolves in fluids containing or evolving chlorine, e. g., in in nitrohydrochloric acid. The solution contains auric chloride, Au Cl,. 2. AurIc OXIDE (Au, 0,) is a blackish-brown powder, AuRIa HYDROXIDE (AURIC ACID) Au (Ql), is a chestnut-brown powder. Both are reduced b1y light and heat, and dissolve readily in hydrochloric acid, but not ill dilute oxygen acids. Concelltrated nitric and sulphuric acids dissolve a little auric oxide; water reprecipitates it from these solutions; alric hydroxide dissolves in potassa with formation of potassiuml aurate, K A 01 O+ 3 II, O. AuRous OXIDuE, Au,0, is violet black; it is decomposed by heat into gold and oxygen. 3. OXYGEN SALTS Of g(ld are nlearly unknown. Tile HALOID SALTS are yellow, and their solutions exhibit this color at a high degree of dilution. The whole of them are readily decomposed by ignition. Solution of auric chloride reddens litmus-paper. 4. liljdroqem sulptidde precipitates from neutral or acid solutions the whole of the metal, from cold solutions as AURIC SULPHIII)E Au, S,, from boiling solutions as AUROUS SULIIIDE:, Aun,S. Thee precipitates are insoluble in hydrochloric and in nitric acid, but soluble in nitrohydrochloric acid. They are insollble in colorless amnlonium sulphide, but soluble in yellow aminonium sulphide, and more readily still in yellow sodium sulphide or potassium sulphide.

Page  170 170 REACTIONS. GROUP VI. DIV. I. [ 127. 5. Ammoniumn s8?phide prccipitates brownishl-black AURtI SULJPHIDE, twhich rledissolves in an excess of the precipitant only if the latter con.taina an exc(c, of sulphur. 6. A,mmoizia p)roduces, though only in concentrated solutions of gold, reddishll-yellow precipitates of flldmictatineg gold. The more acid the solution and tile greater thle excess of amlmonia added, the more gold remains in solution. 7. Stannous cidor'ide, containinlo an admixture of staflmic chloride (Nwhich may be easily prepared by mixing solution of stannous chloride with a little chlorine water), produces eveln ill extremely dilute solutions of gold, a purple-red precipitate (or coloration at least), which sometimes inclines rather to viol t or to brownish-red. This plecipitate, which has received the name of PURPLE OF CASSIUS, is insoluble in hydrochloric acid. Its constitution is not established. 8. rerw0ous saclts reduce aurie chloride in its solutions, and precipitate METALLIc GoLD in form of a most minutely divided brown powder. The fluid in which the precipitate is suspended appears of a blackish-blue (color by transmitted light. The dried precipitate shows metallic lustre when pressed with the blade of a knlife. 9. Potassium nitrite produces a precipitate of metallic gold. In very dilute solutions the fluid at first only appears colored blue, but in time the wvhole of the gold separates. 10. Potassa or soda added in excess to auric chloride leaves the fluid clear, bhut upon addition of tanimic acid metallic gold sel)arates. Warmling assists the precipitation. 11. All comnpounlds of gold are reduced in thle stick of ek'arcoal (p. 27). By triturating the charcoal afterwards, yellow spangles of metal will be obtained, urhic are insoluble in nitric acid, but readily soluble in aqua iregia. ~ 127. 6. PLATINUM, Pt., 197'4. 1. METALLIC PLATINUM has a light steel-gray color; it is very lustrous, moderately hard, very difficultly fusible; it does not oxidize upon ignition in the air, and is insoluble in hydrochloric, nitric, and sulphuric acids. It dissolves in nitrlhydrochloric acid, especially upon heating. The solution contains platinic chloride. 2. PLATINIC OXIDE, Pt 2O, is a blackish-brown powder. PLATINIC HYDROXIDE (PLATINIC ACIDI) Pt (OHI)4 is a reddish-brown powder. Both are reduced by heat; they are both readily soluble in hydrochloric acid, and difficultly soluble in oxygen acids. PLATINOUS OXIDE) Pt 0, is black; PLATINOUS HIYDROXIDE, Pt (01I),, brown; they are both by ignition reduced to the metallic Btate.

Page  171 ~ 127.] PLATINUM. 171 3. The P4ATINIC SALTS are vellow, and are decomposed at a red heat. PLATINIC CHLORIDE, Pt Cl4, is reddish-brown, its soltttion reddish-ll ellow, which tint it retains up to a high degree ofdiThtion. The solution reddens litlnus paper. Exposure tc a very low red heat converts platinic chloride into platinous chloride, Pt C1,; application of a stronger red heat reduces it to the metallic state. Solution of platinlic chloride, containing platillous chloride, has a deep browll color. 4. hIydrloyen s 2phide throws down from acid and neutral platilhic solutiolls, but always only after the lapse of some time, a bckish-brown precipitate of PL&TINIC SULPHIDE, Pt S2. If the solution is heated after the addition of the hydrogen sulphide, the precipitate forms immediately. It dissolves in a great excess of alkali sulphides, more particularly of the higher degrees of snlphuration. Platinic sulphide is insoluble in hydrochloric acid and in nitric acid; but it dissolves in nitrohydrochloric acid.' 5. Amlnmonium szdphicde produces the same precipitate; this redissolves completely, though slowly and with difficulty, in a large excess of the precipitant if the latter contains an excess of sulphur. Acids reprecipitate the platinic sulphide unaltered from the reddish- brown solution. 6. Potassi'nts chloride and acnmonoiun chloride (and accordingly also potassa and ammonia in presence of hydrochloric acid) produce in not too highly dilute solutions of platinic chloride, yellow crystalline precipitates of POTASSIU.M and AM3toNIIt PLATINIC CHLORIDE, which are as insoluble in acids as in water, but are dissolved by heating with solution of potassa. From dilute solutions these precipitates are obtained by evaporating the fluid mixed with the precipitants on the water-bath, and treating the residue with a little water or with dilute spirit of wine. Upon ignition alnmoniumn platinic chloride leaves spongy platiinum behind; potassium platinic chloride leaves platinum and potassium chloride. The decompositioll of potassium platinic chloride is complete only if the ignition is effected in a current of hydrogen gas, or with addition of some oxalic acid. 7. Stcannzozs chloride imparts to platinic solutions containing much free hydrochloric acid an intensely dark brownish-red color, owing to a reduction of the platinic chloride to platinous chloride. But the reagent produces no precipitate in suclh solutions. 8. Fer'rous sulphate does not precipitate solution of platinic chloride, except upon very long-continued boiling, in which case the platinum ultimately suffers reduction. 9. On igniting a compound of platinumn mixed with sod~;una carbonate on the loop of a platinum wire in the upper oxidcizingflamne, a gray spongy mass is obtained, which on trituration in an agate mortar yields silvery spangles, insoluble in hydro chloric and nitric acid, but soluble in aqua regia.

Page  172 172 REaCTIONS. GROUP I. Gi. HI.. [ 129 ~ 128. iccaypit alation and 2nmalcrks. — The reactions of gold and platinlumn enable us, in many eases, to detect those two metals directly in the presence of many others, Where platinum and gold ale present in the same solution, the liquid is most conveniently evaporated to dryness at a gentle heat with alnlmo. niunm chloride, and the residue treated with dilute alcohol, in order to obtain the gold in solution and the platinum in the residue. The precipitate will thus give platinum by ignition, anld the gold may be precipitated from the solution by ferrous sulphate, after removing the alcohol by evaporation. SECOND DIVISION. Special neactions. ~ 129. a. Tin,* Sn. 118, AND STANiNOUS COMIPOUNDS. 1. TIN has a light grayish-white color and a high metallic lustre; it is soft and malleable; when bent it produces a crackling sound. Heated in the air it absorbs oxygen and is converted into grayish-white stanllic oxide; heated on charcoal before the blowpipe it forms a white incrustation. Concentrated hydrochloric acid dissolves tin to stannoas chloride, with evolution of hydrogen gas; nitrohydrochloric acid dissolves it, according to circumstances, to stannic chloride or to a mixture of stannlous and stannic chlorides. Tin dissolves with difficulty in dilute sulphuric acid; concentrated sulphurlic acid collverts it, with tile aid of heat, into stallnic sulphate; noclderately- concentrated nitric acid oxidizes it readily, particularly withl the aid of heat; the white hydroxide formed (nmetastalliec acid, Sn5I-I,00.5) does not redissolve in an excess of the nitric acid. 2. STANNOUS HYDROXIDE, Sn 11-2 O, is white. By ignlition in carbon dioxide it yields STANNOUS OXIDE, Sn 0, as a black or rayish-black powder. Stannous oxide is reduced to metal by flsion with potassium cyanide, it is readily soluble in hydrochloric acid. Nitric acid converts it into metastannic acid. wlhich is insoluble in an excess of the acid. 3. The sTANNOUS SALTS are colorless; they are decomposed by heat. The soluble normal salts, redden litmus-paper. The * In the stannous compounds tin is bivalent, in the stannio compounds it it quadrivalent.

Page  173 ~ 129.] TIN. 173 stannous salts rapidly absorb oxygen from the air, and are partially or entirely converted into stannic salts. Stannous chloride, no matter whether in crystals or in solution, also absorbs oxvgen from the air, which leads to the formation of insoluble stannous oxvchloride and stannic chloride. Hence a solution of stannons chloride becomes speedily turbid if the bottle is often opened and there is only little free acid present; and hence it is only quite recently prepared stannous chloride which will completely dissolve in water free from air, whilst crystals of stannous chloride that have been kept for any time will dissolve to a clear fluid only in water containing hydrochllorik acid. 4. h-ydroqen su,7tide throws down from neutral and acid solutions a dark brownl precipitate of STANNOUS SULPITIDE Sn S. This reagent does not precipitate alkaline solutions, or at least not. completely. The precipitation may be prevented by the presence of a very large quantity of free hydrochloric acid. The precipitate is insoluble, or nearly so, in colorless alnimo niuim sulphide, but dissolves readily in the yellow sulphide. Acids precipitate froln this solution yellow stannic sulphide, inixed with sulphur. Stallnous sulphide dissolves also in solutions of soda and potassa. Acids precipitate it again from these solutions unaltered. Boiling hydrochloric acid dissolves it, with evolution of lhydrogen sulphide; boiling nitric acid converts it into insolulllle inetastannic acid. 5. Ammonium sulphide produces the same precipitate of STANNO US SITLPHIDE. 6. Potassa, sod.a, ammonia, and carbonates of the alkali-metals pr(cduce a white bulky precipitate of STANNOUS HYDROXIDE, Sn H12 02, which redissolves readily in an excess of potassa or soda, but is insoluble in an excess of the other precipitants. If the solution of stannous hydroxide in pctassa (potassium stannite) is lbriskly evalporated potassium stannate Sn 0 (() K)2 is formed, which remains in solution, whilst metallic tin precipitates; but upon evaporating slowly crystalline st annous oxide separates. 7. Auric chloride produces in solutions of stannous chloride and in solutions of other stannous salts mixed with hydrochloric acid a precipitata which varies in color bet.ween brown, reddish brown, and purple-red, according to the presence of more or less stannic chloride and the state of concentration (compare ~ 126, 7). In very dilute solutions a more or less brown or red coloration merely is produced. 8. Solution of mercquric chloride, added in excess, to soluntions of stannous chloride or of a stannons salt mixed with hydrochloric acid, produces a white precipitate of MERCUROUS CIIL,oRIDE, owing to the stannous salt withdrawing fromn the mercuric chloride half of its chlorine. 9. If a fluid containing a stannous salt and hydrochloric acia is added to a mixture of potassium ferricyanide and ferric chloride a precipitate of PRUSSIAN BLUE separates immediately. This reaction is extremely delicate, but it can be held to be decisive only in cases where no othet reducing agent is present. 10. Zinc precipitate from solutions mixed with hydrochloric acid METAL

Page  174 174 REACTIONS. GROUP VI. DIV. II. [~ 130. LrC TIN in the form of gray lanmine or of a spongy mass. If the experinent is m ide in a platinum capsule, the latter is not colored black. 11. If stannous compounds, mixed with sodium carbonate and some borcrx, or better still, Awith a mixture of equal parts of sodialz m carbonate and eanide are exposed on a charcoal support to the inner blowpipeflame, malleable gr'ains of MZEITALLIC TIN are obtained on cutting out and forcibl) tlitUrating the surrounding parts of charcoal with water in a smnall mortar, and washing off the charcoal from the metallic particles. Upon strongly heating the grains of metallic tin on a charcoal support tle latter becomes covered with a coating of white stallllic oxide. The stick of charcoal (p. 27) is also admirably adapted for the reduction of til. 12. If, to a borax bead colored slightly blue by copper, a trace of a stannons compound is added and the bead is heated in the lower reclucing fl(me of the gas lamp (p. 26), it will becomne reddish-brown to ruby-red in consequellce of the formlation and separation of cuprous oxide (compare ~ 120, 14). A compound of tinl is essential to this reaction. ~ 130. b. TIN, Sn. 118. STANNIC COMPOUNDS. 1. STANNIC OXIDE, Sn 02, is a powder varying in color from white to straw-yellow, and which upon heating transiently assumes a brown tint. The IYDROXIDE precipitated by alkalies from solution of stannic chlloride (obtained by heating tin in chlorine gas, or by dissolving it in aqua regia), dissolves readily in hydrochloric acid-it is STANNIC ACID, S11n II, O. The IYDROXIDE formled by the action of nitric acid upon tin-M-ETASTANNIC ACID (Sn5 II100 1?) —remains undissolved. But if lnetastannic acid is boiled for some time with hydrochloric acid it takes up chlorine; if the excess of the acid is then poured off and water added, a clear solution of metastannic chloride is ob'tained. The aqueous solution of the stannic chloride is not precipitated by concentrated hydrochloric acid, whilst the acid produces in the aqueous solution of the mnetastannic chloride a white precipitate of tile latter compound. The solution of stannic chloride is not colored yellow by addition of stannous chloride, as is the case in a remarkable degree if the solution contains metastannic chloride (L6WENTIIAL). The dilute solutions of both chlorides give upon boiling precipitates of the hyvdroxides corresponding to the chlorides. 2. The STANNIC SALTS are mostly colorless, but stannic iodide, is oranlle-red. The soluble salts are decomposed at a red heat; they redden litlnns-paper. STANNIc CHLORIDE, Sn CL,, is a volatile liquid, strolurly ftinning in the air. 3. _lydroycgn StpTdAice throws down from all acid and neu.

Page  175 ~ 131.] ANTIMONY. 175 tral stannic solutions, particularly upon heating, a white flocculent precipitate if the stannic solution is in excess; a dull yellow precipitate if the hydrogen sulphide is in excess. The former, in the case of a solution of stannic chloride, probably consists of a mixture of stannic chloride and stannic sulpide (it has not however as yet been analyzed); the latter consists of STANNIC SULPIJIDE Sn1 S2. Alkaline solutionls are not precipitated by hydrogen sulphide. Presence of a very large quantity of hydrochloric acid may prevent precipitation. Stannie sulphide dissolves readily in potassa or soda, alkali sulphides, and concentrated boiling hydrochloric acid, as also in aqua regia. It dissolves with some difficulty in ammonia, is nearly insoluble in arnmonlium carbonate, and insoluble in hydrogen potassium snliphite. Concentrated nitric acid converts it into insoluble metastannic acid. Upon deflagrating stannic sulphide with sodium nitrate and carbonate, sodium sulphate and stannic ox i(le are obtained. If a solution of stannic sulphide in potassa (potassium sulphostannate, Sn S ([K S)2) is boiled with bisrmlluth trioxide, insoluble bismuth trisulphide and soluble potassium stannate are formed. 4. Ammnonium sulphide produces the same precipitate of STANNIC SULPIItDE; the precipitate redissolves readily in an excess of the precipitant, as ammoniu-m sulphostannate. From this solution acids reprecipitate the stannic sulphide unaltered. 5. Potassa, soda, and ammonia, sodium and ammonium ca-b7haataq produce white precipitates which, according to the nature of the solutions, consist of stannic acid, or of metastannic acid. The former readily dissolves in a slight excess of potassa, slightly in a large excess; on the other hand it dissolves only after considerable dilution in a slight excess of soda, and on addition of more soda almost all the stmnnic acid separates again. The latter is hardly soluble in excess of potassa or soda. 6. Sodium suliphate or ammonium nitrate, in fact, most normal alkali salts, when added in excess, tLroxv down from stannic or inetastannic solutions, provided they are not too acid, the whole of the tin as STANNIC ACID or METASTANNIC ACID. Heating pronmotes the precipitation: Sn C14 + 4 (Na2 S 04) + 3 H2 0 = Sn H2 03 + 4 Na Cl + 4 (Na H S 04). 7. Metallic zinc precipitates from solutions of stannic or metastannic chloride, in the presence of free acid, METALLIC TIN in the shape of small gray scales, or as a spongy mass. If the operation is conducted in a platinum dish, no blackening of the latter is observed (difference between tin and antimony). 8. The stannic and metastannic compounds show the same reactions before the blowppipe or in the gas flame as the stannons compounds. Stannic oxide is also readily reduced when fused with potassium cyanide in a glass tube or in a crucible. ~ 131. C. ANTIMONY. Sb. 122. 1. METALLIC ANTIMONY has a bluish tin-white color and is Ilustrous; it is hard, brittle, readily fusible, volatile at a very

Page  176 176 REACTIONS. GROUP VI. DIV. II. [, 131. high temperature. When heated on charcoal before the blowpipe it emits thick white fumes of antimonious oxide, which form a coating on the charcoal; this combustion continlles for some time, even after the removal of the metal from the flame; it is the most distinctly visible if a strong current of air is thrown by the blowpipe directly upon the sample on the charcoal. But if the fumes ascend straight, the hot metallic bead becomes surrounded with a net of brilliant aCeiecllar crystals of antimonious oxide. Nitric acid oxidizes antimony readily; the dilute acid converts it almost entirely into antimonolious oxide, the more concentrated the acid the more metantimonic acid is formed; boiling concentrated acid converts it almost completely into metantimonic acid. Neither of the two is alto-.ether insoluble in nitric acid; traces of antimlony are thereTore always found in the acid fluid filtered from the precipitate. IIydrochloric acid, even boiling, does inot attack antimony. In nitrohydrochloric acid the metal dissolves readily. The solution contains antimonious chloride, Sb C1,, or altirnonic chloride Sb C15, according to the degree of concentration of the acid and the duration of the action. 2. According to the mode of its preparation ANTIMONIOUS OXIDE (Sb, 0,) occurs in white and brilliant crystalline needles, or as a white powder. It fuses at a moderate red heat in a closed vessel; at a higher temperature it volatilizes without decomposition. It is almost insoluble in nitric acid, but dissolves readily in hydrochloric and tartaric acids. No separation of iodine talkes place on )boiling it with hydrochloric acid (free from chlorine) and potassium iodide (free from iodic acid). BUNSIEN. Antimonious oxide is easily reduced to metal by fusion with potassium cyanide. 3. METAnTIMONIC ACID (Sb 0, O H),* produced by the action of concentrated nitric acid on antimony and PYROANTIMroNJI ACID (Sb, 0, H11?), t which is formed when antimonic chloride is treated witlh much water, are white. They both redden moist litmus-paper; they are only very sparingly soluble in water, and almost insoluble in nitric acid, but dissolve pretty readily in hot concentrated hydrochloric acid: the solution contains ANTIMONIC CIILORIDE (Sb C15) and turns turbid upon addition of water. On boiling metantimonic acid with hydrochloric acid and potassium iodide, iodine separates which dissolves in the hydriodic acid present to a brown fluid (BUNSEN). Upo01 heating metantirnonic acid or pyroantimonic acid, just short of * Or Sb f O H, antimonic acid of former editions. 2 (OH)2 Sb 0 t O0 metantimonic acid of former editions. Sb 0

Page  177 , 131.] ANTIMONY. 177 redness, ANTIMONIC OXIDE (Sb. 05) is obtained as a yellow powder insoluble in water and acids. By stronger ignition the latter loses oxygren, and is collverted into infusible ANTIMONIOUS A'NTIMroNATE or antimony tetroxide (Sb2 O4). Of the metantimonates and pyroantimonates the potassium and ammonium salts are almost the only ones soluble in water. Potassium metantilionate (Sb O,3) obtained by fusing antinony or its sulphides with nitre is a white mass nearly insoluble in cold water. On boiling with water it gradually dissolves to the readily soltible orthoantilnonate (S0I, 0, 1K). On fusing either of the above salts, or metantimonie acid with a large excess of potassa, a mass is obtained which readily dissolves in water. From the solution by evaporation crystals of potassium pyroantimonate (Sb2 O, K4) may be obtained, which are only permanent in preselnce of excess of potassa and are decomposed by water illto potassa and hydrogen potassium pyroantimonate (Sb2 07 I12 I2) (~ 54). The sodiuln nmetantilmonates are nearly, the sodium pyroantimonates, are quite insoluble in water. The soluble potassiuml antimonates are accordingly precipitated by sodiumn chloride (~ 90, 2).'On treating mnetantimnolates and pyroantimonates with acids, lnetaiitimonic and pyroantimionic acids are precipitated. 4. The gileater part of the ANTIMONTIOLTS SALTS are decomposed upon ignllition; the haloid salts volatilize readily and unaltered. The soluble normal antimlony salts redden litlnus-paper. With a large quantity of water they are decomposed with formation of insoluble basic salts and separation of free acid. Thus, for instance, water throws down from solutions of antimonious chloride in hydrochloric acid a white bulky precipitate of ANTIMIONIOUS OXYCILORIDE (powdel of Algaroth), which soon beconles heavy and crystalline. 4 Sb Cl2 + 5 II 0 2 (Sb O C1) Sb, O,, + 10 H C1. Tartaric acid dissolves this precipitate readily, ald therefore prevents its formation if mixed with the solution preeviously to the addition of the water. It is by this property that this alltimonly colnpound is distinguished from the basic bismuth salts formed under similar circumstances. 5. If/ycrogenz sl2phiide precipitates from acid solutions (if the quantity of free mineral acid present is not too large) the whole of the metal as orange-red amorphouls ANTmIOSIOUS SULPHIDEI (S b2 S). Ill alkalille solutions this reagent fails to produce a precipitate or, at least, it precipitates theln only imperfectly; neutral solutions also are only imperfectly thrown down by it. The alltimonious sulphide produced is readily dissolved by potassa and by alkali sulphides, especially if the latter contain an excess of sulphur; it is but sparingly soluble inl ammonia, and, if free from antimonic sulphide, almost insoluble in hydrogen ammonium carbonate. It is insoluble in dilute acids, as also in hydro,gen potassium sulplite. Concentrated boiling hyarochlo

Page  178 178 REACTIONS. GROUP VI. DIV. II [~ ]31 ric acid dissolves it, with evolution of hydrogen sulphide. By heating in the air it is converted into a mixture of antimony tetroxide with antimonious sulphide. By deflagration with sodium nitrate it ives sodium sulphate and netantimona If a potassa solution of antimonious sulphide (containing potassium sulphantimonite) is boiled with bismuth trioxide, bismuth trisulphide precipitates, and potassium orthoant lonate remains in the solution. On. fusing antimonious sulphide with potassiuml cyanide, etallic antimony and potassiunt sulphocyanate are produced. If the operation is co-e ducted in a small tube expanded into a bulb at the lower end, or in a stream of carbon dioxide (see ~ 132, 13), no sublimate of antimony is produced. ]But if a mixture of antimonious sulphide with sodium carbonate or with potassium cyanide and sodium carbonate is heated in a glass tube in a stream of hydrogern gas a mirror of antimony is deposited in the tiube, inmedliately behind the spot occupied by the mixture. From a solution of antimonic acid in hydrochloric acid sulphuretted hydrogen throws down ANTIMONIC SULPHIDE (St)b2 S) mixed with antimmonious sulphide and sulphur. The preeitate dissolves readily when heated with solution of soda or amlnonia (formring, e.y., sodium sulphantimonate, Na Sb S,) and equally so in concentrated boiling hydrochloric acid with evolution of hydrogen sulphide and separation of sulphur, but dissolves only very sparingly in cold solution of hydrogen aminoIniumni carbonate. 6. Ammtoniuzrn suphide produces in solutions of antimonious salts an orange-red precipitate of ANTIMONIOUS SU LPLIDE which readily redissolves in an excess of the precipitant if the latter contains an excess of sulphur, with formation of amoIiium sulphantimonate. Acids. throw down from this solution antimonic sulphide. IHowever, the orange color appears in that case usually of a lighter tint, owing to an admixture of free sulphur. 7. Potassa, soda, ammonia, sodium carbonate, and ammonium carbonate throw down from solutions of antimonious chloride, and also of siple antinmonious salts,-but far less completely, and mostly only after soe tine, from solutions of tartar emetic or analogous compounds,-a white bulky precipitate of ANTIMONIOUS HYDROXIDE, which redissolves pretty readily in an excess of potassa or soda, but requires the application of heat for its re-solution in sodium carbonate, and is almost insoluble in ammonia. 8. 3fetallic zinc precipitates from all solutions of antimoni ous oxide, if they contain no free nitric acid, ME'rALLIC ANTImONY as a black powder. If a few drops of a solution of antimony, containing some free hydrochloric acid, are put into a platinum capsule (the lid of a platinum crucible), and a fragment of zinc is introduced, hydrogen containing antimonetted hydrogen is evolved and antimony separates, staining the part of the Nlatinum covered by the liquid brown or black, even li

Page  179 ~ 131.] ANTIMONY. 179 the case cf very dilute solutions: this reaction is equally delicate and characteristic. Cold hydrochloric acid fails to remove the stain, heating with nitric acid removes it immediately. 9. If a solution of antimonious oxide in solution of soda (sodium anti monite) is mixed with solution of silver nitrate, a deep black preciplitate of ARGENTOUS OXIDE forms with the grayish-brown precipitate of argentic oxide. Upon now adding ammonia in excess, the argentic oxide is redissolved, whilst the argentous oxide is left undissolved (H. RosE). The formation of the argentous oxide in this process is explained as follows: Na Sb 02 + 2 Ag2 O0 = Na Sb 03 + Ag4 O. This exceedingly delicate reaction affords an excellent mleans of detecting antimonious oxide or antimonites in presence of antimonic acid. 10. If any solution of antimony in hydrochloric or sulphuric acid is introduced into a flask in which lhydrogen gas is being evolved from -Dure zinc and diluted suph/uric acid a portion o4 the antimony separates in the metallic state; but another portion of the metal combines with hvdlrog en, forminlg ANTIAO. NETTED HYDROGEIN GAS (Sb H3). If this operation is conducted in a gas-evolution flask, connected by means of a perforated cork with a bent tube endilo in a jet,* and the hydrogen passing through the jet is is ignited after the atmospheric air is coinpletely expelled, the flame appears of a bluish-green tint. which is impalrted to it by the alntimony separating and bulrninlg ill the flame. White funmes of antililollious oxide rise froim the flame, which condense readily upon cold substances, and are not dissolved by water. But if a cold body, such as a porcelain dish (which answers the piurpose best), is now depressedl upon the flame, METALLIC ANTIMONY is deposited upon the surface in a'state of the most minute division, formling a deep; black and almost lustreless spot. If the middle part of the tube throsugh which the gas is passing is heated to redness the bluish-gcreen tint of the flame decreases in intensity, and a mnetallie mlirror of antimony of silvery lustre is formed within the, tube on both sides of the heated part. As compounds of arsenic give under the same circumstances. similar stains of metallic arsenic, it is always necessary to carefully examine the spots produced, in order to ascertain whether they really consist of antimony or contain any of that metal. With stains deposited on a porcelain dish the object in view is most readily attained by treating them with a solution of sodiumn hyppochlorite (prepared by mixing a solution of "chloride of lime" with sodium carbonate in excess, and filtering); which will immediately dissolve arsenical stains, leavinlg those proceeding from antimony untouched, or, at least, remonvilg them only after a very protracted action. A mirror within the g.ass tube, on the other hand, mnay be tested by heating it * In accurate experiments it is advisable to use MAnsH's apparatus (~ 132, 10). By the employment of a platinum jet rolled from a bit of thin foil andi inserted in the end of the glass delivery tube, the color of the flame will be rendered very distinct.

Page  180 180 REACTIONS. GROUP VI. DIV. H. [H 132. whilst the current of hydrogen gas still continnes to pass through the tube: if the mirror volatilizes only at a higher temnpelature, and the hydrogen gas then issuing from the tube does not smell of garlic; if it is only with a strong current that the ignlited gas deposits spots on porcelain, and the mirror before volatilizing fuses to small lustrous globules distinctly discernible through a magnifying glass,-the presence of antimony may be considered certain. Or the metals may be distilnguished with great certainty by conducting through the tube a very slow stream of dry hydrogen sulphide, and heating the mirror, proceeding in an opposite direction to that of the current. The antimonial mirror is by this means converted into antimonious sulphide, which appears of a more or less reddish-yellow color, and almost black when in thick layers. If a feeble stream of dry hydrochloric acid gas is now transmitted through the glass tube, the antimonious sulphide, if present in thin layers onlly, disappears immediately; if the incrustation is somewhat thicker it takes a short time to dissipate it. The reason for this is, that the antimonious sulphide decomposes readily with hydrochloric acid, and the antimnonious chloride formed is exceedingly volatile in a stream of hydrochloric acid gas. If the gaseous current is now conducted into some water the presence of antimhony in the latter fluid may readily be proved by means of hydrogen sulphide. By this combination of reactions antimony may be distinguished with positive certainty from all other metals. The reaction which hydrogyen gas containing antirmonetted hydrogen shows with solution of silver nitrate and with solid potassa will be folnd in ~ 134, 6. 11. If a mixture of a compound of antimony with sodiuqn carbonate and potassium cyantide is exposed on a charcoal support to the reducing cflame qf the blowlipe, brittle globules of METALLIC ANTIMONY are produced, which mnay be readily recognized by the peculiar reactions that mark their oxidation (comnpare ~ 131, 1). 12. In the upper reducing flame of the gas lamp (p. 26) compounds of antimony give a greenish-gray color, and no odor. The metallic incrustation is black, sometimles dull, somletinmles bright. The incGrastation of oxide is white. When moistened with silver nitrate and then blown oil with ammlonia, it gives a black spot of argentous antilnonate (BUNsEN). ~ 132. d. ARSENIC, AS. 75, and ARSENIOUS COMPOuNDS. 1. lIMETALLIC ARSENIC has a blackish-gray color and high metallic lustre, which it retains in dry air, but loses in moist air; the metallic arsenic of commerce is therefore commonly dull, with a diln bronze lustre on the planes of crystallization. Ar

Page  181 ~ 132.] ARSENIC. ARSENIOUS CO.MPOUND. 181 senic is.lot very hard, but very brittle: at a dull red heat il volatilizes without f usion. The fumnes have a most characteris tic odor of garlic. Heated with free access of air, arsenic burns-at an intenise heat with a bluish flame-emitticng white fltmles of arselious oxide, which condelnse on cold bodies. If arselice is heated in a glass tube sealed at the lower elnd the greater part of it volatilizes unoxidized, and recondenlses above the heated spot as a lustrous black sublimlate (arsellical mirror); a very thin coatinlg of the sublimate appears of a brownishblack color. In contact with air and water arsenic oxidizes slowly to arsenious acid. Weak nitric acid converts it, with the aid of heat, into arsenious acid, which dissolves only sparinlgly in all excess of the acid; strolng nlitric acid converts it partially into arse'nic acid. It is insoluble in hydrochloric acid alld dilute sulphuric acid; concentratedl boiling sulphuric acid oxidizes it to arsenious oxide, with evolution of sulphur dioxide. 2. ARSENIOUS OXIDE. As2 03, oienerally presents the appearance either of a tranlsparent vitreous or of a white porcelain-like mass. By trituration it gives a heavy, white, gritty powder Wheni heated it volatilizes in white inodorous fumnes. If the operation is conducted ill a glass tube a sublimate is obtained consisting of slmall brilliant octahedrons and tetrahedrons. Asellious oxide is only difficultly moisteled by water; it coin-ports itself in this respect like a fatty substance. It is sparingly soluble in cold, but more readily in hot water. The solution is asbsumned to contain arsenioas acid, As (O 11)3. This hydroxide, however, is not knlown to exist separately. It is copiously dissolved by hydrochloric( acid, as well as by solution Af soda anld potassa. Ulon boiling with nitrohydrochloric asid it dissolves to arsenic ac(id. It is highlly poisonous. 3. The ARSENITEs are mostly decomlposed upon ignitioni either illto arsenates and metallic arsenic, which volatilizes, or into arsellious oxide and the base with which it was comrbilled. Of the arsenites those only with alkali bases are soluble inl water. The iiisoluble arsenites are dissolved, or at least dec(,onposed, by hydrochloric acid. Anhvdrous ARSENsIOUs CHLORIDE (As Cl3) is a colorless volatile liquid, funuing in the air, which will bear thle addition of a little water, but is decomposed by a laroger amount into arsenious oxide, which partly separates, alld hlydrochloric acid, which retains the rest of the arsenious oxide in soltution. If a solution of arsenious oxide in hydrochloric acid is evaporated by heat, arsenious chloride escapes along with the hydrochloric acid. 4. Jlydroye' sb8aphiide colors aqueous solutions of arsenions acid yellow, but produces no precipitate in them; it fails equally to precipitate aqueous solutions of norinal alkali arsenites, but upon addition of a strong acid a bright yellow precipi. tate of ARSENIOUS SULPHIDE (As2 S3) forlms at once. The salne precipitate fq rms in like malner in the hydrochllloric acid sola

Page  182 182 REACTIONS. GROUP VI. DIV. 11. r[ 132. tion of arsenlites insoluble in water. Even a large excess of ILy drochloric acid does not prevent colmplete precipitation. Alkaliine solutions arie not precipitated. The precipitate is realdily anld completely dissolved by alkalies, alkali carlb)ollates alnd allkali hydrogen carbolnates, and also by allkali suilphides; Iltt it is nearly insoluble in hydrochlloric acid, even thongl1i c(illeelltrated and boiling. Boiling nitric acid decomlposes anua dissolves the precipitate readily. If recently precipitated arsenious sulphide is digested with sulphurous acid and hydrogen potassium sulphite, the precipitate is dissolved; upon heating the solution to boiling the fluid turns turbid, owing to the separation of sulphur, which upon continued boiling is for the greater part redissolved. The fluid contains, after expulsion of the sulphur dioxide, potassium arsenite and potassium thiosulphate 2 (As2 S3) + 8 (K2 S 03) + 8 S O = 4 (KAs 02) + 6 (K2 S2 03) + S3 + 7 S 02 (BUNSEN). The deflagration of arsenions sulphide with sodium carbonate and nitrate gives rise to the formation of sodium arsenate and sulphate. If a solution of arsenious sulphide in potassa is boiled with basic bismuth nitrate or bismuth hydroxide, bismutll trisulphide and potassium arsenite are produced. 5. Ammonium sulphide also causes the formation of ARSENIOUS SULPHIDE. In neutral and alkaline solutions, however, the arsenious sulphide does not precipitate, but remains dissolved as ammonium sulpharsenite (N H4)3 As S3. From this solution arsenious sulphide precipitates immediately upon the addition of a free acid. 6. Silver nitrate leaves aqueous solutions of arsenious acid perfectly clear, or at least produces only a trifling yellowishwhite turbidity in theim; but if a little ammonia is added a yellow precipitate of SILVER ARSENITE (Ag3 As 03) separates. The same precipitate forms of course immediately upon the addition of silver nitrate to the solution of a normal arsenite. The precipitate dissolves readily in nitric acid as well as in ammonia, and is not insoluble in ammnoniuin nitrate; if therefore a small quantity of the precipitate is dissolved in a large amount of nitric acid, and the latter is afterwards neutralized with anmlonia, the precipitate does not make its appearance again, as it remains dissolved in the amnmoniutm nitrate formled. If an anrnmoniacal solution of silver arsenite is heated to boiling, METALLIC SILVER separates, the arsenious acid being converted into arsenic acid. 7. Cupric su8lphate produces under the same circumstances as the silver nitrate a yellowish-green precipitate of cutrIO ARSENITE. 8. If to a solution of arsenious oxide in an excess of solution of soda or potassa, or to a solution of an alkali arsenite mixed with potcassa or voda, a few drops of a dilute solution of cupric sulphate are added, ta clear blue fluid is obtained, which upon boiling deposits a red precipitate of CUPrtOUs OXIDE, leaving potassium arsenate in solution. This reaction is exceedingly dielicate, provided not too much of the cupric sulpllate be used. Even should the red precipitate be so exceedingly minute as to escape detection on looking across the tube, yet it will always be discernible

Page  183 ~ 132.] ARSENIC. ARSENIOUS COM2POUNDS. 183 with great distinctness upon looking down the test-tube. Of course this reaction, although really of great importance in certain instances as a confirmatory proof of the presence of arsenious acid, and more particularly also as a means of distinguishing that acid from arsenic acid, is yet entirely inapplicable for the direct detection of arsenic, since grape sugar and other organic substances produce cuprous oxide from cupric salts in the same manner. 9. If a solution of arsenious oxide mixed with hydrochloric acid is heated with a perfectly clean slip of copper or copper wire, an iron-gray metallic film is deposited on the copper, even in highly dilute solutions; when this film increases in thickness it peels off in black scales. If the coated copper, after washing off the free acid, is heated with solution of ammnonia, the film peels off flrom the copper, and separates in. form of nminute spangles (REINSCH). These are not pure arsenic, but consist of COPPER ARSENIDE'(Cu5 As2). If the substance, either sillply dried or oxidized by ignition in a current of air (which is attended with escape of somle arsenious acid), is heated in a current of hydrogen, there escapes relatively but little arsenic, alloys richer in copper being left behind (FRESENIUS, LIPPERT). It is only after the presence of arsenic in the alloy has been fully demonstrated that this reaction can be considered a decisive proof of the presence of that metal, as antimony and other metals will under the same circumstances also precipitate in a similar manner upon copper. Ill H Fig, 36. 10. If an acid or neutral solution of arsenious acid or any of its compounds is mixed with zinc, water, anld dilate sap/hqvric acid, ARSENETTED iHYDROGEN (AS H-)* is forllced, ill the samiue manner as compounds of antimony give under allalo-ots cilrcumstances antimonetted hydrogen. (Compare ~ 131, 10.) This reaction affords us a most delicate test for the detection of even the most minute quantities of arseic. The opelation * [This gas is a deadly poison, and the utmost care should be taken not to inhale it or smell at the point of delivery. No harm can be experienced if the issuing gas be kept inflamed.- -ED.]

Page  184 184 REACTIONS. GROUP VI. DIV. II. [ 1o. is conducted in the apparatus illustrated by fiT. 36, or in one of simnilar constructionl.* a is the evolution flask, b a bull: intended to receive the water carried with the gaseous current. c a tube filled with cotton wool alnd smlall lumps of calcinll chloride for dryiiing the gas. This ttube is connected witlh b and d by india-rubber tubes which have been boiled in solutionl of soda; d should have an inner dialeter of 7 min. (fig. 37), and must be made of difficultly fusible glass free fromn lead. In experiments requiring great accluracy the tube should be drawn out as shown in fig. 36. The operation is now commenced by evolvinll in ca a rnodFig. 37. erate and uniform current of hydrogen (as, from pure granulated zinc and pure sulphurie acid diluted with 3 parts of water. Addition of a few drops of platinlic chloride will be found useful. When the evolution of hydrogen has proceeded for some time, so that it may safely be concluded the air has been completely expelled from the apparatus, the gas is kihldled at the open end of the tube d. It is advisable to wrap a towel round the flaskl before kindling the gas, to g'uard against accidents in case of an explosion. It is now absolutely necessary first to ascertain whether the zinc and the sulphuric acid are quite free from any admixture of arsenic. This is done by depressing a porcelain dish horizontally upon the flamle to make it spread over the surface: if the hydrogren contains arsenetted hydrogen brownish or brownish-black stains of arsenic will appear on the porcelain; the non-appearance of such stains may be considered as a proof of the freedom of the zinc and sulphuric acid from arsenic. In very accurate experiments, however, additional evidence is required to insure the positive certainty of the purity of the reagents employed; for this purpose the part of the tube d shown in fig. 36 over the flame is heated to redness with a Berzelius or gas-lainp, anld kept for fifteen minutes in a state of ignition: if no arsenical coatiilg makes its appearance in the narrowed part of the tube the agents employed lnay be pronounced free from arsenic,t and the operation proceeded with, by pouring the fluid to be tested for arsenic through the funnel tube into the flask, and afterwards some water to rinse the tube. OQt/y a very little of the flaid oty/ht to bepourecl in t at/ 2ts, as ill cases where the quantity of arsenic present is considerable, alld a somewhat large supply of the fluid is poured into the flask, tle evolution of gas oftenl proceeds with suclll violelmee as to stop the further progress of the experiment. The remainder of the arsenical solution should be added gradually in small portions at a time. * The very convenient form of M.RSH's apparatus recommended by OTTO. f [If no mirror is obtained in 10 to 15 minutes the materials are pure enough for toxical examinations. It is not easy, however, to obtain reagents s, free from arsenic as not to give a faint arsenical mirror in an hour or two. -ED.I

Page  185 ~ 132.] ARSENIC. ARSENIOUS COMPOUNDS. 18 Now if the fluid contains an oxygen or halogen compound of arsenic there is immediately evolved, along with the hydrogen, arlsenetted hyclrogren, which at once imparts a bluish tint to the flame of the kindled gas, owinlg to the combustion of the particles of arsenic separatincg from the arsenetted hydrogren. At the same time white frnmes of arseniouls oxide arise, which condense upon cold objects. If a l)orcelain plate is now depressed npon the flame the separated and not yet reoxidized arsenic condenses upon the plate in black stains, in a similar manner to antimony. (See ~ 131, 10.) The stains formed by arsenic incline, however-e, more to a blackish-brown tint, and show a bright metallic lustre; whilst the antimonial stains are of a deep black color and but feebly lustrous. The arseenical stains may be distingunished, moreover, from. the antihnonial stains by solution of sodiuml hypochlorite (compare ~ 131, 10), which will at once dissolve arsenical stains, leaving antimonial stains unaffected, or removing them oIly after a considerable time. If the heat of a Berzelius or gas-lamp is now applied to the part of the tube d, shown in fic. 36, over the flame, a brilliant arsenical mirror makes its appearance in the narrowed portion of thle tube behind the heated part; this imirror is of a darker ald less silvery-white hue than that produced by antimony under similar circumstances; from which it is, moreover, distinguished by the facility with which it may be dissipated in a (current of hydrogen gas without previous fusion, and by the characteristic odor of garlic emitted by the escaping (unkindled) gas. If the gas is kindled whilst the mirror in the tube is being heated the flame will, even with a very sliTht curellnt of gas, deposit arsenical stains on a porcelain plate. The reactions and properties just described are amply sufficient to enable us to distinguish between arsenical and antimonial stains and mirrors; but they will oftell fail to detect arsenic wvith positive certaillty ill presence of antimolly. In cases of this lkind the following process will serve to set at lest all possible doubt as to the presence or absence of arsenic:Heat the long tube through which the gas to be tested is passilln to relness in several parts, to produce distinct mnetallic mirrols; then translnit through the tube a very weak stream of dry hydrogen sulphide, and heat the metallic mirrors proceedillg from the outer towards the inner border. If arsenic alone is present yellow arsenious sulphide is formed inside the tube; if antimony alone is present an orange-red or black antimno nious sulphlide is produced; and if the mnirror consisted of both metals tile two sulphides appear side by side, the arsenious sul. phide, as the more volatile, lying invariably before the anlltiollious sulphide. If you now transmit through the tube containing either sulphide, or both sulphides together, dry hydrochloric gas, without applying heat, no alteration will take

Page  186 186 REACTIONS. GROUP VI. DIV. II. [~ 132 place if. arsenious snulphide alone is present, even though the gas l)e transmitted throu-gh the tube for a considerable time. If antimonious sulphide alone is present this will entirely disappeal, as already stated (~ 131, 10), and if both sulplhides are present, the antinonious sulphide will immediately volatilize, whilst the yellow arsenious sulphide will remain. If a small quantity of ammonia is now drawn into the tube the arsenious slulphide is dissolved, and may thus be readily distinguished from sulphur which mnay have separated. Mly personal experience has convinced nme of the infallibility of these combined tests for the detection of arsefice. The reactionl of hydrogen containing arsenetted hydrogen witl solution of silver nitrate will be found in ~ 134, 6. MARsH was the first whlo suggested the method of detecting arsenic by the production of alsenetted hydrogen. [11. When to a solution of arsenious chloride or of arsenious oxide, or of an arsenite in fumninzg Iydrochloric accid, crystals or Fig. 38. highly concentrated solutions of stanlnouzs chloride are added, and the still fulming mixture boiled, all the arsenic present separates in darkl-brown crystalline flocks of an ALLOY OF ARSENIC AND TIN (containing 3 to 6 per cent. of tini). In dilllte hydrochloric acid (with less than 20 per cent. II Cl) the pliecipitationl is incomplete or does not occur at all. The precipitate after settling may be washed, first with hydrochloric acid, sp. gr. 1'1, then with water or alcohol, and dried at a geltle warmth. Aportion of it is then heated in a tube like that shown in fig. 38, to procure the arsenical mirror. In liquids containing very minute traces of arsenic, the precipitate remains a long time suspended in the liquid, giving it a brownish color. This color distinctly appears in solutiolls containing but 1000000 of arsenic. Antimony is not thrown down by stannous chloride under any circumnstances whatever. BETTENDORF.] 12. If a small lump of arsenious oxide (a) be introduced into the pointed end of a drawn-out glass tube (fig. 38), a fragment

Page  187 ~ 132.] ARSENIC. ARSENIOUS COMPOUNDS. 187 of quite recently ignited charcoal (b) pushed down the tube to within a short distance of the arsenious oxide, and filrst the charcoal then the arsenious oxide heated to redlless, a MIRROR OF METALLIC ARSENIC will form at c, owing to the reduction of the arsenious oxide vapor by the red-hot charcoal. If thile tube be now cut between b and c and then heated in an inclined position, with the cut end c turned upwards, the metallic mirror will volatilize, emitting the characteristic odor of garlic. This is both the simplest and safest way of detecting pure arsenious oxide. 13. If arsenites, or arsenious oxide, or arsenious sulphide are fused with a mixture of equal parts of dry sodium carbocnate and potassium cyanide the whole of the arsenic is reduced to the metallic state,* and so is the base also, if easily reducible; the eliminated oxygen converting part of the potassium cyanide into potassium cyanate. In the reduction of arsenious sulphide potassium sulphocyanate is formed. The operation is conducted as follows:-Introduce the perfectly dry arsenical compound into the bulb of a small bulb-tube (fig. 39), and cover it with six times the quantity of a perfectly dry mixture of equal parts of sodium carbonate and of potassium cyanide. The whole quantity must not much more than half fill Fig. 39. the bulb, otherwise the fusing potassium cyanide is likely to ascend into the tube. Heat the bulb grently; should some water still escape, wipe the'nside of the tube perfectly dry with a twisted slip of blotting paper. It is of the highest importance for the success of the experiment to bestow great care upon expelling the water, drying the mixture, and wiping the tube clean and dry. Apply now a strong heat to the bulb, to effect the reduction of the arsenical compound, and continue this for some time, as the arsenic often requires some timle for its complete sublimation. The mirror which is deposited at b is of exceeding purity. It is obtained from all arsenites whose Lbases remain either altogether unaffected, or are reduced to such metallic arsenides as lose their arsenic partly or totally upon the simple application of heat. This method deserves to be particularly recommended, even in cases where only minute quantities of arsenic are present. For the direct production of arsenic from arsenious sulphide it is superior to all other methods. The delicacy of the reaction is heightened by heating the mixture in a stream of dry carbon dioxide. The most accurate and satisfactory results * [According to Rose and Mohr, the reduction of the arsenic is never complete, and when excess of sulphur is mixed with the As2 Ss, no metallic arse. nic whatever can be made to appea:. —ED.]

Page  188 188 REACTIONS. GROUP VI. DIV. II. [ 1832. are obtained in the following manner. Figs. 40 and 41 sh( w the apparatus in which the process is conducted. The self-regulating gas-generating apparatus is like that already described for preparing hydrogen sulphlde (see ~ 34, fig. 35), but is charged with lumpis of nmarble, and the delivery tube passes a cork in the mouth of a flask containing oil of vitriol, in order to dry the gas, whence it streams tlrougll the reduction tube, which should have an inner diameter of about Fig. 40. three-eighths of an inch. This tube is represented of one-third its proper size, in fig. 41. When the apparatus is full of carbon dioxide, triturate the perfectly dry arsenious sulphide or arsenite in a slightly heated mortar with about twelve parts of a well-dried mixture consisting of three parts of sodium carbonate and one part of potassium cyanide. The mixture must of course be quite free from arsenic (~ 46). Put the powder upon a narrow slip of paper, bent into the shape of a gutter, and push this into the reductiontube down to e; turn the tube now half-way round its axis, when the mixture will drop into the tube between e and d, every other part remaining perfectly clean. Connect the tube now with the gas apparatus, and pass through it a moderate stream of carbon dioxide. Heat the tube in its whole length very gently until the mixture in it is quite dry. When every trace of water is expelled, reduce the gas stream so that the single bubbles d, e e h Fig. 41. pass through the sulphuric acid at intervals of one second, and heat the reduction tube to redness at c (fig. 41). When c is red-hot, apply tlhe flanme of a second lamp to the mixture, proceeding from d to e, until the whole of the arsenic is expelled. The far greater portion of the volatilized arsenic recondenses at h, whilst a small portion only escapes through i, imparting to the air a garlic odor. Advance the flame of the second lamp slowly and gradually up to c, by which means the whole of the arsenic which may have condensed in the wide part of the tube is driven to h. Wher you have effected this, close the tube at the point i by fusion, and

Page  189 ~ 133.] ARSENIC COMIPOUNI)S. 189 apply heat, proceeding from i towards h, by which means the extent of the mirror is narrowed, whilst its beauty and lustre are correspondingly increased. In this manner perfectly distinct mirrors of arsenic may be produced from'0002 grnm. of arsenious sulphide, No mirrors are obtained by this process from antimonious sulphide, or from ally other compound of antimony. 14. If arsenious oxide or an arsenite is exposed oil charcoal to the reducingllfamze of the blowpipje a highly cllalacteistic garlic odor is emitted, luore especially if soine sodium carbonate is added. This odor has its origin in the reduction and reoxidation of the arsenic, and enables us to detect very milnute quantities. This test, however, like all others that are based upon the indications of the sense of smnell, cannot be implicitly relied on. ~ 133. e. ARSENIC COMPOUNDS, As. 75. 1. Orthoarsenic acid crystallizes in prisms or plates of the formula As 0,411. 11, 0 O or As () () II),. 1 11, 0, which de liquesce in the air. The water of crystallization escapes at 100~; at 180~ under loss of water, it is converted into pyroarsenic acid (As, 0, I-,), at 2060 it passes into mletarseniic acid (As O, I1). IIeated to faint redness these hydroxides leave arsellic oxide (As, O,). This agaill oi strong igllitionl splits inlto oxygen and arsenious oxide. Arsenlic oxide dissolves but slowly in water. The meta- and pyroarselic acids dissolve in water to orthoarsenic acid, and the lleta- and pyroarseiiates whllicll are soluble dissolve at once as orthoarsellnates. Arseiiie acid is poisonous. 2. Most of the ARSENATES are insoluble in water. Of the orthoarsenates those with alkali bases alone are soluble in water. Most of the di- and triinetallic arsenates can bear a strong red heat without suffering decomposition. The moliometallic orthoarsenates lose acid upon ignition, which passes off in the form of arsenlious oxide anld oxygen. A solution of arsenic acid or of an arselnate in hydrochloric acid imay be boiled for a long time without losing arsenic, provided too much hydrochloric acid is not present. But when the residual fluid contains about half its volume of hydrochloric acid of specific gravity 1-12, traces of arsenious chloride begin to escape with the hydrochloric acid. 3. Hydroyen svutphide fails to precipitate alkaline and neutral solutions; but in acidified solutions it causes first redlletion of the arsenic acid to arsenious acid, with separation of sulphur, thenl precipitation of arsenious sulphide. This process coltinues until the whole of the arsenic is thrown down as As, 2, mixed witi 2 S (WXACcEENRODER, LUDWIG, II. ROSE). The action never takes place immediately, and in dilute solutions frequent

Page  190 190 REACTIONS. GROUP VI. NV. v.. [ 133, ly only after the lapse of a considerable tilne (twelve to twentyfour hours, for instance). Heating (to about 70~) greatly accelerates the action. If a solution of arsenic acid, or of an arsenate, is mixed with snlphurous acid, or with sodium sulphite and somie hydrochloric acid, the sulphurons acid is converted into sulphurili acid, and the arsenic acid reduced to arsenious acid; application of heat promotes the change. If hydrogen sulphide is now added, the whole of the arsenic is ilmmlediately thrown down as arsenious sulphide. 4. Aminmoniurmn su]phide, especially upon boiling and evaporating therewith, converts the arsenic acid in neutral anld alkaline solutions of arsenates into ARSENIC SULPIIDE (As2 S,), whiChl remains in solution as arnmonliun sulpharsenate (N H4)3 As S,4. Upon the addition of an acid to the solution this salt is decomposed, and arsenic sulphide precipitates. The separation of this precilitate proceeds inmore rapidly than is the case when acid solutions of arsenates are precipitated with hydrogell sulphicle. It is pmromnoted by heat. The precipitate formed is As2 8,, and not a mixture of As2 S3 with S2. 5. Silver imitrate produces under the circumstances stated ~ 132, 6, a highly characteristic reddish-brown precipitate of SILVER ARSENATE (Ag, As 04), which is readily soluble in dilute nitric acid and in aimmonia, and dissolves also slightly in aIimonium nitrate. Accordingly, if a little of the precipitate is dissolved in a large proportion of nitric acid, neutralization vith amlmonia often fails to reproduce the precipitate. The ammonliacal solution of silver arsellate does nlot deposit silver ulpon boiling (difference between arsenic and arsenious acids). 6. (Jupric sulphate produces under the circumstances stated ~ 132, 7, a greellish-blue precipitate of HYDROGEN CUPRIC ARSENATE (I-I (u As 04). 7. If a dilute solution of arsenic acid mixed with some hydrochloric acid is heated with a clean slip of copper the metal remains perfectly clean (WVERTIIE, I1mINSCH); but if to one volume of the solution two volumes of concentrated hydrochloric acid are added, a gray film is deposited on the copper, as in the case of arsenious acid. The reaction is under these circumstances equally delicate as with arsenious acid (REINSCII). 8. With zinc in presence of sulphuric acid, with stannous chloride, with potassium, cyanide, and before the blowpipe, the compounds of arsenic acid comport themselves in the same way as those of arsenious acid. If the reduction of arsenic acid by zinc is effected in a platinum capsule, the platinum does not turn black (difference from antimony). 9. If a solution of arsenic acid, or of an arsenate soluble in water, is added to a clear mixture of magnesium sulphate, ammoniuzn chloride, and a sufficient quantity of ammonia,c* a crystalline precipitate of AM3MONIUM MAGNESIUM ASJENArTE * The " magnesia mixture" is prepared by dissolving together 1 part of crystallized magnesium sulphate and 2 parts of pure ammonium chloride in S parts of water, adding 4 parts solution of ammonia, and filtering after stand. ing some days.

Page  191 ~ 134.] SEPARATIONS. METALS OF GROUP VI. DIV. II. 191 (N I, Mg As 04. 6 IT, O) separates; from concentrated solutions immediately, from dilute solutions after some time. If a slnall portion of the precipitate is dissolved on a watch-glass in a drop of nitric acid, a little silver nlitrate added, and the soluticn touched with a glass rod dipped in ammonia, brownish-red silver arsenate is formed. Or if a small portion of the precipitate is dissolved in hydrochloric acid and hydrogen sulphide is passed into the solution with warming, a yellow precipitate is formed. (Differences between ammonium magnesium arsenatc and phosphate.) ~ 134. RPeccaitalation and rerncarks.-I will here describe first the different ways adapted to effect the detection or separation of tin, antimony, and arsenic, when present together, and afterwards the means of distinguishing between the several oxides and acids of the tllree mnetals. 1. If you have a mixture of sulphides of tin, antimony, and arsenic, triturate 1 l)art of it with 1 part of dry sodiulm carbonate and 1 part of sodium nitrate, and transfer the mixed powder gradually to a small porcelain crucible containing 2 parts of sodium nitrate kept in a state of fusion at a not overstrong heat; oxidation of the sulphides ensues, attended with slight deflagration. The fused mass contains stannic oxide, sodium arsenate and antimonate, with sodium sulphate, carbonate, nitrate, and nitrite. You must take care not to raise the heat to such a degree, nor continue the fusion so long, as to lead to decomposition of the sodium nitrite. with formation of sodium stannate soluble in water. Upon treating the mass with a little cold water stannic oxide and sodium antimonate remain undissolved, whilst sodiuln arsenate and the other salts are dissolved. If the filtrate is acidified with nitric acid, and heat is applied to remove carbonic and nitrous acids, the ARSENIC ACID may be detected and separated,' either with silver nitrate, according to ~ 133, 5, or with a mixture of magnesium sulphate, ammnonium chloride, and ammonia, accordillg to ~ 133, 9. If the undissolved residue, consisting of stannic oxide and sodiumn antimonate is, after being( washed once with cold water alnd three times with dilute alcohol, treated with some hydrochloric acid in the lid of a platinum crucible, and a gentle heat applied, the mass is either completely dissolved or, if the tin is present in a large proportion, a white residue is left undis. solved. If, regardless of the presence of this latter, a fragment of zinc is added, the compounds are reduced to the metallic state, when the ANTIMONY will at once reveal its presence by blackening the platinum. If, after the evolution of hydrcgen has nearly stopped, the remainder of the zinc is taken

Page  192 192 SEPARATIONS. MIETALS OF GROuP VI. DIV. IT. [~ 134. away, and the contents of the lid are heated with some hydrochloric acid, the TIN dissol\ves to stanlnous chloride, whilst the antimony is left undissolved in the form of black flakes. The tin may then be more distinctly tested in the solution, with mercuric chloride, or with a mixture of ferric chloride and potassium ferricyanide, and the antimony, after solution in a little aqua regia, with hydrogen sulphide. As this method of detecting arsenic, tin, and antimony in presence of each other is adopted in the systematic course of analysis, I have here sil mply explained the principle upon which it is based, and refer for the details of the process to ~ 185. 2. If the mixed sulphides, after being freed from t'he greater part of the adhering water, by laying the filter containing them on blotting paper, are treated with fuming hydrochloric acid, with application of a gentle heat, the sulphides of antimony and tin dissolve, whilst tile arsenious sulphide is left almost completely undissolved. By treating this with aimmonia, and evaporating the solution obtained, with addition of a small quantity of sodium carbonate, an arsenical mirror may easily be produced from the residue, by means of potassium cyanide and sodium carbonate in a stream of carbonic acid gas (~ 132, 13). The solution, which contains the tin and the antimony, may be treatted as stated in 1. If a great excess of antimony is present the latter solution may also bo mixed with the transparent portion of commercial " carbonate of ammonia," in excess, and boiled; when a large proportion of the antimony will dissolve, leaving stannic oxide behind, mixed with but little alltimonious oxide, in which undissolved residue the tin may now be the more readily detected by the method described in 1 (BLoxXa). 3. If the mixed slllphides are digested at a gentle heat with some solid ammonium carbonate and water, arsenious sulphide dissolves, whilst the antimony and tin sulphides remain uncldissolved. But this separation is not quite absolute, as traces of antimony are apt to pass into the solution, whllilst some arsenious sulphide remains in the residue. The arsenious sulphlide precipitating from the alkaline solution upon acidifying this latter with hydrochloric acid must therefore, especially if consisting only of a few flakes, after washing, be treated with ammonia, the solution evaporated, with addition of a small quantity of sodium carbonate, and the resi — due fused with potassium cyanide in a stream of carbon dioxide, to make quite sure by the production of an arsenical imirror. The residue, insoluble in ammonium carbonate, should be treated as directed in 2. 4. If tile sulph.ides of antimony, tin, and arsenic are dissolved in potassium sulphide, a large excess of a concentrated solution of sulphurous acid added, the mixture digested for some time on the water-bath, boiled until all sulphurous acid is expelled, then filtered, the filtrate contains all the arsenic as arsenious acid (which may be precipitated from it by hydrogen sulphide), whilst antimonious sulphide and stannic sulphide are left behind undissolved (BUNSEN). These latter may then be treated as directed in 2. 5. In the analysis of alloys, metastannic acid, antimoniouss >xide, and arsenic acid are often obtained together as a resimlte inlsolubl)e in nitric acid. The best wav is to fuse this residute withl sodium hydroxide in a silver crucible, to treat the mnass with water, and add one-third (by volume) of alcohol; thenl to filter the fluid off from the sodliln antimonate. whichl remains undissolveil, alld wash the latter with alcohol mnixed wvith a few drops >f #olution of sodiuln carbonate. In the

Page  193 ~ 134.] SEPARATIONS. METAIS OF GROUP VI. DIV. It. 193 presence of much tin it is advisable to repeat the above treatment on the residue, in order to extract all the tin. The filtrate is acidified with hydrochloric acid, and the tin and arsenic are then precipitated as sulphides, with the aid of heat. On heating the precipitated sulphides in a stream of hydrogen sulphide the whole of the tin is left as sulphide, whilst the arseniouis sulphide volatilizes, and may be received in solution of ammonia (II. ROSE). 6. For the method of separating antimony and arsenic, and distinguishing between the two metals, by treating the mirror produced by MARSH's process, with hydrogen sulphide, and separating the resulting sulphides by means of hydrochloric acid gas, I refer to ~ 132, 10. Antimony and arsenic may, however, when llixed together in form of hydrogen compounds, be separated also in the following ways. a. Conduct the gases mixed with an excess of hydrogen, first through a tube containing glass splinters moistened with solution of lead acetate to retain the hydrochloric and hydrosulphuric gases, then in a slow stream into a solution of silver nitrate. Almost all the antimony in the gas falls down as black silver antimonide (Ag3 Sb), whilst the arsenic passes into the solution as arsenious acid, with reduction of the silver, and may be detected in the fluid! as silver arsenite, by cautious addition of ammonia, or-after precipitating the excess of silver by hydrochloric acid —by means of hydrogen sulphide. Since, however, a little antimony always passes into the solution, the plrecipitate by hydrogen sulphide must not be put down as arsenious sulphide without further examination, according to ~ 132, 13. In the precipitated silver antimonide, which is often mixed with much silver, the antimony may be most readily detected, by heating the precipitate- thoroughly freed from arsenious acid by boiling with water-with tartaric acid and water to boiling. This will dissolve the antimony alone, which may then be readily detected by means of hydrogen sulphide in the solution acidified with hydrochloric acid (A. W. W. FMARN). b. Conduct the gases mixed with an excess of hydrogen through a rather wide glass tube, 3 or 4 inches of which are filled with caustic potassa in small lumps. The potassa decomposes the antimonetted hydrogen entirely, becoming coated with a lustrous film of metal. The arsenetted hydrogen is on the contrary not decomposed, and may be detected readily on its exit from the tube by the production of the arsenical mirror (~ 132, 10) or by its action on solution of silver nitrate (DRA.GENDOFF). 7. Stannouis and stannic compounds may be detected in presence of each other, by testing one portion of the solution for the first with mercuric chloride, auric chloride or a mixture of potassium ferricyanide and ferric chloride, and another portion for stannic compounds, by pouring it into a concentrated hot solution of sodium sulphate. For the last test the solution must not contain much free acid. 8. Antimonious oxide in presence of antimonic acid may be identified by the reaction described in ~ 131, 9. Antimon'ic acid in presence of antimo niouzs oxide, by heating the oxide, which must be free from other bodies, with hydrochloric acid and potassium iodide (~ 131, 2 and 3). 9. Arseniozus acid and arsenic acid in the same solution may be distinguished by means of silver nitrate. If the precipitate contains little arsenate and much arsenite of silver it is necessary, in order to identify the former, to add cautiously 13

Page  194 194 RARE METALS. GROUP VI. [~ 135. and drop by drop most highly dilute nitric acid, which dissolves the yellow silver arsenite first. A still safer way to detect small quantities of arsenic acid in presence of arsenious acid is to precipitate the solution with a mixture of magnesium sulplhate, amnmonium chloride, and ammonia (~ 132, 9), by which means an actual separation of the two acids is effected. Arsenious acid may be recognized in presence of arsenic acid by the imnmediate precipitation of the acidified solution with hydrogen sulphide in the cold; also by the reduction of cuplic oxide ill alkaline solution; also by the separation of metallic silver by boiling the ammoniacal solution of the silver salts. To ascertain the degree of sulphluration of arsenic in a sulphnr salt, boil the alkaline solution of the salt under examination with bismuth hydroxide, filter off fromn the bismuth trisnlphide forlned, and test the filtrate for arsenious and arsenic acids. To distinguish between the arsenious and arsenic sulphides, extract first the sulphur which may be present by means of carbon disulphide, then dissolve the residue in ammonia, add silver nitrate in excess, filter off the silver sulphide, and observe whether arsenite or arsenate of silver is formed upon addition of ammonia. Special Reactions of the r arer Metals of the Sixth Group. ~ 135. a. IRIDIUM, Ir. 198. IRiDIUM is found in combination with platinum and other metals in platinum ores; also, and more especially, as a native alloy of osmium and iridium. Alloyed with platinum, it has of late been employed for crucibles, etc. Iridium resembles platinum, but it is brittle; it fuses with extreme difficulty. In the compact state, or reduced at a red heat by hydrogen, it dissolves in no acid, not even in aqua regia (difference between iridium and gold and platinum); reduced in the moist way, say by formic acid, or largely alloyed with platinum, it dissolves in aqua regia to tetrachloride. Potassium disulphate in a state of fusion will oxidize, but nlot dissolve it (difference between iridiuml and rhodium). It oxidizes l)y fusion with sodium hydroxide, with access of air, or by fusion with sodium nitrate. The sodium periridiate which is formed in this process dissolves partially in water; by heating with aqua r'gia it gives a deep black-red solution of iridic sodium chloride, Ir C14. 2 Na C1. If iridium powder is mixed with sodium chloride, the mixture heated to incipient redness, and treated with chlorine gas, iridic sodium chloride is formed, which dissolves in water to a deep red-brown fluid. Potassa, added in excess, colors the solutions greenish, a little brownish-black iridic potassium chloride precipitating at the same time. If the solution is heated, and exposed some time to the air, it acquires at first a reddish tint, which changes afterwards to azure blue (characteristic difference between iridium and platinum); if the solution is now evaporated to dryness, and the residue treated with water, a colorless fluid is obtained, with a blue deposit of iridic hydroxide, Ir (O H)4, left undissolved. Hydrogen sultphide in the first place decolorizes solutions of iridic tetrachloride,

Page  195 ~ 135.] MOLYBDENUM. 19a5 irid.ious chloride, Ir2 C13, is formed, with separation of sulphur, and finally brown iridium sulphide precipitates. Amfmonium sulphide produces the same precipitate, which redissolves readily in an excess of the precipitant. Potassium cltloride precipitates iridic potassium chloride as a dark-brown powder, insoluble in a concentrated solution of potassium chloride. Am moniuln chloride precipitates from concentrated solutions iridic ammonium chloride in the form of a dark-red powder, consisting of microscopic octahedrons, insoluble in concentrated solution of ammoniutn chloride. This double-salt (and also the corresponding potassium compound), especially when in hot solution, is turned olive-green by potassium nitrite, owing to the formation of iridious potassium chloride Ir2 Cl6. 6 K C1. 6 H2 0; this double salt crystallizes out on cooling. On heating or evaporating the green solution with an excess of, potassium nitrite'it turns yellow, and when boiled deposits a white precipitate which is hardly soluble in water and hydrochloric acid. (This reaction may be taken advantage of to separate iridium from platinum, GIBBS.) If the iridic ammonium chloride is dissolved in water by boiling, and oxalic acid is added, a reduction to the iridious salt takes place, and on this account the solution remains clear onl cooling (here iridium differs from platinum, C. LiEA). If stannous chloride is added to iridic chloride and the solution is boiled, and then excess of potassa is added and the mixture is boiled again, a leather-colored precipitate is formed. Ferrous sul#phate decolorizes the solution, but does not produce a precipitate. Zinc precipitates black metallic iridium. On suspending iriclic hydroxide in a solution of potassium sulphite, saturating with sulphurous acid and boiling with renewal of the evaporating water till all the free sulphurous acid is expelled, the whole of the iridium is converted into insoluble iridic sulphite (any platinum which may be present will remain dissolved as platinous potassium sulphite, C. BIIntNBAUI). I(nited with sodiuzmn carbo;nate in the upper oxidizing flame, compounds of iridium yield the metal, which when washed out is gray, devoid of lustre, and without ductility. b. MOLYBDENUM, 1Mo. 96. MOLYBDENUM is not largely disseminated in nature, and is found only in moderate quantities, more especially as molybdic sulphide AIo S2 and as lead molybdate (yellow lead ore). Since the use of ammonium molybdate as a means of detecting and determining phosphoric acid, molybdenum has acquired considerable importance in practical chemistry. MiOLYBDENUM is tin-white and hard; when heated in the air it oxidizes, it is soluble in nitric acid and very difficult to fuse. The MONOXIDE iS black, the DTOXrDE is dark-brown. When heated in the air or treated with nitric acid the metal and oxides are all converted into TRIOXIDE or molybl)ic anhydride Mo 03. The trioxide is a white porous mass, which in water separates into fine scales, and dissolves to a slight extent as molybdic acid; it fuses at a red heat, in close vessels it volatilizes only at a very high telmperature, in the air it volatilizes easily at a red heat and sublimes to transparent laming and needles. On igniting it in a current of hydrogen it is first converted into the dioxide, and afterwards by strong and long-continued heating into the metal. The non-ignited trioxide dissolves in acids. The solutions are colorless; the hydrochloric solution is colored by contact with zinc soon, on addition of stannous chloride immediately; the color being brown, green or blue according to the proportion of reducing agent and the concentration of the fluid. Digested with copper the sulphuric acid solution turns blue, the hydrochloric acid solution brown. The reaction often requires some time. [Molybdic acid heated with a few drops of stronq sulphuric acid on platinum foil until copious fumes are evolved, is converted into molybdous sulphate, and when the mass is allowed to cool, and is then breathed upon, it acquires an ultramarine blue color (dis

Page  196 196 RARE METALS. GROUP TI. [~ 1 35. tinction from Ti. W. and V.; SCIIi5NN, MIMASCIKE). ED.] P)taSSiumfcro 0cyanide produces a reddish brown p)recipitate, i)JWshio oqf galls a green precipi. tate. Hlydrolgent sulohide, added in small proportion, imparts a blue tint to the solutions of trioxide; added in larger p)roportion it lprodluces a br>ownlishblack precipitate; the fluid over the latter at first appears green. But after being allowed to stand for some time, and heated, additional quantities of hydrosullphuric acid being repeatedly conducted into it, the whole of the molybdenum present will ultimately though slowly separate as brownishblack molybdenunm trisulphide Mo S3. The precipitated mlolyldenuml trisulphide dissolves in sulphides of the alkali metals; acids precipitate from the sulphomnolybdates thus formed molybdenum trisulphide again, application of heat promotes the separation. By heating to redness in the air, or by heating with nitric acid, molybdenum sulphides are converted into trioxide. If a solution of trioxide in excess of ammllonia (i.e. ammonium molybdate) is mixed with yellow ammonium sulphide, and boiled for some time, a dark-red liquid of great depth of color is formed in addition to the b)rownish-black precipitate, unless a very large excess of ammonium sulphide is present. Potassium sulphocyanate, if added to a solution of trioxide or of a molybdate containing hydrochloric acid, produces no color until zinc is added, when the fluid becomes crimson; the coloration is due to the formation of a sulphocyanate of molybdenum. Phosphoric acid does not destroy the color (difference from ferric sull)hocyanate). On shaking the red fluid with ether, the latter becomes colored (C. D. BRAUN). To recognize molybdenum in presence of ferric oxide and nitrogen tetroxide, which likewise give a red color with potassium sulphocyaniate, the solution is treated with sulphurous acid or an alkali sulphite and hydrochloric acid, until no coloration is produced in it by potassium sulphocyanate alone. Ferric oxide is thus reduced to ferrous oxide, and nitrogen tetroxide to a lower oxide. On now adding solution of potassium sulphocyanate and a fragment of zinc, the reaction at once becomes manifest.- (EDITOR.) [Miolybdic solutions acidified with dilute hydrochloric acid impart a brown tint to turmeric paper.-(A. MuiLLER.) (Compare zirconia and boric acid). ED.] Molybdenum trioxide dissolves readily in solutions of alkalies and alZkali carbonates; from concentrated solutions nitric acid or hydrochloric acid throws down mnolybdic acid (Mo 0 (O H)2?), which redissolves in a large excess of the precipitant. The solutions of molyl)dates of the alkali mIetals are colored yellow by hydrogen su7phide, and give afterwards, upon addition of acids, a brownish-black precipitate. For the deportment of molybdic acid with orthophosphoric acid and ammonia, see ~ 142, 10. Molybdenum trioxide volatilizes when heated on charcoal in the oxidizing flame, coating the charcoal with a yellow, often crystalline, powder, which turns white on cooling. In the 7reducingyflame the acid suffers reduction to the metaillic state, the molybdenum is obtained as a gray powder by elutriating the charcoal support. Molybdenum sulphide gives in the oxidizing flame sulphur dioxide and an incrustation of molybdenlum trioxide on the charcoal. c. TUNGSTEN, W. 184. This metal most commonly occurs in nature in the forms of calcium tungstate and of the ferrous manganous tungstate called wolfram. Obtained by the reduction of tungstic oxide in a current of hydrogen at an intense red heat, it is an iron-gray powder, very difficultly fusible. This powder is converted by ignition in the air into tungstic oxide (or anhlydride) (W 03); by ignition in a current of dry air-free chlorine into dark violet hexach loride (W Cle) which sublimes. and the still more volatile red peutachloride. These chlorides are decomposed by water into the corre

Page  197 ~ 135.] TELLURIUM. 197 sponding hydroxides ana hydrochloric acid. Tungsten is insoluble oi scarcelvy soluble in acids, even in aqua regia, and also in potassa; it dissolves, however, in the latter if mixed with sodium hypochlorite. TUNGSTEN DIOXIDE is brown; by intense ignition with free access of air it is converted into tungstic oxide (trioxide). TUNGSTIC OXIDE is lemon-yellow, fixed, insoluble in water and acids. By fusing tungstic oxide with l)otassium disulphate, and treating the fused mass with water, an acid solution is obtained, which contains no tungstic acid; after the removal of this solution the residue, consisting of potassium tungstate and a larle excess of tungstic acid, completely dissolves in water containing ammoniuma carbonate (means of separating tungstic from silicic acid). Alkali tungstates soluble in water are formed readily by fusion with alkali carbonates, blut with difficulty by boiling with solution of the same. Hydrochloric acid, nitric acid, and sulphuric acid produce in the solution of these tung states White precipitates of tungstic acid (W O (O H)4) which turn yellow (W 02 (O H)2) on boiling and are insoluble in an excess of the acids (difference from molybdic acid), but soluble in ammonia. Upon evaporatincg with an excess of hydrochloric acid to dryness, and treating the residue with water, the tungstic acid is left undissolved. Barium chloride, calciufl chloride, lead acetate, silver nitrate, mercurous nitrate produce white precipitates. Potassiu nferrocyanide, with addition of some acid, colors tha fluid deep brownisll-red, and after some time produces a precipitate of the same color. Tincture of galls, with a little acid added, produces a brown precipitate. Hydrogen sulphide barely precipitates acid solutions. Ammoniumm smulphide fails to precipitate solutions of alkali tunogstates; upon acidifying the mixture light-brown trisulphide precipitates, which is slightly soluble in pure water, but insoluble in water containing salts. Stannous chloride produces a yellow precipitate; on acidifying witl hydrochloric acid, and applying heat, this precipitate acquires a beautiful blue color (highly'delicate and characteristic reaction). If solutions of alkali tungstates are mixed with hydrochloric acid, or better still, with an excess of phosphoric acid, and zinc is added, the. fluid acquires a beautiful blue color. Fusing sodium metaphosphate dissolves tungstic oxide. The l)ead, exposed to the oxidizing flame, al)pears clear, varying from colorless to yellowish; in the reducing flame it acquires a pure blue color, and upon addition of ferrous oxide a blood-red'color. By mixing with a little sodium carlbotate, and exposing in the cavity of the charcoal support to the reducing flame, tungsten in powder is' obtained, which may b)e separated by washing. The tungstates which are insoluble in water may, most of them, be decomposed by digestion with acids. Wolfram, which strongly resists the action of acid, is fused with alkali carbonate, when water will dissolve out of the fused mass the alkali tungstate formled. d. TELLURIUM, Te. 128. TELLURIUM is not widely disseminated, and is found in small quantities only in the native state, or alloyed with other metals, or as tellurous oxide. It is a white, brittle, but readily fusible metal, which may be subllimed in a glass tube. Heated in the air it ulrns with a greenish blue flale, emitting thick white fumes of tellirous oxide. Tellurium is insoluble in hvdrochloric acid, but dissolves readily in nitric acid to tellurous oxide (Te 02). Tellurium in powder dissolves in cold concentrated sulphuric acid to a purple- colored fluid, froml which it separates again upon addition of water. TELLUtROUS OXIDE is white; at a gentle red heat it fuses to a yellow fluid; it is volatilized by stronog ignition in the air, forming no crystalline sublimate. It dissolves readily in hydrochloric acid, sparingly in nit.ric acid, freely in solution of potassa, slowly in ammonia, barely in water. TErLLUROUs HYDROXIDE (H2 Te 03) or TELLUROUS ACID is white; it is perceptibly soluble in cold water, and dissolves in hydrochloric acid and in nitric acid,

Page  198 198 RARE MIETALS. GROUP VI. [I 135 forming tellurous chloride (To C14) and nitrate (Te (N 03)4). Addition of wiate to these salts throw down the hydroxide again, and from the nitlic.cicd solution tellurous oxide separates after some time as a crystalline precipitate. Alkalies and alkali carbonates throw down from tellurium chloride solution white hydroxide which is soluble in an excess of the preciiitant. Hy.drogen sul2phide produces in acid solutions a brown precil)itate of TELLUROUS SULPIIIDE (Te S2, in color like stannous sulphide), whichl dissolves very freely in amlnonium sulphide. Sodium sulphite, stmanous c/lor ide. and zinc precipitate black metallic tellurium. By fusing tellurium or tellurites with alkali nitrates and carbonates ALKALI TELLURITES ('. J.. Na12 Te 03) are formed. The fused mass is soluble in water. The solution remains clear upon acidifying with hydrochloric acid in the cold; but up)on boiling chlorine is disengaged, and tellurous chloride formed, and the solution is therefore now precipitated by water if the excess of acid is not too great. If tellurium, its sulphide, or an oxygen compound of t he metal is fused with potassium cyanide in a stream of hydrogen, a tellurium potassium cyanide is formed. The fused mass dissolves in water, but a current of air throws down from the solution the whole of the tellurium (difference and means of separating tellurium from selenium). When tested in the dry way by BuNsEN's method (p. 26) the compounds of tellurium give a grayish-blue color in the upper reducing flame, while at the same time the upper oxidizing flame appears green. The volatilization is unaccompanied by any odor. The incrustation produced by reduction is black, with a blackish-brown edge, and gives a crimson solution when heated with concentrated sulphuric acid. The incrustation qf' oxide is white, scarcely visibie: stannous chloride colors it black, metallic tellurium being separated. When heated with sodium carbonate in the stick qf charcoal, compounds of tellurium yield sodium telluride, which when placed on clean silver and moistened produces a black stain, and when treated with hydrochloric acid (in the presence of enough tellurium) gives an odor of telluretted hydrogen with separation of tellurium. e. SELENIUM, Se. 79'4. SELENIUM occurs in nature in the form of selenides of metals. It is found occasionally in the dust of roasting-furnaces, and also in the Nordhausen oil of vitriol. It resembles sulphur in some respects, tellurium in others. Fused selenium is grayish-black; it volatilizes at a high temperature, and may be sublimed. Heated in the air it burns to selenious oxide (Se 02), exhaling a characteristic smell of decaying horse-radish. Concentrated sulphuric acid dissolves selenium without oxidizing it; upon diluting the solution the selenium falls down in red flakes. Nitric acid and aqua regia dissolve selenium to SELENIOUS ACID (Se O (O H)2). When the solution of the latter is evaporated it loses water and is converted into sclenious oxide, which, at 200~, volatilizes as a yellow gas. Sublimed sele nious oxide appears in form of white four-sided needles, selenious acid in the form of crystals resemblling those of potassium nitrate. Selenious oxide dissolves in water to selenious acid, making a strongly acid fluid. Of the normal salts only those with the alkali metals are soluble in water; the solutions have alkaline reactions. All selenites dissolve readily in nitric acid, with the exception of the selenites of lead and silver, which dissolve with difficulty. Hydrogen sulphide produces in solutions of selenious acid or of selenites tin presence of free hydrochloric acid) a yellow precipitate of SELENIUM SULPHII)E (?), which, upon heating, turns reddish-yellow, sol uble in ammonium sulphide. Barium chloride produces (after neutralization of the free acid, should any be present), a white precipitate of BARIU.M SELENITE, which is soluble in hydrochloric acid and in nitric acid. Stant nous chloride or sulphurous acid, with addition of hydrochloric acid, ploduces a red precipitate of SELENIUM, which turns gray at a high tempera

Page  199 ~ 136.] ACIDS AND TIIEIR RADICALS. 199 ture. M'etallic copper, when placed in a warm solution of selenious acid containing hydrochloric acid, becomes immediately coated black; if the fluid remains long in contact with the copper, it turns light red from separation of selenium (REINSCI). By heating selenium or its compounds with alkali carbonates and nitrates, alkali SELENATES are formed. The fused nmass dissolves in water; the solution remains clear upon acidifying with hydrochloric acid; when concentrated by boiling, it evolves chlorine, whiilst the selenic acid (Se 02 (O H)2) is reduced to selenious acid. By fusing selenium or its compounds with potassium cyanide in a stream of hydrogen gas,. a selenium potassium cyanide is obtained, from which the selenium is not eliminated by the action of the air (as is the case with tellurium); it separates, however, upon long-continued boiling, after addition of hydrochloric acid. When tested according to p. 26, compounds of selenium give a blue color to the flame, and by volatilizationz and combustion of the vapor the above-mlentioned odor is emitted. The incrustation produced by reductionz is brick-red to cherry-red, and gives a dirty green solution with concentrated sulphuric acid. The incrustation of o ide is white, and when moistened with stannous chloride becomes red from separated selenium. In the charcoal stick with sodium carbonate sodium selenide is formed, which when placed on silver and moistened produces a black stain, and when treated with acids yields selenetted hydrogen. B.-DEPORTMENT OF THE ACIDS AND THEIR IRADICALS.* ~ 136. The reagents which serve for the detection of the acids are divided, like those used for the detection of the metals, into GENERAL REAGENTS, i.e., such as indicate the GROUP to which thle acid under examination belongs; and SPECIAL REAGENTS, i.e., such as serve to effect the identification of the INDIVIDUAL ACIDS. These acid groups can scarcely be defined with the salne degree of precision as those inlto which the bases are divided. The two principal groups are those of INORGANIC and ORGANIC ACIDS. WVe base this division ulpon those chlaracteristics by which the ends of analysis are most easily attained. We call organ;ic those acids of which the salts-(particularly those of an alkali or an alkali-earth metal)-are decomposed upon igllnition, with separation of carbon. A most simple prelimlinaryl experiment thus determines the class to which an acid belongls. The salts of organic acids with alkali or alkali-earth metals are converted into carbonates when heated gently to redless. Before proceeding to the special study of the several acids, I give here a general view of the whole of them classified in groups. I. INORGANIC ACIDS. FIRST GROUP: Division a. (Jhrornic acid (sulphurous and thiosulphuric acids, iodic acid). * Compare pp. 41-43.

Page  200 200 INORGANIC ACID. GROUP I. [ 137 Division b. Sulphuric acid (hydrofluosilicic acid). Division c. Phosphoric acid, boric acid, oxalic acid, lydro. fuoric acid (phosphorous acid). Division d. Carbonic acid, silicic acid. SECOND GROUP: Cldorine and hydrochloric acid; bromine and ydclrobromic acid; iodine and hydriodic acid; cyanogen and hydrocyanic acid, together with hydlcofeirroand hydrojfrricyanic acids; sulphur and hydrosulphuric acid (hydrogen sulphide) (nitrous acid, hypochlorous acid, chlorous acid, hypophosphorous acid). THIRD GROUP: Nitric acid, chloric acid (perchloric acid). II. ORGANIC AcIDs. FIRST GROUP: Oxalic acid, tartaric acid, citric acid, malic acid (racemic acid). SECOND GROUP: Succinic acid, benzoic acid. TIIRD GROUP: Acetic acid, formic acid (lactic acid, propionic acid, butyric acid). The acids printed in italics are more frequently met with in the,examination of minerals, waters, ashes of plants, industrial products, medicines, etc.; the others are more rarely met with. I. INORGANIC ACIDs. ~ 137. First Group. ACIDS WHICH ARE PRECIPITATED FROM PNEUTRAL SOLUTIONS BY BARIUM CHLORIDE. This group is again subdivided into four divisions, viz.: 1. Acids which are decomposed in acid solution by hydrogen sulphide, and to which attention has therefore been directed already in the testing for bases, viz., CHROImIC ACID (sulphur. ous acid and thiosulphuric acid, the latter because it is decorn,)osed and detected by the mere addition of hydrochloric

Page  201 ~ 138.] DIV. I.-CIIROMIC ACID. 201 acid to the solution of one of its salts; and also iodic acid).* 2. Acids which are not decomposed in acid solution by hydrosulphuric acid, and the barium compounds of which are insoluble in hydrochloric acid: SULPHURIC ACID (hydrofluosilicie acid). 3. Acids which are not decomposed in acid solution by hvdr6sulphuric acid, and the barium compounds of which dissolve in hydrochlori6 acid, apparently without decomposition, inasmnuch as the acids cannot be completely separated fromn the hydrochloric acid solution by heating or evaporation: PiosPRIORIC ACID, BORIC ACID, OXALIC ACID, HYDROFLUORIC ACID (phosphorous acid). (Oxalic acid belongs inole properly to the organic group. We collsider it, however, here with the acids of the inorganic class, as the property of its salts to be decomposed upon igllition without actual carbonization may lead to its being overlooked as an organic acid). 4. Acids which are not decomposed in acid solution b)y hydrosulphuric acid, and the barium salts of which are soluble in hydrochloric acid with separation of the acid: CARBONIC ACID, SILICIC ACID. First Division of the First Grop of tle Ji2organic Acids. ~ 138. CHROMIC ACID, Cr 0, (O H),t (Cr. 52.5.) 1. CHROMIUM TRIOXIDE or CHROMIC ANI-IYDRIDE appealrs as a scarlet crystalline mass, or in the form of distinct acicular crystals. Upon ignition it is resolved into chromic oxide, Cr2 03,, and oxygen. It deliquesces rapidly upon exposure to the air. It dissolves in water, imparting to the fluid a deep reddishyellow tint, which remains visible in very dilute solutions. 2. The CLIROMATES are all red or yellow, and for the most part insoluble in water. Part of them are decomposed upon iclnition. Those with alkali bases are soluble in water; the solutions of the nlormnal alkali chromates, e.g., K, Cr 04,, are yellow, those of the alkali dichrolates (anllydroehrolnates or " bihroinates ") e.g., IK, Cr2 0,~ are reddish-yellow. These * To this first division of the first group of inorganic acids belong properly also all the oxygen compounds of a distinctly pronounced acid character, which have been discussed already with the Sixth Group of the metals (acids of arsenic, antimony, selenium, etc.). But as the reaction of these compounds with hydrosulphuric acid tends to lead to confounding them rather with other metals than with other acids, it appeared the safer course to class these compounds with the metallic radicals. f The radical, Cr 0,, so analogous to S 0,, appears incapable of uniting with hydroxyl, since not only is chromic acid unknown as a distinct substance, but no chromates containing basic hydrogen exist. OK Cr-O K Cr4. t CrO,<O K. ~ 0 <Cr 0.K —0 KC

Page  202 202 INORGANIC ACIDS. GROUP I. [~ 138. tints are visible in highly dilute solutions. The -ellow coloi of the solution of a.normal'salt changes to reddish-yellow on the addition of an acid. 3. Iydclrosurlphuric acid acting upon the acidified solutioll produces first a brownish coloration of the fluid, then a green colorationr, arising from the formation of a chromic salt; this change of color is attended with separation of cslpllhlr, which imparts a milky appearance to the fluid [K, Cr, 0, + 4 (1, S 04) + 3 H2 S - K2 S 04,+ Cr2 (S 04)3 + 3 S +7 12, O]. HIeat promotes this reaction, part of the sulphur being in that case converted into sulphuric acid. 4. Ammnonlium sulphicZe, when added in excess to a solution of an allkali dichromate, immediately produces a bluish-graygreen precipitate of CHROMIIC YDROXIDE; on boiling the whole of the chromium separates as green chromic hydroxide. In a solution of normal potassium chromate at first a dark brownishl coloration alone is produced, but the bluish-gray-green precipitate above mentioned soon separates. 5. Clromlic acid may also be reduced to chromic oxide by means of many other substances, and more particularly by sulpharous acid, bly heating with concentrated hydrochloric acid, or with the dilute acid and alcohol (in which case ethyl chloride and aldehyde are evolved), by nzetallic zinc, by heating with tartaric acid, oxalic acid, etc. All these reactions are clearly characterized by the change of the red or yellow color of the solution to the green or violet tint of the chromic salt. 6. cBarima cdloride produces in aqueous solutions of clhlomates a yellowish-white precipitate of BAxRIUM C IROAT'rE, Ba Cr 04, soluble in dilute hydrochloric and enitric acids. 7. Silver nit-rate produces in aqueous solutions of chlllomates a dark purple-red precipitate of SILVwR cIrnosrrxTE, A c Cr 0(, soluble in nitric acid and in ammonia; in slightly avid solutions it produces a precipitate of SILVER DICIIROMATE, Ag2, Cr 0,. 8. Lead acette produces in an aqueous or acetic acid solution of a chromate a yellow precipitate of LEAD CIOIOMAT'E, Pb Cr 0,,* soluble in potassa, sparin3ly soluble in dilute nitlic acid, insoluble in acetic acid. Upon heating with alkalies the yellow normal salt is converted into red diplumlbic chromate, Pb2 Cr O.-t 9. If a very dilute acid solution of hydrogen dioride: (about 6 or 8 c.c.) is covered with a layer of ether (about half a centimetre thick), and a fluid containing chromic acid is added, the solution of hydrogen dioxide acquires a fine blue color. By inverting the test-tube, closed with the *Cr 02<0 >Pb. t Pb Cr O. Pb O = O<pb_O>r 2. $ Solution of hydrogen dioxide may be easily prepared by triturating a fragment of barium dioxide (about the size of a pea) with some water, and adding it with stirring to a mixture of about 30 c.c. hydrochloric acid, and 120 c.c. water. The solution keeps a long time without suffering decomposition. In default of barium dioxide impure sodium dioxide may be used in. stead, which is obtained by heating a fragment of sodium in a porcelain cap. sule until it takes fire, and letting it burn.

Page  203 ~ 1 39.] DIV. I.-SULPIIHUROUS ACID. 203 tlhum) repcatedly, without much shaking, the solution becomes colorless, whilst tle ether acquires a blue color. The latter reaction is particularly characteristic. One part of potassium chromate in 40,.000 parts -f watei suffices to 1)roduce it distinctly (STORElm); presence of vanadic acid mate. rially impairs the delicacy of the test (WEnrHERm).* The cause of this blue coloration is not certainly known. After some time the ether is decolorized. 10. If insoluble chromates are fused with sodtium caronate and nitrate, and the fused mass is treated with water, the fluid obtained appears yellow from the alkali chromnate which it holds in solution; upon the addition of an acid the yellow color changes to reddish-yellow. The bases are left either as oxides or carbonates, unlless they are soluble in the sodium hydroxide formned from the nitrate. 11. The alkali chromlates show the same reactions with sodiain mnetap/wsaphate and with borax in the blowpipe flame, as chromic oxide and chromium salts. 12. Very minute quantities of chromic acid may be detected by one of the following methods: a. mix with the fluid, slightly acidified with sulphuric acid, a little tincture of guaiacum (1 part of the resin to 100 p)arts of alcohol of 60 per cent.) when an intense blue coloration of the fluid will at once make its appearance, speedily vanishing again, however, where mere traces of chromic acid are present (H. SCHIFF); 6. mix the solution of the alkali chromate, which must be as neutral as possible, with some dilute decoction of logwood, when a very intense black coloration will be produced; in the presence of exceedingly small quantities of chromic acid the color is violet-red (R. WILDENSTEIN). Chrolnic acid being reduced by hydrosulphuric acid to chromiic oxide, this acid is in the course of analysis always fould ill the examination for bases. The intense color of the soltitions containing chromic acid, the excellent reaction with hydrogen dioxide, and the characteristic precipitates produced by solutions of lead salts and silver salts, affolrd moreover ready means for its detection. For the discovery of traces of chlro-)mniumn presenlt in many ininlerals, for instancee in serpenltine, the reactiotns in 12. nmay be used after the minieral has been fused with sodium carbonate and nitrate. Rarer Acids of the First Division. ~ 139. a. SULPHUROUS ACID, H2 S 0s. SULPHUR DIOXIDE or SULPHUIROUS ANHYDRIDE, S 02, is a colorless, unin. flammable gas, which has the stifling odor of burning sulphur. It dissolves copiously in water. The solution, in which we may assume thle existence of SULPHUROUS ACID, 112 S 03, has the odor of the gas, reddens litmus-paper, and bleaches Brazil-wood paper. Sulphurous acid absorls oxygen from the air, and is thereby converted into sulphuric acid. The salts are colorless. Of the normal sulphites, those with alkali oase only * Journ. f. prakt. Chem. 83, 195.

Page  204 204 RARER AClDS. GROUP I. [~ 139 are readily soluble in water; many of the sulphites insoluble or sparingly soluble in water dissolve in an aqueous solution of sullphulous acid, but fall down again on boiling. All the sullphites evolve sulphur dioxide when treated with sulphuric acid. Chlorine weater dissolves most sulphites to sulphllates. Barium chloride precipitates normlal sulphites, but not free sulphurous acid. The precipitate dissolves in hydrochloric acid. Hydrosullphuric acid decomposes the free sulphurous acid, water and pentathionic acid being formed with separation of sulphur. If to a solution of sulphurous acid, mixed with an equal volume of hydrochloric acid, a piece of clean colpper wire is added, and the mixture is boiled, the copper appears black, as if covered with soot, if much sulphurous acid is present; but only dull if a little is present (H. RErNsciI). If a trace of sulphurous acid or of a sulphite is introduced into a flask in which hydrogen is being evolved from zinc or aluminium and hydrochloric acid, hydrosulphuric acid is immediately evolved along with the hydrogen, and the gas now produces a black coloration or a black precipitate in a solution of lead acetate to which has been added a sufficient quantity of soda to redissolve the precipitate which forms at first. Sulphurous acid is a powerful reducing agent: it reduces chromic acid, permlanganic acid, mlercuric chloride (to mercurous chloride), decolorizes iodized starch, produces a blue precipitate in a mixture of potassium ferricyanide and ferric chloride, etc. With a hydrochloric acid solution of stanlrous chloride a yellow precipitate of STANNIC SULPIIIDE is formled after somle time. If an aque-' ous solution of an alkali sullphite is lnixed with acetic acid just to give it an incipient acid reaction, and is then added to a relatively large amount of solution of zinc sulphate mixed with a very small quantity oft sodium nitroprusside, the fluidc acquires a red color if the quantity of the sulphite present is not too inconsiderable, but when the quantity of the sulphite is very minute the coloration nlakes its appearance only after addition of some solution of potassium ferrocyanide. If the quantities are not altogether too minute, a purple-red plrecil)itate will form uponlthe addition of the potassiuml ferrocyanide (B3DDErKE). Thiosulphates of the alkalies do not show this reaction. b. THIoSULPHURIC (HYPosuLrHUIous) AcID, 12 S2 O. This acid does not exist in the free state. Most of its salts are soluble in water. The solutions of most thiosulphates may b)e boiled witllout suffering decomposition; calcium thiosulphate is resolved upon bloiling into calcium sulphite and sulphur. If hydrochloric acid or sulphuric acid is added to the solution of a thiosulphate, the fluid remains at first clezar and inodorous, but after a short time-the, shorter the more concentrated the solution —it becomes more and more turbid, owing to the separation of sulphur, and exhales the odor of sulphur dioxide. Application of heat promotes this decomposition. Sileer nitrate produces a white precipitate of SILVER TI1IOSULPHATE, which is soluble in an excess of the thiosulphate; after a little while (upon heating almost immediately) this precipitate turns black, being decomposed into silver sulphide and sulphuric acid. Sodium thiosulphate dissolves silver chloride; upon the addition of an acid the solution remains clear at first, but after some timle, and imlnlediately upon boiling, silver sulphide separates. Barium chloride produces a white precipitate, which is soluble in much water, more especially hot water, and is decomposed by hydrochloric acid..Ferric chloride colors the solutions of alkali thiosulphates reddish-violet (here they differ from alkali sulphites); on standing the liquid loses its color, especially when heated, ferrous chloride being formed. Acidified solution of chromic acid is immediately reduced by thiosulphates, iodized starch is at once decolorized WTith zinc or ale,,ninium and hydrochloric acid the thiosulphates behave like the sulphites

Page  205 ~ 140.] DIV. II -SULPHURIC ACID. 205 Where it is required to find sulphites and thiosulphates of the alkali metals in presence of alkali sulphides, as is often the case, solution of zinc sulphate is first added to the fluid until the sulphide is decomposed: the zinc sulphide is then filtered off, and one part of the filtrate is'ested for thiosulphuric acid by addition of hydrochloric acid, another portion for sulphurous acid with sodium nitroprusside, etc. c. IoDIc ACID, H I Os. IoDnr ACID crystallizes in white, six-sided tables or rhombic crystals; at a moderate heat it is resolved into iodine vapor and oxygen; it is readily soluble in water. The salts are decomposed upon ignition, being resolved either iito oxygen and a metallic iodide, or into iodine, oxygen, and metallic oxide: the iodates with an alkali base alone dissolve readily in water. Barium chloride throws down from solution of iodates of the alkali metals a white precipitate of BARIUM IODATE, which is soluble in nitric acid; silver nitrate a white granular-crystalline precipitate of SILVEe JO1D)TE which dissolves readily in ammonia, but only sparingly in nitric acid. Ii.ydrosulphuric acid throws down from solutions of iodic acid IODINE, which then dissolves in hydriodic acid; the precipitation is attended with separation of sulphur. If an excess of hydrosulphuric acid is added, the fluid loses its color, and a further separation of sulphur takes place, the iodine being converted into hydriodic acid. Iodic acid combined with bases is also decomposed by hydrosulphuric acid. So]7phurous acid throws down IODINE, which upon addition of an excess of the acid is converted into hycdriodic acid. Addition of psre H C1 or H1 S 04 to an iodate in presence of K I causes separation of iodine which tinges the liquid yellow and may be further identified with starch paste. Second Division of the First Group of the Inorganic Acids. SULPHURIC ACID, IH S 04, (S. 32.) ~ 140. 1. SULPHUR TRIOXIDE or SULPHURIC ANHYDRIDE, S 3,, is a Twlite feathery-crystalline mass which emits strong fumes upon exposure to the air; SULPHIIRIC ACID, H2 S 04, forms an oily liquid, colorless and transparent like water. Both the anhvdride alnd the acid char organic substances, and combine with vwater in all proportions, the process of combination being attended with considerable elevation of temperature, and in the case of the anhydride with a hissing noise. 2. The normal SULPHATES are readily soluble in water with the exception of the snlphates of barium, strontium, calciumn, and lead. The basic sulphates of the heavy metals which are insoluble in water dissolve in hydrochloric acid or in nitric acid. Most of the sulphates are colorless or white. The sulphates of the alkali metals are not decomposed by ignition. The other sulphates are acted upon differently by a red heat, some of them being readily decomposed, others with difficulty, and some resisting decomposition altogether. 3. Barizum chloride produces even in exceedingly dilute solu

Page  206 2206 INORGANIC ACIDS. GROUP I. [~ 140 tions of sulphuric acid and of the sulphates a finely pulverulent. heavy, white precipitate of BARIUFM SULPHATE (Ba S 04), insolil. ble in dilate hydrochloric and nitric acids. From very dilute solutions the precipitate separates only after stauding for some time. Concentrated acids and concentrated solutions of many salts impair the delicacy of the reaction. 4. Lead acetate produces a heavy white precipitate of LEAD SULPHIATE (Pb) S 04) which is sparingly soluble in dilute nitric, but dissolves completely in hot concentrated hydrochloric acid. 5. The sulplates of the alkali-earth metals which are insoluble in water and acids are converted into CARBONATES, by fusion with alcali carbonates. But lead sulphate yields LEAD OXIDE whlen treated in this manner. In both cases an alkali sulphate is formned. The sulphates of the alkali-earth metals and of lead are also resolved into insoluble carbonates and soluble alkali sulphate by digestion or boiling with concentrated solutionlls of carbonates of the alkali metals (comlp. ~~ 95, 96, 97). 6. Uponl fusing sulphates with soditiu carbonate on charcoal in the inner flame of the blowpipe, or heating them in the stick of charcoal (p. 27) in the lower reducing flame, the sulphuric acid is reduced, and sodium sulphide formed, which may be readily recognized by the odor of hydrosulphuric acid emitted upon moistening the sample and the part of the charcoal into which the fused mass has penetrated, and adding some, acid. If the fused mass is transferred to a clean silver plate, or a polished silver coin, and then moistened with water and some acid, a black stain of silver sulphide is immediately formed. (Compounds of tellurium and selenium give the same reaction.) Jemarks.-The characteristic and exceedingly delicate reaction of SULPIRRIC ACID with barium salts renders the detection of this acid an easier task than that of almost any other. It is simply necessary to take care not to confound with barium sulphate precipitates of barium chloride, and particularly of barium nitrate, which are formed upon mixing aqueous solutions of these salts with fluids containing a large pro(portion of free hydroclloric acid or free nitric acid. It is very easy to distinguish these precipitates from barium sulphate, sinlce thev redissolve immediately upon diluting the acid fluid with water. It is a rule that should never be departed from, in testillg for sulplulic acid with barium chloride, to dilute the fluid largely; a little hydrochloric acid should also be added, which counteracts the adverse influenlce of many salts, as, for instance, citrates of the alkali letals. Where very minute quanltities of sulplhuric acid are to be detected the fluid should be allowed to stand teveral hours at a gentle heat; the trace of barium sulphate

Page  207 ~~ 141, 142.] DIV. III.-ORTOPHOSPHORIC ACID. 207 formed will in that case be found deposited at the bottom of the-vessel. When the least uncertainty exists the nature of the precipitate produced by barium chloride ill presence of hydrochloric acid, the reaction in 6. will at once set all doubt at rest. In looking for very small quantities of sulphuric acid in the presence of much hydrochloric (or nitric acid, the greatel part of the latter should first be evaporated off or neutralized. To detect free sulphturic acid in presence of a sulphate the fluid is mixed with a very little cale-sugar, and evaporated to dryness in a porcelain dish at 1000. If free sulphuric acid was present a black residue remains, or in the case of most minute quantities, a blackish-green residue. Other free acids do not decompose cane-sugar in this way. ~ 141. HYDROFLUOSILICIC ACID, 2 HF. Si F4. Hvdrofluosilicic acid is a very acid fluid; upon evaporation on platinum it volatilizes completely as silicon fluoride and hydrofluoric acid. When evaporated in glass it etches the latter. With bases it forms water and silico-fluorides of the metals, which are most of them soluble in water, redden litmus-paper, and are resolved upon ignition into metallic fluorides and silicon fluoride. Barium chlor-ide forms a crystalline precipitate with hydrofluosilicic acid (~ 95, 6). Strontiumr chloride and lead acetate form no precipitates with this acid. Potassium salts precipitate transparent gelatinous POTASSIUM SILICO-FLUORIDE; armmonia in excess precipitates SILICIC ACID, with formation of ammonium fluoride. By heating metallic silico-fluorides with concentrated sulphuric acid dense fumes are emitted in the air, arising from the evolution of hydrofluoric and silicofluoric gas. If the experiment is conducted in a platinum vessel covered with glass the fumes ETCH the glass (~ 146, 5,: the residue contains the sulphates formed. Third Division of the First Group qf the Inorganic Acids. g 142. a. PHOSPHORUS, P. 31, AND ORTHOPHOSPIIORIC AcrD OR TRIHYDROGEN PHOSPHATE, HI3P 04 or P O (O H),. 1. COMMON PHOSPHORUS is a colorless, transparent, solid body, of 1.84 specific gravity; it has a waxy appearance. Taken internally it acts as a virulent poison. It fuses at 44.30, and boils at 290'. By the influence of light, phosphorus kept under cwater turns first yellow, then red and is finally covered with a white crust. If phosphorus is exposed to the air at the common temperature, it exhales a highly characteristic and most disagreeable odor, copious fumes being evolved which are luminous in the dark. These fumes are formed by oxidation of the vapor of phosphorus, and consist of phosphoric and phosphor

Page  208 208 INORGANIC ACIDS. GROUP I. [~ 142 ous acids. When the air is moist, ozone, hydroogen dioxide, and ammoniul m nitrite are produced at the same time. iPhospho rus very readily takes fire, burning with a luininous flame tc phosphoric oxide, which appears in the form of white fumes. By the protracted influence of light, or by heating to 250~, phosphorus is converted into RED (so-called amorphous) PIosPHorus. Red phosphorus does not alter in the air, it is not luminous, its inflaimmability is much decreased, and it has a specific gravity of 2.1. Nitric acid and nitrohydrochloric acid dissolve phosphorus pretty readily upon heating. The solutions contain at first, besides phosphoric acid, also phosphorous acid. Hydrochloric acid does not dissolve phosphorus. If phosphorus is boiled with solution of soda or potassa, or with milk of lime, hypophosphites and phosphates are formed, whilst spontaneously inflammable phosphoretted hydrogell gas escapes. If a substance containing unoxidized phosphorus is placed at the bottom of a flask, and a slip of paper moistened with solution of silver nitrate is by means of a cork loosely inserted into the mouth suspended inside the flask, and a gentle heat applied (from 30~ to 40~), the paper slip will turn black in consequence of the reducing action of the phosphorus fumes, even thougl only a most minllte quantity of the phosphorus should be present. If after the termination of the reaction the bllackened part of the paper is boiled with water, the unldecoinposed portion of the silver salt precipitated with hydrochloric acid, the fluid filtered, and the filtrate evaporated as far as practicable on the water-bath, the presence of phosphoric acid ill the residue nlay be shown by means of the reactions described below. (J. SCHERER.) It must be borne in mind that the silver salt is blackened also by hydrosulpllhric acid, formic acid, volatile products of putrefaction, etc., and also that the detection of phosphoric acid in the slip of paper can be of value only where the latter and the filtering paper were perfectly free from phosphorus. As regards the deportment of phosphorus upon boiling with dilute sulphuric acid, and in a hydrogen evolution apparatus supplied with zinc and dilute sulphluric acid, see ~ 220. 2. PHosPHoRIC OXIDE (PHOSPHORIC ANInI-YRIDE), P2 0~, iS a white, snowlike mass, which rapidly deliquesces in the air. When treated with water it hisses like a red-hot iron, aond is at first only partially dissolved, in time, however, the solution is complete. It forms with water and bases three series of comnpounds, viz., with three molecules of water or of base, orthophosphoric acid or common phosphates, e.g., P, O5 + 3 H11 O 2 [P O (O 1)3]; with two molecules of water or of base, pvrophosphoric acid or pyrophosphates; with one molecule of water or of base, mnetaphosphoric acid or metaphosphates. As the meta- and pyrophosphoric acids are comparatively rare they will be treated in a supplemental paragraph.

Page  209 ~ 142.] DIV. I.-ORTIIOP IIOSPIIORIC ACID. 209 3. The ORT1IOPHOSPITORIC ACID*, P 0 (O II):, forms colorless and pellucid crystals, which deliquesce rapidly in the air to a syrupy non-caustic liquid. The action of heat changes it into meta- or pyrophosphoric acid, according as either one or two molecules of water are expelled. Heated in an open platinum dish orthophosphoric acid, if pure, volatilizes completely, tllough with difficulty, in white fumnes. Orthophosphoric acid forms three series of salts, mnonometallic, dimetallic, or monohydric, and trimetallic, according to the extent to which its hydroxyl is repla(ed by basic radicals.t 4. The action of heat fails to decompose the ORTnHOPOSPHATES with fixed bases, but converts them into pyrophosphates if they contain one hydroxyl or one ammonium, and into metaphosphates if they contain two hydroxyls or other volatile radicals. Of the normal orthophosphates those with alkali base alone are soluble in water. The solutions manifest alkaline reaction. If pyro- or metaphosphates are fused -with excess of. sodium carbonate, the fused mass contains only ortho. phosphates. 5. Barium chloride does not precipitate aqueous solutions of orthophosphoric a(id. In aquleous solutions of climetallic phosphates of the alkali metals it produces a white precipitate of HYDROGEN BARIUM PIIOSPIIATE, Ba II P 04 In solutions of trimetallic (normal) phosphates it gives white TRIBARIUM PIOSPITATE% Ba3 (P 0,)2t. Both precipitates are soluble in hy* The names phosphoric acid and phospph ates, when not qualified by prefixes, apply to the ortho compounds. t The univalent basic radicals form three phosphates, e.g., /0 Na trimetallic, P0- Na trisodium phosphate. \oNa /0 H monohydric or dimetallic, P 0-0 Na hydrogen disodium phosphate. \O Na /0 H monometallic, P 0-O H sodium dihydrogen phosphate. \O Na * Barium and other bivalent basic radicals, with or without hydrogen, form three phosphates, viz.: /~> Ba P 0-0 trimetallic, O Ba tribarium phosphate (basic phosphate of baryta). PO o>Ba /0 H monohydric, P OO>Ba hydrogen barium phosphate (neutral phosphate >a of baryta). /0 H PO-O H monometallic. \8O>Ba tetrahydrogen barium phosphate (acid phosphate P 0/0 H of baryta). \o H

Page  210 210 INORGANIC ACIDS. GROUP I. [~ 142. drochloric and nitric acids, but sparingly soluble in chloride of ammonium. 6. Solution of calcium sulphate produces in neutral or alkaline solutions of phosphates, but not in solutiols of phosphoric acid, a white precipitate of HYDROGEN CALCIUM PIIOSPIIATE, Ca HI P 04, or of T'r'ICALCIUM PHOSPHIATE, Ca3 (P 04)2, Awhich dissolves readily in acids, even in acetic acid, and is soluble also in ammonium chloride. 7. [cfagnzesium sulphaate produces in concentrated solutions of dimetallic alkali phosphates, a white precipitate of HYDROGEN MAGNIESIUM PHOSPHATE, M/g II P 04 + Aq., which often separates only after some time; upon boiling, a precipitate of TRIMAGNiSIUM PHOSPHAT'E, 3g, (P (),)2 - 21 Aq., is thrown down imnnediately. The latter precipitate forms also upon addition of mIagnesium sulphate to the solution of a trimnetallic alkali phosphate. But if a mixture* of magnesium sulphate and amlnlonia with sufficient ammonium chloride to hold in solution or to redissolve magnesium hydroxide is added to a solution of phosphoric acid or of an alkali phosphate, a white, crystalline, and quickly subsiding precipitate of AMMONIUM MAGNESIUMI PNOSPHATE, N Ia Mg P 04 + 6 Aq., is formed, even in highly dilute solutions. This precipitate is insoluble in ammonia, and most sparingly soluble in ammonium chloride, but dissolves readily in acids,' even in acetic acid. It makes its appearance often only after the lapse of some time; stirring promotes its separation (~ 98, 8). The reaction can be considered decisive only if no arsenic acid is present (~ 133, 9). 8. Silver nitrate throws downr from solutions of di- and trimetallic alkali phosphates a light-yellow precipitate of SILVER PIIOSPIATE, Ag, P 04, which is readily soluble in nitric acid and in ammonia. If the solution contained a trimetallic phosphate the fluid in which the precipitate is suspended manifests a neutral reactionl; whilst the reaction is acid if the solution contained a dimnetallic phosphate. The acid reaction in the latter case arises from the circumstance that the nitric radical receives, for the 3 atoms of silver which it yields to the phosphoric acid, only 2 atoms of alkali metal and 1 atomn of hydrogen K.II tIP O, + 3(At N O,)= Ag: P04 (K + 2 ( ) + IIN 03. 9. If to a solution contaiiiing phosphoric acid and the least possible excess of hydrochloric or nitric acid a tolerably large amount of sodium acetate is added, and then a drop of ferric chloricde, a yellowish-white, floccnlent-gelatinons precipitate of FERRIC PHOSPIIATE, (Fe, (P 0O), + 2 aq.) is formed. An excess of ferric chloride must be avoided, as ferric acetate (of red color) would thereby be formed, in which the precipitate is not insoluble. This reaction is of importance, as it enables us to detect phosphoric acid in phosphates of the alkali-earth metals; but it can be held to be decisive only if no arsenic acid is * See note p. 190.

Page  211 ~ 142.] DIV. III. ORTHOPHOSPHORIC ACID. 211 present, as this shows the same reaction. To effect the corn plete separation of phosphoric acid from the alkaliearth metals a sufficient quantity of ferric chloride is added to ilnpart a reddish color to the solution, which is then boiled (whereby the whole of the iron is thrown down, partly as phosphate, partly as basic acetate), and filtered hot. The filtrate contains the alkali-earth metals as chlorides. If you wish to detect, by means 6f this reaction, phosphoric acid in presence of a large proportion of ferric salts, boil the hydrochloric acid solution with sodium sulphite until the ferric chloride is reduced to ferrous chloride, as indicated by decoloration; add sodium carbonate ultil the fluid is nearly neutral, then sodiluml acetate, and finally one drop of ferric chloride. The reason for this proceedin(g is, that ferrous acetate does not dissolve ferric phosphate. 10. When 2 or 3 drops of a neutral or acid solution containing phosphoric acid, anld free from chlorides, are poured inlto a test tube filled to tile depth of ~ to 1 inch with solution of ammonium molybdate in nitric acid (~ 55), there is formed in the cold; either immediately or after the lapse of a short time, unless the solution under examlination contains only a very minute amount of phosphoric acid, a pulverulent pale-yellow precipitate of AMMONIUM PITOSPIIO-MOLYBDATE, 10 }Mo O, + P 04 (N 114)3 + 1 II, 0 is formed, which gathers upon the sides and bottomn of the tube. If the precipitate does not appear within a few minutes, the operator may add cautiously and by degrees, more of the substance to be tested. Only when the phosphoric acid is present in exceedingly minute quantity, e.g., 0'00002 grin., is it requisite to wait some hours and to apply a gentle heat, ilot to exceed 40~ C., before the precipitate appears. When other coloring matters are not present, the liquid above the precipitate is colorless. It is indispensable not to add too much of the solution to be tested for phosphoric acid, as the yellow precipitate is soluble in phosphoric and other acids (and therefore is not formed) unless a considerable excess of the molybdic solution be present. A yellow coloration of the liquid is not to be regarded as proof qf the presence of phosphoric acid. By operating in the manner above described, there is no dainger of mistaking any other substance for phosphoric acid; because, arsenic acid gives in the cold, lno precipitate with the nlolybdic solution, though a yellow precipitate is formed on heatincg and especially on1 boiling (the liquid above the arsenlical precipitate has a yellow color), and silicic acid does not react at all in the cold, though on heating it causes a strong yellow coloration, but gives no precipitate. The PHOSPHO-MOLYBDATE OF A3MMIONIUM contains only a small amount (about 1-9 per cent.) of PIIOSPHORUS. Its formation is prevented not only by excess of phosphoric acid, but likewise by certain organic substances, e.g., tartaric acid. The precipitate is easily recognized even in dark-colored liquids, by giving it

Page  212 212 INORGANIC ACIDS. GROUP TI. f 143 time to settle. If it be washed with the same molvbdic solu. tion employed in producing it (in which it is totally insoluble) and be then dissolved in ammonia, addition of " magnesia mixture" (see note p. 190), to the solution will throw down amlmonium magnesium phosphate. 11. If a finely-powdered substance containing phosphoric acid (or a metallic phosphide) is intimately mixed with 5 parts of a flux consisting of 3 parts of sodium carbonate, 1 part of sodiniym nitrate, and 1 part of silicic acid, the mixture fused in a platinum spoon or crucible, the fused mass boiled with water, the solution obtained decanted, ammonium carbonate added to it, the fluid boiled again, and the silicic acid which is therel)v precipitated filtered off, the filtrate now holds in solution alkali plhosphate, and may accordinigly be tested for phosphoric acid as directed in 7, 8, 9, or 10. 12. On igniting and pulverizing a substance containing phosphoric acid, placing it ilto a tube of the thickness of a straw and sealed at one end, adding a fragment of magnesium wire about two lines long (or a small piece of sodium), which should be covered by the sample, and then heating, a vivid incandescence will be observed and magnesium (or sodium) phosphide will be formed. When the black contents of the tube are crushed and moistened with water they exhale the characteristic odor of phosphoretted hydrogen. (WINKELBLECH, BUNSEN.) 13. TVWite of egy is not precipitated by solution of orthophosphoric acid, nor by solutions of orthophosphates mixed with acetic acid. ~ 143. a. Pyrophosphoric acid or tetrahydrogen phosphate, 114 P2 07. The solution of pyrolhosphoric acid is converted by boiling into solution of orthophosphoric acid,H4 P2 07 + H2 0 = 2 (H3 P 04). The solutions of the salts bear heating without suffering decomposition; but upon boiling with a strong acid the pyrophosphoric acid is converted into orthophosphoric acid. If the salts are fused with sodium carbonate in excess orthophosphates are produced. Of the tetra-metallic pyrophosphates only those with alkali base are soluble in water; the acid salts, e. g., Na2 H2 P2 07, are by ig'nition converted into metaphosphates, e.g., Na P 03. Barium chloride fails to p)recipitate the free acid; from solutions of the salts it precipitates white BARIUM PYROPHOSPHATE, Ba2 P2 O,,soluble in hydrochloric acid. Silver nitrate throws down from a solution of the acid, especially upon addition of an alkali, a white earthy-looking precipitate of sILVER PYROPHOSPHATE, Ag4 P2 O7,which is soluble in nitric acid and in ammonia. Magnesiumn tulphate precipitates MAGNESIUM PYROPHOSPHATE, Mg2 P2 07. The precipitate dissolves in an excess of the pyrophosphate, as well as in an' excess. of the magnesium sulphate. Ammonia fails to precipitate it from these solutions. Upon boiling the solution it separates again (means of detecting pyrophosphoric acid in presence of phosphoric acid). A concentrated solution of luteo-cobaltic chloride added to an alkali pyrophosphate produces an immediate precipitation of pale reddish-yellow spangles. (Here pyrophosphoric acid differs from phosphoric and metaphosphoric acids. C. D. BRAUN.) White of egg is not precipitated by solution of the acid, nor }Yy

Page  213 [~ 144. DIV. 1I1.-BORIC ACID. 213 solutions of the salts mixed with acetic acid. Ammonium molbbdate, with addition of nitric acid fails to produce a precipitate. b. MJety.aphosiJhoric acid. Five sorts of mnetaphosphates are known., and the acids also corresponding to most of these have been produced. The several reactions bly which to distinguish b)etween these I will not enter u-pon here, and confine myself to the simnple observation that the meta1phosphoric acids differ from the pyro- and orthophosphoric acid in this that the solutions of the metajphosphoric acids precipitate wohite of egg at once. and the solutions of their salts after addition of acetic acid. Those acids and salts which are precipitated by silver nitrate produce with that reagent a white precipitate. A mixture of magnlesium sulphate, ammonium chloride and ammlonia fails to precipitate the metaphosphoric acids and their salts, or produces precipitates soluble in ammonium chloride. All mletaphosphates yield upon fusion with sodium carbonate, sodium orthouhosphate. ~ 144. b. BoRIC OR BoRACIC ACID. B (O IH), (B. 11). 1. BORIC OXIDE,, 2 03, is a colorless, fixed glass, fusible at a red heat. OrTHOBORIC ACIr, B (O tl),, appears as small, scaly crystals; on heating to 100~ C., it is transformed into Inetaboric acid, B O 0 H, a porous white mass. Orthoboric acid is soluble in water and in alcohol; upon evaporating the solutiolIs a large proportion of boric acid volatilizes along with the aqtleots and alcoholic vapors. The solutions redden litnmuspaper, and impart to turmneric-paper a faint brown-red tint, which acquires intensity upon drying. The borates are not decomposed upon ignition; those with alkali bases alone are readily soluble in water. The solutions of borates of the alkali metals are colorless, and all of them, even those of the acid salts, manifest alkaline reaction. 2. Barirm chloride produces in solutions of borates, if not too highly dilute, white precipitates of BARIUM BOIRATE, which are soluble in miuch water as well as in acids and amnmoniumsalts. The composition of this precipitate depends upon that of the borates in whose solutions they are forllled as well as npon the telnperature and dilution of the liquid. 3. CYalcunim cldoridce deports itself toward solutions of borates the saine as bariumn chloride. 4. Silrer nitrate produces in concentrated solutions of borax, a whlite precipitate which dissolves in a laroge amount of water. If thle iborax solution is first diluted with nearly enlough water to dissolve the silver borate, the addition of silver nitrate plroduces a brown precipitate of silver oxide. All these precipitates dissolve in nitric acid and in ammolia. 5. If dilute s8l7tphuric acid or hydrochloric acid is added to hlighly concentrated, hot prepared solutions of alkali borates, C)RTIOBORIC ACID separates upon cooling, in the form of shinfing r rystallinle scales. 6. If alcohol is poured over free boric acid or a borate —with

Page  214 214 INORGANIC ACIDS. GROUP I. [~ 144 addition, in the latter case, of a 8sfle7ient qaanztty qf concew? trated 8ultpAzuric acid to liberate the boric acid, alld the alco, hol is kinldled, the flamne appears of a very distillct YELLOWISHrGT;UrE1N color, especially ulpon stirrinog the lixturle; this tilnt is imnparted to the flame by the boric acid which volatilizes w-ith the alcohol. The delicacy of this reaction Inay be conlsiderably heightened by heatiicg the dish Whlich contains the alcoholic mixture, killdliilng the alcohol, allowing it to burn for a shllrt tille, then extilguishing the flame, and afterwards rekindling it. At the firlst flickering of the flame its borders will now appear green, even though the quantity of the boric acid be so minute that it fails to produce a perceptible coloring of the flame when treated in the usual manner. As salts of copper also impart a green tilnt to the flamle of alcohol, the copper which mig'ht be present must first be removed by lleans of hydrogen sulrphide. Presence of metallic chlorides also mlay lead to mistakes, as the ethyl chloride formed in that case colors the borders of the flamne bluish-green. 7. If a solution of boric acid, or of a borate of an alkali netal or of an alkali-earth metal, is mixed with hydrochloric acid to sli(ht, but distinct, acid reaction, and a slip of turmyeric p)cper is half dipped into it, and thell dried on a watch-glass at 1000, the dipped half shows a peculiar RED tint (H. RosE). This reaction is very delicate; care imust be taken not to con. found the characteristic red coloration xwith the blackish-brown color which turmeric-paper acquires when moistened'with rather concentrated hydrochloric acid, and then dried; nor wvith the brownish-red coloration which ferric chloride, or a hydrochloric acid solution of ammonium molybdate or of zirconia, gives to turineric-paper, more particularly upon drying. By moistening turimeric-paper reddened by boric acid with a solution of all alkali or an alkali carbonate, the color is changed to bluish-blaclk or greenlish-black; but a little hydrochloric acid -will at once restore the brownish-red color (A. VOGEL, II. LuDwIG). 8. if a substance containing boric acid is reduced to a fine powder, this with addition of a dlrop of water, mixed with 3 parts of a flux colnposed of 41 parts of potassium disulphlate and 1 palrt of finlely pulverized calcium fluoride, free front boric acid, and the paste exposed on the loop of a platinuml wire in the outer mantle of the Biunsen gas flame, or at the apex of the inner flamle of the blowpipe, boron fluoride escapes, which imparts to the flame-though only for ail instanlt-a greell tint. With readily decomposed compounds the reaction mL.ay be obtained by simply moistening the sample with hydrofluosilicie acid, and holding it in the flame. 9. Boric acid or bolates, fused with sodium carbonate on the loop of a platinum wire, give, when placed in the flalne of the spectrum aI2paratus, a spectrum of four well marked liles of

Page  215 ~ 145.] DIV. III.-OXALIC ACID. 215 equal width, equidistant from each other. B1 is liilliant vellowish-green (coinciding with Ba 7y), B2 is brilliant light-green (coinciding with Ba,), 13 is pale bluish-green (nearly coincidilng with the blue barium line), B4 is blue, very pale, close to S1r 8 (SIMMLER). ~ 145. C. OXALIC AcID, C2 H2 01, = 02 02 (0 H )2, 0* 1. OXALIC ACID is a white powder; the CRYSTALLIZED ACID., C,2 H2, + 2 H, O, forms colorless rhombic prisms. Both dissolve readily in water and in alcohol. By heatingl rapidly in open vessels part of the acid undergoes. decomposition, wlilst another portion volatilizes unaltered. The fumes of the volatilizin( acid are very irritating and provoke coughing. If the acid is heated in a test-tube part of it sublimes unaltered. 2. The OXaLATES undergo decomposition at a red heat yielding carbon monoxide and carbon dioxide. The oxalates of the alkali metals, and of barium, Strontium and calcium are in this process converted into carbonates (if pure, and if the heat is gentle, almost without separation of charcoal).. MIagnesiuli oxalate is converted into magnesia even by a very gentle red heat. The other metallic oxalates leave either the pure metal or an oxide behind, according to the reducibility of the metallie oxide. The alkali metal oxalates, and some others are soluble in water. 3. Bariumn chloride produces in neutral solutions of alkali oxalates a white precipitate of BARIUM OXALATE Ba C2 04, which dissolves very sparingly in water, more readily in water containing ammoniumn chloride, acetic acid, or oxalic acid, freely in nlitric, acid and in hydrochloric acid; ammonia precipitates it from the latter solutions unaltered. 4. Silver nitrate produces in solutions of oxalic acid aiid of allkali oxalates a white precipitate of SILVER OXALATE Ag2 C2 04, which is readily soluble in concentrated hot nitric acid and also in ammonia, but dissolves with difficulty in dilute nitric acid, and is most sparingly soluble in water. 5. Lime water and all the soluble calcium salts, inclulding solutionz of calcium sulphate, produce in even highly dilute solutions of oxalic acid or of oxalates of the alkalies, white finely pulverulent precipitates of CALCIUM OXALATE:, Ca C2 04 + H2 0, and sometimes Ca C2 04 + 3 112 0, which dissolve readily in hydrochloric acid and in nitric acid, but are nearly insoluble COOH COONa * Oxalic acid =; Sodium oxalate =; C00OH C00Na COOH COO Hydrogen sodium oxalate -- J Calcium oxalate =I > Ca. COONa COO

Page  216 216 INORGANIC ACIDS. GROUP I. [~ 146. ill oxalic acid and in F,etic acid, and practically illsoluble in water. The presence.f amnmonium salts does not illtelfere with the formation of these precipitates. Addition of ammollia considerably promotes the precipitation of free oxalic acid by calcium salts. In highly dillte solutions the precipitate is only folrlned after solme time. 6'. If oxalic acid or an oxalate, in the dry state, is heated Nwith all excess of concentrated sultphuric acid, it is decomposed into CARBON MONOXIDE and CARBON DIOXIDE, with formation of water or a sulphate if a base be present, the two gases escaping with effervescence, e. g., C2 I12 04 C 0 + C 02 + 112 0. If the quantity operated upon is not too minute the carbon monoxide mnay be kindled; it burns with a blue flalne. Should the snlphuric acid acquire a dark color in this reaction, this is a proof tliat the oxalic acid contained some organic substance in admixture. 7. If oxalic acid or an oxalate is mixed with finely pulverized mzanganese dioxide (which must be free from carbonates), a little water added and a few drops of sulphuric acid, a lively effervescenc(e ensues, caused by escaping CARBON DIOXIDE, C2 II2 04 + Mn 02 + - S 04 = 2 0C 02 + 2 20 + Mn S 04. 8. If oxalates of alkali-earth metals are boiled with a concentrated solution of sodciun carbonate, and filtered, sodium oxalate is obtained in the filtrate, whilst the precipitate contains the base as carbonate. With oxalates of heavy metals, this operation is not always sure to attain the desired object, as many of these oxalates, e. g., nickel, feri'ic and chromic oxalates, will partially dissolve in the alkaline fluid, with formation of double salts. Metals of this kind should therefore be separated as sulphides. ~ 146. d. IIYDROFLUORIC ACID, H F. (F. 19.) 1. HYDROFLLUORIC ACID is a colorless corrosive gas, which fumes in the air, and is freely absorbed by water. Aqueous hydrofluoric acid is distinguished froln all other acids by the property of dissolviig crystallized silicic oxide, and also the silicates which are insoluble in hyrdochloric acid. IIydrofluosilicic acid and water are formed in the process of solution, Si 02 + 6 H F - I2 Si F6 + 2 IT2 0. With metallic oxides and hydroxides hydrofluoric acid forms metallic fluorides and water. 2. The FLUORIDES of the alkali metals are soluble in water; thie solutions have an alkaline reaction. The fluorides of the netals of the alkali-earths are either insoluble or very difficultly soluble in water. AluIninium fluoride is readily soluble. Most of the fluorides of the heavy metals are very sparingly soluble

Page  217 ~ 146.] HYDPROFLUORIC ACID. 217 in water, as the fluorides of copper, lead, and zinc; Inany others dissolve ill water without difliculty, as the ferric, stannons and inercurous fluorides. Many of the fluorides ilsoluble or dificultly soluble in water dissolve in hydrofltuoric acid; others do not. Alost of the fluorides bear ignition in a cruciI,le without sufferingc decomposition. 3. _Barium chloride precipitates aqueous soltutions of hvdrofluoric acid, but much more completely solutions of fluorides of the alkalies. The bulkv white precipitate of BNRIUM FLUORIDE (Ba F2) is almost absolutely insoluble in water, but dis solves in large quantities of hydrochloric acid or nitric acid, -roln which solutionls ammonia fails to precipitate it, or throws it down only very incompletely, owing to the dissolving action of' the ammonium salts. 4. (alciuam chloride produces in aqueous solutions of hydrofluoric acid or of fluorides a gelatinouts precipitate of CALCIUM FLUORIDE (Ca F2), which is so transparellt as at first to induce the belief that the fluid has remained perfectly clear. Addition of lamlionia promotes the comeplete separation of the precipitate. The precipitate is practically insoluble in water, and olll very slightly soluble in hydrochloric acid and nitric acid inl tle cold; it dissolves somewhat nmore largely upon boiling with hydrochloric acid. Ammnlnia produces no precipitate in the solution, or only a very triflin one, as the ammonium salt formed retainls it in solution. Calcium fluoride is scarcely more soluble ill hydrofluoric acid thanl in water. It is insoluble in alkaline fluids. 5. If a finely pulverized fluoride, no matter whether soluble or insoluble, is treated in a platinum crucible with just enough comwcentrated sulphruric acid to make it into a thin paste. the crucible covered with the convex face of a watch-glass of hard glass coated with beeswax, which has been removed again in sonie places by tracing lines in it with a pointed piece of wood, the hollow of the glass filled with water, and the crucible gently heated for the space of half an hour or an. hour, the exposed lilies will, upon the removal of the wax, be found more or less deeply ETCHED into the glass. (The coating is made by heating the glass cautiously, puttinlg a small piece of wax upon the convex face, and spreadilg the wax equally as it melts. The wax is removed by heating the glass gelltly, and wiping with paper.) If the quantity of hydrofluoric acid disenlgaged by the sulphuric acid was very milnute, the etchillng is oftenl invisible upon the removal of the wax; it will, however, in such cases appear when the glass is breathed upon. This appearance of the etched lines is owing to the unequal capacity of condensing water which the etched and the untouched p)arts of the plate respectively possess. The impressions which thus appear upon breathinlg on the glass may, however, owe their Drigin to other causes; therefore, thouglt their noll-appearance

Page  218 218 INORGANIC ACIDS. GROUP I. DIV. III. [~ 14G6. may be held as a proof of the absence of fluorine, their appearance is not a positive proof of the presence of that element. At all events, they ought only to be considered of value -where they canll be developed again after the glass has been properly washed with water, dried, and wiped.* This reaction fails if there is too much silicie oxide or of a silicate present, or if the substance is not decomposed by sulphuric acid. In such eases one of the two following methods is resorted to, according to circumstances. 6. If we have to deal with a fluoride decomnpoeable by sulphuric acid, but mixed with ajlarge proportion of silicic oxide or of a silicate, the fluorine in it may be detected by heating the mixture in a test-tube with concentrated s8LutpAuric acid, as FLUOSILICIC GAS (Or1' SILICON FLUORIDE Si F4) is evolved in this process, which forms dense white fumes in moist air. If the gas is conducted into water through a bent tube moistened inside, the latter has its transparency more or less impaired, owing to the separation of silicic acid. If the quantity operated upon is rather considerable, silicic acid separates in the water, and the fluid is rendered acid by hydrofluosilicic acid. Compare ~ 146, 1. The following process answers best for the detection of small quantities of fluorine: Heat the substance with concentrated sulphuric acid in a small flask closed with a cork with double perforation, bearing two tubes, one of which reaches to the bottom of the flask, whilst the other termlinates immediately under the cork. Conduct throuogh thle longer tube a slow stream of dry air into the flask, and conduct this, upon its reissuing through the other tube, into a U tube containing a little dilute ammonia, and connected at the other end witll an aspirator. The silicon fluoride which escapes with the air, decomposes with the amlnonia, Inore particularly upon the application of a gentle heat towards the end of the process, amnmonium fluoride and silicie acid being forlnmed. Filter, evaporate in a platinum crucible to dryness, and examine the residue by 5. For more difficultly decomposable substances potassium disulphate is used instead of sulphuric acid, and the mixture, to which some marble is added (to insure a continuous slight evolution of gas), heated to fusion, and kept in that state for some time. 7. Silicates not decomposable by sulphuric acid must first be fused with four parts of sodium carbonate. The fused mass is treated with water, the solution filtered, the filtrate concen* J. NIClKLES states that etchings on glass may be obtained with all kinds of sulphuric acid, and, in fact, with all acids suited to effect evolution of hydrofluoric acid. I have tried watch-glasses of Bohemian glass with sulphuric and other acids, but could get no etchings in confirmation of this statement. Still, proper caution demands that before using the sulphuric acid, it should first be positively ascertained that its fumes will not etch glass. Should the sulphuric acid contain hydrofluoric acid, the latter may be easily removed by diluting with an equal volume of water and evaporating in a platinum dish to the original strength.

Page  219 ~ 147.] SEPARATIONS. 219 trated by evaporation, allowed to cool, transferred to a platinum vessel, hydrochloric acid added to feeblv acid reaction, and the fluid allowed to stand until the carbon dioxide has escaped. It is then supersaturated with amlnnonia, heated, filtered into, a bottle, caliumn chloride added to the still hot fluid, the bottle closed, and allowed to stand at rest. If a precipitate separates after some time it is collected on a filter, dried, and examined by the method described in 5 (Il. RIOSE). 8. Minute quantities of metallic fluorides in minerals, slags, &c., may also be readily detected by means of the blotopipe. Bend a piece of platinumn foil, and insert it in a glass tube as shown in fig. 42, introduce the finely triturated substance mixed with fused and powdered sodium metaphosphate, and let the blowpipe flame play upon it so that the products of combustion may pass into the tube. A metal- F g. 42. lie fluoride treated in this way yields hydrofluoric acid gas, which betrays its presence by its pungent odor, the dimming of the glass tube (which becomes perceptible only after cleaning and drying), and the yellow tint which the acid air issuing from the tube imparts to a moist slip of Brazil-wood paper * (BERZELIUS, SNITIISON). When silicates containing metallic fluorides are treated in this manncr gaseous silicon fluoride is formed, which also colors yellow a moist slip of Brazil-wood paper inserted in the tube, and leads to silicic acid being deposited within the tube. After washing and drying the tube, it appears here and there dimmed. A small quantity of a fluoride present in a mineral containing water may generally be detected by heating the subBtance by itself in a glass tube sealed at one end and inserting a slip of Brazil-wood paper in the tube; under the circumstance the paper will usually turn yellow (BERZELIUS). ~ 147. Recapitulation and remarks.-The barium compounds of the acids ot the third division are dissolved by hydrochloric acid, apparently without decomposition; alkalies therefore reprecipitate theml unaltered, by neutralizing the hydrochloric acid. The barium compounds of the acids of the first division show, however, the same deportment; these acids, must, therefore, if present, be removed before any conclusion regarding the presence of plospllolric acid, boric acid, oxalic acid, or hydrofluoric acid, can be drawn from the reprecipitation of a barium salt by alkalies. But even leaving this point altogether out of the question no great value is to be placed on this reaction, not even so far as the simple detection of these acids is concerned, and far less still as regards their separation from other acids, since ammonia fails to reprecipitate from hydrochloric acid solutions the barium salts in question, and more particularly barium borate and barium fluoride, if the solution contains any considerable proportion of free acid or of an amImonium salt. Boric acid is well characterized by the coloration which it imparts to the flame of alcohol, and also by its action on turmeric paper. The latter reaction is more particularly suited for the detection of very minute traces. Heavy metals, if present, are * Prepared by moistening slips of fine printing-paper with decoction of Brazil-wood.

Page  220 22.0 INOR1GANIC ACIDS. GROUP I. DIV. HI. [~ 147. most conveniently removed first by bydrosulphuric acid or amnmo(niuln sulphide. Before proceeding to concentrate dilute solutions of boric acid the acid must be combined with all alkali, otherwise a large portion of it will volatilize with the aqueous vapolrs. Small quantities of boric acid may also be safely and easily detected by the spectroscope. The detection of phosphoric acid in compounds soluble in water is nlot difficult; the reaction with magnesium sulphate, &c.. is the best adapted for the purpose. The detection of phosphoric acid ill insoluble compounds cannot be effected by means of magnesinm solution. Ferric chloride (~ 142, 9) is well suited for the detection of phosphoric acid in its salts with the alkali-earth metals, and more particularly for the separation of the acid from the allkali-earth metals; the nitric acid solution of ainmoniuln molybdate is more especially adapted to effect the detection of phosphoric acid in presence of aluininiun alld iron. I must repeat again that both these reactions demand the strictest attention to the directions given. If present in combination with oxides of the fourth, fifth, or sixth group, phosphoric acid may be separated by the inethod given ~ 142, 11, or by precipitating the bases with hydrosulphuric acid or amlmonium su]phide. Oxalic acid may alwvays 1)e easily detected in aqueous solutions of oxalates of the alkalies, by solution of calciuln sulphate. The formation of a finely pulverulent precipitate, insoluble in acetic acid, leaves hardly a doubt Oll the point, as racelnic acid alone, which occurs so very rarely, gives the same reaction. In case of doubt the calcium oxalate may be readily distinguished from the racemate, by simple ignition, withl exclusion of air, as the decomposed racemate leaves a considerable proportion of charcoal behilld; the racemate dissolves moreover ill cold solution of potassa or soda, in which calcium oxalate is illsolul)le. The deportment of the oxalates with sulphurie acid, or with manganese dioxide and sulphuric acid, affords also sufficient means to confirm the results of other tests. In insolullle salts the oxalic acid is detected most safely by decomplosigllr thleln by boilillg with solution of sodium carbonate, or by 1hydrosulph 1lric acid or arnlnonium sulphide (~ 145, 8). I miust finally also call attention here to the fact that there are certain soluble oxalates which are not precipitated by calcium salts; these are more particularly chromic oxalate and ferric oxalate. Their nlonplecipitation is owing to the circumstance that these salts form soluble double salts with calcium oxalate. liydroJfuoric acid is readily detected in salts decomposable by sulphuric acid; only it must be borne in mind that an over large proportion of sulphuric acid impedes the free evolution Af hydrofluoric gas, and thus inpairs the delicacy of the reaction; also that the glass cannot be distinctly etched if, instead Af hydrofluoric acid, silicon fluoride alone is evolved; and

Page  221 ,~ 148, 149.] Dy. I. Iv. CA.RBONIC ACID. 221 therefore, in the case of compounds abounding in silicon, t1he safer wayv is to try, besides the reaction given ~ 146, 5, also the one given in 6. In silicates which are not decomposed by sulphuric acid, the presence of fluorine is often overlooked, because the analyst omits to examine the compound carefully by the method given in 7. ~ 148. PHOSPHOROUS ACID, H3 P 03. Phosphorous oxide (P2 03) is a white powder, which admits of sublimation, and burns when heated in the air. It forms with a small proportion of water a thickish fluid, which by long standing yields crystals of phosphorous acid. Heat decomposes phosphorous acid into phosphoric acid, and phosphoretted hydrogen gas, which does not spontaneously take fire. It freely dissolves in water. Of the salts those with alkali base are readily soluble in water, all the others sparingly soluble; the latter dissolve in dilute acids. All the salts are decomposed by ignition into phosphates, which are left behind, and hydrogen, or a mixture of hydrogen and phosphoretted hydrogen, which escapes. With silver nitrate separation of metallic silver takes place, more especially upon addition of ammonia and application of heat; with mercurous nitrate, under the same circumstances, separation of metallic mercury. From mercuric chloride in excess phosphorous acid throws down mnercurous chloride after some time, more rapidly upon heating. B(arium chloride and calcium chloride produce in not over-dilute solutions of phosphorous acid, upon addition of ammonia, white precipitates, soluble in acetic acid. A mixture of magnesium sulphate, ammonium chloride, and ammonia will precipitate only rather concentrated solutions. Lead acetate throws down white lead phosphite, insoluble in acetic acid. By heating to boiling with sulphurous acid in excess phosphoric acid is formed, attended by separation of sulphur. In contact with zinc and dilute sulphuric acid phosphorous acid gives a mixture of hydrogen with phosphoretted hydrogen, which accordingly fumes in the air, burns with an emerald-green color, and precipitates silver and silver phosphide from solution of silver nitrate. Fourth Division of the First Group of the Inorganic Acids. ~ 149. a. CARBON C, 12, AND CARBONIC ACrD, H2 C 03. 1. CARBON is a solid tasteless and inodorous body. The very highest degrees of heat alone can effect its fusion and volatilization. All carbon is combustible, and yields carbon dioxide, when burnt with a sufficient supply of oxygen or atmospheric air. In the diamond the carbon is crystallized, transparent, pellucid, exceedingly hard, difficultly combustible; in the form of graphite it is opaque, blackish-gray, soft, greasy to the touch, difficultly combustible, and stains the fingers; as charcoal produced by the decomposition of organic matter it is

Page  222 222 INORGANIC ACIDS. GROUP I. DIV. IV. [~ 149. black, opaque, non-crystalline-sometimes dense, shining, and difficultly combustible, and sometimes porous, dull, ar,d readily comnbustible. 2. CARBON DIOXIDE OR CARBONIC ANHYDRIDE, C 02, at the comn. mon temperature and common atmospheric pressure, is a colorless gas of far higher specific gravity than atmospheric air, so that it may be poured fromn one vessel into another. It is inodorous, has a sourish taste, and reddells moist litmus-paper; but the red tint disappears again upon drying. Carbon dioxide is readily absorbed by solution of soda formning a carbonate; it dissolves pretty copiously in water, and the solutionl may be assumed to contain CARBONIC ACID, 112 C 03 (= C02 + 1120), although this body llas not been isolated.* 3. The AQUEOUS SOLUTION OF CARBONIC ACID has a feebly acid and pungent taste; it transiently imparts a red tint to litnmls-paper, and colors solution of litmus wile-red; it loses car bonl dioxide w-hen shaken with air in a half-filled bottle, and morle completely still upon application of heat. Some of the CARBONATES lose carbon dioxide by ignition; most of them are white or colorless. Of the normal carbonates olnlv those with alkali base are soluble in water. The solutions manlifest a very strong alkaline reaction; most of the carbonates insoluble in water dissolve in aqueous carbonic acid. 4. The carbonates are decomposed by all free acids soluble in water, with the exception of hydrocyanic acid and hydrosulphuric acid. Most carbonates are decomposed in the cold, but several (lnagnesite, for instance) require heat. The decomposition is attended with EFFERIVESCEZNCE carbon dioxide being disengaged as a colorless and inodorous gas, which transiently imparts'a reddish tint to moist litmus-paper. It is necessary to apply the decomposing acid in excess, especially when operating uponl carbonates with alkali base, since the formation of hydrogen carbonates will frequently prevent effervescence if too little of the decomposing acid be added. Substallnces which it is intended to test for carbonic acid should first be heated with a little water, to' prevent any mistake which might arise from the escape of air-bubbles upon g teat ie dry substances with the acid. Where there is reason to appreheld loss of car bonic acid upon boiling with water, lime water should be used instead of pure water. If you wish to prove tlhat the escaping gas is really carbon dioxide, dip a glass rod in baryta water alld thold it inside the test-tube near the fluid; a white pellicle will form on the baryta-water, as is explained in 5. 5. Lime water and barytac-water, brought into contact with carbon dioxide, carbonic acid, or with soluble carbolates, proOH Sodium carbon- 0ONa *Carbonicacid,C0<0 H ate (normal), C O<Na; Hydrogen sodium C H Barium O carbonate (acid < C O >arbonate, Ba carbonate (acid), 0 Na carbonate, 0

Page  223 ~ 150.] SILICIC ACID. 228 duce white precipitates of normal CALCIUM CARBONATE, Ca C O, or BARIUM CARBONATE, Ba C 03. In testilg for free carbonic acid the reagents ought always to be added in excess, as the carbonates of the alkali earths are soluble in aqueous carbonic acid. The precipitates dissolve in acids, with effervescence and are not reprecipitated fromn such solutions by ammonia, after the complete expulsion of the carbonic acid by ebullition.. Aslime-water dissolves very minute quantities of calcium carbonate, the detection of exceedingly minuilte traces of carbonic acid requires the use of a lime-water saturated with calciuln carbonate by long digestion therewith (WELTER, BERTItOLLET). 6. Calcium chloride and barium chloride immediately produce in solutions of normal alkali carbonates, precipitates of CALCIUM CARBONATE or of BARIUM CAKBONATE; in dilute solutions of acid carbonates these precipitates are formed only upon ebullition; with aqueous carbonic acid these reagents give no precipitate. ~ 150. b. SILICIC ACID, Si (O II)4 (Si. 28). 1. SIIICIC OXIDE or SILICA is colorless or white, in the common blowpipe flame unalterable and inlfusible. It fuses in the flame of the oxyhydrogen blowpipe. It is met with in the crystalline:tate (quartz, tridymite), and arnorphols. It is insoluble in water and acids (with the exception of hydrofluoric acid, which dissolves the amorphous variety easily, the crystalline varieties with more difficulty). The amorphous silicic oxide dissolves in hot aqueous solutions of potassa alld soda and their carbonates; but the crystallized silicic oxide is insoluble or nearly so in these fluids. If either of the two is fused with excess of a caustic alkali or alkali carbonate, a basic silicate of the alkali is obtained which is soluble in water. The SILICATES with alklali base alone are soluble in water. 2. The solutions of the alkaline silicates are decomposed by all acids. If a large proportion of hydrochloric acid is added at once to even concentrated solutions of alkali silicates the separated silicie acid remains in solution, probably as the nor mal acid, Si (O 11)4; but if the hydrochloric acid is added gradually drop by drop, whilst stirring the fluid, the greater part of the silicic acid separates in a gelatinous form. The more dilute the fluid, the more silicic acid remains in solution, and in highly dilute solutions no precipitate is formed. If the solution of an alkali silicate, mixed with hydrochloric or nitric acid in excess, is evaporated to drynhess silicic acid separates in proportion as the acid escapes; uponI treating the residue with hydrochloric acid and water the silicic acid remains as an insolu

Page  224 224 INORGANIC ACIDS. GROUP I. DIV. IV. [ ~ 150 ble white powder.* Ammolninm chloride produces in not over-dilute solutions of alkali silicates precipitates of silicic acid (containing alkali). Heating promotes the separation. Silicic acid is readily soluble ill hot solution of potassa or soda and in hot solutions of normal potassium and sodium carbonates. 3. Some of the silicates insoluble in water are decomposed by hydrochloric acid or nitric acid, others are not affected by (these acids, even upon boiling. In the decomposition of the former the greater portion of the silicic acid separates usually in the gelatinous, more rarely in the pulverulent form. To effect the complete separation of the silicic acid, the lhydrochloric acid solution, with the precipitated silicic acid suspended in it, is evaporated to dryness, the residue heated with stirring, at a uniform temperature, somewhat above the boiling point of water until no more acid fumes escape, then moistened with hydrochloric acid, heated with water, and the fluid containing the bases filtered from the residuary insoluble silicic acid. Of the silicates not decomposed by hydrochloric acid many, e.a., kaolin, are completely decomposed by heating with a mixtulre of S parts of strong sulphuric acid and 3 parts of water, the silieic acid being separated in the pulverulent form; many others are acted upon to some extent by this reagent. Silicates not decomposable by boiling with hydrochloric or sulphuric acid in the open air, may generally be completely decomposed by heating in a state of fine powder with the acids in sealed glass tubes at 200~ —210 in an air or paraffin bath. 4. If a silicate, reduced to a fine powder, is fused with 4 parts of sodium carbonate until the evolution of carbon dioxide has ceased, and the fused mass is then boiled with water, the greater part of the silicic acid dissolves as sodium silicate, whilst alkali earth and earth metals (with the exception of aluminium and berylliuml, which pass more or less completely into the solution), and heavy metals are left undissolved as carbonates or oxides. If the fused mass is treated with water, then, without previous filtration, hydrochloric or nitric acid added to strongly acid reaction, and the fluid evaporated as directed in 3, the silicic acid is left undissolved, whilst the bases are dissolved. 5. If an insoluble silicate containing alkali metals is mixed in the state of powder with 3 times its weight of precipitated calcium carbonate and one-half its weight of ammonium chloride, and the mixture is heated in a platinum crucible for half an hour to redness, too high a heat being avoided, a somewhat sintered mass is obtained, which, on being digested in hot water, falls to powder, and yields a solution containing, besides calcium chloride and hydroxide, all the alkalies of the silicate, in the form of chlorides (J. LAWRENCE SMITH). 6. If hydrofluoric acid, in concentrated aqueous solution or in the gaseous state, is made to act upon silicic oxide, fluosilicic gas escapes (Si 02 + 4H1 F= Si F4 + 2H2 0); dilute acid dissolves silica to hydrofluosilicic acid (Si 02 + 6H F = H2 Si F6 + 2H2 O). Hydrofluoric acid acting upon silicates gives rise to the formation of silicofluolides (Ca Si 03 + 6H F.Ca Si Fs + 3H2 O), which by heating with hydrated sulphuric acid are * The gelatinous silicic acid, and the dried "silica" are probably anhydro acids, analogous to pyrophosphoric acid and metaphosphoric acid.

Page  225 . 151.] SILICIC ACID. SEPATRXTIoVS. 225 changed to sullphates, with evolution of hydrofluoric and fluosilicic gases. If the powdered silicate is mixed Nwith 3 parts of ammonium fluoride, or 5 parts of calcium fluoride in powder, the mixture made into a paste with concentrated sulphuric acid, and heat applied (best in the open air) until no more fumes escape, the whole of the silicic acid present volatilizes as fluosilicic gas. The bases present are found in the residue as sulphates, mixed, if calcium fluoride was used, with calcium sulphate. 7. On mixing 1 part of finely powdered silica, or a silicate with 2 parts of powdered cryolite or fluor spar (free from silica), and 4 or 5 parts of concentrated sulphuric acid, heating the mixture moderately in a platinum crucible, but not allowinlg it to spurt, and then holding close over the surface the loop of a stout platillnm wire which has been freshly ignited, and now contains a drop of water; a pellicle of silicic acid will soon form on the latter from decomposition of the escaping silicon fluoride (BARFOED). 8. If silicic oxide or a silicate is fused with a small proportion of sodium carbonate in the loop of a platinumn Wire FROTHING is observed in the bead owingr to the evolution of cuarbon dioxide. The bead obtained with pure silicie acid, or silicic oxide, is always clear when hot, with silicates when they are rich in silicic acid (as the felspathic rocks), the bead is also clear, otlerwise it is opaque. The clearncess of the cold bead depends upon the proportion between silicic acid, sodiumn and other bases. 9. Sodium metcpho.shate, in a state of fusion, fails nearly altogether to dissolve silicic oxide. If therefore silicic acid or a silicate is fused, in small fragments, with hydrogen ammoniuml sodiumr phosphate on a platinum wire the bases are dissolved, whilst silicic oxide separates and floats about in the clear bead as a more or less translucent mass, exhibiting the shape of the fragment of substance used. ~ 151. Recapitulation and remnarks. —Carbon dioxide or free car — 7onic acid is readily known by the reaction with lime-water; the carbonates are easily detected by the evolution of an inodoroIs gas, when they are treated with acids. When operating upon compounds which evolve other gases besides carbon dioxide, the gas is to be tested with line-water or baryta-water. Silicic acid, both in the free state and in silicates, may usually be readily detected by the reaction with sodium mnetaphosphate. It differs moreover from all other bodies in the formn in which it is always obtained in analyses, by its insolubility in acids (except hydrofluoric acid), and in fusing potassium disulphate, and its solubility in boiling solutions of alkalies anld alkali carbonates; and from many bodies (especially from. titanic oxide), by completely volatilizing upon repeated evapor

Page  226 '226 INORGANIC ACIDS. GROUP II. [~ 152. ationl in a platinum dish, with hydrofluoric acid (or ainloniuIn fluoride) and sulphurie acid. Secon.dc Groiup. ACmDS WHICTI ARE PRECIPITATED BY SILVER NITRATE, BUT NOT BY BAMIITUM CHLORIDE: I[/Jdrochloric Acid, yddrlobromic Acid, Ifydriodic Acid, Hflydrocyanic Acid, fJ/cdrqferro- and 11qdir'ofrricycatnqic Acid, Hfydcrozpub2)/tric Acid (Nitrons Acid, Hypochlorons Acid, Chlorous Acid, Hypophosphorous Acid). The silver compounds corresponding to the haalogen and sulpl/tr acids of this grollp, are insoluble in dilute nitric acid. These acids decolnpose with metallic oxides, and hydroxides, the metals combining with the chlorine, bromine, iodine, cyanogen, or sulphur, whilst the oxygen of the metallic oxide, or the hydroxyl of the hydroxide, formts water with the hydrogen of the acid. ~ 152. a. CHLORINE, C1. 35.5, AND HYDROCIILORIC ACID, H C1. 1. CHrLoRNE is a heavy yellowish-green gas of a disagreeable and suffocating odor, which has a most injurious action upon tile respiratory orgoans: it destroys many vegetable colors (litnmUS, indigo-blue, &c.); it is not inflammiable, and supports the combustion of few bodies only. Minlutely-divided antimony, tin, &c., spontaneously ignite in it, and are converted illto chlorides. It dissolves pretty freely in water; the chlorine water formed has a faint yellowish-green color, sliells strongly of the gas, bleaches veg'etable colors, is decomposed by the action of light (~ 31), and loses its smell when sllaken with mnercury, the latter being converted into a mixture of mercurous clhloride and metal. Slnall quantities of free chlorine mlay be ieadily detected in a fluid by the red color inpalrted to a mixturle of potassium sulphocyanate anld a ferrous salt, or —in the abIbsence of nitrous acid —by the blue color imparted to a mixtuare of starch paste and potassium iodide (see ~ 154, 9). 2. IIYDROCHLORIC ACID, at tile conllnon temperature and coilmon atmospheric pressure, is a colorless ras, which forl'ns dellse fumes in the air, is suffocating and very irritating, and dissolves in water with exceeding facility. The concentrated solution (funiing hydrochloric acid) loses a large portion of its gas upon heating. 3. The normal METALLIC CHLORIDES are readily soluble in vwater, with the exception of lead, silver, and mnercurous chlorides; most of the chlorides are white or colorless. Many of them volatilize at a high temperature, without suffering decom

Page  227 ~ 152..] HYDROCHLORIC ACID. 2 7 position; others are decomposed upon ignition, and many of them are fixed at a moderate red heat. 4. Silver nitrate produces in even highly dilute solutions of free hydrochloric acid or of metallic chlorides white precipitates of ARGENTrIC CHLORIDE, Ag C1, which upon exposure to light change first to violet, then to black by reduction tc ARGENTOUS CHLORIDE, Ag2 C1; they are insoluble in dilute nitric acid, but dissolve readily in ammonia as well as in potassiulm cyanide, and fuse without decomposition when heated. (Comlpare ~ 115, 7.) 5. lMlercurous nitrate and lecad acetate produce in solutions containing free hydrochloric( acid or metallic chlorides precipitates of 5MERCUROUS CIILORIDE, IHg2 Cl2, ald LEAD CHLORIDE, Pb Cl2. For the properties of these precipitates see ~ 116, 6, and'~ 117,7. 6. If hydrochloric acid is heated with mangcnese dioxide, or a chloride with mnazgycaneese dioxide and 8szl)/ uric acid, CHLORINE is evolved, which may be readily recognized by its odor, its yellowish-green color, and its bleaching action upon vegetable colors.. The best way of testing the latter is to expose to the gas a moist slip of litnmus-paper, or of paper colored with solution of indigo. 7 If a metallic chloride is triturated with potassium dichromzate, the dry mixture treated with concentratedl sulphuric acid in a tubulated retort, and a gentle heat applied, the deep brownish-red gas of cIRmoMIc OXYcrLORIDE, Cr 02 C12, (" CHLOROcHROMIC ACID ) is copiously evolved, which condenses into a fluid of the same color, and passes into the receiver. If this distillate is mixed with ammonia in excess, a yellow-colored liquid is produced, fromn the formation of anlmonium chromlate, Cr O2 C12 + 4 N 113 2 11 O = Cr 04 (N 4)2 q~ 2 N I-14 C1. Upon addition of an acid the color of the solution changes to a reddish-yellow, owing to the formationl of amlnonium dichromate. 8. In the metallic chlorides insoluble in water and nitric acid the chlorine is detected by fusing them with sodium car5bow;tte, and treating the fused mass with water, which will dissolve, besides the excess of the sodium carbonate, the sodiumn chloride forlmed in the process. 9. If in a bead of sodciuam metcaposphate on a platinum wire, cuptrice oxide be dissolved in the outer blowpipe flame in sufficient quantity to make the mass nearly opaque, a trace of a substance containing chlorine added to it, while still in fusiol), and the bead then exposed to the reducirng flame, a fine BLUECOLORED flame, iielilining to PURPLE, Will be seen encircling it so long as chlorine is present (BERZELIUS). With regard to the spectrlrn of copper chloride, compare ~ 157.

Page  228 228 INORGANIC ACIDS. GROUP II. r 153. ~ 153. b. BROMINE, Br. 80, AND IHYDROBnROMIC ACID, I Bn. 1. BROMINE is a heavy reddish-brown fluid of a very disagree. able chlorine-like odor; it boils at 63~, and volatilizes rapidly even at the common temperature. The vapor is brownish-red. Bromine bleaches vegetalle colors like chlorine; it is pretty soluble in water, but dissolves more readily in alcohol, and very freely in ether. The solutions are vellowish-red. 2. HYDROBROMIC ACID GAS, its AQUEOUS SOLUTION, and the MIETALLIC BROMIDES offer in their,general deportment a great analogy to the corresponding chlorides. 3. Silver nitrate produces in aqueous solutions of hydrobromic acid or of bromides a yellowish-white precipitate of SILVER BROMIDE, Ag Br, which chainges to gray upon exposure to light; this precipitate is insoluble in dilute nitric acid, and somewhat sparingly soluble in ammonia, but dissolves with facility in potassium cyanide. 4. Palladious nitrate, but not palladious chloride, produces in neutral solutions of metallic bromides a reddish-brown precipitate of PALLADIOUS BROMIDE. In concentrated solutions this precipitate is formed immediately; in dilute solutions it makes its appearance only after standing some time. 5. Nitric aoid decomposes hydrobromic acid and the bromides, with the exception of silver and mercury bromnides, 1upon the application of heat, and liberates the bromine, by oxidizing the hydrogen or the metal. In the case of a solution, the liberated bromine colors it yellow or yellowish-red. With bromides in the solid state or in concentrated solution, brownishred (if diluted, brownish-yellow) vapors of bromine gas escape at the same time, which, if evolved in sufficient quantity, condense in the cold part of the test-tube to small drops. nll the cold, nitric acid, even the red fuming fails to liberate the bromine in very dilute solutions of bromides, nor is it liberated 1by solution of nitrogen tetroxide in sulphuric acid,* or by hydrochloric acid and potassium nitrite. 6. Chlorine, in the gaseous state or in solution, immediately liberates bromine in the solutions of its compounds; the fluid assunming a yellowish-red tint if the quantity of the bromine present is not too minute. A large excess of chlorine must be avoided, since this will cause formation of bromine chloride, which will destroy the color wholly or nearly so. This reaction is nmade much more delicate by addition of a fluid which dissolves bromine and does not mix with water, as carbon disulPhide or chloroform. Mix the neutral or feebly acid solution in a test-tube with a little of one of these fluids, sufficient te * See the first note, p. 231.

Page  229 153.] HYDROBROMIC ACID. 22 0 form a large drop at the bottom, then add dilute chlorine-water drop by drop, and shake the tube. With appreciable quantities of bromine, e.g., 1 part in 1000 parts of water, the drop at the bottom acquires a reddish-yellow tint; with very minute quantities (1 part of bromine in 30,000 parts of water), a pale yellow tint, which, however, is still distinctly discernible.'Ether was formerly used for this reaction; this agent is by no neans so well suited for it. A large excess of chlorille-water lnust be avoided in this experiment also, and it must always be ascertained first whether the chlorine-water, mixed with a large quantity of water and some carbon disulphide or chloroform, and shaken, will leave these reagents quite uncolored. If not, the chlorine-water is not suited for the intended purpose. If the solution of bromine in carbon disulphide or chloroform is mixed with some solution of potassa, the mixture shaken, and heat applied, the yellow color disappears, and the solution now contains potassium bromide and bromnate. By evaporation and ignition the potassium bromate is converted into potassium bromide, and the ignited mass may then be fur.. ther tested as directed in 7. 7. If bromides are heated with mangangczese dlioxide and sulp/aurie acid, BROWNISH-RED VAPORS OF BROMINE are evolved. Presence of chlorides in large proportion is not favorable to the reaction and requires addition of some water, and the sulphlurie acid to be added gradually in very small quantities. If the bromine is present only in very minalte quantity, the color of these vapors is not visible. But if the mixture is heated in a small retort, and the vapors are trallsmitted through a long glass condenser, the color of the brorinle mllay generally be seen by looking lengthways through the tube, and the first drops of the distillate are also colored yellow. The first vapors and the first drops of the distillate should be received in a testtube containing some starch moistened with water; since 8. If moistened starch* is brought into contact with free bromine, more especially in form of vapor, YELLOW BROMIZED STATRC is forllled. The coloration is not always instantaneous. The reaction is rendered most delicate })y sealing the test-tube which contains the moistened starch and the first drops of the distillate from 7, and then cautiously inverting it, so as to cause the moist starch to occupy the upper part of the tube whilst the fluid occupies the bottom. The presence of even the slightest trace of bromine will now, in the course of from twelve to twenty-four hours, impart a yellow tint to the starch, which, however, after some time, will again disappear. The reaction may be called forth in a simple nmanner, almost with the same degree of delicacy, by gently heating the fluid containinl free bromine, or also the original mixture of bromide, manganese dioxide, and sulphuric acid, in a very small beaker, covered with a watchglass with a slip of paper attached to the lower side, moistened with starch paste, and sprinkled with starch powder. * [See that the starch-is not of the kind which, as powder, is made yellcw by kdine. Such starch, boiled to a paste, reacts blue with iodine. NAGELI.1

Page  230 230 INORGANIC ACIDS. GROUP II. [~ 154. 9. If sulphuric acid is poured over a mixture of a bromide with potas sium dichlromczte, and heat is then applied, a brownisb-red gas is evolved, exactly as in the case of chlorides. But this gas consists of pure Br1.Om(3INE, and therefore the fluid passing over does not turn yellow, but becomes colorless UI)on supersaturation wvith ammnonia. 10. If a solution of hydroblronic acid or a bromide is mixed Nwith a little auric chlor1ide, a straw color or dark orange color is produced flrom the forlmation of AunIc BIOMIDE. If'iodine is present it must be removed b)efore the solution of gold is added (BILL). 11. In thle mletallic bromides which are insoluble in water and nitric acid, the bromine is detected in the same way as the chlorine in the corresponding chlorides. 12. If a substance containing bromine is added to a sodium zmetaphosphate bead satarated with cupric oxide. and the bead is then ignited in the inner blowpipe flame, the flame is colored BLUE, incl-ining to GREEN, more particularly at the edges (BERZELIUS). With regard to the spectrum of copper bromide see ~ 157. ~ 154, C. IODINE, I. 127, AND I-IYDRIODIC ACID, H I 1. IOI)NE is a solid soft body of a peculiarly disagreeable odor. It is generally seen in the form of black, shiningr, crystalline scales. It fuses at a gentle heat; at a somewhat higher temperature it is converted into vapor, which has a beautiful violet-blue color, and condenses upon coolinlg to a black sublimate. It is very sparingly soluble in water, but readily in alcohol and ether, as well as inl solution of potassium iodide. The aqueous solution is lioht-brown, the alcoholic, ethereal, and potassium iodide solutions are deep red-brown. Iodille clestroys vegetable colors only slowly and imperfectly; it stainls thle skiii brown. Crystals of iodine, its vapor and its solutions (best the aqueous) give to mzoist starch powder, sometimes a y-ellow, most usually a purple or blue color, with stacrch-pa<ste always an intensely purple or dclee blue. The color of iodized( stcerch is destroyed by alkalies, by chlorine and bromine, and bly sulphurous acid and other reducing agents. 2. IIYDRIODIC ACID GAS resembles hydrochloric and hvdrobromlic acid gas; it dissolves copiously in water. The cololrless solution of hydriodie acid turins speedily to a reddishbrown in (contact with the air, water being formed, and a solution of iodine in hydrioliec acid. 3. The IODIDES also correspond in many respects with the chlorides. Of the iodides of the heavy metals, however, imanly more are insoluble in water than is the case with the coliespondllCig chlorides. Manly iodides have characteristic colors. e.g., lead iodide, mereurous iodide anlld ereuric iodide. 4. Silvele nitrate produces in aqueous solutions of hydriodic acid andc of iodides Yellowish-white precipitates of ARGENTIC iommDn Ag I, which blacken on exposure to light; these pro. -— r`~ —--- -- In

Page  231 ~ 154.] HYDRIODIC ACID. 231 c(ipitates are insoluble in dilute nitric acid, and ver'y sj'arini72y soluble in ammonia, bullt dissolve readily in potassium cyanide. 5. Palladious chloride and palltadious nitrate produce even in very dilute solutions of hydriodic acid or metallic iodides, a brownish-black precipitate of PALL,ADIOUS IODIDE (Pd Ia), which dissolves to a trifling extent in saline solutions (sodium chloride, magnesium chloride, &c.), but is insol uble or nearly so in dilute cold hydrochloric and nitric acids. 6. A solution of 1 part of cuoric s&ellph7xte and 2~ parts of ferrotls sulphate throws down from neutral aqueous solutions of the iodides cuPnous IODIDE (Cu2 I2), in the form of a dirty white precipitate. The addition of ammonia promotes the complete precipitation of the iodine. Chlorides and bromides are not precipitated by this reagent. Instead of using the above mixture of sulphates, cul)ric sulphate alone may be added, and afterwards enough sulphurous acid to remove the brown color produced by separated iodine. 7. Pure nitric acid, free from nitrous acid, decomposes hydriodic acid or iodides only when acting upon them in its colcentrated form, particularly when aided by the application of heat. But nitrous acid and 9nitrogen trioxide decompose hydriodic acid and iodides with the greatest facility even in the most dilute solutions. Colorless solutions of iodides therefore acquire immediately a brownish-red color upon addition of some red fuminllg nitric acid, or of a mixture of this with col. centrated sulphuric acid, or, better still, upon addition of a solution of nitrogen tetroxide in sulphurie acid,* or of potas sium nitrite and some sulphurie or hydrochloric ac(id. Froin more concentrated solutions the iodile separates in the forln ol black scales, whilst nitrogen dioxide and iodine vapor escape. 8. As the blue coloration of IODIZED s'ARCH (see 1.) remainls visible in much more highlv dilute solutions than the yellow color of solution of iodine in water, the delicacy of the reaction just now described (7.) is considerably heightened by mixillg the fluid to be tested for iodille first with sotne tllin to:lerably clear starch/paste,t then acdillg a few drops of dilute sulpllluric acid, to make the fluid strongly acid, and finally one of tlme rea(ents given in 7. Of the solution of nitrogen tetroxide in sulphulric acid a single drop oil a glass rod suffices to produce the reactionl most distinctly. I can therefore strongly recomnmend this reagellt, which was first proposed by OTTO. Red funrillg nitric acid must be added in somnewhat larger quantity, to call forth the reaction in its highest intensity; this reagent therefore is not well adapted to detect very minute quantities of iodine. The reaction with potassium nitrite also is very delicate. The fluid to be tested is mixed with dilute sulphuric acid or with hydrochloric acid to distinctly acid reactionl, allnd a drop or two of a concentrated solution of potassium nitrite is then added. In cases where the quantity of iodine present * Obtained by heating starch with nitric acid, and passing the evolved gases into oil of vitriol. t Prepared by heating a mixture of starch with 50 parts of cold water tc }oiling.

Page  232 232 INORGANIC ACIDS. GROUP II. [~ 154. is very lninute the fluid turns reddish, illstead of blue. An excess of the fluid containing nitrous acid or nitrogen tetroxide does not materially impair the delicacy of the reaction. As iodized starch becomes colorless in hot water, the fluids lunst of necessity be cold; the colder they are the molre delicate the reaction. To attaill tle highest de(ree of delicacy, cool the fluid with ice, let the starch deposit, anld place the test-tube upon white paper to observe the reaction (cornpare also ~ 157). 9. Chlorine gcs and chlorine-wcater decompose compounds of iodiine also, setting the iodine free; but if the chlorile is applied in excess the liberated iodine combines with it to colorless iodine chloride. A dilute solution of a metallic iodide, mixed with starch-paste, acquires therefore upon addition of a little chlorine-water at once a blue tint, but becomes colorless again upon addition of more chlorine-water. As it is therefore difficult not to exceed the proper limit, especially where the quantity of iodine present is only small, chlorine-water is not well adapted for the detection of minute quantities of iodine. 10. If a solution containing hydriodic acid or an iodide is mnixed with chloroform, or carbon disulphide, so as to leave a few drops undissolved, and one of the agents by which iodine is liberated (a drop of a solution of nitrogen tetroxide in sulphuric acid-hydrochloric acid and potassium nitrite-chlovine-water, &c.) is added, the mixture vigorously shaken, and then allowed to stand at rest, the chloroform or the carblon disulphide colored violet-red by the iodine dissolved in it, subsides to the bottom. This reaction also is exceedingly delicate. If a solution containiing free iodine is shaken with petroleum, benzol, or ether, the two former are colored red, the ether reddish-brown or yellow. Iodine colors ether much more intensely than an equal quantity of bromine. 11. If metallic iodides are heated with concentrated sulphuric acid, or with sullhuric acid and manganese dioxide, or with sualphuric acid and potassiumn dichromate, or with ferric chloride and a little hydrochloric acid, iodine separates, which may be known by the color of its vapor, or in the case of very minute quantities, by its action upon a slip of paper coated with starch-paste. 12. The iodides which are insoluble in water and nitric acid comport themselves upon fusion with soditum carbonate in the same manner as the correspondilng chlorides. 13. A sodium metap/hosp.hate bead, saturated with eupric oxide, when touched with a substance containing iodine, and ignited in the inner blowpipe flame, imparts an intense GREEN color to the flame. With regard to the spectrum of io(lide of copper see ~ 157.

Page  233 ~ 155.] CYANOGEN AND HYJDIWOCYANIC ACID. 233 ~ 155. d. CYANOGEN, C N OR CY. AND IYDROCYANIC ACID, H C N. 1. CYANOGEN is a colorless gas of a peculiar penetrating odor; it burnls with a crilnson flame, and is pretty soluble ill water. 2. HYDROCYANIC ACID is a colorless, volatile, inflammable liquid, the odor of which distantly resembles that of bitter almonds; it is miscible with water in all proportions; il the pure state it speedily suffers decomposition. It is extremely poisonous. 3. The CYANIDES of the alkali and alkali-earth metals are soluble in water; the solutions smell of hydrocyanic acid. They are readily decomposed by acids, even by carbonic acid. Potassium and sodium cyanides are not decomposed by fusion if air is excluded; when fused with oxides of lead, copper, antimony, tin, &c., they reduce these oxides, ald are converted into cyanates. Only a few of the cyanides with heavy metals are soluble in water; all of them are decomposed by ignition, the cyanlides of the noble metals being converted into cyanogen gas and inetal, the cyanides of the other heavy metals into nitrogenl gas and metallic carbides. Many of the cyanides with heavy metals are not decomposed by dilute oxygen acids, and only with difficulty by concentrated nitric acid. By heating and evaporation with concentrated sulphuric acid all cyanides are decomposed; hydrochloric acid decomposes a few of them; hydrosulphuric acid decomposes lmany cyanides. 4. The CYANIDES have a great tendency to combine with each other; hence most of the cyanides of the heavy metals dissolve in potassium cyanide. The resulting compounds are either: a. Double salts, e. g., nickel potassium cyanide, Ni (C N)2 + 2.K C N. Fromn solutions of such double salts acids, by decomposing the potassillm cyanide, precipitate the mnetallic cyanide which was combined with it.-Or, b. Ilaloid salts, in which a metal, e. g., potassium, is combined with a comlpound radical consisting of cyanogen and another mIetal (iron, cobalt, managallese, cllhromium). The ferro- and the ferricyanide of potassium, (Fe (C N),. 4 K ON, also I4 Fe Cy, or K, Cfy and Fe2 (C N),. 6 1K C N, also KG Fe2 Cy,, or K6 Cfdy), and cobalticvanide of potassiuln (KI0 C Cy2) are compounds of this kind. From solutions of conmpounds of this nature dilute acids do not separate metallic cyanides in the cold. If the potassium is replaced by hydrogen, corresponding hydrogen acids are formed, which umust not be confounded with hydrocyanic acid. We will now first consider the reactions of hydrocyanic acid * In ferrocyanides Fe is bivalent (ferrous); in ferricyanides and cobalticy muides Fe2 and Co2 are sexivalent (ferric and cobaltic). See page 235.

Page  234 234 INORGANIC ACIDS. GROUP II. I~ 55.1 and the simple cyanides, then, in an appendix to this paragraph, those of lydroferro- and hydroferricyallic acid. 5. Silvcw? nii-trate produces in solutions of free hydrocyanlie acid and of cyanides of the alkali metals white precipitates of SILVER CYANIDE, Ag C, llwhich are readily soluble in potassiuml cyanide, dissolve with somne difficulty in ammonia, ald are insoluble ill dilute nitric acid; these precipitates are decomllposed by ignitionI, leaving metallic silver with some silver parayanllide. 6. If a solution of fer;'ous sulphate and a few drops of ferric chloride are added to a solution of free hydrocyanic acid no alteration takes place; but if solution of jotassa or soda is now added a bluishl-green precipitate fornms, which consists of a mixture of Prussian-blue, F1e, Cy,8, and ferrous-ferric hSdroxide. Upon now adding hydrochloric acid (best after previous application of heat) the ferrous-ferric hydroxide dissolves, whilst the P-russIAN-BLuIE remains undissolved. If only a -very iniunte quantity of hydrocyanic acid is present the fluid simply appears gleen after the addition of the hydrochloric acid, and it is only after long standing that a trifling blue precipitate separates fromn it. The sane final reaction is observed when a mixture of ferrous and ferric salt is mlixed with the solutioll of an alkali cyanide, and hydrochloric acid is then added. 7. If a liquid containing a little hydrocyanic acid or potassium cyanide is mixed with sufficient yellow amlmonium sulphide to impart a yellowish tint to the fluid, then with a little ammonia, and the mixture is warmled in a porcelain dishl, with renewal of the water if necessary, until it has )become colorless, and the excess of ammonium sulpllide is decomposed or volatilized, the fluid contains now ammonium sulphocvanate, and after being acidifiled with hydrochloric acid (which mnust not be attended with disengagement of hydrosulphuric gas), acquires a blood-red tint upon addition of ferric chloride (v. LIEBIG). This reaction is exceedingly deliclate. The following formula expresses the transformation of hydrocyanic acid into ammlllonium sulphocyanate, N H4S +4 N H +411 Cy=4(N H, Cy S) +N H4 S. If an acetate* is present the reaction takes place only upon addition of more hydrochloric acid. To discover the cyanogen in inlsoluble comopoends by converting it into ferric sulphocyanate you may proceed as follows:Fuse some sodium thiosulphate ('hyposulphite of soda") in the loop of a platinum wire till the water of crystallization has escaped, and the mass swells out, dip it in the substance, heat for a little time, removing it from the flame as soon as the sulphur iegins to burn, and theni dip the mass in a few drops of ferric chloride mixed withl a little hydrochloric acid. A permanent blood-red color will be produced. If the substance is heated too long the reaction fails, as the sodium sulphocyanate formed is then destroyed again. This method is well suited to distinguish silver chloride, bromide, or iodide from cyanide (A. FitnIDE). 8. On m ixing a moderately concentrated solution of an alkali metal cyanide with a little picric acid solution (1 of picric acid to 250 of water) and boilang, the fluid aptpears dark-red from formation of alkali metal picrocyamlate, the coloration increasing in intensity by standing. If the solution of thlle cyanide is very dilute, no more piclic acid must b)e added than is sufficient just to color the fluid lemon yellow. After boiling, the red coloration often does not make its appearance till the fluid has cooled and stood some time, The reaction is very delicate (C. D. BRAUN). * Or one of the salts mentioned ~ 111, 8.

Page  235 [~ 155. HYDROFERRICYANIC ACID. 235 9. On saturating filter papel with freshly prepared tincture of guaiacunm contliining 3 or 4 per cent. of the resin, allowing the alcohol to evaporate, moistening the paper with solution of copper sulphate containing ~ pet cent. of the salt, and then exposing it to air, in which a trace of hld:lrocyanic acid is l)resent, it becomes blue from liberation of oxygen, 3Cu 0 + 4H Cy —Cu3 Cy4+ 2H2 0 + O (PAGENSTECnHER, SCH6NBEIN). 10. If a very dilute solution of iodized starch is mixed with a trace of hydrocyanic acid, or after addition of dilute sulphuric acid, with a trace of an alkali-metal cyanide, the bllue color will disappear imlmediately, or after a short time, the iodine and the hydrocyanic acid being transformed into cyanogen iodide and hydriodic acid (SCHiINBEIN). This is a very delicate reaction, but cannot be relied upon without further tests, as many other substances decolorize iodized starch. 11. Neither of the above methods will serve to effect the detection of cyanogen in mercuric cyanide. To detect cyanogen in that compound the solution is mixed with hydrosulphuric acid; mercuric suipllide precipitates, and the solution contains free hydrocyanic acid. In solid mercuric cyanide the cyanogen is most readily detected by heating in a glass tube. (Comlpare 3.) Ap pendix. a. Hydrqferrocyanmc acid, 114 Fe" CyT or 11, Cfy. iHydro ferrocyanic acid is soluble in water. Some of the ferrocyanides, as those containing alkali and alkali-earth metals are soluble in water; but the greater part of them are insoluble in that meulstruutm. All the ferrot-yanides are decollposed by ignition; where they are not quite anhydrous, hydrocyallic acid, carbonlic acid, and ammloia escape, otherwise nitrogen and occasionally cyalogen. In solutions of hydroferrocyallic acid or ferrocyanides ferric chloride produces a blue precipitate of FERRIC FERROCYANIDE, Fe'/ (Fe" Cy,)3 or Fe7 C,8; curic suplz]ate a browvish-red precipitate of cuPRIC FERROCYANJIDE, Cu2 Fe Cy,; silver nitrate a white precipitate of ARGENTIC FERlROCYAnIDE, Ag4 Fe Cy,, which is insolublle in nitric acid id in ammonia, but dissolves ini potassiumn cyanide. If a iiot too dilute solutioll of an alkali-mletal ferroct anide is mixed with h/ydroc/doric acid, and solne ether is poured hon the top of the lixture, 1lYDRlO1ER-OMCYANIC ACID will separate inl the crystalline forml where the two fluids meet. Insofluble ferrocyalides are decomposed by boiling with solution of soda, sodiuml ferro(valnide beillg forlled, and the mnetals separate as hydroxides, ulless they are soluble in soda. If ferrocyanides are heated with a mixture of 3 parts concentrated sulphuric acid, and 1 part water, till the free acid is expelled, they are decomposed, anld the cyanogen is driven off in the form of hydroeyalic acid; the metals remain behind as sulphates. On projecting mletallic cyanides into fusing potassium nitrate, the cyanogel is collverted into carbon dioxide and nlitrogen, and the metals are converted into oxides, which remain inl the crucible. b. ]Jydroferricyanitc acid, 11 Fe/"' Cy,2, or 1-, Cfdy. l vIroferricyanic acid and many of the ferricyanides are soluble in water; all ferricyanides are decomposed by ignition like

Page  236 236 INORGANIC ACIDS. GROUP H. [~ 156. the ferrocyanides. In the aqueous solutiolns of hydroferricyanic acid and its salts jerric chtloride produces no blue precipi. tate; but jferrous sulphate produces a blue precipitate of FERROUS FEIRICYANIDE, Fe3" Fe21' Cy,, or 1Fe, Cfdy; cupric sulpAate a Yellowish green precipitate of CUPRIC FERRICYANI)E, Cu, Cfdy, which is insoluble in hydrochloric acid; silver nitrate an orange-colored precipitate of SILVER FERRICYANIDE, Ag, Cfdy, whlich is insoluble in nitric acid, but dissolves readily in ammonia and in potassium cyanide. The insoluble ferricyanides are decomposed by boiling in solution of soda, metallic oxides, or hydroxides beilg thrown down; in the fluid filtered off from them either sodiuln ferricyanide alone is found, or a mixture of sodiaum ferro- with ferricyanide. By heating with a imixture of 3 parts concentrated sulplllhuric acid, and 1 part water, and also by fusing with potassium nitrate, the ferricyanides are decomposed like the ferrocyeanides. ~ 156. e. SULPHnUR, S, 32, and IHYDROSULPHURIC ACID, II, S. 1. SULPHuR is a solid, brittle, friable, tasteless body, insoluble in water. It occurs occasionally in the form of yellow or brownish crystals, or crystalline masses of a yellow or brownish color, and occasionally in that of a yellow or yellowish-white, or grayish-white powder. It melts at a moderate heat; upon the application of a stronger heat it is converted into brownlishyellow vapors, which in cold air condense to a yellow powder, and on the sides of the vessel to drops. IIeated in the air it burns with bluish flame to sulphur dioxide, which betrays its presence at once by its suffocating oder. Concentrated nitric acid, nitrohvdrochloric acid, and a mixtlre of potassilum clllorate and hydrochloric acid, or, better, nitric acid, dissolve sulp)hur gradually, with the aid of a moderate heat, and con<lvert it into sulphuric acid; in boiling solution of soda sulllhur dissolves to a yellow fluid, which contains sodium polysulpllide antd sodium thiosulphate, Na, S2 0; in cold ammollnia it is illsoluble, in warml ammonia it dissolves to a small extent. Carbon disulphide dissolves the ordinary variety of sulphur with ease, but there is a kind which is insoluble in this menstrluulm. 2. HYDROSULPHURIC ACID, HYDROGEN SULPHIDE OR SULPIHURETTED HYDROGEN, at the common temperature, and under commonl atmospheric pressure, is a colorless inflammable gas, soluble in water, readily recognized by its smell of rotten eggs; it transiently imparts a red tint to moist litmns-paper. 3. Of the SULPHIDES only those of alkali and alkali-earth metals are soluble in water. These, as well as the sulphides of iron, manganese, and zinc, are decomposed by dilute mineral

Page  237 ~ 156.] HYDROSULPITUEIC ACID. 237 acids, with evolution of hydrosulphuric acid gas, hillch may be readily detected by its smell, and by its action upon solution of lead (see 4). The decomposition of polysuilphides is attended also with separation of sulphur in a finely-divided state; the white precipitate may be readily distinguished from similar precipitates by its deportment on heating. Part of the sulphides of the metals of the fifth and sixth groups are decomposed by concentrated and boiling hydrochloric acid, with evolution of hydrosulplhuric acid gas, whilst others are not dissolved by hydrochloric( acid, but by concentrated and boilinrg nitric acid. The compounds of sulphur with nlercury, gold, and platinum, resist the action of both acids, but dissolve in nitrohydrochloric acid. Upon the solution of sulphides in nitric acid, and in nitrohydrochloric acid, sulphuric acid is formed, and in most cases sulphur is also separated. I any metallic sulphides, more especially those of a higher degree of sulph-uration, give a sublimate of sulphur when heated in a tube sealed at one end. All sulphides are decomposed by f nsion with sodium nitrate and carb(onate; on extractinlg the fusion with water the sulphur is found in solution as sodium sulphate. 4. If hydrosulphuric acid, in the gaseous state or in solution, is brought into contact with silver nitrate or lead acetate, black precipitates of SILVER SULPHIDE 01o LEAD SULPHIDE are formed. In cases therefore where the odor fails to afford sufficient proof of the presence of hydrosulphuric acid, these reagents will remove all doubt. If the hydrosulphuric acid is present in the gaseous form the air suspected to contain it is tested by placing in it a minall slip of paper moistened with solution of lead acetate and a little ammonia; if the gas is present the slip becomes covered with a brownish-black shiiiing film of lead sulphide. To detect a trace of an alkali sulphide in presence of a free alkali or an alkali carbonate, the best way is to mix the fluid with a solution of lead hydroxide in soda, which is prepared by mixing solution of lead acetate with solution of soda until the precipitate which forms at first is redissolved. 5. If a fluid containing hydrosulphuric acid or an alkali sulphide is mixed with solution of soda, then with sodium nitroprusside,* it acquires a fine reddish-violet tint. The reaction is very delicate; but that with solution of lead hydroxide in soda is still more sensitive. 6. If metallic sulphides are exposed to the oxidizing flame of the blowpipe, the sulphur burns with a blue flame, emitting at the same time the well-known odor of sulphur dioxide. If a metallic sulphide is heated in a glass tube open at both ends, in the upper part of which a slip of blue litmus-paper is inserted, and the tube is held in a slanting position during the * As nitroprusside of sodium can very well be dispensed with, I have omitted giving it a place among the reagents.

Page  238 238 INOItGANIC ACIDS. GROUP II. [~ 157. operation, the escaping sulphur dioxide reddens the litmuspaper. 7. If a finely-pulverized metallic sulphide is boiled in a porcelain dish with solution of soda, and the mixture heated to incipient fusion of the caustic soda, or if the test specimen is fused in a platinum spoon with caustic soda, and the mass is, in either case, dissolved in a little water, a piece of brilght sil ver (a polished coin) put into the solution, andc the fluid warmed, a brownish-black filmn of silver sulphide forms on the metal. This film may be removed afterwards by rubbing the metal with leather and quicklime (v. KOBELL). 8. If the powder of a sulphide which is decomposed by bhydrochloric acid with difficulty, or not at all, is mixed in a small cylinder, or in a wide-necked flask, with an equal volunme of finely-divided iron free from sulphur (ferrum alcoholisatum), and some moderately dilute hydrochloric acid (1 volume of concentrated acid to 1 volunme of water) is poured over the mixture, in a layer a few lines thick, hydrosulphuric acid escapes along with the hydrogen. This may be easily detected by placing a slip of paper moistened with solution of lead acetate, and dried again, under the cork, so that the bottom is covered by it, the ends of the slip projecting on both sides, and then loosely inserting the cork into the mouth of the flask. Realgar, orpiment, and molybdenite do not show this reaction (v. KOBELL). ~ 157. Recapvitt,ation and remnarks.-i- lost of the acids of the filrst group are also precipitated by silver nitrate, but the precipitates ca.nnot well be confounded with the silver compounds of the acids of the second group, silce the formner are soluble in dilute pitric acid, whilst the latter are insoluble in that menstrunm. The presence of IIYDROSutLPHURIC ACID interferes with the testing for the other acids of the seconld group; this acid mnst therefore, if present, be removed before the testing for the other acids can be proceeded with. The removal of the hydrosulphuric acid, when present in the free state, mav be effected by simple ebullition; and when present in the form l of an alkali sulphide, by the addition of a metallic salt, such as will not precipitate any of the other acids, or at least will not precipitate them from acid solutions. IYDRIODIC and HYDROCYANIC AcIDs may be detected, even in presence of hydrochloric or hydrobromic acid, by the equally characteristic and delicate reactions with starch or carbon dislulphide (with addition of a fluid containing nitrous acid), and with solution of ferrous with a little ferric salt. lBut thle detection of CHLORINE and BRiOMIINE is inore or less difficult in presence of iodine and cyanogen. These latter must therefore, if present, be removed before the tests for chlorine and bromine can be applied. The separation of the cyanllogen may be readily effected by converting the wh(ole of the radicals present into silver salts and icnitinlg; the silver cyanide is decomposed in this process, whilst the chloride, bromide, and iodide of silver remain unaltered. Upon fusing the ignited residue with sodium carbonate and boiling the

Page  239 ~ 157.] SEPARATIONS. 239 fused mass with water, sodium chloride, bromide, and iodide are ol)tained in solution. The fused silver compounds may also be readily decomposed with zinc; all that is required for this purpose is to pour water over thleln, to add a little sulphuric acid and a fragment of zinlc, to let the mixturee stu. soine time, and finally to filter the solution of zinl (;hloride bromlide, or iodide from the separated metallic silver. The iodine Inay be separated from the chlorine and bromine, by treating the silver conlpounds with ammonia, but more accurately by precipitating the iodine as cuprous iodide. From bromine iodine is separated most accurately by palladious chloride, which only precipitates the iodine; from chlorine it is separated by palladious nitrate. _BRoi1NE ill presence of iodine and chlorine may be identified by the following simple operation: MAix the fluid with a few drops of dilute snlphuric acid, then with some starcll-paste, and add a little red finning lnitric acid or, better still, a solution of mlitrogen tetroxide in sulphuric acid, whereupon the iodine reaction will show itself immnediately. Add now chlorinewater drop by drop until that reaction has disappeared; then add solne more chlorlne-water to set the bromine also free, which may thern be separated and identified by inealis of chloroform or carbon disulphide. Or the iodile after beillg liberated in a highly dilute fluid may be also taken np with chloroforml or carbon disulphide, the aqueous fluid may then be filtelmed through a moist filter, alld the bromile detected in the filtrate by means of chloroform or carbon disulphide anld chloriine-water. For the latter process you may substitute the following: inmmnediately after the liberationi of thle iodine cautiously add chlorine-water, when tile violet-red coloration will gradually fade away, and give place to the brownish-red color indicative of bromi-ne. The detectionl of CHLORIDEs in presence of bromides and iodides is best effected by precipitating with silver nitrate, washing thle precipitate, digestiiig it with a mixture of 1 part ammonia and 3 parts water, filterilg off thle silver iodide, precipitating the filtrate with nitric acid, washing the precipitate (which contains silver chloride ald bromide with a trace of iodide), drying it, fusing with sodium carbonate, extracting the fusion with Nwatelr, neutralizing the solution with sulphuric acid (the reaction imay be somewhat alkaline), evaporlating to dryness. fusing the residue with potassium dichromate, and treating the fusion accordinlg to ~ 152, 7. The presence of much iodine interferes with the reaction, therefore it is directed to be removed. As regards the starch reaction, it must be noted that many salts (alum, alkali sulphates, magnesium sulphate, &c.) diminish its delicacy. Also as regards this and the carbon disulphide reaction, when nitrogen tetroxide is used to liberate the iodine, the presence of sulphocyanates may occasion mistakes (NADLER,) since a reddish color may occur in the absence

Page  240 240 RARER INORGANIC ACIDS. GROUP II. [, 158 of iodine from formation of pseudosulphocyanogen. By shaking with carbon disulphide the coloring substance is for the most part taken up. Besides the above mentioned agents for liberating iodine many otherE have been proposed, and may be employed; thus, for instance, iodic acid or alkali iodate and hydrochloric acid (v. LIEBIG); ferric chloride and sulphuric acid, or platinic chloride with addition of some hydrochloric acid (HEMPEL); potassium permanganate in slightly acidified solution (HENRY), &c. With respect to these agents I have to observe that iodic acid must be used with the greatest caution, as a, in presence of reducing substances iodine is set free from the reagent, and b, an excess of iodic acid will at once put an end to the reaction. Ferric chloride, with addition of sulphuric acid, will not act immediately upon very dilute solutions, but after a time the reaction will make its appearance, revealing the presence of even the minutest trace of iodine; the delicacy of the reaction is not materiallv impaired by an excess of the reagent. Ferric chloride may be used with advantage when iodine is to be liberated in the gaseous state, which should be done in the presence of sulphocyanates. The fluid is then heated nearly to boiling, and the escaping fumes are made to act on paper smeared with fresh starch paste. Potassium permanganate acts immediately, even in the most dilute solutions. However, as a fluid colored by minute traces of iodized starch is also apt to look reddish, the coloration imparted by the permanganic acid alone may lead to mistakes in using the starch test. From six to twelve hours should therefore always be allowed to elapse before judging of the actual nature of the coloration. The modtts operandi may of course be modified in various ways to increase the delicacy of the starch reaction; interesting particulars upon this point may be found in the papers of MOItIN* and HEMPEL.t Chlorine, bromine, and iodine, may also be distinguished from each other by the spectroscope, for the splectra of their copper salts, though containing many blue and green lines, vary in the position and prominence of the lines; they may also be detected in presence of one another, for by cautiously heating the silver salts with cupric oxide in a current of hydrogen, and lighting the escaping gas, the flame will be colored first by the copper chloride, then by the copper bromide, and lastly by the copper iodide (AL MrTSCIIEnLICIn).t The use of this method requires considerable practice in consequence of the similarity of the spectra, and the method therefore appears to me of more scientific interest than practical importance. ~ 158. Rarer Acids of the Second Group. 1. NITROUS ACID, H N 02, or N 0. 0 I. NITROGEN DIOXIDE, N2 02, is a colorless gas evolved in the action of metals (copper, silver, &c.) on nitric acid; mixed with ~ its volume of oxygen it forms at low temperatures N2 03; with - its volume of oxygen it yields at common temperatures N2 04. NITROGEN TRIOXIDE or NITROUS ANHYDRIDE, N2 03, exists as a deep blue liquid at temperatures below 0. Above 0~ it decomposes partially into N2 02 and N2 04, and at common temperatures the mixtllre appears as a brownish-red gas. In contact with a little cold water it yields probably nitrous acid, N2 03+H.2 0=2 (H N 02). With much and warm water it is converted for the most part into nitric acid, which dissolves, and nitrogen dioxide, which escapes as gas when the quantity of water ii not very large, 3 N2 03+H2 0=2 H N 03+ 2 N2 02. * Journ. f. prakt. Chem. 78, 1. tALn. d. Chem. u. Pharm. 107, 102 I Zeitschr. f. anal. Chem. 4, 153.

Page  241 ~ 158.1] HYPOCCILOROUS ACID. 241 NITROGEN TETROXIDE, N2 04, at 20~ is a colorless crystalline mass which melts at 12Q and boils at 28~, yielding a red gas. Mixed with water it yields nitrous and nitric acid, N2 04 + H2 O=H NO2 + H N 03. With an alkali it yields a nitrite and a nitrate. The NITRITES are decomposed by ignition; many of them are soluble in water. When nitrites or concentrated solutions of nitrites are treated with dilute sulphuric acid nitric acid is formed and nitrogen dioxide is evolved. In concentrated solutions of alkali nitrites, siluer nitrate produces a white precipitate, which dissolves in a very large proportion of water, especially upon application of heat; ferrous salphate, upon addition of a small quantity of acid, produces a dark blackish-brown coloration, which is due to the nitrogen dioxide dissolving in the ferrous solution. Hydrosulphuric acid produces in solutions containing nitrous acid, after neutralization by an acid of the free alkali, should any be present, a copious precipitate of sulphur, the reaction being attended also with forma. tion of ammlloniurn nitrate. Pyrogallic acid imparts a brown color to even very dilute solutions of nitrites acidified with sulphuric acid (SCIIONBEIN). On addition of potassium cyanide to an alkaline nitrite, then of some neuw tral solutions of cobalt chloride, and a little acetic acid, the fluid becomes orange-rose colored from the formation of cobalt potassium nitrocyanide (C. D. BIRAUN). But the most delicate reagent for nitrous acid is solution of potassium iodide mixed with starch paste, especially upon addition of sulphuric acid (PRIcE, SCIHIONErX). Water containing the one hundred thousandth part of potassium nitrite, together with free sulphuric acid, is colored distinctly blue by this reagent in a few seconds, and a few minutes suffice to produce ths same effect in water containing one millionth part of potassium nitrite. This reaction is trustworthy only where no other substance is present that mlight exercise a decomposing action upon potassium iodide, such, for instance, as iodic acid, ferric salts, &c. On adding indigo solution to water till the latter has lost its transparence from the depth of color, then hydrochloric acid and afterwards a solution of alkali polysalphide with stirring, till the blue color just vanishes, filtering and adding to the clear filtrate a solution of the merest trace of nitrous acid, a most distinct bluish coloration will at once be produced. This reaction is to l)e recommended in the presence of other reducing bodies which interfere with the action of nitrous acid upon an acidified solution of starch and potassium iodide (SCHiSNBEIN). But it must not lbe overlooked that other oxidizing substances reproduce the blue color. On mixing' a solution of nitrous acid (for instance, a solution of potassium nitrite acidified with acetic acid) with potassium sdlplhocyanate the fluid is not colored, but on the further addition of nitric acid, a dark-red color makes its appearance, which vanishes on addition of alcohol or after heating for a short time (difference from ferric sulphocyanate). The coloring substance is mostly taken up from this by shaking with carbon disulphide. It will be evident that this reaction is due to nitrogen tetroxide, and not to nitrous acid, hence it may be used to distinguish between the two. 2. HYrocHLonous ACID, H C1 0. HYPocmiLOROus OXIDE, C12 O, at the common temperature, is a deep yellowish-green gas of a disagreeable irritating odor, similar to that of chlo, rine. It dissolves in water, forming HYPOCHLOROUS ACID, C12 0 + H2 0 = 2H C 10; the dilute aqueous solution bears distillation. The rYrOCiLO. RITTES are usually found in combination with metallic chlorides, as is the case, for instance, in "chloride of limle " or calcium hypochlorite, plus calcium chloride, Ca C12 02 + Ca C12, eau de Javelle, or solution of sodium hypochlorite, plus sodium chloride. The solutions of hypochlorites undergo alteration by b)oiling, the hypochlorite being resolved into chloride and chlorate, attended, in the case of concentrated, but not in that of dilute 16

Page  242 242 RARER INORGANIC ACIDS. GROUP II. [p 158. solutions, with evolution of oxygen. If a solution of " chloride of lime " is mixed with hydrochloric acid or sulphuric acid, chlorine is disengaged, whilst addition of a little nitric acid leads to the liberation of hypochlorous acid. Silver nitrate throws down from solution of " chloride of lime " silver chloride [the silver hypoclllorite which forms at first is speedily resolved into silver chloride and chlorate, 3Ag C1 O = Ag C1 03 + 2Ag Cl]; lead nitrate produces a precipitate which from its original white changes gradually to orange-red, and ultimately, owing to formation of lead dioxide to brown; manganese salts give brown-black precipitates of manganese dioxide. Solution of potassium permanganate is not decolorized. Solutions of litmus and indigo are decolorized even by the alkaline solutions of hypochlorites, but still more rapidly and completely upon addition of an acid. If a solution of arsenious oxide in hydrochloric acid is colored blue with solution of indigo. and a solution of "chloride of lime " is added, with active stirring, the decoloration will take place only after the whole of the arsenious oxide has been converted to arsenic acid. 3. CHLOROIJS ACID, H C1 02. CHLOROUS OXIDE, C12 03, is a yellowish-green gas of a peculiar and very disagreeable odor; it is soluble in water, with production of CHLOROUS ACID. The solution has an intensely yellow color, even when highly dilute. Most of the CHLORITES are soluble in water; the solutions readily suffer decomposition, the chlorites being resolved into chlorides and chlorates. Silver nitrate precipitates white silver chlorite, which is soluble in much water. A solution of potassium permanganate is immediately decomposed, and a brown precipitate separates after some time. Tincture of litmus and solution of indigo are instantly decolorized, even if mixed with arsenious oxide in excess. If a slightly acidified dilute solution of aferrous salt is mixed with a dilute solution of chlorous acid, the fluid transiently acquires an amethyst tint, and assumes only after the lapse of a few seconds the yellowIsh coloration of ferric salts (LENssEN). 4. HrPOProsPronous ACID, H3 P 02. The concentrated solution of HYPOPRHOSPHOROUS ACID is of syrupy consistence, and resembles that of phosphorous acid (see ~ 148), with which it also has this in common, that it is resolved by heating, with exclusion of air, into phosphoric acid and not spontaneously inflammable phosphoretted hydrogen gas. Almost all hypophosphites are soluble in water; by ignition all of them are resolved into phosphate and phosphoretted hydrogen, which in most cases is spontaneously inflammable. Barium chloride, calcium?, chloride, and lead acetate fail to precipitate solutions of hypophosphitcs (difference from phosphorous acid). Silver nitrate gives with hypophosphites at first a white precipitate of silver hypophosphite, which turns black even at the common temperature, but more rapidly on heating, the change of color being attended with separation of metallic silver. From excess of mercuric chloride, hypophosphorous acid precipitates mercurous chloride slowly in the cold, more rapidly on heating. With zinc and dilute sulphuric acid hypophosphorous acid gives hydrogen mixed with phosphoretted hydrogen. (Compare ~ 148, Phosphorous Acid.)

Page  243 ~ 159.] NITRIC ACID. 243 Third Group. AcIDS WHICH ARE NOT PRECIPITATED BY BARIUM SALTS NOR BY SILVER SAILTS: Nitric Acid, C(Jloric Acid (Perchloric Acid). ~ 159. a. NITRIC ACID, H N O,. 1. NITROGEN PENTOXIDE, N2 0, crystallizes in six-sided prisms. It fuses at 2995~, and boils at about 450 (DEVILLE). Pure NITRIC ACID is a colorless, exceedingly corrosive fluid, which emits flnumes in the air, exercises a rapidly destructive action upon organic substances, and colors the albuminoids intensely yellow. Nitric acid containing nitrogen tetroxide, N2 04, has a red color. 2. All the NORMAL SALTS of nitric acid are soluble in water; only some of the basic nitrates are insoluble. All nitrates uudergo decomposition at an intense red heat. Nitrates of the alkali metals at first yield oxygen, and chancge to nitrites, afterwards they yield oxygen and nitrogen. Those with other bases yield oxygen and nitrogen trioxide, N2 0,, or tetroxide. 3. If a nitrate is thrown upon red-hot ch/arcoal, or if charcoal or some organic substance, paper for instance, is brought into contact with a nitrate in fusion, DEFLAGRATION takes place, i.e., the charcoal burns at the expense of the oxygen of the nitric acid, with vivid scintillation. 4. If a mixture of a nitrate withpotassiumb cyanide in powder is heated (use very smll gqanztities!) on platinum foil, a vivid DEFLAGRATION ensues, attended with distinct ignition and detonation. Even very minute quantities of nitrates may be detected by this reaction. 5. If a nitrate is mixed with copper jftligqs, and the mixture heated in a test-tube with concentrated sulphuric acid, the air in the tube acquires a yellowish-red tint, owing to the nitrogen dioxide, N2 02, which is liberated upon the oxidation of the copper by the nitric acid, combining with the oxygen of the air to nitrogen tetroxide. The coloration may be observed most distinctly by looking lengthways through the tube. 6. If the solution of a nitrate is mixed with an equal volume of concentrated sullpuric acid, free from nitric acid and oxides of nitrogen, the mixture allowed to cool, and a concentrated solution of ferrous sulphate then cautiously added to it so that the fluids do not mix, the junction shows at first a purple, afterwards a brown color, or, in cases where only a very minute quantity of nitric acid is present, a reddish color. On mixing the fluids a brownish purple-red clear fluid is obtained. In this process ferrous nitrate passes into ferric nitrate, breaking up

Page  244 244 INORGANIC ACIDS. GROUP III. [~ 160, nitric acid and liberating hydrogen which reacts on mnore nitric acid giving water and nitrogen dioxide, 6 Fe"(N 03)2 + 6 II N O, =3 Fevi, (N 0,), + H6 and HE6+2 II N 03-4 I-1, O +N, O. The nitrogen dioxide unites with a portion of ferrous salt, and forms with it a peculiar compound, which dissolves in water to a brownish-blackl color. A similar reaction is observed in presence of selenious acid; but on mixing the fluid and letting it stand, red seleniuml separates (WITTSTOCK). 7. If a little brucict is dissolved iin pure concentrated snlphnric acid (to which it gives a faint rose tint) and a small quantity of a fluid containing nitric acid added to the solution, the latter immediately acquires a magnificent red color. This reaction is extraordinarily delicate. The color soon passes into reddish yellow. Chloric acid gives the same reaction. 8. Dissolve one part of carbolic acidY in four parts of strong sulphuric acid, and add two parts of water. A drop or two of this fluid added to a solid nitrate (e. g., to the residue obtained by evaporating a few drops of well-water containing nitrates) gives a reddish-brown color, from the formation of a nitrocompound. On addition of a drop or two of strong ammonia, this color turns yellow, sometimes passing through a green shade. A very delicate reaction (II. SPRENGEL). 9. If some hydrochloric acid is boiled in a test-tube, one or two drops of very dilute indigo solution added, and the mixture boiled again, the fluid remains blue (provided the hydrochloric acid was free from chlorine). If a nitrate, solid or in solution, is now added to the faint lightblue fluid, and the mixture heated again to boiling, the color disappears owing to the decomposition of the indigo blue. This is a most delicate reaction. It must be borne in mlind, however, that several other substances also cause decoloration of solution of indigo-free chlorine more particularly produces this effect. 10. Very minute quantities of nitric acid may be detected also by reducing the nitric acid first to nitrous acid, which may be effected both in the moist and in the dry way; in the former by heating the solution of the nitric acid or of the nitrate for some time with finely-divided zinc, best with zinc amalgam, and then filtering (SCRHiNBEIN); in the dry way by fusing the substance with sodium carbonate at a moderate heat, extracting the mass, after cooling, with water, and filtering. Upon adding either of the filtrates to a solution of potassium iodide mixed with starch-paste and dilute sulphuric acid the fluid acquires a blue color from iodized starch (comp. ~ 158, 1). ~ 160. b. CHLoRnc ACID, H C1 0,. 1. CITLoRIC ACID, in its most highly concentrated solution, is a colorless or slightly yellowish oily fluid; its odor resembles that of nitric acid, It first reddens litmus, then bleaches it. Dilute chloric acid is colorless and inodorous. 2. All CIILORATES are soluble in -water. When chlorates are heated to redness, the whole of the oxygen escapes an)d metallic chlorides remain. 3. Heated with chlarcoal or some organic substance the chlo(

Page  245 ~ 161.] RECAPITULATION. 245 rates DEFLAGRATE, and this with far greater violence than the nitrates. 4. If a mixture of a chlorate withpotassium cyanide is heated on platinum foil, DEFLGRATrION takes place, attended with strollng detonation and ignition, even though the chlorate be present only in minute quantity. This experiment should be made with very small quantities and with great caution 5. If the solution of a chlorate is colored light-blue with solution of indigo, a little dilute sulphuric acid added, and a solution of sodiuln sulphite dropped cautiously into the blue fluid, the color of the indigo disappears ilmlnediately. The cause of this equally characteristic and delicate reaction is, that the sulphurous acid deprives the chloric acid of its oxygen, thus setting free chlorine or a lower oxide of it, which then decolorizes the indigo. 6. If chlorates are heated with moderately dilute hydrochloric acid the constituents of the two acids transpose, fornling water, chlorine, and chlorine tetroxide: 2 11 C] 0, + 2 II C1-2 HII O + 2 C1 +C12 04. The test-tube in -which the experiment is made becomes filled in this process with a greenish-yellow gas of a -very disagreeable odor resembling that- of chlorine; the, hydrochloric acid acquires a greellish-yellow color. If the hydrochloric acid is colored blue with indigo solution, the presence of very minute quantities of chlorates will suffice to destroy the indigo color at once. 7. If a little chlorate is added to a few drops of concentrated sufphuric acid in a watch-glass, the liberated chloric acid breaks up into perchloric acid and chlorine tetroxide: 3 II C10 - 11 C1 04 + C12 04 + II2 O. Chlorine tetroxide imparts an intensely yellow tint to the sulphuric acid, and betrays its presence also by its odor and the greenish color of the evolved gas. The application of heat must be avoided in this experiment, and the quaftities operated upon should be very small, since otherwvise the decomnposition might take place with such violence as to cause a dangerous explosion. 8. Chloric acid shows the same deportment as nitric acid towards brucia dissolved in concentrated sulphuric acid (LucK). Compare ~ 159, 7. ~ 161. Reccpitulation and remrarks.-Of the reactions which have been given to effect the detection of NITRIC ACID, those with ferrous sulphate and snlphuric acid, with copper filings and sulphuric acid, with carbolic acid, and also those based upon the reduction to nitrites, give the most positive results; with regard to deflagration with charcoal, detonation with potassium cyanide, decoloration of solution of indigo and coloration with brucia, we have seen that these reactions belong equally to chlorates as

Page  246 246 RARER INORGANIC ACIDS. GROUP III. [~ 162. to nitrates, and are consequently decisive only where no chloric acid is present. The presenc(e of free nitric acid in a fluid may be detected by evaporating in a porcelain dish on the waterbath to dryness, having first thrown in a few white quill-cuttillgs: yellow coloration of these indicates the presence of nitric acio (RLNTGE). The best way to ascertain whether CULORIC ACID is present or not (in the absence of other oxygen compounds of chlorine) is to ignite the substance, with addition of sodium carbonate, dissolve the mass, and test the solution with silver nitrate. If a chlorate is present, this is converted into a chloride upon ignition, and silver nitrate will produce a precipitate of silver chloride. However, the process is thus simple only if no chloride is present with the chlorate. In presence of a chloride, the chlorine of the latter must be removed by adding silver nitrate to the solution as lonll as a precipitate continues to form, and filtering; the filtrate is then, after addition of pure sodium carbonate, evaporated and ignited. It is, however, generally unnecessary to pursue this circuitous way, since the reactions with concentrated sulphuric acid, and with indigo and sulphurous acid, are sufficiently marked and characteristic to afford positive proof of the presence of chloric acid, even in presence of nitrates. The best way of detecting nitrie acid in presence of a large proportion of chloric acid is to mix the substance with sodium carbonate in excess, evaporate, ignite the residue gently, but sufficiently long to convert the chlorate into chloride, and then test the residue for nitric acid, or for nitrous acid. ~ 162. PERCHLORIC ACID, H C1 04. Pure anhydrous perchloric acid is a colorless, mobile fluid, which forms dense white fumes in the air, and explodes with great violence when dropped on wood-charcoal (RoSCOE). The hydrate H C1 04. H2 0 CryStallizes in needles; the concentrated aqueous solution is oily and heavy. The dilute solution gives by distillation first water, then dilute acid, and finally concentrated acid. All perchlorates are soluble in water, most of them freely. They are all decomposed by ignition, those with alkali lbases leaving chlorides behind, with disengagement of oxygen. Potassi am salts produce in not too dilute solutions a white crystalline precipitate of potassium perchlorate, K C1 04, which is sparingly soluble in water, insoluble in alchohol. Bariumn salts and silver salts are not precipitated. Concentrated sulphuric acid fails to decompose perchloric acid in the cold, and decomposes it with difficulty on leating (difference from chloric acid). Hydrochloric acid, nitric acid, and sulphurous acid fail to deconmpose aqueous solutions of perchloric acid or perchlorates; solution of indigo, therefore, previously added to it, is not decolorized (difference from all other acids of chlorine).

Page  247 ~ 163.] ORGANIC ACIDS. GROUP I. 247 II. ORGANIC ACIDS. hrst Group. TIlie ACIDS OF THE FIRST GROUP ARE DECOMPOSED ENTIRELY OR P'ARTIALLY BY IGNITION.* THE ACII)S ARE DECOMPOSED BY BOIIING WITH CONCENTRATED NITRIC ACID.t THEIR CALCIUMI SALTS ARE INSOLUBLE OR DIFFICULTLY SOLUBLE IN WATER. TIE SOLUTIONS OF THEIR NORIMAL ALALI SALTS ARE NOT PRECIPITATED BY FERRIC CIILORIDE: OXCaliC Acid, Tartaric Acia (Racemic Acid), Citric Acid, icalic Acid. ~ 163. a. OXALIC ACID. For the reactions of oxalic acid I refer to ~ 145. b. DEXTRo TARTARIC ACID, C2 IA (O )2 (C O O H)2 - C4 H6 O 1. Ordinary or DEXTRO TATAIZIC ACID forms colorlless crystals of an agreeable acid taste, which are persistent in the air, and soluble in water and in alcohol. Heated to 100~, tartaric acid loses no water; heated to 170~, it fuses; at a higher temperatnre it becomes carbonized, emitting during the process a very peculiar and highly characteristic, odor, which resemblles that of burnt sugar. Aqueous solution of tartaric acid, as also of almost all tartrates, turns the plane of polarization of light towards the right. By heating with nitric acid tartaric acid is converted into oxalic, acetic, and saccharic acids. 2. The TARTRATES of the alkali metals are soluble in water, and so are the tartrates of the metals of the third and fourtlh groups. Evaporated on the water-bath to syrupy consistence, the solution of ferric tartrate deposits a pulverulent basic salt. Those of the tartrates which are insoluble in water dissolve in hydrochloric or nitric acid. The tartrates suffer decomposition when heated to redness; charcoal separates, and the salne peculiar odor is emitted as attends the carbonization of free tartaric acid. 3. If to a solution of tartaric acid, or to that of an alkali tartrate, solution of an alumninic or qf aferric salt is added in not too large proportion, and then ammonia or potassa, no precipitation of alunninic or ferric hydroxide will ensue, since the double tartrates formed are not decomposed by alkalies. Tar* Oxalic acid, when cautiously heated, partially sublimes unaltered. t The decomposition of oxalic acid by boiling nitric acid into carbon dioxide and water is but slow.

Page  248 248 ORGANIC ACIDS. GROUP I. [~ 163. taric acid prevents also the precipitation of several other hby dioxides by alkalies. 4. Free tartaric acid produces, with jotcassiLun sCait8, anld more particularly with the acetate, a sparilngly soluble precipi. tate of IlYDROGECN I'OTASSIUM TAIRTRATE 04 15 K O. A simil-.r plecilpitate is formed when potassium acetate and free acetic acid are added to the solution of the normal tartrate. Tlhe hydrogen potassium tartrate dissolves readily in alkalies anld niiiienral acids; tartaric acid and acetic acid do not increase its solubility in water. The separation of the hydrogen potassium tartrate precipitate is greatly promloted by shaking, or by rubbing tile sides of the vessel with a glass rod. The delicacy of the reaction mIay be heightened by concentrating the solution of the tartaric acid. Addition of an equal volume of alcohol heightens the delicacy of the reaction. In the presence of boric acid potassium fluoride must be used instead of potassium acetate; this forms potassium borofluoride, and prevents the production of the soluble compound of boric acid, tartaric acid, and potassium (BARFOED). 5. 6alcitm chloride added in excess * throws down from solutions of normal tartrates a white precipitate of CALCIUA TALrTRATE C4 HI4 Ca 06 + 4 Aq. Presence of ammoniuml salts retards the formation of this precipitate for a more or less considerable space of time. Agitation of the fluid or friction on the sides of the vessel promotes the separation of the precipitate. The precipitate is crystalline, or invariably becomes so after some time; it dissolves in a cold, not over dilute solution of potassa or soda, pretty free from carbonate, to a clear fluid. But upon boiling this solution, the dissolved calcium tartrate separates again in the form of a gelatinous precipitate, which redissolves upon cooling. 6. Limezwateir added in excess * produces in solutions of normal tartrates —and also in a solution of free tartaric acid,.if added to alkaline reaction —white precipitates which, floccuJlent at first, assume afterwards a crystalline form; so long as they remain flocculent they are readily dissolved by tartaric acid:as well as by solution of ammoniurn chloride. Fromn these solutions the calcium tartrate separates again, after the lapse of several hours, in the form of small crystals deposited upon the sides of the vessel. 7. Solution of calcium sul2phate added in excess * fails to iproduce a precipitate in a solution of tartaric acid: in solutions of normal tartrates of the alkali metals, it produces a triflilg precipitate after the lapse of some time. 8. If solution of ammonia is poured upon even a very minute quantity of calcium tartrate, a small fragment of crystallized silver nitrate added, * Potassium or sodium tartrate dissolves calcium tartrate (as well as certain other salts insoluble in water, such as calcium phosphate, barium sulphate, &c) Hence the alkali tartrate must be fully decomposed by the reagent.

Page  249 ~ 16-4.] CITRIC ACID. 249 and the mixture slowly and gradually heated, the sides of the test-tube are covered with a bright coating of metallic silver. If, instead of a crystal, solution of silver nitrate be used, or heat be applied more rapidly, the reduced silver will separate in a pulverulent form (AI.RT1UR CASSELMANN). 9. Lead acetate produces white precipitates in solutions Of tartaric acid and its salts. The washed precipitate (C4 H4 Pb 06) dissolves readily in nitric acid and in ammonia free from carbonic acid.; O. Silver nitrate does not precipitate free tartaric acid; but in solutions of normlal tartrates it produces a white precipitate of SILVER TARTRATE (C4 114 Ag2 06), which dissolves readily in nitric acid and in ammonia; upon boilin1g it turns black, owing to reduction of the silver. 11. Upon heating tartaric acid or a tartrate with concentrated salphurie acid, the latter acquires a brown color almost simultaneously with the evolution of gas. ~ 164. c. CITRIC Acm, C, H,4 (O H)(C O 0 I), - 1, H, O,. 1. CRYSTALLIZED CITRIC ACID, obtained by the cooling of its solution, has the formula 2 Cc IH8 07. -H O. It crystallizes in pellucid, colorless and inodorous crystals of an agreeable strongly acid taste, which dissolve readily in water and in alcohol, and effloresce slowly in the air. Heated to 1000 the crystallized acid loses its water of crystallization; when subjected to the action of a stronger heat, it fuses at first, and afterwards carbonizes, with evolution of pungent acid fumes, the odor of which may be readily distinguished from that emitted by tartaric acid upon carbollization. By heating with a little nitric acid, citric acid gives oxalic and acetic acids; with much nitric acid it gives. acetic acid only. Citric acid is tribasic. 2. The crnrATEs with alkali base, whether normal or acid, are readily soluble in water; solution of citric acid therefore is iot precipitated by potassium acetate. Various citrates contamninlg weak bases, such as ferric citrate, for instance, are also flreely soluble in water. Evaporated oil the water-bath to syrupy consistence tie solution of ferric citrate deposits no solid salt. Citrates, like tartrates, and for the same reason, prevent the precipitation of aluminic and ferric hydroxide, &c., by alkalies. 3. Calciwum chloride fails to produce a precipitate in solution of free citric acid, even upon boiling; but a precipitate of NORMAL CALCIUM CITRATE (C6 II, 07) Ca,. H, 0 forms immediately upon saturating with potassa or soda the concentrated solution of citric acid, mrixed with calcium chloride in excess.* The precipitate is insoluble in potassa, but dissolves freely in *Alkali citrates are actual solvents for many compounds insoluble in water (barium sulphate, calcium phosphate, calcium oxalate, &c.). Hence the alkali citrate must be fully decomposed by the reagent.

Page  250 250 ORGANIC ACIDS. GROUP I. [~ 164. solution of ammonium chloride; upon boiling this amlnonium chloride solution, normal calcium citrate separates again in the form of a white crystalline precipitate, which however is now no longer soluble inamimnoninum chloride. If a solution of citric acid mixed with excess of calcium chloride * is saturated with ammonia, a precipitate will form in the cold only after mans hours' standing; but upon boiling the clear fluid, normnal cal cium citrate of the properties just stated will suddenly precipitate. By heating calcium citrate with ammonia and silver nitrate the latter salt is not reduced, or only to a trifling extent. 4. Limne-water added in excess * produces no precipitate in cold solutions of citric acid or of citrates. But upon boiling some time with a tolerable excess of hot prepared lime-water, a white precipitate of CALCIUM CiTRATE is formed, of which the greater portion redissolves upon cooling. 5. Bariumn acetate added in excess to a solution of ain alkall citrate, whether hot or cold, produces an amorphous precipitate of the formula (C6 115 0,), Ba,. 7 HI, 0. Baryta water added in excess to citric acid produces the same precipitate. The precipitate does not make its appearance in dilute solutions, because it is not insoluble in water, but if such solutions are heated, a precipitate separates which is first amorphous and soon turnls to microscopic needles of the formula (C6 IH, 0,), Ba,. 5 -1,0. On heating this or the amorphous salt with excess of barium acetate for two hours on the water-bath, another veryv characteristic salt is formed. The latter consists of well-forlned elinorhonbie prisms, and has the fornmula (C8 II5 0,)2 Ba,. 31 1I, 0. If the solution is very dilute the salt does not form till after evaporation. This is an infallible reaction for citric acid t' (II. KisirMmEER). From experiments made in nmy laboratory it appears that the addition of a drop of acetic acid materially assists the transition to the characteristic salt. 6. Lead acetate added in excess to a solution of nitric acid produces a white amorphous precipitate of LEAD CITRATE, which after washing is readily soluble in ammonia free from carbonate. By digestion for several hours with water or acetic acid on a water-bath, the precipitate becomes crystalline, and then has the formula (C6 H5 07)2 Pb3. 3 H, O. The microscope does not reveal the presence of well-fornled crystals. 7. Silver nitrate produces in solutions of normal citrates of the alkali metals a white flocculent precipitate of SILVER CITRATE, C6 H5 07 Ag3. On boiling a rather large quantity of this precipitate with a little water a gradual decomposition sets in with separation of silver. 8. Upon heating citric acid or citrates with concentrated sulphuric acid, carbon monoxide and carbon dioxide escape at first, the sulphuric acid retaining its natural color; upon continued ebullition, however, the solution acquires a dark color, and sulphurous acid is evolved. * See note, ante. t The microscope is needed for identifying these crystals which are figured in Fres. Zeitschrift; vol 8, p. 299.

Page  251 ~ 165.] MALIC ACID. 251 ~ 165. d. MALIO AcrD, C, E, (O H) (C O O HI), = 4, H,0,. 1. IMALIC ACID crystallizes with difficulty, forming crystalline crusts, which deliquesce in the air, and dissolve readily in water and in alcohol. Exposed to a temperature of 140~ malic acid is slowly converted, with loss of two molecules of water, into funaric acid, C, H2 (C 0 O H)2- C4 H4 O,; heated more strongly malic acid is resolved into water and MAS.IC ACID (isomeric with fumnaric acid) which volatilizes. This deportment of malic acid is highly characteristic. If the experiment is made in a small spoon, pungent acid vapors are evolved with frothing; if the experiment is made in a small tube, the maleic acid first, and afterwards the fumaric acid also will condense to crystals in the colder part of the tube. By heating with nitric acid inalic acid readily yields oxalic acid, with evolution of carbon dioxide. 2. Malic acid forms with most bases salts soluble in water. Hydrogen potassium malate is not difficultly soluble in water; potassium acetate fails therefore to precipitate solutions of malic acid. Malic acid prevents, like tartaric acid, the precipitation of ferric hydroxide, &c., by alkalies. 3. Calcium chloride added in excess fails to produce a piecipitate in solutions of free malic acid. Even after saturation with ammonia or soda no precipitate is formed. But upon boiling, a precipitate of CALCIUM MALATE, C, I11 O0Ca. H2 O, separates from concentrated solutions. If the precipitate is dissolved in a very little hydrochloric acid, amnmoTlia added to the solution, and the fluid boiled, the calcium malate separates again; but if it is dissolved in a somewhat larger quantity of hydrochloric acid, it will not reprecipitate, after addition of ammonia in excess, even upon continued boiling. On adding one or two measures of alcohol the calcium malate separates in white flocks. If the fluid is previously heated nearly to boiling and hot alcohol is added, the precipitate is deposited in the form of soft lumps which adhere to the sides of the vessel; on cooling they harden and crumble by pressure to a crystalline powder (BAIrFOED). When heated with ammonia and silver nitrate, calcium malate causes no separation of silver or hardly any. 4. Lime-water produces no precipitate in solutions of free malic acid, nor in solutions of malates. The fluid remains perfectly clear even upon boiling, provided the lime-water was prepared with boiling water. 5. Lead acetate throws down from solutions of malic acid and of malates a white precipitate of LEAD MALATE, C,4 -14 O, Pb. 3 HI, 0. The precipitation is the most complete if the fluid is neutralized by ammonia, as the precipitate is slightly soluble

Page  252 252 ORGANIC ACIDS. GROUP I. [~ 166, in free mlalic acid and acetic acid, and also in ammonia. If the fluid in which the precipitate is suspended is heated to boiling, a portion of the precipitate dissolves, and the remainder fuses to a translucent mass resembling resin melted under water, which on standing under the liquid gradually crystallizes. To obtain this reaction with small quantities, warm at first gently till the precipitate has shrunk together, then pour of the principal quantity of the fluid and heat the rest with the precipitate to boiling. This reaction is distinctly marked only if the lead malate is tolerably pure; if mixed with other lead salts-if, for instailce, ammonia is added to alkaline reaction-it is only imnperfect or fails altogether to make its appearance. 6. Silver nitrate throws down from solutions of normal malates of the alkali 1metals a white precipitate of SILVER MALATE which upon long standing o hboiling turns a little gray. 7. 011 mixingr the warm solution of free malic acid with mcagnesia or magnesium carbonate, till the acid reaction is destroyed, filtering, evaporating, and mixing the hot solution with hot alcohol, magnesium malate, C4 H4 05 M(g, separates as a glutinous mass on the sides of the vessel. It is hard when cold. Malic acid cannot be distinguished from citric acid by this reaction (BARFOED). 8. Upon heating malic acid with concentrated sulphuric acid, carbon dioxide and carbon monoxide are evolved at first; the fluid then turns brown and ultimately black, with evolution of sulphur dioxide. ~ 136. Recapittlation and rennarks.-Of the organic acids of this group oxalic acid is characterized by the instant precipitation of its calcium salt from its solution in hydrochloric acid by ammonia, and also by sodium acetate, as well as by the innmediate precipitation of the free acid by solution of calciuln sulphate. Tartaric acid is characterized by the sparing solubility of the hydrogen potassium salt, the solubility of the calcium salt in cold solution of soda and potassa, the reaction of the calcium salt with ammonia and silver nitrate, and the peculiar odor which the acid and its salts emit upon heating. It is most safely detected in presence of the other acids by means of potassium acetate or potassium fluoride (~ 163, 4). C. D. BIAUN'S test for distinguishing tartaric acid from the other organic acids by means of hexamincobaltich chloride will be found in Zeitsch. f. anal. Chem. 7, 349. Citric acid is usually recognized by its reaction with lime-water, or with calcium chloride and ammonia in presence of ammonium chloride; but in this we always presuppose the absence or the removal of malic and tartaric acids, and also the employment of a sufficient quantity of lime-water or calcium chloride. A very safe characteristic of citric acid also consists in the microscopic appearance of its barium salt (~ 164, 5). 1falic acid would be sufficiently characterized by the

Page  253 ~ 166.] SEPARATIONS. 253 deportment of lead malate when heated under water, were this reaction more sensitive, and not so easily prevented by the presence of other acids. The safest means of identifying malic acid is to convert it into maleic acid and fumaric acid by heating in a glass tube; but this conversion can be effected successfully only with pure malic acid. Lead malate is sparingly soluble ir ammonia, whilst the citrate and tartrate of lead dissolve freely in that agent; this different deportment of the lead salts of the acids affords a means of distinguishing between them. If only one of the four acids is present in a solution, lilmewater will suffice to indicate which of the four is present; since mnalic acid is not precipitated by this reagent, citric acid is precipitated only upon boiling, tartaric acid and oxalic acid being thrown down in the cold; and the calcium tartrate redissolves upon addition of ammonium chloride, whilst the oxalate does not. If the four acids together are present inl a solution, the oxalic acid and tartaric acid are usually precipitated first by calcium chloride and ammnonia, in presence of ammonium chloride. But it must be noted here that the calcium tartrate requires some time for complete precipitation (it is separated from the oxalate by solution of soda), and also that alkali citrate when present in any quantity prevents the thorough separation of oxalic acid and still more of tartaric acid. On adding alcohol in moderate quantity cautiously to the filtrate, the calcium citrate separates (and with it the rest of the calcium oxalate and' tartrate). On filtering again and mixing the filtrate with more alcohol, calcium malate is thrown down. From this the acid is prepared by dissolving it in acetic acid, adding alcohol, filtering if necessary, mixing the filtrate with lead acetate, neutralizing with ammonia, washing the precipitate, suspending it in water, treating witll sulphuretted hydrogen, filtering and evaporating the filtrate to dryness. A better method for the detection of malic acid in the presence of the three other acids consists in combining the acids with ammonia, concentrating strongly, neutralizing the still warm fluid with ammonia (to dissolve the acid salts produced in the evaporation) and adding 8 volumes of alcohol of 98 per cent. After 12 or 24 hours the solution of ammonium malate is filtered from the undissolved oxalate, tartrate, and citrate of ammonium, the malic acid is precipitated with lead acetate and the pure acid is prepared from the precipitate (BARFOED). Where a small quanltity of citric acid or malic acid is to be detected in presence of a large proportion of tartaric acid, the best way is to remove the latter first by potassium acetate, with addition of an equal volume of strong alcohol. The other acids may then be completely precipitated in the filtrate by excess of calciunl chloride and ammonia if the quantity of the alcohol is a little in. Greased.

Page  254 253 ORGANIC ACIDS. GROUP II. [~~ 167, 168. ~ 107. RACE.MIC ACID, C4 IH 06. The formula of CRYSTALLIZED RACEMIC ACID is C4 He O6. 12 0. The crys. tallization water escapes slowly in the air, but rapidly at 100~ (difference between racemic acid and tartaric acid). To solvents the racemic acid comports itself like the tartaric acid. The RnACEMATES also show very similar deportment to that of the tartrates. However, many of them differ in the amlount of water they contain, and in form and solubility from th3 corrcsponding tartrates. The aqueous solution of racemic acid and the racemates exercises no diverting action upon polarized light. Calcium chloride precipi tates fromn the solutions of free racemic acid and of racemates CALCIUMJ RACEMATE, C4 114 06 Ca. 4 H2 O, as a white crystalline powder. Ammonia throws clown the precipitate from its solution il hydrochloric acid, either immediately or at least very speedily (difference between racemic acid and tartaric acid). It dissolves in solution of soda and potassa, but is reprecipitated from this solution by boiling (difference between racemic acid and oxalic acid). Liome-water added in excess produces immediately a white precipitate insoluble in ammonium chloride (difference between racemic and tartaric acid). Solution of calcium sulphate does not immediately produce a precipitate in a solution of racemic acid (difference between racemic and oxalic acid); however, after ten or fifteen minutes, calcium racemate separates (difference between racemic acid and tartaric acid); in solutions of normal racemates the precipitate forms immediately. With potassium.valts racemic acid comports itself like tartaric acid. By letting sodium and potassium racemate or sodium and ammonium racemate crystallize, two kinds of crystals are obtained, which resemble each other as the image reflected by a mirror resembles the object reflected. The one kind of crystals contain common or dextro tartaric acid (which turns the plane of polarized light towards the right); the other kind contains laevo tartaric acid, i. e., an acid which is the same in every respect as tartaric acid, with this exception only, that it turns the polarized light towards the left. If the two kinds of crystals are redissolved together, the solution shows again the reactions of racemic acid. Second Group. THE ACIDS OF THE SECOND GROUP SUBLIME WITHOUT ALTERATION. BY HIEATING WITH NITRIC ACID THEY ARE EITHER LEFT UNCHANGED (SUCCINIC ACID), OR MERELY CONVERTED INTO NITRO-ACID (BENzOIC ACID). THE CALCIUM SALTS ARE READILY SOLUBLE IN WATER (BENZOIC ACID), OR DIFFICULTLY SOLUBLE (SUCCINIC ACID). THE SOLUTIONS OF THE NORMAL ALKALI-SALTS ARE PRECIPITATED BY FERRIC CHLORIDE: Succinic Acid, Benzoic Acid. ~168. a. SuccINIC ACID, C02 H (C 0 0 H)2 0C4 1H 0O 1. SUCCINIC ACrD forms colorless and inodorous prisms or tables (rhombic prisms or rhomboid tables). It has a slightly acid taste, is readily soluble in water and alcohol, slightly soluble in ether, difficultly soluble in nitric acid, and vola~til Is when exposed to the action of heat, leaving only a little charcoal b dl.l,ad. The officinal acid has an empyreumatic odor, and leaves a somewhat larger carbonaceous residue upon volatilization. Succinic acid

Page  255 ~ 169.] BENZ0TC ACID. 255 is not destroyed by heating with nitric acid, and may therefore be. easily obtained in the pure state by boiling witl that acid for half an hour, by which means the oil of amber, if present, will be destroyed. By sublimation crystalline needles of silky lustre are obtained. The acid loses water in this process, so that by repeated sublimation succinic anhydride is ultimately obtained. Heated in the air succinic acid burns with a blue flame, free from soot. 2. The SUCCINATES are decomposed at a red heat; those which have an alkali metal or alkali-earth metal for base are converted into carbonates with separation of charcoal. Most of the succinates are soluble in water. Sodium succinate is scarcely soluble in strong alcohol and crystallizes well both as normal and acid salt; hence it may be readily obtained in a pure state from very impure fluids. This property may be utilized for the detection and separation of the acid. * On heating the succinates with potassium disulphate in a tube the acid sublimes. The acid may be also obtained from the salts by decomposing them with sulphuric acid, and extracting with warm absolute alcohol. 3. On mixing a cold neutral moderately dilute solution of an alkali suecinate with calcium chloride, no precipitate is formed; on then addiing alcohol a gelatinous precipitate of CALCIUM SUCCINATE falls, readilv soluble in ammonium chloride. From this solution more alcohol reprecipitates the gelatinous salt; in case of great dilution no precipitate is produced at first, but in a short time the calcium succinate separates in the crystalline form C4 H4 04 Ca. 3 H2 O. 4. Ferric chloride produces in neutral solutions of the succinates of the alkali metals a brownish pale red bulky precipitate of FERRIC SUCCINATE; some succinic acid is liberated in this reaction, and retains part of the preci.pitate in solution if the fluid is filtered off hot. The precipitate dissolves readily in mineral acids; ammonia decomposes it, causing the separation of a less bulky precipitate of a highly basic ferric succinate, and combining with the greater portion of the acid to ammonium succinate which dissolves. 5. Lead acetate when added drop by drop to a solution of free succinic acid, or of an alkali succinate, produces a white amorphous precipitate which is immediately redissolved in excess of succinic acid, in alkali succinate, and in lead acetate, but in a short time separates from such solutions in the crystalline form. The precipitate consists of normal LEAD SUCCINATE, C4 H4 04 Pb: it is barely soluble in water, acetic acid, succinic acid, and lead acetate, readily soluble in nitric acid; by ammonia it is converted into a basic salt C4 H4 O Pb. 6. A mixture of alcohol, ammonia, and barium chloride produces in solutions of free succinic acid and of succinates a white precipitate of BARIUM BUCCINATE, C4 H4 04 Ba. ~ 169. b. BEZOIC ACID, C6 H5 C O O H = C7 H1 02. 1. Pure nENzorc ACID forms inodorous white scales or needles, or simply a crystalline powder. It fuses when heated, and afterwards volatilizes completely. The fumes cause a peculiar irritating sensation in the throat, and provoke coughing; when cautiously cooled, they condense to brilliant needles; when kin 1led, they burn with a luminous sooty flame. The common officinal benzoic acid has the odor of benzoin, and leaves a small carbonaceous residue upon volatilization. Benzoic acid is very sparingly soluble in cold water, but it dissolves pretty freely in hot water and in al* Compare MEISSNER and JOLLY, Zeitschr. f. anal. Chem., 4, 502.

Page  256 256 ORGANIC ACIDS. GlOUPT II. [g 1 70, 171 cohol. Addition of water imparts therefore a milky turbidity to a saturated solution of the acid in alcohol. 2. Most of the BENZOATES are soluble in water; only those with weak bases, e.g., ferric benzoate, are insoluble. The soluble benzoates have a pe culiar pungent taste. The addition of a str'ong acid to concentrated aque. ous solutions of benzoates displaces the benzoic acid, which separates in the form of a dazzling white sparingly soluble powder. Benzoic acid is expelled in the same way from the insoluble benzoates by such strong acids as form soluble salts with the bases with which the benzoic acid is combined. 3. Ferric chloride precipitates solutions of free benzoic acid incompletely: neutral solutions of benzoates of the alkali metals completely. The precipitate of basic FERRIC BENZOATE is bulky, flesh-colored, insoluble in water. It is decomposed by ammonia in the same manner as ferric succinate, from which salt it differs in this, that it dissolves in a little hydrochloric acid, with separation of the greater portion of the benzoic acid. 4. Lead acetate fails to precipitate free benzoic acid, but it produces flocculent precipitates in solutions of alkali benzoates. The precipitate is insoluble in sodium benzoate, but dissolves in lead acetate. 5. A mixture of alcohol, ammonia and barium chloride, or calcium chloride produces no precipitate iu solutions of benzoic acid or of the alkali benzoates. ~ 170. Recapitulation and remarcks.-Succinic and benzoic acids are distin. guished from one another by the color of their ferric salts, and also by their different deportment with barium chloride or calcium chloride and alcohol; but principally by their different decgrees of solubility, succinic acid being readily soluble in water, whilst benzoic acid is very difficult of solution. Succinic acid is seldom perfectly pure, and may therefore often be detected by the odor of oil of amber which it emits. The detection of the two acids, when present in the same solution with other acids, may be effected as follows: precipitate with ferric chloride, warm the washed precipitate with ammonia, filter, concentrate the solution, divide it into two parts, and mix one part with hydrochloric acid, the other with barium chloride and alcohol. Succinic acid and benzoic acid do not prevent the precipitation of ferric hydroxide, aluminium hydroxide, etc., by alkalies. Th/ird Grozp. THE ACIDS OF THE THIRD GROUP AMAY BE DISTILLED WITH WATER (LACTIC ACID WITH DIFFICULTY). THE CALCIUAI SALTS ARE READILY SOLUBLE IN WATER. TIlE SOLUTIONS OF TIlE NORMAL AL KALI-SALTS ARE NOT PRECIPITATED IN THE COLD BY FERRIC CH-ILORIDE: Acetic acid, Formic acid (Lactic Acid, Propionic Acid, Butyric Acid). ~ 171. a. ACETIC ACID, C H, C 01 = C2_ H-, 0,. 1. ACETIC ACID forms transparent crystalline scales, which fuse at 17~ to a cl lorless fluid of a peculiar pungent and pene. — r —--— r —— i

Page  257 ~ 171. ] ACETIC ACID. 5 7 trating odor, and exceedingly acid taste. When exposed to the action of heat it volatilizes completely, forming pungent vapors, which burn with a blue flame. It is miscible with water ill all proportions; it is to such mixtures of thle acid with water that the name of acetic acid is commonly applied. Acetic acid is also soluble in alcohol. 2. The ACETATES undergo decomposition at a red heat; among the products of this decomposition we generally find acetic acid, and almost invariably acetone, C 0 (C II0),. The acetates of the alkali metals aind alkali-earth metals are colverted into carbonates in this process; of the other metallic acetates many leave the metal behind in the pure state, others in the form of oxide. Most of the residues wh]ich the acetates leave upon ignition are carbonaceous. Nearly all acetates dissolve in water and in alcohol; most of them are readily soluble in water, a few only are diflicult of solution in that melstrum.ln if acetates are distilled with dilute sulphuric acid, the free acetic acid is obtained in the distillate. 3. If frrric chloride is added to acetic acid, and the acid is then nearly saturated with ammonia, or if a neutral acetate is mixed with ferric chloride, the fluid acquires a deep red color, owing to the fornmation of FERRIC ACI''ETATE. 1)' bo()ililln' the fluid becomes colorless if it contains an excess of ac.etate, the whole of the iron precipitating as a basic acetate, in the form of brown-yellow flakes. Ammonia precipitates from it the whole of the iron as hydroxide. By addition of hydrochloric acid a fluid which appears red from the presence of ferric acetate turns yellow (d ifferen ce from ferric stilphocyanate). 4. Neutral acetates (but not free acetic acid of a certain degree of dilution) give with silver nitrate white crystalline precipitates of SILvER ACETATE, C02 H, 0 Ag, which are very sparingly soluble in cold water. They dissolve more easily in hot water, but separate again upon cooling, in the form of very fine crystals. Ammonia dissolves them readily; free acetic acid does not increase their solubility in water. 5. Mercurous nitrate produces in acetic acid, and more readily still in acetates, white scaly crystalline precipitates of MERCUnoUS ACETATE (C2 H3 02)2 Hg2, which are sparingly soluble in water and acetic acid in the cold, but dissolve without difficulty in an excess of the precipitant. The precipitates dissolve in water upon heating, but separate again upon cooling, in the form of small crystals; in this process the salt undergoes partial decomposition; a portion of the mercury separates in the metallic state, and imparts a gray color to the precipitate. If the mercurous acetate is boiled with dilute acetic acid, instead of water, the quantity of the metallic mercury which separates is exceedingly minute. 6. Mercuric chloride produces no precipitate of mercurous chloride with acetic acid or acetates upon heating. 7. By heating acetates with concent7rated sudjlphuric acid acETIC aCID is evolved, which may be known by its pungent odor. But if the acetates are heated with a mixture of about 17

Page  258 2 8 ORGANIC ACIDS. GROUP III. [ 172. equal volumes of concentrated su7phuzic acicZ and alcohol,. ETHYL ACETATE, C2 H15 C2 H13 02, is formed. The odor of this ether is highly characteristic and agreeable; it is most distinct upoin shaking the mixture when somewhat cooled, and is mnuch less liable to lead to mistakes than the pulngent odor of the acid. 8. If dilute acetic acid is heated with an excess of lead oxide, part of the latter dissolves as triplumbic diacetate. The fluid has an alkaline reaction; it gives no crystals on cooling. ~ 172. b. FoIMtc ACID, H C O O H = C 112 02. 1. FonRMI ACID is a transparent and colorless slightly fuming liquid of a characteristic and exceedingly penetrating odor. When cooled to below 0~, it crystallizes in colorless plates. It is miscible in all proportions with water and alcohol. Wllen exposed to the action of heat, it volatilizes completely; the vapors burn with a blue flame. 2. The FORMATES, like the corresponding acetates, leave upon ignition either carbonates, oxides, or metals behind, the process being attended with separation of charcoal, and escape of carbon dioxide and water. All the compounds of formic acid with bases are soluble in water; alcohol also dissolves many of them, but not all. 3. Formic acid shows the same reaction with ferric chloride as acetic acid. 4. Silver nitrate fails to precipitate free formic acid, and decomposes the alkali formnates only in concentrated solutions. The white, sparingly soluble, crystalline precipitate of SILVER FORMATE, C H 02 Ag, acquires very rapidly a darker tint, owing to the separation of metallic silver. Complete reduction of the silver to the metallic state takes place, even in the cold, after the lapse of some time; but immediately upon applying heat to the fluid containing the precipitate. The same separation of metallic silver takes place in a solution of free formic acid, and also in solutions of formates so dilute that the addition of the silver nitrate fails to produce a precipitate. But it does not take place in presence of an excess of ammonia. 5. Mercurous nitrate gives no precipitate with free formic acid; but in solutions of alkali formates this reagent produces a glistening white sparingly soluble precipitate of MERCUROUS FORMATE (CH 0)2o Hg2, which rapidly becomes gray, owing to the separation of metallic mlercurv. Complete reduction ensues, even in thll cold, after the lapse of some time, but is immediate upon application of heat. This reduction is also attended with the formation of carbon dioxide and water, and takes pllace both in solutions of free formic acid and in fluids so highly dilute that the mercurous formate is retained in solution. 6. If formic acid or an alkali formate is heated with mercuric chloride to between 60~ and 70~, MERCUROUS CHLORIDE precipitates. Presence of free hydrochloric acid or of somewhat considerable quantities of alkali chlorides prevents the reaction. 7. If formic acid or a formate is heated with concentrated siuphuric acid the formic acid is resolved into water and CARBON MONOXIDE g'as, which latter escapes with effervescence and, if kindled, burns with a blue falame. The fluid does not turn black in this process, C H112 02 C 0 + H2 O. Upon heating formates with dilute sulphuric acid in a distilling apparatus free formic acid is obtained in the distillate, and may mostly be readily detected

Page  259 ~~ 173, 174.] LACTIC ACID. 259 by its odor. Upon heating a formate with a mixture of strong sulphuric acid and alcohol ETHYL FORIMATE iS evolved, which is characterized by its peculiar rum-like smell. 8. If dilute formic acid is heated with excess of lead oxide, the latter partially dissolves. The fluid has an alkaline reaction. On cooling the solution, which, if necessary, is concentrated by evaporation, LEAD FORIMATE (C H 02)2 Pb, separates in brilliant prisms or needles. ~ 173. Recapitulation and Remarks.-Acetic acid and formic acid may be distilled over with water, and form with quadrivalent iron soluble neutral salts which dissolve in water, with a blood-red color, and are decomposed upon boiling. These reactions distinguish the two acids of the third group from the other organic acids. From each other the two acids are distingunished by their odor and the odor of their ethyl compounds, and by their different reactions with silver salts and salts of mercury, with lead oxide and conce ntrated sulphuric acid. The separation of acetic acid from formic acid is effected by heating the mixture of the two acids with an excess of mercuric oxide or argentic oxide. Formic acid reduces the oxide, and suffers decomposition, whilst the acetic acid dissolves the oxide and remains in solution as an acetate. ~ 174. Rarer Acids of the Third Group. 1. LACTIC ACID, C3 16 03.* Lactic acid is developed in animal fluids, vegetable matters that have turned sour, &c. Lactic acid is a colorless syrupy liquid; it has a pure acid, sharp taste. When it is slowly heated in a retort to 130~, water containing a little lactic acid distils over, leaving a residue of lactic anhydride, C6 H0o 05 which between 250~ and 300~ is decomposed into carbon mnonoxide, lactide Cs H4 02 and other products. Lactic acid dissolves freely in water, alcohol, and ether. Upon boiling the aqueous solution a little lactic acid volatilizes with the aqueous vapor. All the lactates are soluble in water and alcohol, the greater part of them, however, only sparingly: they are all insoluble in ether. The production of some of these salts and the examination of their form under the microscope supply the means for the detection of lactic acid; calcium lactate and zinc lactate are the best suited for this purpose. Calcium lactate may be conveniently prepared from animal or vegetable juices by the following method devised by ScHERER:-Dilute the liquid, if necessary, with water, mix with baryta-water, and filter. Distil the filtrate with some sulphuric acid (to remove volatile acids),. digest * Four isomeric lactic acids are now believed to exist. That produced in fermentation or Ethylidene lactic acid, and the two existing together in the juice of flesh, viz., Ethylene lactic acid and Paralactic acid, agree quite closely in general properties.

Page  260 260 RARER ORGANIC ACIDS. GROUP III. [~ 174, the residue several days with strong alcohol, distil the acid solution with a little milk of lime, filter warm from the excess of lime and calcium sulphate, conduct carbon dioxide into tile filtrate, hleat once more to boiling, filter from the precipitated calcium carbonate, evaporate the filtrate, warm the residue with strong alcohol, filter, and let the neutral filtrate stand several days to give the calcium lactate time to crystallize. Should the quantity of lactic acid present be insufficient to allow the formation of crystals. evaporate the fluid to syrupy consistence, mix with strong alcohol, let the mixture stand some time, decant or filter the alcoholic solution into a vessel that can be closed, and add gradually a small quantity of ether. This process will cause even minute traces of calcium lactate to separate from the fluid. Calcium lactate shows under the microscope the form of minute crystalline needles aggregated in tufts with short stalks, pairs of them always being joined at the stalked ends, so as to look like paint-brushes unlited together. —Zinc lactate deposited quickly from its solution shows under the microscope the form of spherical groups of needles. The slow evaporation of solution of zinc lactate gives first crystals resemlbling clubs truncated at both ends; these crystals gradually increase in size; the two ends apparently diminish, whilst the middle parts increase in size (FUNKE). 2. PROPIONIC ACID, C2 H15 C O O H=C3 H6 02, and 3. BUTYRIC ACID, C3 Hi C O O H=-C4 118 02.* PRoPIroNc AcrD is formed under a great variety of circumstances; it is chiefly found in fermented liquids. The pure acid crystallizes at low temperature; it boils at 140.5~; it dissolves readily in water. Propionic acid floats as an oily stratum on concentrated aqueous solution of phosphoric acid and on solution of calcium chloride. It has a peculiar smell, which reminds both of butyric and acetic. acid. Upon distilling the aqueous solution, the propionic acid passes over into the distillate. NORMALx BUTYMIC or ETHACETIC ACID (C Ha. C H12. C H2. C O O H) is frequently found in animal and vegetable matter, more particularly also in fermented liquids of various kinds. The pure acid is a colorless, mobile, corrosive, intensely sour fluid, of a disagreeable odor, a combination of the smell of rancid butter and acetic acid; it boils at 163~. It is miscible in all proportions with water and alcohol. It is separated from the concentrated aqueous solution by calcium chloride, concentrated acids, &c., in the form of a thin oil. The smell of butyric acid is particularly strong in the aqueous solutiop of the acid. Upon distilling the aqueous solution, the acid passes over with the aqueous vapors. Calcium butyrate is less soluble in hot than in cold water. Propionic acid and butyric acid are often found associated with formic acid and acetic acid in fermented liquids, in guano, and in many mineral waters. The detection of the several acids may in such cases be effected as follows: dilute the substance sufficiently with water, acidify with sulphuric acid, and distil; saturate the distillate with baryta-water, evaporate to dryness, and treat the residue repeatedly with boiling alcohol of 85 per cent. This will leave the barium formate and part of tile barium acetate, the remainder of the acetate, together with the propionate and butyrate, dissolving in the alcohol. Evaporate the alcoholic solution, dissolve the residue in water, decompose cautiously with silver sulphate, boil, filter, and let the fluid (which ought rather to contain a little undecomposed barium salt than any silver sulphate) evaporate under the desiccator. Take out *Nfomal butyric acid and isobutyric or dimetlzacetic acid (C H) (C H3)2 (C O O H; have the same compositions and nearly the same properties. The reactions above given are those of the normal and most commonly occurring acid. Isobutyric acid, existing in the carob bean, boils at 154~; its calcium salt is more soluble in hot than cold water.

Page  261 ~ 174.] PROPIONIC AND BUTYRIC ACIDS. 261 separately the crystals which form first, those which form after, and those which form last, and examine them to ascertain their nature. Silver acetate emits upon solution in concentrated sulphuric acid the odor of acetic acid, and gives no oily drops; silver propionate and butyrate emit the peculiar odor of the acids, and give oily drops, which, however, with minute quantities are visible only under the microscope. To distinguish positively between propionic and butyric acid, it is indispensable to determine the amount of silver in the separated silver salts, and to fix by this the molecular weight of the acids. If much barium acetate has passed into the solution, with a small quantity only of butyrate and propionate, the barium is first exactly precipitated with sulphuric acid from the aqueous solution of the barium salts soluble in alcohol, half of the acid fluid neutralized with. soda, thile other half added, the fluid then distilled, the distillate, which now contains principally propionic and butyric acids, saturated with baryta, then decomposed with silver sulphate, and the remaining part of the process conducted as above.

Page  262 PART II. SYSTEMATIC COUIRSE OF QUALITATIVE CHEMICAL ANALYSIS. PRELIMINARY REMIARKS. TIE knowledge of reagents and of the deportment of bodies xwith them enables us to ascertain at once whether a collpound. of which the physical properties permit an inference as tc its nature, is in reality what we suspect it to be. Thus, for instance, a few simlple reactions suffice to show that a body which appears to be calcite is really calcium carbonate, and that another which we hold to be gypsum is actually calciumn sulphate. This knowledge usually suffices also to ascertain whether a certain body is present or not in a mixture; for instance, whether or not a white powder contains mlercurous chloride. But if our design is to ascertain the chemical nature of a substance entirely unknown to us —if we wish to discover all the constituents of a mixture or chemical compound —if we intend to prove that, besides certain bodies which we hlave detected, no other substance can possibly be present —if colsequently a corplete qualitative analysis is our object, the mere knowledge of the reagents, and of the reactions of bodies with them, will not suffice for the attainment of this end; this requires the additional knowledge of a systematic co~urse of analysis, in other words, the knowledge of the oder, in which solvents, and general and special reagents, should be app)lied, both to effect the speedy and certain detection of every eleiment present, and to prove with certainty the absence of all others. If we do not possess the knowledge of this systelnatic course, oi if, in the hope of attaininhg our object more rapidly, we adhere to no method, analyzillg becomes (at least in the hands of a novice) mere guess-work, alld the results obtained are no longer the fruits of scientific calculation, but mere matters of accident, which sometimes may prove lucky hits, and at others total failures. Every analytical investigation must therefore be based npon a definite method. But it is not by anly means necessary that

Page  263 PRELIMINXARY REMIARKS. 2 3 this method should be the same in all cases. Practice, reflection, and a due attention to circumstances will, on the contrary, generally lead to the adoption of different methods for different cases. However, all analytical methods agree ill this, that the substances to be looked for are in the first place classed illto grl'oups, which are then again subdivided, until the individual detection of the various substances present is finally acconmplished. The diversity of analytical inethods depends partly on the order in which reagents are applied, and partly on their selection. Beforle we can venture upon inventing methods of our own for illdividual cases, we must first malke ourselves thoroughly convlersant with a course of chemical analysis in. general. This system nmust have passed through the ordeal of experience, and must be adapted to every imaginable case, so that afterwards, when we have acquired some practice in analysis, we may be able to determine which modification of the general method will be best adapted to a givenl case. The exposition of such a systematic course, adapted to all cases, tested by experience, and conlbining simplicity with the greatest possible security, is the object of the Fi_-st Section. The elemenlts and compounds comprised in it are the same whllich we have studied in Part I., with the exception of those discnssed more briefly, and marked by the use of smaller type. The subdivisions of this systematic course are, 1, Preliimiinary Examination; 2, Solution; 3, Actual Ainalysis. The third subdivision (the Actual AnaUlysis) is adapted for the full investigation of any mixture or comnpound in whicll all the substances treated in the present work may be presenlt. With respect to the latter I have to remark that where the preliminary examination has not clearly demonstrated the abseince of certain groups of substances, the student cannot safely disregard any of the para~graphs to which reference is llade, inl consequtenee of the reactiolls he has observed. In cases where tlhe intention is silnply to test a mixture for certain substances, and not to ascertain all its constituents, it will be easy to select the particular paragraphs which ought to be attended to. As the construction of a universally applicable systematic course of analysis requires due provision for every contingeuc.y that may possibly arise, it is self-evident that, though in the system here laid down the various bodies comprised in it have been assumed to be mixed up together in eveiry conceivable way, it was absolutely indispensable to assnume that no foreigln or:yanic mratters were present: since the presence of such mnattels would initroduce various complications. Although the general analytical course laid down here is devised and arranged in a manner to suit all possible contingencies, still there are special cases in which it may be advisable to modify it. A preparatory treatment of the smubstance is also

Page  264 264 PART II. GENERAL COURSE OF ANALYSIS. [ 1 75 sometimes hecessary, before the actual analysis can be proceeded with; the presence of coloring or slimy organic mIatters luore especially requires certain preliminlarv operations. The Secolond.Section will be found to contaill a detailed descriptionl of the special Inethods eimployed to meet certainl cases whiclh frequently ocur. Some of these imethods sllow how the analytical process becomes simnplified as the number of substalnces decreases to which regard must be had. In colclusion, as an. intelligenlt and successful purssuit of analysis is possible only with an accurate knllowledge of tle plrinciples whereon the detection and separation of bodies depend, I have given in the Third Section an explanation of thle general alalytical process, with numerous additions to tle practical operations. As this third section may properly be regarded as the key to the first and second sections, I strongly 1ecornnmeld students to make themselves early and thoroughly acquainted with it. I have devoted a special section to this theoretical explanation, as I think it will be understood better in a connected form than it would have been by explanatory additions to the several paragraphs, which, moreover, might llave materially interfered with the perspicuity of the practical process. I have also in this tlhird section taken occasion to point out in. what residues, solutions, precipitates, &c., which are obtained in the systematic coulse of analysis, the rarer elements, acids,,or rtadicals may be expected to be met with; and also to give instructions how to proceed with a view to insure the detection of these bodies also systemnatically. Finally, the student should, at the outset of his analytical work, form the habit of keepillng a full and systematic record of his results, and of everyv item of experience which it may be useful to refer to. See Appendix II1. SECTION I. PRACTICAL PROCESS FOR THE ANALYSIS OF COM. POUNDS AND MIXTURES IN GENERAL. I. PRELIMINARY EXAMINATION. F Do not fail to consult the observations in the Third Section of Part I.. page 365. ~ 175. EXAMINE, in the first place, the external properties, such 1* as the color, shape, hardness, gravity, odor, etc., of the sub* These marginal numbers are simply intended to facilitate reference.

Page  265 g 176.] PRELIMINARY EXAMIINATION. SOLIDS. 26b stance, since these will often enable you in some measure to infer its nature. Before proceeding, if the quantity of the substance is limited, you must consider how much may safely be spared for the preliminary examination. A reasonable economy is in all cases advisable, even thlogh you may possess the sunbstance in large quantities; but, under all circumstances, let it be a fixed rule never to use up the whole of what you possess of a substance, but always to keep a portion of it for unforeseen contingencies, and for confirmatory experiments. For a general view of the subdivisions of the COUIRSE OF ANALYSIS, see the Table of Colltents of Part II., at the bePginning of the book. A. THE BODY UNDER EXAMINATION IS SOLID. I. IT IS NEITHER A METAL NOR AN ALLOY. ~ 176. 1. The substance is fit for examination if in powder or in 2 minute crystals; but in the case of larger crystals or solid pieces, a portion must, if practicable, be first reduced to finepowder. Bodies of the softer kind may be triturated ill a porcelain mortar; those of a harder nature must first be broken into small pieces in a steel lnortar, or upon a steel anvil, and the pieces then be triturated in an agate mortar. 2. PUT SOME OF THE POWDER INTO A GLASS TUBE, S]EAIED 3 AT ONE END, ABOUT 2 INCHES LONG AND -3-THS OF AN INCItI WIDE, AND HEAT first gently over the spirit or gas-lamlp, then intensely in the blowpipe flame. The reactions resulting may lead to many positive or probable conclusions regarding the nature of the substance. The following are the most important of these reactions, to which particular attentioll ought to be paid; it often occurs that several of them are observed in the case of one and the same substance: a. TIE SUBSTANCE REMAINS UNALTERED: absence of 4 organic matters, salts containing water of crystallization, readily fusible matters, and volatile bodies (except carbon dioxide, which often escapes Vithout visible change). b. THE SUBSTANCE DOES NOT FUSE AT A MODERATE HEAT, 5 BUT SIMPLY CHANGES COLOR. From white to yellow, turning white again on cooling, indicates ZINC OXIDE; from white to yellowish brown, turning to a dirty light yellow on coolillg, indicates STANNIC OXIDE; from white or yellowish-red to brownish-red, turning to yellow on

Page  266 266 PART HI. GENERAL COURSE OF ANALYSIS. [, 17C cooling, the body fusing at a red heat, indicates LEAD OXIDE; from white, or pale-yellow, to orange-yellow, up to reddish-brown, turning pale-yellow on11 coolillg, the body fusing at an intense red heat, indicates BISMUTIr TRIOXIDE; fromn brownish-ired to black, turlling brownish-red again on cooling, indicates FERRIrC OXIDE; from yellow to dark-oraRnge, the b(ody fusing, at an intense heat, indicates POTASSIUM CIIROMATE, &C. C. THIE SUBSTANCE FUSES WITHOUT EXPULSION OF AQUE- 6 OUS VAPORS. If, by intense heating, gas (oxygen) is evolved, and a small fragment of charcoal thrown in is energetically coiisumed, NITRATrES or CHIORATES are indicated. d. AQUEOUS VAPORS ARE EXPELLED, WIHICII CONDENSE 7 IN THE COLDER PART OF THE TUBE: this indicates either (a) SUBSTANCES CONTAINING CRYSTAL WATER, ill which case they will generally readily fuse, and resolidify after expulsion of the water; many of these swell considerably whilst yieldinl up their water, e.g., borax, alum; or (8) decomposable HYDROXIDES, in which case the bodies often will not fuse; or (y) anhydrons salts, holding WATER MECHIANICCALLY ENCLOSIED between their lanmellhe, in which case the bodies will decrepitate; or (6) bodies with MOISTUREm externallv adhe;rino to themn. Test the reaction of the co(Tdensed fluid inl the tulbe; if it is alkaline, ainlnonia is indicated; if acid, a volatile acid (sulphuric, snlphurons, hydrofluoric, hydrochlorie, hydrobromic, hyldriodie, nlitrie, &c). e. GASES OR FU.MIES ESCAPEI. Olbserve wllether tlley 8 have a color, a smell, an acid or alkaline reaction, whether they are ilflanmmable, &c. aa. OXYGEN indicates metallic dioxides, chlorates, nitrates, etc. A glilumnering slip of wood is relighted in the gaseous currenlt. bb. SULPHUR DIOXIDE is often produced by decomposition of sulphates; it may be known by its odor and by its acid reaction with moist blue litmnus-paper. cc. NITROGEN TETROXIDE, resultinll from the decomposition of nitrates, especially those of the heavy metals; it may be known by the brownish-red color and the odor of the fumnes. dd. CARBON DIOXIDE indicates carbonates decomposable by heat, or oxalates of reducible metals, or if accompanied by carbonization (see 10) organic bodies. The gas is colorless and tasteless, non-inflammable; a drop of lime-water on a watch-glass becomes turbid on exposure to the gaseous current. ee. CARBON MONOXIDE indicates oxalates and also formates. The gas burns with a blue flamee. n the

Page  267 1 76.] PRELIMINARY EXAM3INATION. SOLIDS. 267 case of oxalates the carbon monoxide is generally mixed with carbon dioxide, and is therefore more difficult to kindle: in the case of formates there is marked carbonization. Oxalates evolve carboii dioxide when brought into contact with manganese dioxide, a little water, and some concentrated sulphuric acid, on a watch-glass; formates evolve no carbon dioxide under similar circumstances. ff. CHLORINE, BROMINE, or IODINE indicate decomposable chlorides, bromides, or iodides. The gases are readily recognized by their color and odor. Iodine, if evolved in any quantity, forms a black sublimate (compare 9). gy. CYANOGEN indicates cyanides decomposable by heat. The gas may be known by its odor, and, when tolerably pure, by the crimson flame with which it burns. hh. HYDROSULPHURIC ACID indicates sulphides containing water; the gas may be readily klnown by its odor. ii. AiMMONIA, resulting from the decomrposition of ammonium salts, or also of cyanides or nitrogenous organic matters, in which latter cases browning or carbonization takes place, and either cyanogen or offensive empyreumatic oils escape with the ammonia..f. A SULIMATE FORMS. This indicates volatile bodies: 9 thile following are those more frequently met withll:aa. SULPHUR. Eliminated from mixtures or from many of the metallic sulphides. Sublimnes in reddishbrown drops, which solidify on cooling, and turn yellow or yellowish-brown. bb. IODINE. Eliminated from mixtures, many iodides, iodic acid, &c. Violet vapor, black sublimate, smell of iodine. cc. AMMIONIUM sALTrs give white sublimates; heated with sodium carbonate alld a drop of water on platinumn foil they evolve alnmlnonia. dcl. -MERCuRY and its compounds. METALLIC MERcuny forms globules; MERCURIC SULPHIDE iS black, lbut acquires a red tint when rubbed; MIERCURIC CHLORIDE fuses before volatilizinlg; oMERCUROUS CIILORIDE sublimes without previous fusion, the sublimlate, which is yellow whilst hot, turns white on cooling. The red MERCURIC IODIDE gives a yellow sublimate. ee. ARSENIC and its compounds. MIETALLIC ARSENIC forms the well-known arsenical mirror; ARSENIOUS OXIDE forms small shining crystals; the SULPHIDES OF ARSENIC give sublimates which are reddish-yellow whilst hot, and turnl yellow on cooling.

Page  268 268 PART 11. GENEIAL COURSE OF ANALYSIS. [~ ANTIMIONIOUS OXIDE fuses to a yellow liquid before subliming. The sublimate consists of brilliant needles. g. I3ENZOIC ACID and SUCCINIC ACID. The officinal impure acids may be known by the odor of their fulnes. /J/1. OxALIC ACID. White crystalline sublimate, thick irritatinlg fumes in the tube. IIeating a small sample on platinumn-foil with a drop of concentrated sulphuric acid gives rise to a copious evolution of gas. g. CARBONIZATION TAKEtS PLACE: organic substances. 10 This is always attended with evolution of gases (acetates evolve acetone) and water, which latter has an alkalinle or acid reaction. If the residue effervesces with acids, whilst the original substance did not show this reaction, or 0gallic acids lnay be assulned to be present ill combination with alkali or alkali-earth metals. Salts containillng readily reducible metals in combination with organic acids, often leave the mnetal behind, with little or no carbon. [Since tlle observations suggested by this paragraph will decide the operator, whether or lnot to look for an organic acid in the subsequent analysis, it may be well to caution the beginner lnot to be too hasty in concluding that carbonization does or does not occur. In addition to what is stated above, we may Imention that: 1. Blcac/enuing is not necessarily carbonization, for salts of volatile acids with certaill metals, as copper, nickel, and cobalt, blacken on ignition from separation of the oxide. 2. Carbonization, i.e., the separation of carbon, is usually attended with the disengagement of vapors, which often condense in oily droplets, or as an oily film on the cold part of the tube, alld which have a "burnt" odor. 3. The carbon remaininilg after these vapors cease to escape usually takes fire when heated in contact with the air, and glows with red-heat until it is consumed. 4. Carbonization is, in general, best observed when the body is heated rapidly to a high temperature. -ED.] 3. PLACE A SMALL PORTION OF THE SUBSTANCE ON A CHAR- 11 COAL SUPPORT (in the cavity scooped out for the purpose), AND EXPOSE TO THE INNER BLOWPIPE FLAME. As most of the reactions described under 2 (3-10) are also produced by this process, only those appearances will be mentioned which are peculiar to this experiment. Evolution of sulphur dioxide, when the flame plays upon the sample, generally indicates a sulphide.. The following are the reactions which will permit pretty accurate conclusions: a. TILE BODY FUSES, AND IS ABSORBED BY THE CHARCOAL OR FORMS A BEAD IN THE CAVITY, nlOt attended by in

Page  269 ~ 176.] PRELIMINARY EXAMINATION. SOLIDS. 269 crustation: indicates more particularly salts of the alkali metals. b. AN INFUSIBLE WHITE RESIDUE REMAINS on the char- 13 coal, either at once or after previous melting in the water of crystallization; consists of or indicates more particularly the oxides of barium, strontium, calciumn, magnesiunm, aluminiuln, zinc (appears yellow whilst hot), and silicic oxide. Among these substances the OXIDES of STRONTIUM, CALCIUM, M-AGNESIET, and zINC are distinguished by strong luminosity in the llowpipe flame. nMoisten the white residue with a drop of cobalt nitrate, and expose again to a strong heat. A fine blue tint indicates ALUMINIUM; a green, ZINC. In the presence of SILICIC OXIDE and of many PHOSPrHTES of the alkaliearth metals a more or less blue coloration is produced with partial fusion. In the case a or b the preliminary examination for alkai and alkali-earth metals may be completed by inspectilg the colors which the substances impart to flamle. For this purpose a little of the substance is attached to the loop of a file platinum wire, moisteled repeatedly with sulphuric acid, dried cautiously near the border of the flamen and tllen held in the fusing zone of BUNSEN'S gas flamne. The colorations caused b)y the alkali metals will make their appearance first, followedafter volatilization of the alkali metals, by that of barium, and finally-after moistening with hydrochloric acidby those of strontium and calcium. For details see ~ 92 and ~ 99. c. THE SUBSTANCE LEAVES A RESIDUE OF ANOTIER 14 COLOR, OR REDUCTION TO THE MIETALLIC STATE TAKES PLACE, OR AN INCRUSTATION FORMS ON THE CHARC()AL. 3Mix a portion of the powder with sodium carbonate and a drop of water, and heat on charcoal in the reducilg flame; observe the residue in the cavity as well as tihe incrustation on the charcoal. a. The sustained application of a strong flame pro- 15 duces a metallic globule, without incrustation of the charcoal, indicates GOLD OR COPPER. The latter is at once recognized by the green coloration of the flame. The compounds of platinumn, iron, cobalt, and nickel are indeed also reduced, but they yield no metallic globules. f3. The charcoal support is coated with an incrus- 16 tation, either with or without formation of a metal lie globule. aa. The incrustation is white, at some distance from the test specimen, and is very readily dissipated by heat, emitting a garlic-like c dor: ARSENIC.

Page  270 270 PART II. GENERAL COURSE OF ANALYSIS. [~ 176. 1b. The incrustation is white, nearer the test specimen than in aac, and may be driven from one part of the support to another: ANTIMONY. M[etallic globules are generally observed at the same time, which continue to evolve white fumes long after the blowpipe jet is discontinued, and upon cooling become surrounded with crystals of antimonious oxide; the globules are brittle. cc. The incrustation is yellow whilst hot, but turns white on cooling; it is pretty near the test specimen and is with difficulty volatilized: ZINC. dd. The incrustation has a.taint yellow tint whilst hot, but turns white on cooling; it surrounds the test specimen closely, and both the inner and outer flame fail to volatilize it: TIN. The metallic globules formed at the same time, but only in a strongl reducing flame, are bright, readily fusible, and malleable. ee. The incrustation has a lemon-yellow color, turning on cooling to sulphur-yellow; heated in the reducing flame it volatilizes, tinging the flame blue: LEAD. Readily fusible, malleable globules are formed at the same timne with the incrustation. ffl: The incrustation is of a dark oranlge-yellow color whilst hot, which changes to lemon-yellow on cooling; heated in the reducing flame it changes its place without coloring the flame: BISMUTH. The metallic globules formed at the same time as the incrustation are readily fusible and brittle. gg. The incrustation is reddish-brown, in thin layers orange-yellow; it volatilizes without coloring the flame: CADMIUM..h. The incrustation is dark-red: SILVER. Where lead and antimony are present at the same time, the incrustation is crimson. To learn, in cases of doubt, whether reduced metal has been separated in this experiment, the charcoal cavity is moistened with water, the charcoal cut out for a little space around and below the cavity, brought into an agate mortar, finely pulverized, and the charcoal powder cautiously washed away. Any metal that may be present remains in the mortar, gold in yellow, copper in red, silver in white, tin in grayisll-white, lead in gray plates or streaks. Bismuth will remain as a reclddishgray, zinle a bluish-gray, antimony a gray powder. When copper and tin or copper and zinc are simlultanleously present, yellow alloys of these metals

Page  271 ~ 176.1 PRELIMINARY EXAMINATION. SOLIDS. 271 may be formed. [Iron, nickel, and cobalt, when reduced on charcoal, remain after washing as black or dark-gray powders, which are lifted by the magnet.] 4. FUSE A SMALL PORTION WITHI A BEAD OF SODIUM META- 17 PHOSPHATE AND EXPOSE FOR SOME TIMIE TO THE OUTER FLAMIE OF THE BLOWPIPE. a. THE SUBSTANCE DISSOLVES READIILY AND COPIOUSLY TO A CLEAR BEAD (WIIILST HOT). a. DThe hot bead is colored: 18 BLUE, )by candlelight inclining to violet-COBALT; GRBEN, upon coolinog blue; in the reducing flame, after coocling, red —coPPER; GREEN, particularly fine on cooling, unaltered in the reducing flame —cHROMIUM; BROWNISH-RED, on0 cooling, light-yellow or colorless; in the reducing flame red whilst hot, yellow whilst cooling, then gureenislh —RON; REDDISII TO BROWNISIt-lRED, 011 cooling yellow to reddish-yellow or colorless; in the reducing flame unaltered-N ICKEL; YELLOWISH-B3ROWN, on cooling light-yellow or colorless; in the redullcing flame almost colorless (especially after addition of a very little tin), blackish-gray on cooling-BISMUTT-IH; LIGHT-YELLOWISHI to OPAL) when cold rather dull; in the reducing flame whitish-gray-SILVER; AMETHYST-RED, especially on cooling; colorless in the reducing flame, not quite clear-MANGANESE.,3. Thae hot bead is colorless: X 9 IT REMAINS CLEAR ON COOLING: ANTIMONY, ALUMINIUM, ZINC, CADMIUM, LEAD, CALCIUMI, MAGNESIUM; the latter five, when added in somewhat large proportion to the sodium metaphosphate, give enamel-white beads; the bead saturated with lead is yellowish; IT BECOMES ENAMEL-WHITE ON COOLING, EVEN VHERE ONLY A SMALL PORTION OF THE POWDER IIAS BEEN ADDED TO THE SODIUM METAPHOS. PHATE: BARIUM, STRONTIUM. b. THE SUBSTANCE DISSOLVES SLOWLY AND ONLY IN 20 SMALL QUANTITY: a. The bead is colorless, and remains so even after cooling; the undissolved portion looks semitransparent; upon addition of a little ferric oxide it acquires the characteristic color of an iron bead: SILICIC OXIDE.

Page  272 272 PART II. GENERAL COURSE OF ANALYSIS. [~,177, 178 /i. The bead is colorless, and remains so after addition of a little ferric oxide: TIN. C. TIIE SUBSTANCE DOES NOT DISSOLVE, BUT FLOATS 21 (IN TIIE METALLIC STATE) IN THE BEAD: GOLD, PLATINUM. 5. MINERALS ARE EXAMINED FOR FLUORINE AS DIRECTED g 146, 8. As the body under examination may consist of a mixture of the most dissimilar elements, reactions may be observed in an experiment which proceed from a combination of two or several cases. Such reactions must of course be interpreted accordingly. After the termination of the preliminary examination, proceed to the solution of the substance, as directed ~ 180 (32). ~ 177. II. THE SUBSTANCE IS A MJETAL OR AN ALLOY. 1. I-IEAT A SMALL PORTION OF TIlE SUBSTANCE WITH WATER 22 ACIDULATED'WITH ACETIC ACID. If HYDROGEN iS evolved this indicates a light metal (possibly also manganese). 2. HEAT A SAMPLE OF THE SUBSTANCE ON CHARCOAL IN THE 23 REDUCING FLAME OF THE BLOWPIPE, and watch the reactionls; for instance, whether the substance fuses, whether an incrustation is formed, or an odor emitted, cc. By this operation the following metals may be detected with more or less certainty: ARSENIC by the smell of garlic; MERCURY b)y its volatility; ANTIMONY, ZINC, LEAD, BISMUTIT, CADMIUM, TIN, SILVER, by fusing, with incrustation of the charcoal (comnp. 16); COPPER by the green coloration of the outer flalue. Further conclusions may be formed when the substance is a single metal nearly pure; thus, for instance, GOLD fuses without incrustation; PLATINUM, IRON, MANGANESE, NICKEL, and COBALT, do not fuse in the blowpipe flalne. 3. HEAT A SAMPLE OF TIlE SUBSTANCE BEFORE TIlE BLOW- 24 PIPE IN A GLASS TUBE SEALED AT ONE END. a. No SUBLIMATE IS FORMED IN THE COLDER' PART OF TH-IE TUBE: absence of mercury. b. A SUBLIMATE IS FORMED: presence of MERCURY, CADMIUM or ARSENIC. The sublimate of mercury, which consists of small globules, cannot be confounded with that of cadmium or arsenic. After the termination of the prelimninary examination, proceed to the solution of the substance as directed ~ 181 (42). ~ 178. B. THE SUBSTANCE UNDER EXAMINATION IS A FLUID. 1. EVAPORATE A SMALL PORTION OF THE FLUID in a plati- 25 Inm capsule, or in a small porcelain crucible, to ascertain

Page  273 ~ 179.] SOLUTION. 2 73 whether it actually contains any matter in solution; if a residue remains, examine this as directed ~ 176. 2. TEST WITH LTTMUS-PAPER (blue and red). a. THE FLUID REDDENS BLUE LITITUS-PAPER. This re- 26 action may be caused by a free acid or an acid salt, as well as by normal salts of the heavy metals,* soluble in water. To distinguish between these two cases, pour a small quantity of the fluid into a watch-glass, and dip into it a small glass rod, after moistening the extreme point of the latter with dilute solution of sodium carbonate; if the fluid remains clear, or if the precipitate which may form at first redissolves upon stirring the liquid, this proves the presence of a free acid or of an acid salt; but if the fluid becomes turbid and remains so, this generally denotes the presence of a soluble salt of a heavy metal. b. REDDENED LITMIU S-PAPER TURNs BLUE: this indicates 27 the presence of an alkali or alkali-earth metal, usually in the state of hydroxide, sulphide or carbonate. 3. SMrECLL TILE FLUID, o01 should this fail. to give satisfactory 28 results, DIsTIL, to ascertain whether the simple solv-et present is water, alcohol, ether, &c. If you find it is not water, evaporate the solution to dryness, and treat the residue as directed ~ 176. 4. If the solution is aqueous, and manifests an acid reac- 29 tion, DILUTE A PORTION OF IT LARGISELY WITIh WATER. Should this imnpart a milky appearance to it, the presence of ANTIMONY 01r BISUTII (or possibly also of tin) may be inferred. Comp. ~ 121, 9, and ~ 131, 4. On completing the Preliminary Examnination of a Fluid 30 the operator may proceed to its Actual Analysis. If the solution is aqueous and reacts neiutral, only bodies which are soluble in water can be present; if, on the contrary, it has an acid reaction, which may be due to the presence of a free acid, it, can no longer be considered simply aqueous, and the analysis must be conducted with regard to the possible presence of substances insoluble in water but soluble in acids. These circumstances being properly considered, the analyst passes over to ~ 182-solutions having an alkaline reaction are also examined according to ~ 182. [I. SOLUTION OF BODIES, OR CLASSIFICATION OF SUBSTANCES, ACCORDING TO THEIR DEPORTMENT WITH CERTAIN SOLVENTS.:m~r Consult the remnarks in the third section, pagtye 366. ~ 179. Water and acids (hydrochloric acid, nitric acid, aqua regia) 31 * I.e., of other than an alkali or alkali-earth metal. 18

Page  274 274 PART n. GENERAL COURSE OF ANALYSIS. L[ 180 are the solvents used to classify simple or compound substances, and to isolate the colnponent parts of mixtures. We divide the various substances illto three classes, according to their respective deportment with these solvents. First class. SUnBSTrANCES SOLUBLE IN WATER. Seconld class.-SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WVATER, BUT SOLUBLE IN IlYDROCHILORIC ACID, NITRIC ACID, OR AQUA REGIA. TY'ird class.- SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER AS WELL AS IN IIYDROCIILORIC ACID, NITRIC ACID, AND AQUA REGIA. The solution of ALLOYS being more appropriately effected in a different manner from that pursued with other bodies, I shall give a special method for these substances (see ~ 181). The process of solution is conducted in the following mallller: A. THE SUBSTANCE UNDER EXAMINATION IS NEITHER A METAL NOR AN ALLOY. ~ 180. i. Put about a gramme of the finely pulverized substance 32 into a small flask or a test-tube, add frorn ten to twelve times the amount of distilled water, and heat to boiling over a spirit or gas-lamnp. a. THE SUBSTANCE DISSOLVES COMPLETELY. In that 33 case it belongs to the first class: regard must be had to what has been stated in the preliminary examination (30) with respect to reaction with test-papers. Treat the solution as directed ~ 182, 46. b. AN INSOLUBLE RESIDUE REMAINS EVEN AFTER PRO- 34 TRACTED BOILING. Let the residue subside, and filter the fluid off, if practicable, in such a mnalner as to retain the residue in the test-tube; evaporate a few drops of the clear filtrate on platinum foil; if nothing remnains, the substance is completely insoluble in water; in which case proceed as directed 35. But if a residue remains, the substance is at least partly soluble; in which case boil again with water, filter, add the filtrate to the first solution, and treat the fluid as directed ~ 182. Wash the residue with water, and proceed as directed 35. 2. Treat a small portion of the residue which has been 35 boiled with water (34) with dilute hydrochloric acid. If it does not dissolve, heat to boiling, and if this fails to effect complete solution, decant the fluid into another test-tube, boil the residue with concentrated hydrochloric acid, and, if it dissolves, add the solution to the fluid in the other testtube.

Page  275 ~ 180.] SOLUTION. 2 7 The reactions which may manifest themselves in this operation and which ought to be carefully observed, are (a) Effervescence, which indicates the presence of carbonic acid or hydrosulphuric acid; (P) Evolution of chlorine, which indicates the presence of metallic dioxides, chromnates, &c.; () Emnission of the odor of hydrocvanic acid, which indicates the presence of insoluble cyanides. The analysis of the latter bodies being effected in a somewhat different manner, a special paragraph will be devoted to them (see ~ 197). a. THE RESIDUE IS COMPLETELY DISSOLVED BY TIIE 36 HYDROCIILORIC ACID (except perhaps that sulphur separates, which may be known by its color and light specific gravity, and may, after boiling some time longer, be removed by filtration; or that gelatinous silicic acid separates). Proceed, according as directed ~ 183, after filtration if necessary. The body belonlgs to the second class. To male quite sure of the actual nature of the sulphur or silicic acid filtered off, examine these residuary matters as directed ~ 196. b. THERE IS STILL A RESIDUE LE~FT. IIn that case put 37 aside the test-tube containing the specimen which has been boiled with the hydrochloric acid, and try to dissolve another sample of the substance insoluble in water, or already extracted with water, by boiling with nitric acid, and subsequent addition of water. Evolution of gaseous oxides of nitrogen, by the action of the nlitric acid, shows that a process of oxidation is takinog place. a. The sample is comnpletely dissolved, or leaves no 38 other residue but sulphur or gelatinous silicic acid; in this case also the body belongs to the second class. Use this solution to test further for metals as directed ~ 182, 46, anld for the rest proceed, as in 36.,3. There is still a residae left. Pass on to 40. 39 3. If the residue insoluble in water will not entirely dis- 40 solve in hydrochloric acid nor in nitric acid, try to effect collplete solution of it by means of nitro-hydrochloric acid. To this end mix the contents of the tube treated with nitric acid with the contents of the tube treated with concentrated Ilydrochlloric acid; heat the mixture to boiling, and should this fail to effect complete solution, decant the clear fluid off from the undissolved residue, boil the latter for some time with concentrated nitro-hydrochloric acid, and add the decanted solution in dilute aqua regia as well as the solution in dilute hydrochloric acid, decanted in 35. Heat the entire mixture once more to boiling, and observe whether complete solution' has now been effected, or whether the action of the concentrated nitro-hydrochloric acid has still left a residue. In the latter case filter the solution-if necessary after addi

Page  276 926 PART II GENERAL COURSE. SOLUTION. [~ 181. tion of some water* —wash thle residue with boiling water, and proceed with the filtrate,?nd tle washlings added to it, as directed ~ 1S3. In the bfbrm-er case proceed with the clear solution in the same way. t 4. If boiling nitro-hydrochloric acid has left an undis- 41 solved residue, wash it thoroughly with water, and then proceed as directed ~.196. B. THIE SUBSTANCE UNDER EXAM:,INATION IS A METAL OR AN ALLOY. ~ 181. The metals are best classed according to their behavior 42 with nitric acid, as follows: I. METALS WHICH ARE NOT ATTACKED BY NITRIC ACID: gold, platinum. II. MIETALS WHICH ARE OXIDIZED BY NITRIC ACID, BUT WHOSE OXIDES DO NOT DISSOLVE IN AN EXCESS OF THE ACID OR IN WATER: antimony, tin. III. METALS WHICH ARE OXIDIZED BY NITRIC ACID AND CONVERTED INTO NITRATES WIHIC.I DISSOLVE IN AN EXCESS OF THE ACID OR IN WATER: all the other metals. Pour nitric acid of 1'20 sp. gr. over a small portion of the substance, and apply heat. 1. COMPLETE SOLUTION TAKES PLACE, EITHER AT ONCE OR 43 UPON ADDITION OF WATER'; this proves the absence- of platinum, t gold, antimony, ~ and tin. P1roceed as directed ~ 182, lII. (53) 2. A RESIDUE IS LEFT. a. A metallic residue. Filter, and treat the filtrate 44 as directed ~ 182, III. (53), after having seen, in the first place, whether anything has really been dissolved. Wash * If the fluid turns turbid upon addition of water, this indicates the presence of bismuth or antimony; the turbidity will disappear again upon addition of hydrochloric acid. t Where the acid solution on cooling deposits acicular crystals, the latter generally consist of lead chloride; it is in that case often advisable to decant the fluid off the crystals, and to examine the fluid and crystals separately. W here on boiling with aqua regia metastannic chloride has been formed fromi stannic hydroxide, the washing water, dissolving this, becomes turbid on dropping into the strongly acid fluid which has run off first. In that case receive the washing water in a separate vessel, and treat the two solutions separately with hydrosulphuric acid, as directed in ~ 183, but filter afterwards through the same filter. 4 Alloys of silver and platinum, with the latter metal present in small proportion only, dissolve in nitric acid. ~ Very minute traces of antimony, however, are often completely dissolved by nitric acid.

Page  277 ~ 182.1 ACTUAL ANALYSIS. 277 the residue thoroughly, dissolve in nitro-hydrochloric acid, and test the solution for GOLD and PLATINUM, according to ~ 128. b. A white ])ulverultent residuee: indicates ANTrIMONY 45 and TIN. Filter, ascertain whether anything has been dissolved, then treat the filtrate as directed ~ 182, III. (53). Wash the residue thioroughly, then test for ANTIMONIOUS OXIDE, STANNIC OXIDE, and ARSENIC ACID, accordin1g to ~ 134, 5. (Part, at least, of the arsenic acid is always found in this precipitate, combined with antimony and tin.) III. ACTUAL ANALYSIS. A. SUBSTANCES SOLUBLE IN WATER, AND ALSO SUCH AS ARE INSOLUBLE IN WATER, BU13UT DISSOLVE IN HYDROCHLORIC ACID, NITRIC ACID, OR NTITRO-HYDROCHLORIC ACID. Detection of lfJetals.* ~ 182. (Treatment with Hfydrochloric Acid: Detection of Silver, Mercury in inercurous comvpounds [Lead].) II~" The operator should carefiully study the Xotes in Sectio~n I, before going furthier, and should review them f/e.quently unttilfamriliar with theitr contents: see pp. 368 and 375. I. THE SOLUTION IS IN WATER. MIX THE PORTION INTENDED FOR TILE DETECTION OF THE 46 METALS WVITH SOME HYDROCHLORIC ACID. 1. THE SOLUTION HAD AN ACID OR NEUTRAL REACTION PREVIOUSLY TO THE ADDITION OF ThE HYDROCHLORIC ACID. a. No rPECIPITATE IS FORME:D: this indicates the absence of silver and (mercurous) mercury. Pass on to ~ 183. b. A PRECIPITATE IS FORMED. Add more H C1, drop by drop, until the precipitate ceases to increase; then add about six or eight drops more of H C1, shake the mixture, and filter. The precipitate produced by I- C1 may consist of silver * Regard is here had also to the presence of those salts of the alkali-earth metals which dissolve in }I C1 and separate again from that solution unal. tered upon neutralization of the acid by N H,4 0 H; viz.: phosphates, borates, &c.

Page  278 278 ACTUAL ANATLYSIS. [ 18 chloride, mercurous chloride, lead chloride, a basic salt of antimony, bismuth oxychloride, metastannic chloride, possibly also benzoic acid. The basic salt of altimollv and the bismuth oxychloride, however, redissolve inl tle excess of HI Cl: colsequently, if the instructions givenl have been strictly followed, the precipitate collected upon the filter canl consist OInly of silver chloride, mercurotis chloride, or lead chloride (possibly also of the very rare metastannic chloride and benzoic acid, which, however, are disregarded Aere). Wash the precipitate collected upon the filter twice with cold water, add the washings to the filtrate, and examine the solution as directed. 183, even though tle addition of the washings to the acid filtrate should produce turbidity in the fluid (which indicates the presence of antimony or bismuth, or possibly also of metastannic chloride). Treat the twice-washed precipitate on the filter as 47 follows: a. Pour hot water over it upon the filter, and test the fluid running off with HI, S and with II, S 04 for LEAD. (The non-formation of a precipitate simply proves that the precipitate produced by H C1 contains no Pb, and does not by any means establish the total absence of this metal, as H Cl fails to precipitate Pb from dilute solutions.) If the II C1 plrecipitate contains Pb C12, wash it several times with hot water to dissolve out the lead.,l. If there is a residue remaining on the filter, treat it with ammonia. If this changes its color to black or gray, it is a proof of the presence of IERucuROUS OXIDE. y. Add to the ammoniacal fluid running off in /3, HI N 0O to strongly acid reaction. The formation of a white, curdy precipitate indicates the presence of sILvER.* (If the precipitate still contained lead, the amlnoniacal solution generally appears turbid, owillg to the separation of a basic lead salt. This, however, does not interfere with the testing for silver, since the basic lead salt redissolves upon the addition of IHNO,.) 2. THE ORIGINAL AQUEOUS SOLUTION HAD AN ALKALINE 48 RE ACTION. a. TH E ADDITION OF HYDROCIILORIC ACID TO STRONGLY ACID REACTION FAILS TO PRODUCE EVOLUTION OF GAS OR A PRECIPITATE, OR THE PRECIPITATE WHICH FORMS AT FIRST REDISSOLVES UPON FURTHER ADDITION OF HYDRIOCIILORIC ACID: pass on to ~ 183. * If the quantity of silver is only very small, its presence is indicated by Dpalescence of the fluid.

Page  279 182.] DETECTION OF METALS. 2 79 b. TIE ADDITION OF HYDROCHLORIC ACID PRODUCES A PRECIPITATE WHICI DOES NOT REDISSOLVE IN AN EXCESS OF THE PRECIPITANT, EVEN UPON BOILING. a. Tle formation of tle precipitate is attended 49 veither with evolution of hydrosullpuric ore of /Agycdrocyanic acid. Filter, and treat the filtrate as directed ~ 183. aCa. THE PRECIPITATE IS WHIITE. It may, in that case, consist of a salt of lead or silver, insoluble, or difficultly soluble in H., 0 and H C1 (LEAD CTI.ORIIDE, LEAD SULPtIATEI SILTVER CHLORIDE, &c.), or it may be SILICIC ACID. Test it for the bases and acids of these comporunds as directed ~ 196, bearing in mind that the lead chloride or silver chloride which may be found may possibly have been formed in the process. bb. THE PRECIPITATE IS YELLOW OR ORANGE. In that case it may consist of ARSENIOUS SULPHIDE, and if the fluid from which it has separated was not boiled long, or only with very diluhte HI C1, also of ANTIMONIOUS SULPHIDE or STANNIC SULPI-IDE, which substances were originally dissolved in ammonia, potassa, soda, sodium phosphate, or solme other allkaline fluid, with the exception of alkali snlphides and cyanides. Examine the precipitate, which may also contain SILICIC ACID, as directed 40. f,. TAe.tbrmation of the prccipitate is attended 50 with evolution of hydrosulphauric acid, but not of,hydrocyanic acid.* aag. TIlE PRECIPITATE IS OF A PURE WHITE COLOR, AND CONSISTS OF SEPARATED SULPIIUR. I11 that case a POLYSULP1HIDE OF AN ALKALI ]METAL is generally present. The presence of such a body nlay b)e detected also by the yellow or brownish-yellow color of the alkaline solution. and the odor of hydrogen disulphide (112 S,), which accompanies that of 112S on the addition of an acid. Boil, filter, and treat the filtrate as directed ~ 187, the precipitate as directed ~ 196. bb. TIHE PRECIPITATE IS COLORED. In that case you may conclude that a SULPI:UR SALT is present.t The precipitate may accordingly Consist of AURIC SULPHIDE, 1'LATINIC SULPHIDE, STANNIC SULPHIDE, ARSENIOUS SULPHIDE, or ANTIMONIOUS SULPlIIDE. It might, however, consist also of MERCURIC SULPHIDE * Should the odor of the evolved gas leave any doubt regarding the aclual presence or absence of H C N, add some potassium chromate to a portion of the fluid, previously to the addition of the H C1. t See p. 43.

Page  280 280 ACTUAL ANALYSIS. [~ 182 or of CUPRIC SULPIIIDE or NICKEL SULPHIDE 01' contain these substances, as thle former wxill dissolve readily in K2 S, and in small quantities ill (N 114) S, and the latter are slighltly soluble ini (N II4)2 S. Filter and treat the filtrate as directed ~ 187, the precipitate as directed 40. y. 7'he fo'rmncation of the precipitate is atten2.cedl 51 with evolutionz of hyd.lrogcyanic acid, with or withoalt siu) lgtaneous disenzycgement of hAydrosaulhAu'ic acid. This indicates the presence of an ALKALI CYANIDE, and if the evolution of I-1 C N is attended with that of HI2 S, also of an ALKALI SULPHIDE. In that case the precipitate may, besides the compounds enurnerated in a and 2, contain many other substances (e.g., nickel cyanide, silver cyanlide, &c.). Boil, with further addition of I-1 C1 or of Il N 0,, until the whole of the 1 C N is expelled, and treat the solution, or, if an undissolved residue has been left, the filtrate as directed ~ 183; and the residue (if any) according to ~ 196 or ~ 197. c. THE ADDITION OF HYDROCHLORIC ACID FAILS TO PRO- 52 DUCE A PERMANENT PRECIPITA'rTE BUT CAUSES EVOLUTION OF GAS. a. Tlhe escaping gas smnells of hydrosulphzuric acid: this indicates a SIMPLE ALKALI SULPHIDE, or A SULPHUR SALT OF AN ALKAII or ALKALI-EARTH METAL. Proceed as directed ~ 187. p. Tbe escafping gas is inodorous: in that case it is CAR.BON DIOXIDE, which was combined with an alkali. Pass on to ~ 183. ry. Thbe escapiny gas smells of hydrocyanic acid: (no matter whether 112 S or C O, is evolved at the same time or not). This indicates an ALKALI CYANIDE. Boil until the whole of the I C N is expelled, then pass onil to ~ 183. II. THE SOLUTION IS IN HYDROCIILORIC ACID OR IN NITROHYDROCHLORIC ACID. Proceed as directed ~ 183. 1I. THE SOLUTION IS IN NITrRI ACID. Dilute a small portion; should this produce turbidity or 53 a precipitate (indicative of Bi), add H N 0, until the fluid is clear again, then 11 Cl. 1. Io PRECIPITATE IS FORMED. Absence of silver and (mercurous) mercury. Treat the principal solution as directed ~ 183.

Page  281 183.] DETECTION OF METALS. 281 2. A PRECIPITATE IS FORMED. Treat a larger portion of the II N 0 solution in the samle way, filter, and examline the precipitate as directed 47, the filtrate as directed ~ 183. ~ 183. E Do not fail to consult page 369 and also paqe 377. (Treatment with Hfydcrosu.phu6ric Acid. Precipitation of the Metals of Group V., 2d -Division, and qf G(rozp vI) ADD TO A small PORTION OF THE CLEAR ACID SOL.UTION IIYDIOSULPIIURIC ACID WATER, UNTIL THE ODOR OF HYDIROSULI'IURIC ACID IS DISTINCTLY PERCEPTIBLE AFTER SHAKING TIlE MIXTURE, ANI) WARM GEN'TLY. 1. NO PRECIPITATE: IS FORMED, even after the lapse of somne 54 time. Pass on to ~ 187; for lead, I)ismuth, cadmimn, copper, mercury, gold, platinum, antimony, till, and arsenicj, are not present; t the absence of tetrad iron and of Chrolnates is also indicated by this negative reaction. 2. A PRECIPITATE IS FORMED. a. ieprecrpititaete is q'f a Spure white color, light, 55 and finely pulvernlent, and doesnlot redissolve on addition of 1I C1. It consists of separated sulphlumr, and indicates the presence of IRON AS A FERRIC SALT.: Nonie of the other metals enumerated in 54 can be present. Treat the principal solution as directed ~ 187. b. ]he precipitate is colored. Add to the larger proportion of the acid or acidi- 56 fled solution, best in a slmall flask, IHI S water in excess, i.e., until the fluid smells distinctly of it after shaking, and the precipitate ceases to increase upon continued addition of the reagent; apply a gentle heat, shake vigorously for some time, filter, keep the filtrate (which containls the metals present of Groups I.-IV.), for further examination according to ~ 187, * Where the preliminary examination has led you to suspect the presence of As O (O H)3, you must endeavor to obtain the most conclusive evidence of the absence of this acid; this may be done by allowing the fluid to stand for some time at a gentle heat (about 70~), or by heating it with sulphurous acid previous to the addition of the H11 S. (Compare ~ 133, 3.) t In solutions containing much free acid the precipitates are frequently formed only after dilution with water.; Sulphur will precipitate also if sulphurous acid, or iodic acid, or bromio acid is present (which substances are not included in our analytical course), and also if chromic acid, or chloric acid, or free chlorine is present. In presence of chromic acid the separation of the sulphur is attended with reduction of the acid to chromic oxide, in consequence of which the reddish-yellow color of the solution changes to green. (Compare ~ 138.) The white sulphur suspended in the green solution looks at first like a green precipitate, which fre. quently tends to mislead beginners

Page  282 282 ACTUAL ANALYSIS. ~ 184.] and thoroughly wash * the precipitate, which contains the sulphides of the metals present of Groulps V. and VI. In many cases, and more particularly where there is any reason to suspect the presence of arsenic, it will be found more convenient to transmit 112 S gas through the solution D)ILUTED WITH WATER, instead of addingl, I S water. When arsenic is suspeected it is also well to keep the fluid at about 70o C. during the transmission of the gas. If the precipitate is yellow, it consists principally 57 of arsenious snlphide, stannic sulpiclde or cadmniulm sulphide; if orange colored, this indicates antimonious sulphide; if brown or black, one at least of the following metals is present: lead, bismnuth, copper, mercury as mercuric salt, gold, platinu-m, dvad tin. IIowever, as a yellow precipitate may contain small particles of an orange-colored, a brown, or even a black precipitate, and yet its color not be very perceptibly altered thereby, it will always prove the safest way to assumne the presence of all the metals named in 54 in any precipitate produced by I-I S, and to proceed as the next paragraphll ( 184) directs. ~ 184. Op CUonsult the notes ore pages 370 and 379. (Treatment of the Precilpitate prodlced by J]ydrosiul-,huric Acid with Ammoniniun Sul7phide; AS'e)aration of the 2d Divis8ion of Group V. frozm Group V.) INTRODUCE A SMALL PORTION OF THE THOROUGHLY WASHEID 58 PRECIPITATE PRODUCED BY HYDROSULPIIURIC ACID IN TIlE ACIDIFIED) SOLUTION INTO A TEST-TUBE,t ADD A LITTLE WATER, AND FROM TEN TO TWENTY DRO-PS OF YELLOW AMIMONIUM STLPHIIDE AND EXPOSE THE MIXTURE FOR A SHORT TIME TO A GENTLE HEAT. 1. THITI PRECIPITATE DISSOIVES COMPLET1ELY IN AMMONIUM 59 SULPHIDE; absence of the metals of Group V.-cadlnium, lead, bismuth, copper,: mercury. Treat the remlaillder of the precipitate, of which you have digested a portion with *Compare ~ 7. t If there is a somewhat large precipitate, this may be readily effected by means of a small spatula of platinum or horn; but, if you have only a very trifling precipitate, make a hole in the bottom of the filter, and rinse the precipitate into the test-tube by means of the washing-bottle, wait until the precipitate has subsided, and then decant the water. t CoPPER, if not already revealed by the preliminary examination, should be tested for, at this stage of the analysis, in a portion of the original solution by means of a clean iron rod (see ~ 120); because it may be dissolved to a considerable extent (as a cuprous sulphur salt), by concentrated and verQ yellow ammonium sulphide, especially in presence of Sn, Sb, and As.

Page  283 ~ 185.] DETECTION OF METALS. GROUP VI.')83 (N I-I4)2 S., as directed ~ 185. If the precilitate produced by H11 S was so trifling that you have used the whole of it in treatillg with (N I14), Sx precipitate the solution obtained in that process by addition of 11 C1, filter, wash the precipitate, and treat it as directed ~ 185. 2. TIIE PRECIPITATE IS NOT REDISSOLVED, OR AT LEAST NOT 60 COMIPLETEILY, even on heating with more alnlnonlium sulphide: presence of metals of Group V. Dilute with 4 or 5 parts of water, filter, and mix the filtrate with II C1 in slight excess. a. A pure white turbidity is occasioned, owing to the separation of S?uphur. Absence of the metals of Group VI.-gold, platinum, tin, antimony, and arsenic.* Treat the rest of the precipitate, of which you have digested a portion with (N I,), S,, according to ~ 186. b. A colored precipitate is formed: presence of met- 61 als of Group VI. and of Group V. Treat the enltire precipitate produced by H, S as you have treated the portion, i.e. digest it with yellow ammonuinm sulphide, let subside, pour the supernatant liquid on a filter, digest the residue in the tube oince more with yellow amn-noilium sulphide, and filter. Wash the residue t (containing the sulphides of Group V.), and treat it afterwards as directed ~ 186. Dilute the filtrate (which contains the metals of Group VI. in the form of sulphur salts), add H C1 to distinctly acid reaction, heat gently, filter off the precipitate, which contains the sulphides of the Inetals of Group VI. mixed with sulphur, wash thoroughly, and proceed as directed in the next paragraph (~ 185). ~ 185. ConLsult the notes in the T2/ird Section: page 378. (Detection of the illettals,of Group V.: Arsenic, Antimony, Tin, Gold, Platinuztn.) If the prlecipitate consisting of the sulphides of Group 62 VI. has a PURE YELLOW COLOR, this indicates principally arse* That this inference becomes uncertain if the precipitate produced by H2 S. instead of being digested with a small quantity of (N H4), S., has been treated with a large quantity of that reagent, is self-evident; for the large quantity of sulphur which separates in that case will of course completely conceal any slight traces of As. S3 or Sn S. which may have been thrown down. Compare also notes to ~ 183 and ~ 184 in the Third Section. f If the residue suspended in the fluid containing (N H4)2 S,, and insoluble therein, subsides readily, it is not transferred to the filter, but washed in the tube by decantation. But if its subsidence proceeds slowly and with difficulty, it is transferred to the filter, and washed, there; a hole is then made in the bottom of the filter, and the residue rinsed into a small porcelain basin by means of a washing-bottle; the application of a gentle heat will now materially aid the subsidence of the residue, and the supernatant water may then be decanted. The sulphides are occasionally suspended in the fluid in a state of such minute division that the fluid cannot be filtered off clear. In cases of the kind solve N H, Cl should be added to the fluid, and it should be allowed to settle at a gentle heat for some time before being filtered.

Page  284 284 DETJSCTiON OF IMETALS. [~ 185,lic aind tetrad till; if in the proved absence of copper it is distinctly ORANGE-YELLOW, antiln)yll is sure to be preselt; if it is II:owN or BLACK, this denotes the presence of dyad tin, platinum, or gold. 13eyolld these general indications the color of the precipitate affords nlo safe fuidance. It is therefore always advisable!to test a yellow precipitate also for antimony, gold, and platinum, since miniute quanitities of the sulphides of these mletals are completely hiddenl by a large quantity of stanIic sulphide, or arsel ious sulphide. Proceed accordingly as follows: ileat a little of the precipitate on the lid of a porcelain crucible, or on a piec(e of porcelain or glass.* 1. Complete volatilization ensues: probable presence of 63 ARSENIC, absence of theother metals of Group VI. Confirm by reductioll of a portion of the precipitate with K C N and Na2 C 0, (~ 132, 13).t WVhether that metal was present in the arsenious or ill the arsellic form may be ascertained by the methods described ~ 134, 9. 2. A fixed residue is lIft. Ill that case all the metals of 64 Group VI. must ble sought for. In absence qf copper,4 dry the remainder of the precipitate thoroughly upon the filter, triturate it with alboutt 1 part of dry Na, C O, and 1 part of Na N O,, and transfer the nmixtmure ill small portions at a time to a porcelain crucible, ill which you have previously heated 2 parts of Na N O, to fusioll.~ As sooll as complete oxidation is effected, pour the mass on to a piece of porcelain. After cooling soak the fused mass 1 (the portion still sticking to the inside of the crucible as well as the portion * That this preliminary examination may be omitted if the precipitate has any other color than yellow, and that it can give a decisive result only if the precipitate has been thoroughly washed, is self-evident. f In cases where the precipitate contains much free S, dissolve the As, S3 which may be present, by digestion in (N H,)2 C 03, filter, evaporate the solution with addition of a small quantity of Na2 C 03, to dryness, and heat the residue with Na, C 03. t [If copper be present in the original substance it may also be contained in this precipitate in such quantities as to render the detection of antimony uncertain. In such a case it is best to treat the remainder of the precipitate at a boiling heat with sodium sulphide, which will dissolve only the sulphides of Group VI. Then filter from the cupric sulphide, dilute the solution, precipitate again the sulphides of Group VI. by addition of H C1 in slight excess, warm, filter, wash thoroughly, and proceed as directed, 64.-EDITOR.] ~ Should the amount of the precipitate be so minute that this operation cannot be conveniently performed, cut the filter, with the dried precipitate ad hering to it, into small pieces, triturate these with some Na, C 0, and Na N OS, and project both the powder and the paper into the fusing Na N 03. It is )preferable, however, in such cases, to procure, if practicable, a larger amount of the precipitate, as otherwise there will be but little hope of effecting the positive detection of all the metals of Group VI. II Supposing all the metallic sulphides of the sixth group to have been present, the fused mass would consist of antimonate and arsenate of sodium, stannic oxide, metallic gold and platinum, sulphate, carbonate, nitrate, and some nitrite of sodium. Compare also ~ 134, 1. When gold and tin are present to. g ther the fused mass often has a peculiar light-red color.

Page  285 ~ 1 85.] GmOUP vL 285 poured out on the porcelain) in cold water, filter from the insoluble residue-which will remain if the mass contained antimony, tin, gold, or platinum —and wash thoroughly with a mixture of about equal parts of xwater and alcohol. (The alcohol is added to prevent the solution of the Na Sb O,. The washings are not added to the filtrate.) The filtrate and the residue are now examined as follows: a. EXAMINATION OF THE FILTRATE FOR ARSENIC (which 65 must be present in it in the form of Na3 As 04). Add nitric acid to the fluid to distinct acid reaction,* heat to expel C 02 and N2 0,, then divide the fluid into two portions. Add to the one portion some Ag N 03 (not too little), filter (in case Ag C1 t or Ag N 0,2 should have separated), pour upon the filtrate, along the side of the tube held slanting, a layer of dilute solution of ammonia -2 parts of water to 1 part of solution of ainmoniaand allow to stand some time without shaking. The formation of a reddish-brown precipitate or cloud between the two layers (seen most readily by reflected light), denotes the presence of ARSENIC. If the arsenic is present in some quantity, and the free nitric acid of the solution is exactly saturated with ammonia, the fluid being stirred during this process, the precipitate of Ag3 As 04, which forins imparts a brownish-red tint to the entire fluid. Add to the other portion of the acidified solution, 66 first, N 1-1 0 11, then magnesia mixture;4 and rub the interior walls of the vessel with a glass rod. A crystalline precipitate of N H, Mg As 04 + 6 H2 0, which often forms only after long standing, and is deposited more particularly on the sides of the vessel, shows the presence of arsenic. By way of confirmation the precipitate may be washed with water containing N II, HI, dissolved in dilute 11 C1, and the solution precipitated by H, S, with the aid of a gentle heat, or the arsenic may be reduced to the metallic state (compare ~ 132 and ~ 133). Whether the arsenic was present in the arsenious or arsenic form, may be ascertained by the methods described ~ 134, 9. b. EXAMINATION OF THE RESIDUE FOR ANTIMONY, TIN, 67 GOLD, PLATINUM. (As the antimony, if present in the residue, must exist as white pulverulent sodium anti* In some cases where a somewhat large proportion of Na2 C 03 has been used, or a very strong heat applied, a trifling precipitate (stannic acid) may separate upon the acidification of the filtrate with H N 03. This may be filtered off, and then treated in the same manner as the undissolved residue. t Ag C1 will separate if the reagents were not perfectly pure, or the pre, cipitate has not been thoroughly washed. + See note to p. 190.

Page  286 286 DETECTION OF'METALS. [~ 186. monate, the tin as white flocculent stannic oxide, the gold and platinllm in the metallic state, the appearance of the residue is in itself indicative of its nature. ITut it must be noted that on account of the solubility of cuprous sulphide in alnmoniumn sulphide, cupric oxide may also be present in this residue [unless copper has been septarated by Na2 S, as directed in the third note, p. 284. -EDITOR]. Transfer the precipitate to the lid of a plati nuln crucible, or to a p]atinum capsule, heat with 1t C1, add a little water, and throw in a small compact lump of pure zinc (more particularly free from lead), no matter whether the precipitate has completely dissolved or not in the HI Cl. This operation leaves the gold and platinum in the same state in which the fused mass contained them, viz., in the metallic state, to which the tin and antimony are now likewise reduced by the action of the zinc. The ANTIMONY reveals its presence at once, or after a short time, by blaokening the platinum. As soon as the disengagement of hydrogen has nearly stopped, take out the lump of zinc, remove the solution of Zn C12 by cautious decantation, warm the metals with HI C1, and test the solution-which, if TIN is present, must contain stannous chloride, with mercuric chloride (~ 129, 8). In what state of quantivalence tin or antimony were originally present mlay be ascertaimned according, to ~ 134, 7 and 8. After removing the tin by repeated boiling with 68 EI Cl, and all the II C1 by thoroughly washing with water, examine the insoluble residue (if one is left) as follows: Heat it in the platinum lid with some water, with addition of a few grains of tartaric acid, then add some nitric acid, and heat gently. If the residue dissolves completely, no gold or platinum is present; if a residue is left undissolved, you. must test it for these metals. For this purpose remove the acid solution (which may be tested again for ANTIMONY with 11i S) by decantation and washing, transfer the residue to a porcelain dish, heat with a little aqua regia, evaporate the solution to a smnall volume, and test for GOLD and PLATINUM as directed ~ 128.. 186. Consult the notes on pages 369 and 378. (Detection of the Metals of' Group V., 2d Division: —Lead, ]Bismuth, Copper. Cadmnitum, Ierctury.) TIIOROUGIILY WASH THE PRECIPITATE WhICH hIAS NOT BEEN 69 DISSOLVED BY AMMIIONIUM SULPHIDE) AND BOIL WITH DILUTE NI

Page  287 ~ 186.] GROUP v. DIV. 2. 287 TRIC ACID. This operation is performed best in a small porcelain dish: the boiling mass must be constantly stirred with a glass rod. A great excess of acid must be avoided. 1. THE PRECIPITATE DISSOLVES, AND THERE REMAINS FLOAT- 70 ING IN TIlE FLUID ONLY THE SEPARATED LIG(IT FLOCCULENT AND YELLOW SULPHUR: this indicates the absence of mercury. CADMIUMS, COPPER, LEAD, and BISMCUTH Imay be present. Filtel' from the separated sulphur, and treat the filtrate as follows (should there be too much 11 N 0, present, the greater part of this must first be driven off by evaporation): Add to a portion of the filtrate dilute "-2 S 04 in moderate quantity, heat gently, and allow to stand some time. a. No PRECIPITATE FORMS: absence of lead. Mix the 71 remainder of the filtrate with N 114 0 II in excess, and gently heat. a. Vo precipitate isformed: absence of bismuth. 72 If the liquid is blue, COPPER is present; very ninute traces of copper, lowever, igiht be overlooked if the color of the arnlnolliated fluid alone were consulted. To be quite safe, and also to test for cadnliuml1, evaporate the amnmoniated solution nearly to dryness, add a little acetic acid, and, if necessary, solne water, and aa. Test a small portion of the fluid for copper 73 with 1i Fe (C N). A reddish-brown precipitate or a light brownish-red turbidity indicates COPPER (in the latter case only to a very trifling amount). bb. To the remainder, if copper is absent, add 74 1H2 S. A yellow precipitate indicates CADMIUM. If copper is present, it is most convenieltly removed in the form of cuprous sulphllocyanate by means of sulphuroun acid and IK C N S, and the filtrate, after being evaporated to drive off excess of S C), is tested for cadmium with H, S. Or both metals may be precipitated by HI[ S, and then separated by K C N (in which case the sulphides must have been recently precipitated) or by boiling dilute 112 S 04 (~ 123).,3. A precipitate is formed. BISMUTH is present. 75 Filter anld test the filtrate for copper and cadmium as directed 72. To test the washed precipitate more fully for bismuth, slightly dry the filter containing it between blotting-paper, remove the still moist precipitate with a platinum spatula, dissolve on a watchglass in the least possible quantity of II Cl, and then add water. The appearance of a inilky turbidity confirms the presence of bismuth. b. A PRECIPITATE IS FORMED. Presence of IEAD. 76 Mix the whole of the It N O, solution in a porcelain

Page  288 288 DETECTION OF MZETALS. [~ 18 dish with a sufficient quantity of dilute I-12 S 04,, evaporate on the water-bath until the H N 0, is expelled, dilute the residue with some water contailing 12 S 04, filter off at once the Pb S 04 left undissolved, and test the filtrate for bismuth, copper and cadmium, as directed 71.* Test the precipitate, after washin g, by one of the methods in ~ 123. 2. THE PRECIPITATE OF THE SULPHIDES DOI:S NOT COMr- 77 PIETELY DISSOLVE IN TIEE BOILING NITRIC ACID, BUT LEAVES A RESIDUE, BESIDES TIEF SULPIVUR THAT FLOATS IN TIIE FLUID. Probable presence of M>ERCURY (as mercuric salt) (whllich may be pronounced allnost certain if the precipitate is heavy and black). Allow the precipitate to subside, filter off the fluid, which is still to be tested for CADMIUM, COPPER, LEAD and BISMUTLr; mix a small portion of the filtrate with a large amount of solution of H12 S, and should a precipitate formn or a coloration become visible, treat the remaillder of the filtrate according to 70. Wash the residue (which may, besides IHg S, also contain Pb S 04, formed by the action of 11 N 02 upon Pb S, and also Sn 02 and possibly Au, S3 and Pt S,, as the separation of the sulphides of tin, gold and platinum from the sulphides of the metals of the fifth group is often incomplete), and examine one-half of it for mercury,t by dissolving it in some H C1, with addition of a very small portion of potassium chlorate, and testing the solution with copper or stannous chloride (~ 119); fuse the other half with K C N and Na, C 0,, and treat the fused mass with water. If metallic grains remlain, or if a metallic powder is left undissolved, wash this residue, heat with 1I N 0,, and test the solution obtained with IH1, S 04 for lead. Wash the residue which the 1-1 N O3 may leave undissolved, and extract from it any metastannie acid which it may contain, according to ~ 130, 1, as metastannic chloride. Should a metallic powder be left undissolved in the process, heat it with aqua regia, and test the solution for gold and platinum as directed ~ 128. ~ 187. C'omopare the notes on pp. 370 and 379. (Preciptaption with Ammoniqzm Sullphide, Separation ana Detection (f the J[etals of Gro tps 11J and IV.: Altamin* For another method of separating Cd, Cu, Pb, and Bi, see the Third Section, page 379. t If you have an aqueous solution, or a solution in very dilute H Cl, the mercury found was present in the original substance in the mercuric form; but if the solution has been prepared by boiling with concentrated II C1, or by heating with H N 03 or aqua regia the mercury may have been originally pres ent in the mercurous form.

Page  289 ~ 187.] GROUPS III. AND IV. 289 umn Chromnivum; Zinc, MJanganese, Nick7el, Cobalt, Iron; and also of those Salts of the Alkali-cEarth MJetals which, are precipitated byi Ammonia from their Solugtion in Ilydrochloric Acid: Phosphates, Borates, Oxalates, Silicates, and Fluorides.) PUT A small portion OF THE FLUID IN WHICH HYDROSUL- 78 PHURIC ACID HAS FAILED TO PRODUCE A PRECIPITATE (54), OR OF TITE. FLUID WHICH HAS BEEN FILTERED FROM THE I'RECIPITATE FORMED (56), in a test-tube, observe whether it is colored or not,* boil to expel the 11, S which may be present, add a few drops of H NT 03, boil, and observe again the color of the fluid; then cautiously add ~N II O 1H just to alkaline reaction, heat, observe whether this produces a precipitate, then add some (N H,4) S, no matter whether ammonia has produced a precipitate or not. a. NEITHER AMMONIA NOR AMMONIUM SULPHIIDE PRO- 79, DUCES A PRECIPITATE. Pass on to ~ 188, for iron, nickel, cobalt, zinc, manganese, chromium, aluminium, are not present,t nor are phosphates, borates,4 silicates, oxalates,~ and fluorides of the allali-earth metals; nor silicic acid, originally. in combination with other metals. b. AMMONIUM SULPHIDEF PRODUCES A PRECIPITATE, AM- 80' MONIA HAVING FAILED TO DO SO: absence of phosphates, borates,: silicates, oxalates,~ and fluorides of the alkaliearth metals; of silicic acid, originally in colnbination with other metals; and also, if no organic matters are present, of iron, chromium and aluminium. Pass on to 82. c. AMMONIA PRODUCES A PRECIPITATE before the addi- 81 tion of (N IH,), S. The course of proceeding to be pursued now depends upon whether, (x) the original solution is simply aqueous, and has a neutral reaction, or (a) the * If the fluid is colorless, it contains no Cr. If colored, the tint will to some extent act as a guide to the nature of the substance present; thus a. green tint, or a violet tint turning green upon boiling, points to Cr; a lightgreen tint to Ni; a reddish color to Co; the turning yellow of the fluid upon boiling with nitric acid to Fe. It must, however, be remembered that these tints, except the last, are perceptible only if the metals are present in large quantity, and also that complementary colors, such as, for instance, the green of the Ni solution and the red of the Co solution, will destroy each other, and that, accordingly, a solution may contain both metals and yet appear colorless. t This only holds goods as regards Al and Cr in the absence of non-volatile organic substances, especially acids such as citric and tartaric acids. Citric acid may also prevent the precipitation of Mn. When the preliminary examination has indicated presence of organic matters, and of metals of Groups III. and IV., fuse a portion of the substance with Na, C 03 and Na N 03, dissolve in dilute HI C1, filter, and test the solution according to 78. t Presence of much N H4 Cl has a great tendency to prevent the precipitation of borates of the alkali-earth metals. ~ Magnesium oxalate is thrown down from H Cl solution by N H4 0 H after some time only, and never completely; dilute solutions are not precipitated, by N H4 0 H. 19

Page  290 290 DETECTION OF METALS. GROUPS m. AND IV. [~ 187 original solution is acid or alkaline. In the former case pass on to 82, since phosphates, borates, oxalates, silicates, and fluorides of the alkali-earth metals, and silicic acid in combination with other metals, cannot be present. In the latter case regard must be had to the possible presence of all the bodies enumerated in 79, and also, in the presence of organic matter, of the coinbinations of alkali-earth metals with citric and tartaric acids; pass on to 94. 1. DETECTION OF THE BASES OF GROUPS III. AND IV. IF 82 PIHOSPHATES, &C., OF THE ALKALI-EARTH METALS ARE NOT PRESENT.* Mix the fluid mentioned at the beginning of 78, a portion of which you have submitted to a preliminary examination, with some N 114 Cl, then with N I4 O I-, just to alkaline reaction, lastly with (N I14)2 S until the fluid, after being shaken, smells distinctly of that reagent; shake the mixture until the precipitate begins to separate in flakes, heat gently for some time, and filter. Keep the FILTRATE,t which may contain bases of Groups II. and I., for subsequent examination according to ~ 188. Wash the PRECIPITATE with water to which a very little (NI-,4)2 S has been added, then proceed with it as follows:a. IT HAS A PURE WHITE COLOR: absence of iron, 83 cobalt, nickel. You must test it for all the other bases of Groups III. and IV., as the faint tints of chromic hydroxide and manganese sulphide are inperceptible in a large quantity of a white precipitate. Dissolve the precipitate by heating it in a small dish with the least possible amount of IOCl; boil-should HII S be evolved until this is completely expelled-concentrate by evaporation to a small T bulk, add concentrated solution of Na O H in excess, boil for some time. a. The precipitate formed at first dissolves cornm- 84 pletely in the excess of soda. Absence of manganese and chromium, presence of aluminium or zinc. Test a portion of the alkaline solution with solution of 112 S (a little, not excess) for ZINC; acidify the remainder with H Cl, add N I-4 0 I slightly in excess, and * This simpler method will fully answer the purpose in most cases; for very accurate analysis the method beginning at 94 is preferable, as this will permit also the detection of minute quantities of alkali-earth metals which may have been thrown down together with Al or Cr. Solutions which are distinctly colored by Cr should always be examined by 94. t If the filtrate has a brownish color, this points to Ni, since Ni S, as is well known, under certain circumstances, is slightly soluble in ammonium sulphide; this, however involves no modification of the analytical course. 4 Compare; 106, 6.

Page  291 18 7.] ABSENCE OF PHOSPHATES, ETC. 291 apply heat. A white flocculent precipitate insoluble in more N It4 Cl, indicates ALUMINIUM.* b. The precipitate formed does not dissolve, or dis- 85 solves only partially, in the excess of soda. Dilute, filter, and test the FILTRATE, as in 84, for zINC and ALUMINIUM. With the undissolved PRECIPITATE, which, if containing manganese, looks brown, proceed as follows: aa. If the color of the solution gives you no reason to suspect the presence of chromium, test the precipitate for MANGANESE, with Nta2 C 03 in the outer blowpipe flame. bb. But where the color of the solution indicates 86 chromium, the examination of the residue insoluble in solution of soda is more complicated, since it may in that case contain also zinc, possibly even the whole quantity present of this metal (~ 112). Dissolve the precipitate therefore in H Cl, evaporate the solution to a small residue, dilute, nearly neutralize the free acid with Na2 C 03 add Ba C O in slight ekcess, allow to digest in the cold until the fluid has become colorless, filter, and test the precipitate for cHRoMrIuM, by fusion with Na2 C 03 and K Cl 03 (~ 102, 8). Remove the Ba from the filtrate, by precipitating with some H2 S,04, filter, evaporate to a small residue, add concentrated solution of Na O H in excess, and test the filtrate for zINC with 12 S, the precipitate, if any, for MANGANESE as in aa. b. IT IS NOT WHITE: this indicates chromium, man- 87 ganese, iron, cobalt, or nickel. If it is black, or inclines to black, one of the three metals last-mentioned is present. Under any circumstances all the metals of Groups III. and IV. must be looked for. Remove the washed precipitate from the filter with a spatula, or by rinsing it with the aid of a wash-bottle through a hole made in the bottom of the filter, into a test-tube, and pour.over it rather dilute cold II C1 ( part of II Cl, sp. gr. 1'12, with about 5 parts of H, 0) in moderate excess. I. It dissolves completely (except perhaps a little 88 sulphur); absence of cobalt and nickel, at least of notable quantities of these two metals. Boil until the 112 S is completely expelled, add II N 03, * It is of course assumed that the Na 0 H used is free from aluminium and silicic acid. In default of pure Na 0 H you may make a counter-experiment with an equal quantity of the alkali alone; if you obtain a very much smaller precipitate now than you obtained in the analysis you may conclude that aluminium is actually present in the substance.

Page  292 292 DETECTION OF METALS. GROUPS II. AND IV. [~ 187 boil, filter if particles of sulphur are suspended in the fluid, concentrate by evaporation to a small residue, add concentrated solution of Na O H in excess. boil, filter the fluid from the insoluble precipitate which is sure to remain, wash the latter, and proceed first to examine the filtrate. then the precipitate. aa. Test a small portion of the Ciltrate with 89 Ir, S for ZINC; acidify the remainder with H C1, then test with ammonia for ALUMINIUM. Coinpare 85. bb. Dissolve a small portion of the precipitate 90 in H C1, and test with 1K4 Fe (C N),, added drop by drop, or with K C N S for IRON.* Test another portion for CHROMIUM by fusing with Na, C 03, and K C1 0,, and boiling the fusion with water (~ 102, 8).t If no chromium has been found, examine the remainder for MANGANESE by Na, C O0 in the oxidizing flame. If chromium is present, on the other hand, test the remainder of the precipitate for manganese and zinc as directed 86. (Under these circumstances the whole of the zinc may be present in this precipitate.) B. The precipitate is not completely dissolved, a 91 black residue being left. This indicates COBALT and NICKEL. This indication is not certain, especially in the presence of much Fe S, particles of which may become enveloped in the separated S, and thus be protected from the action of the H C1. Filter, wash, and examine the filtrate according to 88. Heat the precipitate with the filter in a porcelain crucible till the filter is incinerated, allow to cool, warm with HI C1 and a drop or two of I-IN 0,, add water, then ammonia in moderate excess, and filter. The.ammoniacal filtrate will be blue in prewence of much nickel, brownish in the presence of much cobalt, and will have a less distinct mixed color if both metals are present. Test a portion of it with (N I14), S. If a black precipitate is formed, which does not redissolve on acidifying with II C1, the presence of cobalt or nickel is proved. In that case evaporate the rest of the ammoniacal solution to dryness, drive off the ammonia salts by gentle ignition, and proceed with the residue as follows: * Since Prussian blue dissolves in K4 Fe (C N)6 to a colorless fluid, small quantities of Fe may easily be overlooked if the reagent is added rapidly in large quantity. The original solution must be tested with K6 Fe2 (C N),2 and K. C N S, to learn whether the Fe be in dyad or tetrad form. t If the solution is green from the presence of sodium manganate, heat it with a few drops of alcohol and filter off the Mn 02 formed.

Page  293 ~ 187.] PRESENCE OF PHOSPHATES, ETC. 293 aa. Test a small portion of it with borax, first in 92 the outer, then in the inner blowpipe-flame. If the bead in the oxidizing flame is violet whilst hot, and of a pale reddish brown when cold, and turns in the reducing flame gray and turbid, NICKEL is present; but if the color of the bead is blue in both flames, and whether hot or cold, COBALT is present. As in the latter case the presence of nickel cannot be distinctly recognized, examine bb. the remainder of the residue by dissolving 93 it in II C1 and a little IH N 0,, evaporating nearly to dryness, and adding K N 0,, and, lastly, acetic acid (~ 109, 14). If a yellow precipitate forms, after standing for some time at a gentle heat, this confirms the presence of COBALT. Filter after about twelve hours, and test the filtrate with Na O H for NICKEL. 2. DETECTION OF THIE METALS OF GROUPS III. AND IV. IN 94 CASES WHERE PHOSPHATES, BORATES, OXALATES, SILICATES, FLUORIDES (IN THE PRESENCE OF ORGANIC MATTER, POSSIBLY ALSO TARTRATES AND CITRATIES) OF TILE ALKALI-EARTH MELTALS, OR SILICIC ACID MAY POSSIBLY HAVE BEEN THROWN DOWN, i.e., in cases where the original solution was acid or alkaline, and a precipitate was produced by ammonia in the examination of 78. Mix the fluid mentioned in 78 with some N HI C1, then with N 11 0 I just to alkaline reaction, lastly with (N I-I4), S, until the fluid, after being shaken, smells disti'nctly of the reagent; shake the mixture until the precipitate begins to separate in flakes, heat gently for some time, and filter. Keep the FILTRATE, which may contain bases of Groups II. and I., for subsequent examination according to ~ 188. Wash the PRECIPITATE with water to which a Very little (N 1I4), S has been added, then proceed with it as directed 96. To obtain a clear notion of the obstacles to be overcome in this analytical process, it must be considered that it is necessary to examine the precipitate for the following bodies:. Iron, nickel, cobalt (these show their presence to a certain extent by the black or blackish color of the precipitate), manganese, zinc, chromium (the latter generally reveals its presence by the color of the solution), aluminium, barium, strontiumn, calcium, magnesium, which latter substances may have fallen down in combination with phosphoric acid, boracic.acid, oxalic acid, silicic acid, in form of fluorides, or in combination with chromic oxide. Besides these blodies, silicic acid and free sulphur may be present. (In the presence of organic substances, tartrates and citrates of alkali-earth metals may be also present.)

Page  294 2,~94 DETECTION OF METALS. GROUPS III. AND IV. [~ 187 As the original substance must be afterwards examined 95 for all acids that Inight possibly be present, it is not indis-.)ensable to test for the above enumerated acids at this stage; still, as it is often interesting to detect these acids at olce, especially in cases where a somewhat large proportion of somne alkali-earth metal has been found in this precipitate, a method for the detcction of the acids in question will be found appended by way of supplement to the method for the detection of the metals. As soon as the washing is finished, remove the precipi- 96 tate from the filter with a small spatula, or with the washing-bottle, and pour over it cold dilute HI C1 (1 part of II C1 sp. gr. 1-12, with about 5 parts of water) in moderate excess. a. A RESIDUE REMAINS. Filter, and treat the filtrate 97 as directed 98. The residue, if it is black, may contain sulphides of nickel and cobalt, and, besides these, sllphur and silicic acid, possibly also calcium fluoride (which is rather difficultly soluble). Wash, and examine a sample of it with Na P 03 before the blowpipe in the outer flame. If a silica skeleton remains undissolved (~ 150, 9) this proves the presellce of sILIcIc ACID; the color of the bead will generally at once indicate COBALT or NICKEL, compare 92. Incinerate the rest of the precipitate and test it first for FLUORINE, by heating with 12 S O4 (~ 146, 5). If fluorine is presenlt, on treating the residue with a little water, and adding an equal volume of alcohol, CALCIUM sulphate will remain behind. Finally, if the color of the Na P O0 bead has been ambiguous, remove the alcohol from the sulphuric acid solution by evaporation (if necessary), precipitate the traces of iron generally present by ammonia, and test for nickel and cobalt as in 91 to 94. b. No RESIDUE IS LEFT (except a little sulphur, whose 98 purity is to be proved by washing, drying and burning): absence of nickel and cobalt, at least in any notable proportion. Boil the solution until the H2 S is expelled, filter if necessary, and then proceed as follows: a. Mix a small portion of the solution with dilute 99 H2 SO4. If a precipitate forms, this may consist of BARIUM and STRONTIUM sulphates, possibly also of calcium sulphate. Filter, wash the precipitate and examine it either by the colora:tion of flame (see ~ 99, at end), or decompose it by boiling or fusing with carbonated alkali, wash the carbonates produced, dissolve them in H Cl, evaporate to dryness, take up with water, and test the solution as directed 108. Mix the fluid which has not been precipitated by di

Page  295 ~ 187.] PRESENCE OF PHOSPHrATES, ETC. 29Z lute tI, S 04, or the fluid filtered from the precipitate produced, with 3 volumes of alcohol. If a precipitate forms, this consists of CALCIUMr sulphate. Filter, dissolve in water and add (N 114)2,C 04 to confirm the presence of calciumn.,8. Heat a somewhat larger smrnple with H N 0,, 100 and test a small portion of tile fluid with K, Fe (C N), added drop by drop, or with K C NT S for IRON;* mix the remainder with Fe. C16t in sufficient quantity to make a drop of fluid give a yellowish precipitate when mixed on a watch-glass with a drop of N I4, 0 H, evaporate on a water-bath to a small bulk, add some water, then a few drops of Na, C 0,, just sufficient to nearly neutralize the free acid, and lastly Ba C 0, in slight excess, stir and allow to stand in the cold until the fluid above the precipitate has become colorless. Filter the precipitate (aa) from the solution (bb), and wash. aa. Boil the precipitcate for some time with 101 solution of soda, filters, and test the filtrate for ALUMINIUM4, by acidifying with 1I Cl, adding N I4 O 1H to alkaline reaction and b)oiling. The part of the precipitate insoluble in Na 0 -I is examined for crnooMIur, by fusion with KI Cl 03 and Na2 C 03 (~ 102, 8). bb. Mix the solution, first with a few drops of H C1, boil to expel C O,, then add N tI4 0 HI and (N 114)2 S. aa. oNb precipitate forms: absence of man- 102 ganese and zinc. Mix the solution containing 3a Cl, with.iute 11, S O, in slight excess, boil, filter, supersturate with ZN I-4 O 1 and mix with (N H,4) C, O,. If a precipitate of Ca C, 04 forims, filter and test the filtrate with Na, 1I P 04 for MAGNESIUM.,fi,. A preci2ptate forms. Filter, and pro- 103 ceed with the filtrate according to 102. The precipitate may contain Mn S, Zn S, traces of * Whether the iron was present as a ferric or a ferrous compound must be ascertained by testing the original solution in H C1 with K, Fe, (C N)12 and KCN S. t The addition of Fe, C16 is necessary, to effect the separation of phosphoric acid and silicic acid which may be present and which would go down in combination with alkali-earth metals, on addition of Ba C 03. t If the solution or the Na 0 H contains silicic acid, the precipitate taken for Al, (O H)6 may also contain silicic acid. A simple trial with Na P 03,, on a platinum wire, in the blowpipe flame, will show whether the precipitate really contains Si. Should this be the case, ignite the remainder of the precipitate on the lid of a platinum crucible, add some Na, S2 07, fuse and treat with H Cl, which will dissolve the Al, leaving Si 02 undissolved; precipitate the A] from the solution by N H4 0 H.

Page  296 296 DETECTION OF METALS. tj 188. Co S and Ni S; and also (in the presence of tartrates and citrates of the alkali-earth metals) Fe S. Wash it and test for MANGANESE, ZINC, COBAL'T and NICKEL, according to 87 to 94 (if the last two metals have not been found in 97). ry. If you have found alkali-earth metals in a and104 8, and wish to know the acids in combination with which they have passed into the precipitate produced by (N H,)2 S, make the following experimnents with the remainder of the H Cl solution of the (N I-4)2 S precipitate. aa. Evaporate a small portion in a dish or 105 watch-glass on the water-bath to complete dryness, then treat with HC1. If there was any sILICIC ACID in the solution, this will be left undissolved. Evaporate the solution with H N 0, and test it for PHOSPHORIC ACID, by means of molybdic solution (~ 142, 10). hb. Concentrate another portion bv evaporation, mix it with solution of Na2 C 03 in excess, boil for some time, filter and examine one portion of the filtrate for OXALIC ACID, by acidifying with acetic acid and adding solution of Ca S 04; another portion for BORIC ACID, by slightly acidifying with HI Cl, and testing with tulrneric-paper (~ 144 and ~ 145). (In the presence of organic matter the rest of the filtrate may be used for testing for TARTARrC and CITrIC ACIDS, coimpare 142.) cc. Precipitate the remainder with N H4 0 H, 106 filter, wash and dry the precipitate, and examine it for FLUORINE according to146, 5. ~ 188ss. J Compare the notes on pp. 370 and 380. (Separation and Detection of the 3fetals of Group Il. which are precipitated by Amnmoniutr Carbonate in Presence qof Ammnonium Cloride, viz., BCarium, Strontium, Calciurm.) To A SMALL PORTION OF THE FLUID IN WHICH AMMONIA AND AMMONIUM SULPHIDE HAVE FAILED TO PIRODUCE A PRECIPITATE (79), lt OF THE FLUID FILTERED FROM THE PRECIPITATE, FORM[ED, ADD AMMONIUM CIILORIDE, IF THE SOLUTION CONTAINS NO AMMONIUM SALT, THEN AMMONIUM CARBONAlTE AND SOME ALMIONIA, AND HEAT FOR SOME TIME VERY GENTLY (not to boiling). 1. No PRECIPITATE FORMS: absence of any notable quanltity 107 of barium, strontium, and calcium. Traces of these metals

Page  297 ~ 188.] GROUP II. 297 may, however, be present; to detect them proceed as follows. Add to another portion of the fluid some (N 14,)2 S O, (prepared by supersaturating dilute HII S 04, with N IIt O H); if the fluid becomes turbid, it conlaiths traces of barium. Add to a third portion some (N HII,) C2 04 and allow it to stand; if the fluid turns turbid, traces of calcium are present. Treat the remainder of the fluid as directed ~ 189, after having removed the traces of Ca and Ba which have beenl found by means of the reagents that have served for their detection. 2. A PRECIPITATE IS FORMED: presence of CALCIUJM, BARIUM, 108 or STRONTIUM. Treat the whole fluid of which a portion has been tested with NT 11 0 II and (N II4,) C 0,, the same as the sample, filter off the precipitate formed, after gently heating, and test portions of the filtrate with sulphate and oxalate of ammonium for traces of Ca and Ba, which it nay possibly still contain; remove such traces, should they be found, by lneans of the said reagents, and examine the fluicdthus perfectly freed fromn Ba, Sr and Ca, for magnesium, according to ~ 189. Wash the precipitate produced by (N II4), C 03, dissolve it in the least possible amoulnt of dilute II C1, evaporate to dryness on the water-bath, take up the residue with a little water, and add to a small portion of the fluid a sufficient quantity of solution of Ca S O,. a. 1No precipitate is formed, NOT EVEN AFTER THE LAPSE OF SOME TIME. Absence of Ba and Sr;* presence of CALCIUM. To confirm mix another sample with (N H4) C2 O4,. b. A prec',pitate is formed by solution of calcium sulphate. a. It is formed immediately; this indicates BA- 109 RIM. -Besides this, Sr and Ca nmay also be present. Evaporate the renainlder of the H C1 solution of the precipitate produced by (N II4)2 C 0O to dryness, digest the residue with strong alcohol, decant the fluid from the mundissolved Ba Cl1, dilute with an equal volume of water, mix with a few drops of Si 112 F6 -which will throw down the small portion of barium that had dissolved as Ba C1 —allow to stand for some time; filter, and mix the filtrate with dilute T2, S 04. The formation of a precipitate indicates the presence of strontium or calcium, or of both. Filter after some time, and test the precipitate according to p. 114 for STRONTIUM and CALCIUMt.'The separation by boiling the pulphates with (N 11,), S 0, suffices for ordinary cases; but in * Very minute traces of Sr cannot be detected in this way, as Sr S 04 is not absolutely insoluble. See ~ 99.

Page  298 298 DETECTION OF METALS. MAGNESIUM..[~ 189. very delicate analyses the nitrates must be treated with alcohol and ethel, and the residue examined in the spectroscope. f. It is formed only cfter some time. Absence of 110 barium, presence of STRONTIUM. Mix the remainder of the aqueous solution of the chlorides with a sufficienlt amount of concentrated solution of (N 1I,)2 S O,, and boil for some tilne, renewing the water as it evaporates, and adding ammonia to keep the fluid alkaline. Then filter off the Sr S 04, and test the filtrate for CALCIuM, with (N H4)2 C2 04. ~ 189. (Examination for Ylagnesium.) TO A PORTION OF THE FLUID IN WHICH CARBONATE, SULPIIATE, AND OX&ILATE OF AMMONIUM HAVE FAILED TO PRODUCE A PRECIPITATE (107) OR OF TIlE FLUID FILTERED FROM THE PRECIPITATES FORMED (108), ADD AMMONIA, THEN SOME SODIUM PHOSPHATE, AND, SHOULD A PRECIPITATE NOT AT ONCE FORM, RUB THE INNER SIDES OF TIE TEST-TUBE WITH A'ROD, AND LET THE MIXTURE STAND FOR SOME TIME. 1. No PRECIPITATE IS FORMED: absence of magnesium. 111 Evaporate another portion of the fluid to dryness (preferably in the lid of a platinum crucible), and ignite gently. If a residue rernains, treat the remaillder of the fluid the same as the sample, and examine the residue (freed from ammonia by the moderate ignition) for potassinlnum ad sodinn, according to ~ 190. _4y no res.idue i, left, this is proof of the absence of K, Na and Li; pass on at once to ~ 191. 2. A CRYSTALLINE PRECIPITATE IS FORMrED: presence of 112 MAGNESIUM.* As testing for alkalies can proceed with certainty only after the removal of magnesium, evaporate the remainder of the fluid to dryness, and ignite unltil all aminoniumr salts are removed. Warm the residue with some water, add baryta-water (prepared from the crystals)t as long as a precipitate continues to form, boil, filter, add to * N H,4 Mg P 04. 6H, O is invariably crystalline; if Na2 H P 04 produces a slight flocculent precipitate, you are therefore not justified in concluding that magnesium is present. The slight flocculent precipitate, which is here sometimes obtained, consists of Al P 04. You get it when Al is contained in the original substance, and you use too large an excess of ammonia in precipitating the third and fourth groups. Its production depends upon the fact that Al P 04 is far less soluble in ammonia than Al (O H)3. Al P 04 differs also from Mg N H4 P 04 by its insolubility in acetic acid. If you want to test the precipitate in this manner, it should first be filtered off. From the acetic acid solution of Mg N H, P 04. ammonia would throw down the pure salt. t Or thin milk of lime, freed from every trace of alkali by repeated extraction with water. Add it to the warm fluid with stirring till turmeric-paper is strongly affected.

Page  299 ~~ 190; 191.] DETECTION OF METALS. GROUP I. 299 the filtrate a mixture of (N H4), O 0 and N H,0 -TI in slight excess; heat for solne time gently, filter, evaporate the filtrate to dryness, with addition of some N H4 Cl (to convert into chlorides the alkali hydroxides or carbonates that may happen to form), ignite gently, dissolve in a little water, precipitate if necessary once more with (N H,4), C O, and N 1I40 H, filter, evaporate'agailn, and if a residue remains, ignite this gently, not above faint redness, and examine it according to ~ 190. ~ 190. (Examination for Potassiutm and Sodium.) YOU HAVE NOW TO EXAMINE FOR POTASSIUM AND SODIUM THE GENTLY IGNITED RESIDUE, FREE FROM AMMONIUM SALTS AND ALKALI-EARTH METALS, WHICH HAS BEEN OBTAINED IN 111 or 112. Dissolve it in a little water, filter if necessary, evaporate until there is only a small quantity of fluid left, and transfer one-half of this to a watch-glass, leaving the other half in the porcelain dish. 1. To the one-half in the porcelain dish add, after cool- 113 ing, a few drops of Pt Cl,. If a yellow crystalline' precipitate forms immediately, or after some time, POTASSIUM is present. Should no precipitate form, evaporate to dryness at a gentle heat, and treat the residue with a very small quantity of water, or, if chlorides alone are present, with a mixture of water and alcohol, when the presence of minnte traces of K will. be revealed by a small quantity of a heavy yellow powder being left undissolved (~ 89, 3). In the presence of an iodide the deep brown color of the fluid interferes with the detection of K by Pt C14;' under these circumlstances test with acid sodiumtt tartrate. 2. To the other half of the fluid (in the watchl-glass) add 114 some potassiuh?_myroantimonate. If this produces at once or after some time a crystalline precipitate, SODIUM is presellt. If, after standing twelve hours, no crystals separate, you may conclude that Na is absent. In regard to the crystallinle form of the precipitate, and the precautionary rules, see ~ 90, 2. [The alkali metals may also be tested for by Smitah's method (p. 101). The flame-tests and spectroscope, with due precautions, likewise give speedy and certain results.] ~ 191. (Examination for Ammonium.) THERE REMAINS STILL THE EXAMINATION FOR AMIMONIUM. 115 Triturate some of the substance with an excess of Ca (0 H),

Page  300 300 DETECTION OF INORGANIC ACIDS. [~ 192. and, if necessary, a little water. If the escaping gas smells of ammlronia, if it blues moist red litmus-paper, and forms white fumnes with 1I C1 vapors, brought into contact with it by means of a glass rod, A rIONIIuJM is present. The reaction is the most sensitive if the trituration is made in a small beaker, and the latter covered with a glass plate with a slip of lmoist turmeric or red litmus-paper adhering to the under-side. A, 1. SUBSTANCES SOLUBLE IN WATER. DETECTION OF ACIDS.: Consult also the Notes in the Third Section, p. 371. I. In the Absence of Organic Acids. ~ 192. Consider, in the first place, which are the acids that form with the bases found compounds soluble in water, and let this guide you in the examination. To students the table given in Appendix IV. will prove of considerable assistance (see also 30). The following plan of examination works best when the acids are combined exclusively with alkali or alkali-earth metals, it is therefore sometimes advisable to precipitate any heavy metals preseilt by Hi2 S or (N I4), S before proceeding. The sulphides should be filtered off and the excess of H2 S removed by boiling, or of (N H4)2 S by acidifying with 11 C1, boiling and filtering off the sulphur. It must not be forgotten that sulphur, hydrochloric acid, chromic acid, and chloric acid cannot be looked for in this fluid, and also that' the results of the testing for sulphuric and nitric acids will not be so trustworthy. In absence of sulphides and sulphur' salts, most of the acids (see ~ 145, 8) may also be obtained as sodium salts by boiling,* in a platinum dish, the original solution, with a moderate excess of Na. C 03 and filtering from the precipitate. A portion of the filtrate should be heated to boiling, and very slightly acidified with IH N 03 for treatment according to 116, 2. To be sure that all Na2 C 03 is decomposed, see that litmus-paper, which has been reddened by the liquid, remains red when dried. 1. THE ACIDS OF ARSENIC, CARBONIC ACID, SULPHUR COm- 116 * In all cases until no more C 02 escapes, and if N H4 salts are present until N H3 ceases to be given off from the liquid, kept alkaline.

Page  301 ~ 192.] AQUEOUS SOLUTION. 301 bined with metals or hydrogen, cnRnonc ACID, and SILTCI' ACID will have been usually detected in the examination for metals, see 20 and 35.* Chromic acid is also easily recognized by the yellow or reddish-yellow color of the solution. If in doubt, test for it with Pb (C, 1s O2)2 and C H, 40, (~ 138, 8) or-for very minute quantities —with decoction of logwood (~ 138, 12). 2. Add to a portion of the solution'Ba C1,, or, if lead, silver, or mercurous salts are present, Ba (N O,),, and should the reaction of the fluid be acid, add N H, O H. to neutral or slightly alkaline reaction. a. No PRECIPITATE IS FORMED: absence of sulphuric, 117 phosphoric, chromic, silicic, oxalic, arsenious, and arsenic acids, as well as of notable quantities of boric and hydrofluoric acids.t Pass on to 119. b. A PRECIPITATE IS FORMED. Dilute the fluid, and 118 add PI. C(l or, as the case inay be, II N O,; if the precipitate does not redissolve, or at least not completely, SULPHURIC ACID is present. 3. Add Ag N 0, to a portion of the solution. If this 119 fails to produce a precipitate, test the reaction, and if acid, add to the fluid some dilute N 11, O H, taking care to add the reagent so cautiously that the two fluids do not intermix; if the reaction is alkaline, on the other hand, add with the same care some dilute H N 03,, and watch attentively whether a precipitate or a cloud will form at the junction of the two fluids. a. No PRECIPITATE IS FORMED AT THE JUNCTION OF THE 120 TWO FLUIDS, EITHER IMMEDIATELY OR AFTER SOMME TIME. Pass on to 125; there is neither chlorine, bromine, iodine, cyanogen,: ferro- and ferricyanogen, nor sulphur present; nor phosphoric, arsenic, arsenious, chromic, silicic, oxalic acids, nor boric acid, if the solution was not too dilute. b. A PRECIPITATE IS FORMED. Observe the color ~ of 121 it, then add H N 0,, and shake the mixture. * ARSENIOUS ACID and ARSENIC ACID are distinguished from each other by their reaction with Ag N 03, or with Na O H, and Cu SO; (see ~ 134, 9). CARBONIC ACID and SULPHUR in combination with metals betray their presence by effervescing upon the addition of H Cl; the escaping gases may be distinguished from one another by the smell. The presence of carbonic acid may be confirmed by lime-water (see ~ 149), and that of hydrosulphuric acid by lead acetate (~ 156). Free carbonic acid and free hydrosulphuric acid in aqueous solution may be detected by the same reagents. t If the solution contains an ammonium salt in somewhat considerable proportion, the non-formation of a precipitate cannot be considered a conclusive proof of the absence of these acids, since the barium salts of most of them (not the sulphate) are in presence of ammonium salts more or less soluble in water. t That the cyanogen in mercuric cyanide is not indicated by Ag N 03 has Deen mentioned (73). f Chloride, bromide, cyanide, ferrocyanide, oxalate, silicate and borate of

Page  302 302 DETECTION OF INORGANIC ACIDS. [~ 192 a. The precipitate dissolves complete!y: absence of chlorine, bromine. iodine, cyanoyen, ferro- and ferricyanogell, and also of sulphur. Pass on to 125.,8. A residae is left: chlorine, bromine, iodine, 122 cyanogen, ferro- or ferricyanogen may be present; anld if the residue is black or blackish, HIYDROSUL-'Ir1LIUC ACID or a soluble METALLIC SULPHIDE. The presence of sulphlfr may, if necessary, be readily confirmed, by mixing another portion of the solutionl with Ca S 04, or with a solution of Pb (O H)2 in Na O I. aa. Test another portion of the fluid for IODINE and subsequently for BROIINE, by the methods described in ~ 157. bb. Test a small portion of the fluid with 123 Fe, Cl1 for FERROCYANOGEN; and, if the color of the silver precipitate leads you to suspect the presence of FERRICYANOGEN, test another portion for this latter substance with Fe S 04 (freshly prepared, by warming iron wire with dilute H, S 04). If the original solution has an alkaline reaction, some II Cl must be added before the addition of the ferric or ferrous salt. cc. CYANOGEN, if present in form of a simple cyanide of all alkali metal soluble in water, may usually be readily recognized by the smell of hydrocyanic acid which the substance emits, and which is rendered more strongly perceptible by addition of a little dilute 112 S O4. If ferrocyanogen and ferricyanogen are absent, cyanogen may be detected by the method given in ~ 155, 6. If they are present see ~ 219. dd. Should bromine, iodine, cyanogen, ferrocy- 124 anogen, ferricyanogen, and sulphur not be present, the precipitate which nitric acid has failed to dissolve consists of silver CHLORIDE. But where one or other of these bodies is present, a special examination for chlorine may become necessary, particularly when the quantity of the precipitate does not afford a decided indication.* See ~ 157. 4. CHLORIC ACID is known by the yellow color produced 125 silver are white; iodide, orthophosphate and arsenite of silver are yellow; arsenate and ferricyanide of silver are brownish-red; silver chromate is purple-red; silver sulphide, black. * Supposing, for instance, Ag N 03 to have produced a copious precipitate insoluble in nitric acid, and the subsequent examination to have shown mere traces of I and Br, the presence of C1 may be held to be demonstrated, without requiring additional proof.

Page  303 ~ 193.] AQUEOUS SOLUTION. 303 when a little of the solid substance is brought into contact with concentrated 12 S 04 (~ 160). 5. NITRIC ACID is tested for with Fe S 04 and H2 S 04 (~ 159). The presence of certain other acids (chloric, chromic, hydriodic) impedes this reaction. If such acids are present they must be destroyed or removed. Chloric acid is destroyed by ignition (~ 161, at the end), chromic acid is reduced by sulphurous acid, chromic hydroxide being precipitated afterwards with ammonia; hydriodic acid is removed by silver sulphate. You have still to test for phosphoric acid, boric acid, silicic acid and oxalic acid, as well as for hydrofluoric acid. For the first four acids test only in cases where both Ba C12 and Ag N 03 have produced precipitates in neutral solutions. Compare also foot-note to 117. 6. Test for PHOSPHORIC ACID, by adding to a portion of 126 the fluid N I40 H in excess, then N 114 C and AMg S O4 nixture (~ 142, 7). Very minute quantities of phosphoric acid are detected most readily by means of molvbdic solution (~ 142, 10). Arsenic acid, if present, must be first separated by H.2 S, the solution being acidified and kept at 70~ during the passage of the gas. 7. To detect OXALIC ACID and HYDROFLUORIC ACID, add Ca C1, to a fresh portion of the solution. If the reaction of the fluid is acid, add ammonia to alkaline reaction. If the Ca C1, produces a precipitate which is not redissolved by addition of acetic acid, one or both bodies are present. Examine now a sample of the original substance for fluorine according to ~ 146, 5, another sample for oxalic acid according to ~ 145, 7. 8. Acidulate a portion of the fluid slightly with 1 C1, 127 then test for BORIC ACID, bv means of turmeric paper (~ 144, 7). Chloric, chromic, and hydriodic acids impede the reaction. If present, they must be removed or destroyed as directed 125. 9. Should sILICIC ACID not yet have been found in the course of testing for the bases, acidulate a portion of the fluid with II Cl, evaporate to dryness, and treat the residue with H C1 (~ 150, 2). A, 1. SUBSTANCES SOLUBLE IN WATER. DETECTION OF ACIDS. II. In Presence of Organic Acids. ~ 193. 1. The examination for the INORGANIC ACIDS, including 128 oxalic acid, is made as described ~ 192. As the tartrates

Page  304 304 DETECTION OF ORGANIC ACIDS. [~ 193. and citrates of barium and silver are insolnlle, or difficultly soluble in water, tartaric acid and citric ncid call be present only in cases where both Ba C12 and Ag N 03 have produced precipitates in the neutral fluid; still bear in mind that these salts are slightly soluble in solutions of ammonioi salts. Before testing for the ORGANIC ACIDS, remove Groups III.-VI., as follows:-Where the metal belongs to Group V. or Group VI. the removal is effected by 11, S, where it belongs to Group IV. by (N H4,), S. After filtering off the sulphides, and removing the excess of (N 114,2S by acidifying with II C1, heating, and filtering off the S, proceed to 129. Where the metal is aluminilln or chromium, try first to precipitate these substances by boiling with Na2 C 03; should this fail, as it will where the acid is nonvolatile, precipitate the latter in a fresh portion of the solution with normal lead acetate, wash the precipitate, diffuse it through water, pass 2, S, filter off the Pb S, and treat the filtrate as directed 129. To separate acetic or formic acid from metals which lie in the way of their detection, you may also distil the salt with dilute H, S 0,. 2. Make a portion of the fluid feebly alkaline with 129 ammonia, add some N H1 C1, then a sufficient quantity of Ca C12, shake vigorously, and let the mixture stand from ten to twenty minutes. a. No PRECIPITATE IS FORMED, EVEN AFTER THE LAPSE OF SOME TIME. Absence of tartaric acid; pass on to 130. b. A PRECIPITATE IS FORMED, IMMEDIATELY, OR AFTER SOME TIME. Filter, and keep the filtrate for further examination according to 130. Wash the precipitate, digest and shake it with solution of NaO 1-I, without applying heat, then dilute with a little water, filter, and boil the filtrate some time. If a precipitate separates, TARTARIC ACID is indicated. Filter hot, and test the precipitate with ammonia and AgN 03 (~ 163, s). 3. Mix the fluid in which Ca Cl1 has failed to produce a 130 precipitate, or that which has been filtered from the precipitate formed-in which latter case some more Ca C1l is to -e added-with 3 measures of alcohol. a. No PRECIPITATE IS FORMED. Absence of citric, 131 malic, and succinic acids. Pass on to 134. b. A PRECIPITATE IS FORMED. Filter and treat the 132 filtrate as directed 134. Treat the precipitate as follows: Wash with alcohol, dissolve on the filter in a little dilute H Cl1, add ammonia to the filtrate to alkaline reaction, and bo:l for some time.

Page  305 g 193.] AQUEOUS SOLUTION. 305 a. IT REMAINS CLEAR. Absence of citric acid. Add more alcohol, filter off the precipitate, which may contain malate and succinate of calcium, wash it a little with alcohol, dissolve in a porcelain dish, in a sufficient quantity of strong Ir N 03, and evaporate to dryness on the water-bath. Succinic acid will remain unchanged, malic acid is converted into oxalic acid with evolution of C O,. Boil the residue with excess of solution of Na, C 0,, filter, neutralize exactly with II C1, heat to remove C O,, and mix a small portion of the fluid with solution of Ca S O4. If a white precipitate is formed of Ca C 4O,, MaLIO ACID is indicated. If malic acid is indicated prepare some more of the calcic precipitate, and confirm by testing it according to ~ 166; also test for sutccinic acid by mixing the rest of the fluid with excess of Ca Cl,, filtering, and addillng alcohol to the filtrate; a precipitate indicates SUCCINIC ACID. If nmalic acid has not been found, test the rest of the neutralized fluid for succINxI ACID with e,2 Cl6 (~ 168). A. A HEAVY WHITE PRECIPITATE IS FORMED. Presence 133 of CITRIC ACID. Filter boiling, and test the filtrate for malic and succinic acids as in,X. To remove all doubt whether the precipitate is calcium citrate, redissolve it in I- Cl, heat, supersat-urate again with N 114 OH, and boil; the precipitate will now be thrown down again. (Compare ~ 164, 3.) 4. Heat the filtrate, of 132, or the fluid in which addi- 134 tion of alcohol has failed to produce a precipitate (131), to expel the alcohol, neutralize exactly with H Cl, and add Fe. Cl6. If this fails to produce a light-brown flocculent precipitate, benzoic acid is absent. If a precipitate of the kind is formed, filter, and heat the washed precipitate with ammonia in excess; filter, evaporate the filtrate nearly to drynless, and test for BENZOIC ACID with I- Cl (~ 169, 2). Benzoic acid may generally be readily detected in the original substance, by treating a small portion with dilute 11 C1, which will leave the benzoic acid undlcissolved; it is then filtered off and heated on platinum foil (~ 169, 1). 5. Evaporate a portion of the solution to dryness-if 135 acid, after previous saturation with soda-introduce the residue or a portion of the original dry substance into a test-tube, pour some alcohol over it, add about an equal volume of concentrated H,2 S 04, and heat to boiling. Evolution of the odor of acetic ether demonstrates the presence of ACETIC ACII). The odor is rendered more distinctly perceptible by shaking the cooling or cold mixture. 6. Test for FORMIC ACID by just acidify ing a portion with 136 20

Page  306 306 INORGANIC ACIDS. ACID SOLUTION. [~ 194: 1I Cl (if not acid already), adding Ig C1, and heating. A white turbidity from. the separation of IIg, Cl, indicates formic acid (~ 1772, 6). Confirm by Ag N 0,, and by Hg, (N O),. (~ 172).* A, 2. SUBSTANCES INSOLUBLE IN WATER, BUT SOLUBLE IN HYDROCHLORIC A CID, NITRIC ACID, OR INITRO-HYDROCHLORIC kACID. DETECTION OF THE ACIDS. I. In Absence of Organic Acids. ~ 194. In the examination of these compounds attention must be directed to all inorganic acids, with the exception of chloric acid. Cyanogen compounds and silicates are not examined by this method. (Compare ~ 197 and ~ 198.) 1. CARBONIC ACID, SULPHUR (in the form of metallic sul- 137 phides), ARSENIOUS ACID, ARSENIC ACID, and CHROMIC ACID, if present, have been found already in the examination for bases; NITRIC ACID, if present, has been detected in the preliminary examination, by the ignition in a glass tube (8). 2. Mix a sample of the substance with 4 parts of pure 138 Na,.03, and, should a metallic sulphide be present, add some Na N 03; fuse the mixtiure in a'platin um crucible if there are no reducible metallic compounds present, in a porcelain crucible if such compounds are present; boil the fused mass with water, and add a little H N 0,, leaving the reaction of the fluid, however, still alkalinle; heat again, filter, and proceed with the filtrate according to ~ 192.t 3. As the phosphates of the alkali-earth metals are only 139 incompletely decomposed by fusion with Na2 C 03, it is always advisable in cases where alkaline earths are present, and phosphoric acid has not yet been detected, to dissolve a fresh sample of the substance in 11 N 03, and test for PHOSPHORIC ACID with molybdic solution (~ 142, 10). In. the presence of silicic or arsenic acid, prepare a solution * In the presence of chromic or chloric acid the reduction of the silver and mercury does not take place. If chromic acid is present, mix the original solution with sulphuric acid, add excess of lead oxide and shake, filter, mix the filtrate with excess of dilute sulphuric acid, and distil. Test the distillate as above. If chloric acid is present, saturate the acids with lead oxide, and treat with alcohol; the formate is insoluble, the chlorate soluble. If tartaric acid is present it will also be safer to mix the fluid with dilute EH, S 0O and distil off the formic acid. f In the presence of a metallic sulphide, a separate portion of it must be examined for sulphuric acid, by heating it with C11, filtering, diluting the filtrate, and adding Ba Cl2.

Page  307 ~ 195.] ORGANIC ACIDS. ACID SOLUTION. 307 with H C, separate these acids, add It7NO,, evaporate nearly to dryness, dilute with water containing H N 03,, and then test with molybdic solution. 4. If in the examinllation for bases, alkali-earth metals have been found, it is also advisable to test a separate portion for FLUORINE, by ~146, 5. 5. That portion of the substance which has been treated 140 as directed in 138, can be tested for sILIcIC ACID only in cases where the fusion has been effected in a platinum crucible; when a porcelain crucible has been used, examine a separate portion by evaporating the I- C1 or H lNh 0O solution (~ 150, 3). 6. Examine a separate portion of the substance for oxALIC ACID by boiling with Na2 C 03, see 142. Acidify the alkaline filtrate with acetic acid and test with solution of Ca S O0. If a pulverulent precipitate is formed, this indicates oxalic acid. Confirm by taking a fresh portion of the substance, removing C 02 if necessary by dilute I2, S O,, and then testing according to ~ 145, 7. A, 2. SUBSTANCES INSOLUBLE IN WATER, BUT SOLUBLE IN HYDROCHLORIC AcID, NrrRIC ACID, OR N ITRO-HYDROCHLORIC ACID. DETECTION OF THE ACIDS. II. In Presence of Organic Acids. ~ 195. 1. Conduct the examination for INORGANIC ACIDS accord- 141 ing to ~ 194. 2. Test for ACETIC ACID as directed, ~ 171, 7. 3. To a small portion of the substance in a watch-glass add a little dilute H Cl. If a residue remains, this should be tested for BENZOIC ACID by heating. Any considerable quantity of this acid is most readily detected in this way, but a small quantity might completely dissolve; it is therefore necessary to recur to this acid in 142. 4. Boil a portion of the substance for a few minutes 142 with a large excess of solution of Na2 C 03,, adding some of the solid, if the solution is not strong, and filter. You will now have all the organic acids in the filtrate as sodium salts. Evaporate the filtrate to concentrate it, acidify with HE Cl, heat to drive off C 0, and proceed according to 129. If any heavy metals have passed into solution through the agency of organic acids, these must first be removed by H1 S or (N II,)2 S.

Page  308 308 INSOLUBLE SUBSTANCES. [~ 196. B. SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER, HYDROCHLORIC ACID. NITRIC ACID, AND NITRO-HYDROCHLORIC ACID. DETECTION OF THE BASES, ACIDS, AND NON-METALLIC ELEMENTS. X 196. P Cbompare the Notes in the Tlird Section, p 381. To this class belong the following bodies. 143 BARIUM SULPHATE, STRONTIUM SULPHATE, and CALCIUM SULPH ATE. * LEAD SULPHATE t and LEAD CnHLORIDE.4 SILVER CHLORIDE, silver bromide, silver iodide, silver cyanide,~ silver ferro- and ferricyanide.ll SILICIC OXIDE, SiLICIC ACID, and many SILICATES. Native and ignited ALUMINA, and many aluminates. Ignited chroinic oxide and CHROMIC IRON (a compound of chromic oxide and ferrous oxide). Ignited and native stannic oxide (tin-stone). Some nmetaphosphates and some arsenates. CALCIUM FLUORIDE and a few other compounds of fluorine. SULPHUR. CARBONACEOUS MATTER. Of these compounds those printed in small capitals are more frequently met with. To the silicates a special chapter (~~ 198-201) is devoted. The substance is in the first place subjected to the preliminary experiments described below in a-e, unless the quantity at disposal is too small, when you at once pass on to 149, bearing in mind, however, that the substance may contain all the aforesaid bodies. a. Examine attentively the physical condition of the res- 144 idue to ascertain whether it is homogeneous or not, whether it is sandy or pulvernlent, whether it has the same color throughout, or is made up of variously-colored parti* Calcium sulphate passes partially into the solution effected by water, and often completely into that effected by acids. t Lead sulphate may pass completely into the solution effected by acids. t Lead chloride can here only be found if the precipitate insoluble in acids has not been thoroughly washed with hot water. ~ Bromide, iodide, and cyanide of silver are decomposed by boiling with nitro-hydrochloric acid, and converted into silver chloride; theF can accordingly be found here only in cases where the operator has to deal with a substance which-as nitro-hydrochloric acid has failed to effect its solution-is examined directly by the method described here. I With regard to the examination of these compounds, compare also ~ 197.

Page  309 1 9 6.] INSOLUBLE SUBSTANCES. 309 cles, &c. A microscope, or at least a lens, will be often found needful for this purpose. b. Heat a small sample in a glass tube sealed at one end. 145 If brown fumes arise, and SULPIhUR sublimes, this is of course a proof of the presence of that substance. c. If the substance is black, this indicates, in most cases, 146 the presence of CARBONACEOUS MATTER (charcoal, coal, boneblack, lamp-black, graphite, &e.). Heat a small sample on platinum foil over the blowpipe flane; if the black substance is consumed, it consisted of CARBON in some shape or other. Graphite (which may be readily recognized by its property of communicating its color to the fingers, to paper, &ec.) requires the aid of oxygen for its combustion. d. Heat a small sample, with aslnall lump of K C N and 147 some water, for some time, filter, and test the filtrate with (N H4)2 S. A brownish-black precipitate indicates SILVER. 148 e. If an undissolved residue has been left in d, wash this thoroughly with water, and if white, moisten it with (N HI4), S; if it turns black, LEAD salts are present. If, however, the residue left in d is black, heat it with some ammonium acetate, adding a few drops of acetic acid, filter, and test the filtrate for LEAD, by means of H2 S 0, and H11 S.* The results obtained by these preliminary experiments serve as a guide in the.following course: i. a. LEAD SALTS ARE NOT PRESENT. Pass on to 150. 149 6. LE&D SALTS ARE PRESENT. Heat the substance re-. peatedly with a concentrated solution of amnmonium acetate until the lead salt is completely dissolved out. Test a portionof the filtrate for CHLORINE, another for SULPHURIC ACID, and the remainder for LEAD, the last by addition of 1H2S 0, in excess, and by H11 S. If ammonium acetate has left a residue, wash this, and treat it as directed 150. 2. a. SILVER SALTS ARE NOT PRESENT. Pass on to 151. 150 6. SILVER SALTS ARE PRESENT. Digest the substance free from lead repeatedly with K C N and water, at a gentle heat (in presence of sulphur, in the cold), until. all the silver salt is removed. If a residue is left, wash tllis, and proceed with it according to 151. Of the filtrate, which contains K C N, mix the larger portion with (N HI4), S to precipitate the silver. Wash the precipitated Ag. S, then dissolve in 11 N 03, dilute the solution and add H Cl, to ascertain whether the precipitate really consisted of Ag. S. Test another small portion of the filtrate for SULPHURIc ACID.t * The presence of lead in silicates, e.g., in glass, cannot be detected by this method. f As the K, C 03 contained in the K C N may have produced a total ot partial decomposition of sulphates of the alkali-earth metals.

Page  310 3 10 INSOLUBLE SUBSTANCES. [~ 196 3, a. SULPHUR IS NOT PRESENT. Pass on to 152. 151 b. SULPHUR IS PRESENT. Heat the substance free from silver and lead in a covered porcelain crucible until all the sulphur is expelled, and if a residue is left, treat this according to 152. 4. Mix the substance free from silver, lead, and sulphur 152 with 4 parts of Na2 C 03, and 1 part of K NT 03,* heat in a platinum crucible until the mass is in a state of calmn fusion, place the red-hbt crucible on a thick cold iron plate' to co'4. You will thus generally succeed in removing the fused mass from the crucible in a cake. Soak the mass now in water, boil; fi'lter, and wash the residue until Ba C1.2 no longer produces a precipitate in the washings. (Add only the first washings to the filtrate.) a. The solution so obtained contains the acids 153 which were present in the substance decomposed by fusing. But it may, besides these acids, contain also such bases as are soluble in caustic alkalies. Proceed as follows a. Test a small portion for SULPHURIC ACID.,8. Test another portion (after acidifying with II N 03) with molybdic solution for PHOSPrHOIC ACID and AKSENIC ACID (~ 142, 10). If a yellow precipitate forms, test for arsenic acid with H,2 S, and remove it by the same means if present, separate silicic acid if present, and then test again for phosphoric acid. X'. Test another portion for FLUORINE (~ 146, 7). a. If the solution is vellow, CHROMIC ACID is present. To confirm, acidify a portion of the solution with acetic acid, and test with lead acetate. e. Acidify the remainder with H Cl, evaporate 154 to dryness, and treat the residue with It C1 and \water. If a residue is left which refuses to dissolve even in boiling water, this co11sists of SILICIC ACID. Test the H C1 solution now in the usual wav for those bases which, being soluble in caustic alkalies, may be present. b. Dissolve t/e residue left in 152 in II C1 (effer- 155 vescence indicates the presence of alkali-earth metalsa residue insoluble in 1I1 Cl would have to be examined according to ~ 130, 8, as it might be STANNIC OXIDE), and test the solution for the bases as directed in * Addition of K N 03 is useful even in the case of white powders, as it counteracts the injurious action of lead silicate, should any be present, upon the platinum crucible. In the case of black powders the proportion of K N 03 must be correspondingly increased, in order that carbon, if present, may be consumed as completely as possible, and that any chromic iron present may be more thoroughly decomposed.

Page  311 ~ 196.] INSOLUBLE SUBSTANCES. 311 ~ 183. (If much silicic acid has been found in 154, it is advisable to evaporate the solution of the residue to dryness, and to treat with H C1 and water, in order that the silicic acid remaining may also be removed as completely as possible.) 5. If you have found in 4 that the residue insoluble in 156 acids contains a silicate, treat a separate portion of it according to 157, to ascertain whether this silicate contains alkalies. 6. If a residue is still left undissolved upon treating the 157 residue left in 152 with I1 Cl (155), this may consist either of silicic acid which has separated, or of an undecomposed portion of barium sulphate; it may, however, also be calciuln fluoride, and if it is dark colored, chromic iron, as the last-named two compounds are only with difficulty decomposed by the method givenl in (152.) As to calciumn fluoride, it may be easily decomposed by H, S O. Chromic iron is best treated as follows: Fuse 12 parts of sodiuin disulphate and project 1 part of the finely powdered mineral into the crucible, stir often and keep up the heat for half an hour, first gently, then raisinll it till sulphuric oxide is no longer driven off. Add 6 parts of sodium carbonate, fuse, add gradually 6 parts of potassium nitrate, and after some time increase the heat, stirring diligently with a platinum wire. Finally allow to cool and boil with water. 7. If the residue insoluble in acids contained silver, you 158 have still to ascertain whether that metal was present in the original substance as chloride, bromide, iodide, &c., or whether it has been converted into chloride by the treatnment employed to effect the solution of the originlal substance. For that purpose treat a portion of thle original substance with boiling water until the soluble part is completely removed; then treat the residuary portion in the same way with dilute H N 0,, wash the uldissolved residue with water, and test a small sample of it for silver accordinlg to 147. If silver is present, proceed to ascertain the acid radical with which the metal is combined; this may easily be effected by boiling the remainder of tile residue with rather dilute solution of soda, filtering, altd testing the filtrate, after acidifying it, for ferro- and ferlicyanogen. Digest the washed residue now with finely grannlated zinc and water, with addition of some II,: S 0, and filter after the lapse of ten minutes. You may now at once test the filtrate for chlorine, bromine, iodine, and cyanogen; or you may first throw down the zinc with Na, C 0,, in order to obtain the acid radicals in combination with sodiurn.

Page  312 3192 ANALYSIS OF CYANIDES. [~ 197 SECTION II. PRACTICAL COURSE IN PARTICULAR CASES. I. ANALYSIS OF CYANIDES, FERROCYANIDES, &C., INSOLLTBLJE IN WATER, AND ALSO OF MIXED SUBSTANCES CONTAINING SUCH COMPOUNDS. ompare the Notes in Section III., p. 381. ~ 197. The analysis of ferrocyanides, ferricyanides, &c., by the 159 common method is often attended by the manifestation of such anomalous reactions as easily to Inislead the analyst. Moreover, acids often fail to effect the complete solution of these compounds. For these reasons it is advisable to analyze them, and mixtures containing them, by the followillg special method: 1. Treat the substance with water until the soluble parts are entirely removed, and boil the residue with strong solution of Na O 11; after a few minutes' ebullition add some Na2 C 03, and boil again for some time; filter, should a residue remain, and wash the latter. a. The residue, which is now free from cyanogen, 160 unless the substanlce contains Ag C N, is examined by the usual method, beginning at 35. b. The solution, which, if combinations of com- 161 pound cyanogen radicals (ferrocyanolen, cobalticyanogen, &c.), are presecnt, cotains these comlbined with alkali metals, may also contain other acids, which have been separated from their bases by boiling with NTa, C 0,! and lastly, also, such hydroxides as are soluble in caustic alkalies. Trea~t it as fbllows: a. Mix the alkaline fluid with H2 S to test for 162 metals of the fourth and fifth groups.* aa. 0o'e,;rnanent prec7)intate is formned. Absence of zinc and lead. Pass on to 163. bb. A permrlent preceitcate is formed. Add to the fluid a little yellow sodiumn sulphide, drop by drop, until the metals of the fourth and fifth groups present in the alkaline solution are just * You must, of course, avoid adding solution of H2 S, or conducting the gas into the fluid, until the mixture smells of the reagent. i.e., until the Na O H has been converted into Na S H, since this might lead to the precipitation also of the alumina which may be present in the alkaline solution, and even of sulphides of metals of the sixth group-a precipitation which is not intended here.

Page  313 . 197.] ANALYSIS OF CYANIDES. 313 thrown down, heat moderately, filter, and treat the filtrate as dil ected 163. Dissolve the washed precipitate in IH N 0, which may leave Hg S behind, and examine the solution for copper and lead, as well as for zinc and other metals of the fourth group, which may, in the same way as copper, have passed into the alkaline solution, by the agency of organic matters., To test the alkaline fluid, which now also contains 168 soine sulphide of an alkali metal, for mercury (which may be present, as its sulphide is soluble in sodiumn sulphide) and for metals of the sixth group, mix with a sufficient quantity of water, then with dilute ItI2 S 04 to acid reaction, and if the fluid does not smell strongly of HI2 S, add some more of the latter reagent. aa. No precipitate is formed. Absence of mercury and metals of the sixth group. Pass on to 164. bb. A precipitate is.formed. Filter, wash the precipitate, then examine it for mercury and the metals of the sixth group according to ~ 184. r. The fluid, acidified with II, S 04, may still con- 164 tain those metals which form compound cyanogen radicals (iroll, cobalt, Inanganese, chroumium), and, besides these, also alutniiulln. You have to test it also for cyanogen, ferrocyanogen, cobalticvanogen, &e., and for other acids. Divide it therefore into two parts, aa ald bb. an. Treat it according to ~ 192, or, as the case may be, ~ 193, to detect the acids.* (Cobalticyanogen may be recognized by giving a greenish precipitate with Ni salts and white precipitates with Zn anld Mn salts, which may be proved to contain cobalt by means of the borax bead.) bb. Evaporate it nearly to dryness, add some pure concentrated 1H, S 04 and heat till the free acid is for the most part expelled. Dissolve the residue in water, and test the solution for iron, mangainese, cobalt, aluminium, and chromium, according to ~ 187. 2. Decompose another portion by continued heating with pure concentrated H2 S 04,, remove all other bases and then test for alkali-lnetak. * It must be remembered that ferricyanogen may have been converted into ferrocyanogen thus' —K0 Fe2 (C Nj12 + 2 (Fe C12) + 2 (K 0 H) + H2 O-= 2 [K4 Fe (C N) 6] + Feo20 + 4 H C1.

Page  314 314 ANALYSIS OF SILICATES. [~ 198. II. ANALYSIS OF SILICATES. ~ 198. Whether the substance is a silicate or contains one, is 165 ascertained by the prelimlinary blowpipe examination with iNa P 0); since in the process of fusion the bases dissolve, whilst the separated silicic oxide floats about in the liquid bead as a translucent swollen mass (, 150, 8). The analysis of silicates differs from the usual course in the preparatory treatment required to separate the silicic acid from the bases, and to obtain the latter in solution. The silicates are divided into two classes, which require different methods of aialysis; viz., (1) silicates readily decomposable by acids (II C1, H N O38, I1 S 04), and (2) silicates which are not, or only with difficulty, decomposed by acids. Ma.lny rocks consist of mixtures of the two classes. To ascertain to which class a givenl silicate belongs, reduce it to a very fine powder, and digest a portion with H Cl at a temperature near the boiling-poillt. If this fails to decompose it, try another portion by long-continued heating with a mixture of three parts of concentrated I., S 04 and 1 part of water. If this also fails, the silicate belongs to the second class. Whether decomposition has been effected by the acid or not, may generally be learned from external imldications, as a colored solution forms almnost invariably, and the separated gelatinous, flocculent, or finelrpnlverulent silicic acid takes the place of the original heavy powder, which grated under the glass rod with which it was stirred. But whether the decomposition is complete, or extends only to one of the components of the rock, may be ascertained by boiling the separated silicic acid, after washing, in a solution of Na.2 C O. If perfect solution ensues, complete decomposition has been effected; if not the decomposition is only partial. The results of these preliminary tests will show whether the silicate should be examined according to ~ 199, or ~ 200, or ~ 201. Before proceeding further, examine a portion of the substance also for water, by heating it in a glass tube. If the substance contains hygroscopic moisture,* it must first be dried at 1000 for a long time. Apply a gentle heat at first, but ultimately an intense heat; you may also conveniently combine with this a preliminary examination for ftuorine (~ 146, 8). * [In some cases it is impossible to distinguish between constitutional and hygroscopic water; in other cases, combined water certainly escapes at 100~., -EID.I

Page  315 ~ 199.] SILICATES DECOMPOSED BY ACIDS. 315 A. SILICATES DECOMPOSABLE BY ACIDS. ~ 199. a. Silicates decomposable by hyvdrochloric or nitric acid.* 1. Digest the finely pulverized silicate with H C1 or H N 03 166 at a temperature near the boiling point, until complete decomposition is effected, filter off a small portion of the fluid, evaporate the remainder, together with the silicic acid suspended thereill, to dryness, heat the residue at 100~ (scarcely above), with constant stirring, until hardly any more acid fumes escape, allow to cool, moisten with HI C1, or, as the case may be, with I-I X O, afterwards add a little water, and heat gently for some time. This operation effects the separation of the SILICIC ACID, and the solution of the bases in the formn of chlorides or nitrates. Filter, wash the residue thoroughly, and examine the solution by the usual method, beginning at ~ 182, II. or III. The residual silicic acid must always be tested, as it cannot under any circumstances be considered pure. It frequently contains Ti, occasionally Ba and possibly Sr as sulphates and often a little Al. It is best tested by repeated heating in a platinum dish with tI F and H, S 0,, unlltil all the silicic acid is removed in form of Si F4. The residue is ignited, fused with sodium disulphate, and then treated with cold water. If anything insoluble now remains, it is filtered off and tested according to ~ 99 fol BARIUM and STRONTIUM SULPIIATES. The dilute aqueous solution is' tested by long boiling for TITANIUM t (~ 104, 9), alld the filtrate therefrom is tested by N -I, 0 I for ALUMINIUM. (Should there be any chance of the presence of Ag C1 in the silicic acid, digest a portion with N 11I 0 II, filter, and examine the filtrate by supersaturation. with I1 N 03.) 2. As in silicates, and more particularly in those decom- 167 * H N 03 is preferable to H Cl where Ag or Pb compounds are present. t If the silicic acid has been separated by evaporation on the water-bath, only a small part of the titanic acid will be found remaining with it, the rest will pass into the H Cl solution, and will be precipitated by N H4 O H in conjunction with Fe and Al. To find this, fuse the dried precipitate with sodiumn disulphate, dissolve the fusion in cold water, filter if necessary, dilute considerably, pass H2 S until all iron is reduced to the ferrous state, and (without filtering off the S) keep the fluid boiling for half an hour with a constant current of C 02 passing through it. Filter, wash, and ignite; the S will burn off, titanic oxide will remain. Should it still contain Fe, redissolve it by fusion with sodium disulphate and treatment with cold water, and precipitate bj boiling with sodium thiosulphate.

Page  316 316 SILICATES DECO.MPOSED BY ACIDS. [~ 199 posed by H C1, there are often founlld other acids, as well as mnetalloids, the following instructions must be attended to, t'lat none of these substances may be overlooked: — a. CARBONATES are detected ill treating with HI CI. SULPHIDEs are often detected in the same operationl, otherwise they may be tested for accordilg to ~ 156, 8. O/. If the separated silicic acid is black, and turns white upon ignition in the air, this indicates the presence of cA.RBON or of ORGANIC SUBSTANCES. In presence of the latter, the silicates emit an empyreumatic odor upon being heated in the glass tube.?y. Test the portion of the 1- Cl solution filtered off before evaporating, for SULPHURIC ACID, PHOSPHORIC ACID oand ARSENIC ACID-for sulphurie acid by diluting and adding B3a Cl; for arsenlic acid by heating the solution to 70~ alld conldtlctinlg I-I S ifito it; for phosphoric acid by addinllg I N 0,, evaporating to dryness on the water-bath, warmillg the residue with H N 0,, filtering, and addillg molybdic solution. Where arsenic is found, phosphoric acid is tested for in the fluid filtered from As2 S,. &. BORIC ACID is best detected by fusing a portion 168 of the substance in a platinum spoon with Na2 C O,, boiling the fused mass with water, and testing the solution by ~ 144, 6. e. With many silicates, boiling with water is sufficient to dissolve the CHLORIDES present, which may then be readily detected in the filtrate by Ag N 0,; the safest way, however, is to dissolve the mineral in dilute II N O,, and test the solution with gN 0,.. FLUORIDES, which often occur in silicates in greater or smaller proportion, may be detected by ~ 146, 6. b. Silicates which resist the action of hydrochloric acid, but are decomvposed by concentrated sulphutric acid. Heat the finely pulverized mineral with a mixture of 169 3 parts of concentrated pure I,2 S O0 and 1 part of water (best in a platinum dish), finally drive off the greater portion of the acid, boil the residue with HI Cl, dilute, filter, and treat the filtrate as directed ~ 183, and the residue, which, besides the separated silicic acid, may contain also sulphates of the alkali-earth metals, &c., as directed ~ 199, 1. If you wish to examine silicates of this class for acids and acid radicals, treat a separate portion of the substance according to ~ 200.

Page  317 ~ 200.J SILICATES NOT DECOMPOSED BY ACIDS. 317 B. SILICATES WHICH ARE NOT DECOMPOSED BY ACIDS.* ~ 200. As the silicates of this class are most conveniently de-1 7C composed by fusion with Na, C 0,, the portion so treated cannot, of course, be examined for alkali-metals. The analytical process is therefore divided into two principal parts, a portion of the mineral being examined for the silicic acid and the bases, with the exception of the alkalies, whilst another portion is specially examined for the latter. The Iineral mlist also be examined for other acids. 1. -Detection of the silicic acid and the bases, with the exccption of the alkalies. Reduce the mineral to a very fine powder, mix this with 171 4 parts of Na, C O0, and heat the mixture in a platinum crucible until the mass is in a state of calm fusion. Place the red-hot crucible on a thick cold iron plate, and let it cool there: this will generally enable you to remove the fused cake from the crucible, in which case break the mass to pieces, and keep a portion for the examinIation for acids. Putt the remaillder, or, if the mass still adheres to the crucible, the latter with its contents into a porcelain dish, pour on water, add H Cl, and warln it until the mass is dissolved, with the exception of the silicic acid. Evaporate to dryness, and treat the residue as directed, 166. 2. Detection of the alkcalies. To effect this the silicate must be decomposed by means 172 of a substance free from alkalies. The following methods are the most suitable: [a. PECOMPOSITION BY MEANS OF CALCIUM CARBONATE AND AMMONIUM CHLORIDE. Mix 1 part of the pulverized substance with 6 parts of precipitated Ca C 03, and a part of pulverized N 114 C1, place in a platinum crucible and heat to bright redness for 30 to 40 minutes. The crucible, with its contents (which should be in a coherent, sintered, but not thoroughly fused condition), is placed in a beaker, covered with water and heated to near the boiling point for half an hour. The whole is then brought upon a filter, the filtrate, containing the alkali* It will be understood, from what has been stated ~ 198, that these are not deoomposed by heating with H Cl and H, S O, in open vessels; but by heating them, reduced to a fine powder, in a sealed glass tube, with a mixture of 3 parts of concentrated H, S 04 and 1 part of water, or with H Cl to 200 — 210~, most of them are decomposed, and may accordingly be analyzed also in this manner (AL. MITSCHERLICH).

Page  318 318 SILICATES NOT DECOMPOSED BY ACIDS. [~ 200 metal and calcium hydroxides and calcium chloride, is treated with a little N H, 0 1H and with (N H14) C 03 in slight excess, and heated to boiling, filtered, and the filtrate evaporated to dryness and gently ignited to expel ammonium salts. The residue is dissolved in a little water, one or tivo drops of (N II4). C 03, and a drop of (N4)2, C, 04 added, the mixture is heated, filtered, the filtrate is evaporated to dryness, ignited, and the residual alkali-metal chlorides examined according to ~ 190. (J. L. Smith.)-EDITOR.] b. DECOMPOSITION WITH A FLUORIDE. Mix the finely 173 powdered substance with 5 parts of powdered fluol'spar, and then (in a platinum crucible) with enough concentrated I43 S O0 to make a thin paste, warm gently for some time (where the fumes will pass off in a good draught), and finally heat more strongly until the excess of H, SO4 is expelled. Boil the residue with water, add Ba C1, cautiously as long as it produces a precipitate, then Ba (O H), to alkaline reaction, boil,.filter, treat with (N HI)2 C 03 and N H,40 as long as anything is precipitated, filter, evaporate, ignite, and proceed further as directed, ~ 190. 3. Examination for fluorine, chlorine, boric acid, phosphoric acid, arsenic acid, and su7t1huric acid. Use for this purpose the portion of the fused mass re- 174 served in 171, or, if necessary, fuse a separate portion of the finely pulverized substance with 4 parts of pure Na, CO 3 until the mass flows calmly; boil the fused mass with water, filter the solution, which contains all the fluorine as Na F, all the chlorine as Na C1, all the boric acid as borate, all the sulphuric acid as sulphate, all the arsenic acid as arsenate, and at least part of the phosphoric acid as phosphate of sodium, and treat as follows: a. Acidify a small portion with H N 03, and test for CHLORINE with Ag N 03. b. Test another portion for BORIC ACID as directed ~ 144, 6. c. To detect FLUORINE, treat a third portion as directed ~ 146, 7. d. Acidify the remainder with II Cl and test a small portion with Ba C1, for SULPHURIC ACID; heat the remainder to 70~, and test with H, S for ARSENIC ACID. If no precipitate forms, evaporate the fluid, if a precipitate forms, the filtrate, with addition of H N O0 to dryness, treat the residue with tI N 0, and water, and examine the solution for PHOSPHoRIC ACID with magnesium mixture, or with molybdic solution (~ 142).

Page  319 ~} 201, 202.] MIXED SILICATES. 319 C. SILICATES W'HICH ARE PAI'T.IALLY DECOMPOSED BY ACIDS. ~ 201. Most rocks are mixtures of several silicates, of which 17E some are often dec(omposable by acids, others not. If such substances were analyzed by the same method as the absolutely insoluble silicates, the analyst would indeed detect all the elements present, but the analysis would afford no satisfactory insight into the actual composition of the mineral. It is therefore advisable to examine separately those constituents which show a different deportment with acids. For this purpose digest the very finely pulverized substance for some time with II C1 at a gentle heat, filter off a small portion of the solution, evaporate the relnainder with the residue to dryness, heat the residue at 100~ (scarcely above), with stirring, until no more, or very little acid vapor is evolved, allow to cool, moisten with HI C1, heat gently with water, and filter. The filtrate contains the bases of that part of the mixed mineral which has been decomposed by H Cl; examine this as directed 166. Examine the portion first filtered off as directed 167, y. Test portions of the original substance for other acids as directed 167 a and, and 168. Boil the residue-which, besides the silicic acid separated from the decomnposed portion of the silicate. contains that part of the mixed mineral which has resisted the action of H Clwith an excess of solution of Na, C O0, filter hot, and wash, first with hot solution of Na, CO, finally with boiling water. Treat the residuary undecomposed part of the mineral, thus freed from the admixed separated silicic acid, according to ~ 200. Acidify the allkaline filtrate with H C1, evaporate to dryness, treat with H C1 and water, filter off the silicic acid, render the filtrate alkaline with ammonia, and warm; the precipitate thus formed (if any) is to be treated with the separated silicic acid according to 166, in order to detect titanic acid. In cases is of no interest to effect the separation of the silicic acid of the part decomposed by acids, you may omit the troublesome operation with Na, C 03, and may proceed at once to the decomposition of the residue. III. ANALYSIS OF NATURAL WATERS. ~ 202. In the examination of natural waters the analytical pro- 176 cess is simplified by the circumstance that we know from

Page  320 820 POTABLE WATERS. [_ 203 experience what substances are usually present. Now, although a quantitative analysis alone can properly inform us of the true character of a water, since the differences be tween waters are principally caused by the different proportions of the constituents; still a qualitative analy)sis may render very good service, especially if the analyst notes whether a reagent produces a faint or a distinctly marked turbidity, a slight or a copious precipitate; since these circumstances will enable him to make an approximate estimate of the relative proportions of the constituents. I separate here the analysis of ordinary drinking waters from that of mineral waters, in which latter we may also include sea-water; for, although no well-defined line can be drawn between the two classes, still the analytical examination of the former is necessarily by far the simpler, as the nmnber of substances to be looked for is much more limited. A. ANALYSIS OF POTABLE WATERS (SPRING-WATER, WELL-WATER, IRIVER-WATER, &C.) ~ 203. We know from experience that the substances to be had 177 regard to in the analysis of such waters are the following: c:. METALS: Potassium, sodilll, ammonium, calcium, magnesiini, iron. b. Acmns, &c.: Sulphuric acid, phosphoric acid, silicic acid, carbonic acid, nitric acid, nitrous acid, chlorine. C. ORGANIC MATTER. d. MECHIANICALLY SUSPENDED SUBSTANCES: Clay, &c. Potable waters contain indeed also other constituents besides those enumerated here, as may be inferred from the origin and formation of springs, &c., and as has, moreover, been fully established by the results of analytical investigations; but the quantity of such constituents is so trifling that they commonly escape detection, unless many pounids of the water are subjected to the analytical process. I therefore omit here the mode of their detection (see ~ 204). 1. Boil 1,000 to 2,000 grin. of the carefully collected 178 * CHATIN (Joumn. de Pharm. et de Chim. (3), 27, 418) found iodine in all fresh-water plants, but not in land plants, a proof that the water of rivers, brooks, ponds, &*c., contains traces, even though extremely minute, of metallic iodates or iodides. According to MARCHAND (Comp. Rend., 31, 495), all natural waters contain iodine, bromine, and lithium. VAN ANKUM has demonstrated the presence of iodine in almost all the potable waters of Holland. And it may be affirmed with the same certainty that all, or at all events most, natural waters contain compounds of strontium, barium, fluorine, &c.

Page  321 ~ 203.] POTABLE WATERS. 321 water in a porcelain dish to one-half. (Glass vessels are to be avoided, as boiling water attacks them much more than porcelain.) This generally produces a precipitate. Pass the fluid through a perfectly clean filter (free from iron and lime), wash the precipitate well, after having removed the filtrate, then examine both as follows: a. Examination of the precipoitate. The precipitate contains those constituents of the 179 water which were only kept in solution through the agency of free carbonic acid, or, as the case may be, in the form of bicarbonates, viz., calcium carbonate, magnesium carbonate, ferric hydroxide (which precipitates upon boiling a solution containing ferrous bicarbonate), also ferric silicate, and in presence of phosphoric acid, ferric phosphate; calcium phosphate; also silicicacid, sometimes calcium sulphate (if that substance is present in large proportion) and clay which was mechanically suspended in the water. Dissolve the precipitate on the filter in the least possible quantity of dilute II Cl (effervescence indicates CARBONIC ACID), and treat separate portions of the solution as follows: a. Add K C N S, or KI Fe (C N), drop by drop, to test for IRON. 3. Boil, add N HIT O I, filter if necessary, mix 180 the filtrate with excess of (N II,4) C2 04, and let the mixture stand for some time in a warm place. A white precipitate indicates cALCIUM (in the form of carbonate, or also in that of sulphate if sulphuric acid is detected in y). Filter, mnix the filtrate again with N H, O 11, add some Na2 H P 04, stir with a glass rod, and let the mixture stand for twelve hours. A white crystalline precipitate, which is often visible only on the sides of the vessel when the fluid is poured out, indicates MAGNESIUM (as carbonate. 7y. Add Ba Cl,, and let the mixture stand for twelve hours in a warm place. A precipitate indicates SULPHURTC ACID. If very small it is best seen by cautiously decanting the supernatant clear fluid and shaking the small remaining quantity about in the glass. 8. Evaporate with addition of H N O, to dry- 181 ness, treat the residue with H N 0, and water, filter off any sILICIa ACID, and test the filtrate for rHosPHORIC ACID with molybdic solution (~ 142, 10), or with sodiumn acetate and Fe C016 (~ 142, 9). b. Examination of the filtrate. a. Mix a portion with a little H Cl and Ba C1,. 182 21

Page  322 322 POTABLE WATERS. [~ 203. A white precipitate, which makes its appearance at once, or perhaps only after standing some time, indicates SULPHuRIC ACID.,8. Mix a portion with H N 03 and add Ag N O0. A white precipitate or turbidity indicates CHLORINE. y. Test a portion for PHOSPORIC ACID, by evaporating with H N 0,, taking up with the same and proceeding as inll 181. 8. Evaporate a large portion until highly concentrated, and test the reaction of the fluid. If it is alkaline, if a drop of the concentrated clear solution effervesces when mixed on a watch-glass with a drop of acid, and if calcium carbonate precipitates on the cautious addition of calcium chloride to the alkaline fluid, then CARBONATE OF AN ALKALI-METAL is present. Should this be the case, evaporate the fluid to perfect dryness, boil the residue with alcohol, filter, evaporate the solution to dryness, dissolve the residue in a little water, and test the solution for NITRIC aCID, as directed ~ 159, 7, 8 or 9.e e. Mix the remainder of the filtrate with N I-I, Cl1, N 14 0 H, and excess of (N IH,) C2 04, and let the mixture stand some time. A precipitate indicates CALCIUM. Filter, and — aa. Test a small portion with N I-40 I and Na. H P 04 for MAGNESIUM. 6b. Evaporate the remainder to dryness, ignite, remove the magnesium which may be present (112), and test for POTASSIUM and soDIuMr, according to ~ 190. 2 Acidifv a tolerably large portion of the filtered water 183 with pure 11 Cl, and evaporate nearly to dryness; divide the residue into two parts, a and b. a. Test with Ca (O HI) for AMMONIUM (~ 91, 3).t b. Evaporate to dryness, moisten the residue with I-I C1, add water, warm, and filter if a residue remains. The residue may consist of SILICIC ACID and, if the water has not been filtered quite clear, also Of CLAY; these two substances may be separated by boiling with solution of Na2 C O3. The residue is often dark-colored from the presence of organic substances; but it becomes perfectly white upon ignition. * The nitric acid may often be found without trouble, by evaporating the water to a small residue, and testing this at once for it. t In clear water ammonia may be tested for quite satisfactorily without evaporating either by means of Hg C12 with K2 C 03 or by NESSLER'S test (~ 92).

Page  323 ~ 203.] POTABLE WAVTERS. 323 3. [Mix another portion of the water, freshly taklen, with 184 lime-water. If a precipitate is produced, FIREE CARBONIC ACID o1' BICARBONATES are present. If free carbonic acid is present, no permanent precipitate is obtained when a laroge portion of the water is mixed with only a small amount of lime-water, since in that case soluble calcium bicarbonate is formed. 4. Test for NITROUS ACID,* by mixing a portion of the 185 water with some K I and starch-paste (made of 1 part of the purest K I, 20 parts of starch, and 500 parts of water) anld pure dilute I11 S 04, and observe whether a blue coloration makes its appearance, either at once or at least after a fewv minutes (~ 158, 1). The reagents should be tested by making a counter-experiment with pure water. 5. ORGANIC MATTER is detected by the blackening which 186 occurs when a portion of the water is evaporated to dryness and gently ignited. If this experiment is to give conclusive results, the evaporation as well as the ignlition must be conducted in a flask or retort. 6. FETID SUBTrANCES (decayingl organic matter) are detected best by filling a bottle two-thirds with the water, covering it with the hand, shaking, and smelling. If the smell is of II2S, proceed as directed ~ 205, 3. Whether there are other smelling organic matters present besides, may be ascertained by adding a little Cu S 0, to the water, before smelling it. 7. If you wish to examine the MATTERS MEICHANICALLY 187 SUSPENIDED in a water (in muddy riv-er-water, for instance), fill a large glass bottle with the water, cork securely, and let it stand at rest for several days, until the suspellded matter has subsided; remove now the clear fluid with the aid of a syphon, filter the remainder, and examine the sedimnent remnaining on tile filter. As this sediment may consist of the finest dust of various minerals, treat it first with dilute 11 Cl, then examine the part ilsoluble in that menstruum as directed ~ 198. 8. As LEAD may be present, arising from leaden pipes, treat a large quantity with I12 S, allow to stand for some time, and should a. black precipitate form, examine this as directed ~ 186. To detect very minute traces of lead, acidify 6 or 8 litres of the water'with acetic acid, add a little ammonium acetate, to prevent the lead precipitating as sulphate, evaporate to a small residue, filter, conduct 112 S into the liltrate, and examine a black precipitate which may form by ~ 186. * SCHBBErI found this acid in rain and snow water.

Page  324 324 MINERAL WATERS. [~~ 204, 205. B..ANALYSIS OF MINERAL WATERS. ~ 204. The analysis of mineral waters embraces a larger num- 188 ber of constituents than that of potable water. The following are the principal of the additional bodies to be looked for:CESIUM, RUBIDIUM, THALLIUM, LITHIUM, BARIUM, STRONTIUM, ALUMINIUM, MANGANESE, BROMINE, IODINE, FLUORINE, BORIC ACID, HYDROSULPHURIC ACID (thiosulph1nric or hyposulphurous acid), CRENIC ACID and APOCRENIC ACID (formic acid, propionic acid, &c., nitrogen gas, oxygen gas, methane).* The analyst has moreover to examine the muddy ochreous or hard sinter-deposits of the spring, or also the residue left npon the evaporation of very large quantities of water, for ARSENIC, ANTIMONY, COPPER, LEAD, COBALT, NICKEL) and other heavy metals. The greatest care is required in this examination, to ascertain whether these metals come really from the water, and do not perhaps proceed from pipes, stopcocks, &c. The absolute purity of the reagents employed in these delicate investigations must also be ascertained with the greatest care. 1. EXAMINATION OF THE WATER. a. OPERATIONS AT THE SPRING. ~ 205. 1. Filter the water, if not perfectly clear, through 189 washed filter paper, into large bottles with glass stoppers. The sediment remaining on the filter, which possibly contains, besides the flocculent matter suspended in the water also those constituents which separate at once upon coming in contact with the air (ferric hydroxide and ferric phosphate, silicate, and arsenate), is taken to the laboratory, to be examined afterwards according to ~ 207. 2. The presence of FREE CARBONIC ACID iS usually suffi- 190 ciently evident to the eye. However, to convince yourself by positive reactions, test the water with fresh-prepared solution of litmus, and with lime-water. If carbonic rcid is present, the former acquires a wine-red color; the * Respecting the constituents in brackets, I refer to the corresponding chapter in my Quantitative Analysis, as the detection of these matters generally comprises also their quantitative estimation.

Page  325 ~ 206.] MINERAL WATERS. 325 latter produces turbidity, which must disappear again upon addition of the mineral water in excess. 3. Free HYDROSULPHURIC ACID is most readily detected 191 by the smell. For this purpose half fill a bottle with the mineral water, cover with the hand, shake, and smell the bottle. In this way distinct traces of hydrosulphuric acid are often found which would escape detection by reagents. However, if you wish to have some visible reactions, fill a large white bottle with the water, add a few drops of solution of lead acetate in soda, place the bottle on a white surface, and look in at the top, to see whether the water acquires a brownish color or deposits a blackish precipitate;-or half fill a large bottle with water, and close with a cork to which is attached a slip of paper previously saturated with solution of lead acetate and then moistened with ammonium carbonate; shake the bottle gently from time to time, and observe whether the paper acquires a brownish tint in the course of a few hours. If the addition of the lead acetate has produced a brown color, or precipitate, whilst the test with the paper gives no result, this indicates that the water contains an alkaline sulphide, but no free hydrosulphuric acid. 4. 3Mix a wineglassful of the water with some tannic 192 acid, another wineglassful with some gallic acid. If the former imparts a red-violet, the latter a blue-violet color, FERROUS COMPOUNDS are present. Instead of the two acids, you may employ infusion of galls, whiel contains theln both. Tihe colorations make their appearance only after some time, and increase in intensity from the top-where the air acts on the fluid-towards the bottom of the vessel. 5. Test for NITROUS ACID aiid FETID ORGA.NIC SUBSTANCES 193 according to 185 and 186. If the water contains hydrosulphuric acid, remove it before testing for nitrous acid by very cautious addition of silver sulphate (no silver salt must under any circumstances remain in the solution). b. OPERATIONS IN THE LABORATORY. ~ 206. As it is always desirable to obtain, evenan the qualitative examination, some information as to tihe proportions in which the several constituents are present, it is advisable to analyze a comparatively small portion for the principal constituents, and to ascertain, as far as may be practicable, the relative proportions in which these constituents exist, and thus to determine the character of the water; then to examine a far larger portion for the constituents which are

Page  326 2~3626 MINERAL WATERS. [~ 206. present in sinaL quantity; and finally a very large portion ),f the sinter for those constituents which are present merely in traces. For this purpose proceed as follows:1. EXAMINATION FOR THOSE CONSTITUENTS WHICH ARE PRESENT IN LARGE QUANTITIES. a. Boil about 3 lbs. of the clear water, or of the 194 swater filtered at the spring, in a porcelain dish (a flask is less suitable) for one hour, taking care, however, to add from time to time some distilled water, that the quantity of liquid may remlain undiininished, and thus that only those salts may be separated which owe their solution to the presence of carbonic acid. Filter and examine the precipitate and the filtrate as directed ~ 203. b. Test for AMMONIUM, SILICIC ACID, ORGANIC MATTERS, &c., by the methods given in ~ 203. 2. EXAMIINATION FOR THOSE FIXED CONSTITUENTS WHICH ARE PRESENT IN MINU'TE QUANTI'TIES. Evaporate a large quantity (at least 20 lbs.) of the water 195 in a silver or porcelain dish to dryness; conduct this operation with the most scrupulous cleanliness in a place as free as possible from dust. If the water containls no alkali earbonate, add pure K2 C 0, in slight excess. The process,f evapo'ration nay b)e conducted at first over a gas-lamp, b)nt ultimately the sand-bath must be employed. Heat the dry mass to very faint redness; if in a silver dish, you imay at once proceed to ignite it; but if you have it in a polrcelain dish, first transfer it to a silver or platinum -vessel before proceeding to ignition. If the mass turns black in this process, ORGANIC MATTERS may be assumed to be present.* 3Mix the residue thoroughly, and divide it into 3 portions, a and b being each about a quarter, and c one-half. a. EXAMINATr ON FOR PHOSPHORIC ACID. -Warm the portion a with water, add pure H N} 0, 196 in sufficient excess, evaporate on the water-bath to dryness, warm the residue with II N 03, dilute slightly, filter through paper washed with HI Cl. and test with molybdic solution (~ 142, 10). * This inference is, however, correct only if the water has been effectually I)rotected from dust during evaporation; if this has not been the case, and you yet wish to ascertain beyond doubt whether organic matters are present, evaporate a separate portion of the water in a retort. If you find organic matter, and wish to know whether it consists of crenic acid or of apocrenic acid, treat a portion of the residue as directed ~ 207, 3.

Page  327 206.1 MINERAL WATERS. 327 Z. EXAMINATION FOR FLUORINE. Heat the portion b with water, add Ca C12 as long- as 197 a precipitate continues to form, let deposit and collect the precipitate, which consists chiefly of (alcium and magnesium carbonates, on a filter. Wash, dry, ignite, treat with water in a small dish, add acetic acid in slight excess, evaporate on the water-bath to dryness, keeping the dish on the bath until all smell of acetic acid has disappeared, add water, heat, filter off the solution of the acetates of the alkali-earth metals, wash, dry or ignite the residue, and test it as directed ~ 146, 5. C. EXAMINATION FOR THE RExMAINING FIXED CONSTITUENTS PRESENT IN MINUTE QUANTITIES. Boil the portion c repeatedly with water, filter, and 198 wash the undissolved residue with boiling water. You have now a residue (a), and a solution (p). a. The r'esicdue consists chicfly of calcium carbonate, magnesium carbonate, silicic acid, and-in the case of chlalybeate springs-ferric hydroxide. But it may contain also minute quantities of BARIUMI, STRONTIUM, ALUMINIUM, MANGANESE, and TITANIUM, and must accordingly be examined for these substan ces. Treat it with water in a platinum or porcelain dish, add 1I Cl to slightly acid reaction, then 4 or 5 drops of dilute HI1 S 0(, evaporate oni the waterbath to dryness, moisten with a small quantity of HI Cl, then add water, warm gently, filter, and wash. aa. EXAMINATION OF TIIE RESIDUE INSOLUBLE IN 199 HYDROCIrLORIC ACID. Tlhis will mostly consist of silicic acid; hbut it may contain also sulphates of the alkali-earth metals, titanic acid, and carbon. Heat it in a platinuml dish repeatedly with H IIF or N H14 F with addition of H12 S 4O till all silicic acid is expelled. Finally evaporate to dryness, fuse the residue (if any) with potassium disulphate, treat the fusion with cold water, filter and test the solution for TITANIC ACID by protracted boiling. If there was a residue on treating the fusion with water, wash it and incinerate the filter. When a spectroscope is at disposal, take up the ash on the loop of a platinum wire, expose for some time to the reducing flame, moisten with H C1, and examine for BARIUM. Strontium will not be found here except perhaps in traces. When a spectroscope is not at hand, set aside the ash for subsequent examination. bb. EXAMINATION OF THE HYDROCIILORIC ACID SO- 200 LUTION. Mix in a flask with pure N 11H C1, add

Page  328 83Y MINERAL WATERS. [~ 206 NHI 40 11 until the fluid is just alkaline, then (NI-4), S free from N II, 0 H; close the flask, filled to the neck, and let it stand for 24 hours in a moderately warm place. If a precipitate has formed at the enld of that tilne, filter off, dissolve ill II C1, boil, add K O II (~ 34, c) in excess, boil again, filter, and test the jitrsate fol ALIAT1INIuMr, by acidifying with 1 C1, and heating with N 1t C I0;* divide the residue into two parts, test one for MANGANESE with Na, C 03 before the blowpipe, the other for IRON by dissolving in H Cl and adding K C N S or KI4 Fe (C N),. The filtrate from the ainmonium sulphide precipitate may contain traces of barium and will contain all or nearly all the strontium. Add to it (N H4)2 C O3, filter after long standing, wash the precipitate dry, subject it to ENGELBACH'S process (end of ~ 99), and treat the aqueous extract of the ignited precipitate as follows: If a spectroscope is at command, evaporate it to dryness with -I C1 and examine the residue in the instruient. If a spectroscope is not at command evaporate it nearly to dryness with (N H,), S O, boil with a saturated solution of (N 114), S 04, filter, wash the precipitate, dry, incinerate, add the residue, set aside in 199, fuse with Na, C 03, treat with water, wash, dissolve the residue in H C1, and test the solution according to ~ 99. 3. The alkaline solution contains the salts of the 201 alkali lnetals and usually also magnesium and traces of calciumn. You have to examine it now for NITRIC ACID,t BORIC ACID, IODINE, BROMINE and LITIIIUM. Evaporate -mitil very concentrated, let it cool, and place the dish in a slanting position, that the slnall quantity of liquid may separate from the saline mass; transfer a few drops of the concentrated solution to a watch-glass by means of a glass rod, just acidify with II C1, and test with turineric-paper for BORIc ACID. Evaporate the whole contents of the dish, with stirring, to perfect dryness, and divide the residuary powder into 2 portions, aa being about two-thirds, and bb one-third. * There is no use in testing for aluminium unless the evaporation has been effected in a platinum or silver dish. t The nitric acid originally present may have been destroyed by the ignition of the residue in 195 if the latter contained organic matter. If you have reason to fear that such has been the case, and you have not already found nitric acid in 194, examine a larger portion of non-ignited residue foi that acid, according to the directions of 202.

Page  329 ~ 206] MINERAL WATERS. 329 aa. EXAMINE THE LARGER PORTION FOR NITRIC 202 ACID, IODINE, and BROMINE. Put the powder into a flask, add alcohol of 90 per cent., boil in the water-bath, and filter hot; repeat the same operation a second and a third time. nMix the alcoholic extract with a few drops of potassa, distil almost all the spilit off, and allow to cool. If minute crystals separate these may consist of potassium nitrate; pour off the fluid, wash the crystals with some spirit, dissolve in a very little water, and test the solution for NiTRIC ACID, with indigo, or with brucin, or with potassium iodide, starch-paste and zinc (~ 159). Evaporate the alcoholic solution now to dryness. If you have iot yet found -nitric acid, dissolve a small portion of the residue in a very little water, and examine the solution for that acid. Treat the remainider or, as the case may be, the whole of the residue three times with warm alcohol, filter, evaporate the filtrate to dryness with addition of a drop of KO I0, dissolve the residue in a very little water, acidify slightly with H, S 04, add some pule C S,, and test for IODINE* with K N 02, or a drop of solution of N2 04 in H2 S 04. After having carefullly observed the reaction, test the same fluid for BROMINE with C1 water according to ~ 157. bb. EXAMINE THE SMALLER PORTION FOR LITHIUM. 203 Warm the smaller portion of the residue (which, if lithium is present, must contain that metal as carbonate or phosphate) with water, add H C1 to distinctly acid reaction, evaporate neacrly to dryness, then mix with pure alcohol of 90 per cent., which will separate the greater portion of the lNa C1, and dissolve all the lithium-salt. Drive off the alcohol by evaporation, and, if you have a spectroscope, examine the residue with this for LITHIUM (~ 93, 3). If you have no spectroscope, dissolve the residue ill water and a few drops of II C1, add a little Fe2 C16, then N H, 0 H in slight excess, and a small quantity of (N H,)2 C2 04; let the mixture stand for some time, then filter off the fluid, which is now entirely free from phos* [According to SONSTADT (Chem. News, xxv., pp. 196, 231 and 241), seawater contains iodine in the form of iodates, which do not give the usual reactions for iodine until treated with reducing agents. To test for iodine in seawater, directly, Sonstadt advises to add to 50 or 100 c.c. of the water a few drops of pure H Cl, a bit of magnesium metal. and to shake up with a few drops of C S,. The latter acquires a purple tinge after a few minutes.-ED.]

Page  330 330 MINERAL WATERS. [2 0 7. phoric acid and calcium; evaporate the filtrate to dryness, and gently ignite until the N 114 salts are expelled; treat the residue with some C1 water (to remove I and Pr) and a few drops of H C1, and evaporate to dryness; add a little water and (to remove Mg) some finely divided Hg 0, evaporate to dryness, and gently ignite until the 1Hg O is just driven off; add a drop of I-I C1, treat with a mixture of absolute alcohol and anhydrous ether, filter, concentrate the filtrate by evaporation, and set fire to the alcohol. If it burns with a carmine flame, LITHIUM is present. By way of confirmation convert the lithium found into phosphate (~ 93, 3). 3. EXAMINATION FOR THOSE CONSTITUENTS WIIICH ARE PRESENT IN MOST MINUTE QUANTITIES. Evaporate 200 or 300 lbs. of the water in a large, per- 204 fectly clean iron vessel until the salts soluble in water begin to separate. If the mineral water contains no Na2C O3, add sufficient of that substance to render the fluid distinctly alkaline. After evaporation filter the solution off, wash the precipitate, without adding the washilgs to the first filtrate, and a. Examine the prec;pitate by the method given ~ 207 for silter deposits; b. Mix the solution with H C1, to acid reaction, heat, just precipitate the H, S 0, which may be piresent with BaCl2, filter, evaporate tle filtrate to dryness, digest the residue with alcohol of 90 per cent., and examine the solution for C:ESIUM and RUBIDIuM according to ~ 93, at the end. Treat the residue insoluble in alcohol as followss: Make a hot concentrated solution of it in water, add N4 H OII in excess, filter if necessary, add K I while still hot and allow to stand. If a precipitate forms test it for THALLIUM in the spectroscope. II. EXAMINATION OF THE SINTER DEPOSIT. ~ 207 1. Free the deposit from impurities, by picking, sifting, 205 elutriation, &c., and from the soluble salts adhering to it, by washing with water; digest a large quantity (about 200 grammnes) with water and H C1 (effervescence: CARBONIC acID) at a very moderate heat until the soluble part is com

Page  331 ~ 207.] S1NTER DEPOSIT. 331 pletely dissolved; dilute, let cool, filter, and wash the residue. a. Examination of the filtrate. a. Heat the larger portion to 70~, pass HI, S for 206 some time and also during the cooling. Allow to stand ill a moderately warmn place till the smell of the gas is almost gone, and filter. Wash and dry the precipitate, remove the greater 207 part of the free sulphur by digesting and washing with C S2, warm gently with yellow potassium sulphide, dilute, filter, wash with water containing potassium sulphide, and precipitate the filtrate and washings with H C1. Allow the precipitate to settle, filter it off, wash. dry, extract again with C S,, treat the residue (if any) together with the filter in a small porcelain dish with pure red fuming nitric acid, warm till the greater part of the acid is expelled, add excess of Na2 C 0, then a little Nra N O,, fuse, treat the fusion with cold water, filter, wash with diluted alcohol, and test the aqueous solution for ARSENIC by 65 and 66, the residue for ANTIMONY and TIN by dissolving in dilute H C1 and treating the solution with zinc free from lead in a platinum capsule (67). If a residue remained on treating the H1 S preci- 208 pitate with 12 S, wash, remove from the filter by a jet of water, boil with a snlall quantity of dilute H N 03, filter, wash and treat the contents of the filter first with H, S-in order not to miss lead-sulphate, which may possibly be present here —thell test theim for BARIUMI and STRON'TIUt according to 199. Alix the nitric acid solution with a little pure 112 S 04, evaporate to dryness on a water-bath and treat with water; if a residue, it consists of lead-sulphate. To make sure, filter it off, wash, and see if it turns black with I2 S. Test the filtrate from Pb S U4 with N HI 0 I, aild with K4 Fe (C NT)6 for COPPER Take a portion of the filtrate from the 112 S pre- 209 cipitate, evaporate it to dryness with excess of IH N, on a water-bath, treat with HT N 0 and water, filter, and test the solution for mPIosPHnoRI ACID with molybdic solution. Transfer the remainder of the filtrate from the H2 S precipitate to a flask, add N H14 C1, then N 114 0 H until the fluid is just alkaline, lastly (N H4)2 S free from N H, 0 11, fill the flask to the neck, close the mouth, allow to stand in a moderately warm place till the supernatallt fluid is yellow without a shade of green, filter,

Page  332 332 SINTEIt DEPOSIT. [~ 207 and wash with water contailling (NII4)2 S. Treat the precipitate with dilute HI Cl and proceed to test for COBALT, NICKEL, IRON, MANGANESE, ZINC, ALUMINIUM AND SILICA according to 96-104. To examine for TITANIC ACID throw down a part of this II Cl solution with N -14 O H and treat the precipitate according to 16. In the filtrate from the (N I-4)2 S precipitate throw down the CALCIUM and STRONTIUM and any BARIUM which mlay be present with (N II4), C O0 and (N H4), C2 04, and test the precipitate for the two last by ENGELBACH'S method (end of ~ 99). Finally test the filtrate from the calcium precipitate for tMAGNESIUM.,l. Mix a portion considerably diluted, with Ba Cl,, and allow it to standc 12 hours in a warm place. A white precipitate indicates SULPHURIC ACID. o. Exaczmination oqf thte residue. Consists of sand, silicic acid, clay and organic mat- 210 ter; also sulphur (if the water contained I-1, S), and sulphates of bariumn and strontimn. Boil with a solution of Na, C,3 and Na O II to dissolve the SILICIC ACID and sulphur, filter, and treat on the paper with dilute HI C1 to dissolve barium and strontium and leave the clay and sand. Test the -I C1 solution according to 200 fol BARIIuM and STRONTIrtM. 2. For FLUORINE, take a separate portion of the deposit, 211 mix with about half its weight of pure slacked-lime, (if Ca C 0O is not present in abundant quantity), ignite (blackening, indicates organic matter), add water, and then acetic acid in excess, evaporate till the excess of acid is expelled, and proceed as directed 197. 3. Boil the deposit for a considerable time with concen- 212 trated potassa, and filter. a. Acidify a portion of the filtrate with acetic acid, add N HII O H, allow to stand 12 hours, and then lilter off the precipitate of alumina and silicic acid, which usually forms; again add acetic acid in excess, and then solution of normal cupric acetate. If a brownlish precipitate is formed, this consists of cupric APOCRENATE. Mix the fluid filtered from the precipitate with (N H4), C 0,, until the green color has changed to blue, and warm. If a bluish-green precipitate is produced, this consists of cupric CRENATE. b. If you have detected As, use the remainder of the alkaline fluid to ascertain whether it existed as ARSENIOUS ACID or as ARSENIC ACID. (Compare ~ 134, 9).

Page  333 . 208.1 ANALYSIS OF SOILS. 333 IV. ANALYSIS OF SOILS. S 208. Soils must contain all the constituents which are found in the plants growing upon them, with the exception of those supplied by the atmosphere and the rain. When we find, therefore, a plant, the constituents of which are known, growing in a certain soil, the mere fact of its growing there gives us some insight into the composition of that soil, and may save us, to some extent, the trouble of a qualitative analysis. Viewed in this light, it would appear superfluous to make a qualitative analysis of soils still capable of producing plants; for it is well known that the ashes of plants contain almost invariably the same constituents, and the differences between them are caused principally by differences in the relative proportions ill which the several constituients are present. But if, in the qualitative analysis of a soil, regard is had also to the proportions of the constituents, and to the state in which they are present, an analvsis of the kind, if combined with an examination of the physical properties of the soil, and a mechanical separation of its parts,* may give useful results, enabling the analyst to judge sufficiently of the condition of the soil, to supersede the necessity of a quantitative analysis, which would require much time, and is a far more difficult task. As plants can only absorb substances capable of entering into a state of solution, it is a matter of especial importance, in the qualitative analysis of a soil, to know which constituents are soluble in water;t which require an acid for * With regard to the mechanical separation of the component parts of a soil,. and the examination of its physical properties and chemical condition, compare F. SCHULZE, Journ. f. prakt. Chemie, 47, 241; also FRESENIUS'S Quantitative Analysis, E. WOLFF, Zeitschr. f. anal. Chem. 3, 85, CAILDWELL'S Agricultural Chemical Analysis and especially E. W. HILGARD, Am. Jour. Sci. III. vi. (1873) p. 288. f It was formerly universally assumed that substances soluble in water, or in water containing carbonic acid, circulated freely in the soil so long as there existed agents for their solution; but since it has been discovered that arable soil possesses, like charcoal, the property of withdrawing from dilute solutions the bodies dissolved in them, this notion is exploded, and we now know that arable soil will retain with a certain force bodies otherwise soluble-from which we conclude that the aqueous extract of a soil cannot be expected to contain the whole of the substances present in that soil in a state immediately available for the plant. Neither can we expect to find these matters in the aqueous extract in the same proportion in which they are present in the soil, since the latter will readily give up to water those substances in regard to which its power of absorption has been satisfied, whilst it will more or less strongly retain others. But although, for this reason, the examination of the aqueous extract of a soil has no longer the same value as it was formerly considered to have, yet it is still useful to ascertain what substances a soil will actually give up to water. It is for this reason that I have retained the chapter on the preparation and examination of the aqueous extract.

Page  334 334 ANALYSIS OF SOILS. [~ 209. t;heir solution (in nature principally carbonic acid), and, finally, which are neither soluble in water, nor in acids, and are not, accordingly, in a position for the time being to afford nutriment to the plant. With regard to the insoluble substances, another interesting question to answer is whether they suffer disintegration readily, or slowly and with difficulty, or whether they altogether resist the action of disintegrating agencies; and also what are the products which they yield upon their disintegration.* In the analysis of soils, the constituents soluble in water, those soluble in acids, and the insoluble constituents, must be examined separately. The examination of the organic portion also demands a separate process. The analysis is therefore divided into the following four parts: 1. Preparation and Examination of the Aqueous Extract. ~ 209. About 1,000 grammes of the air-dried soil are used for the 213 preparation of the aqueous extract. To prepare this extract quite clear is a matter of some difficulty: in following the usual course, viz., digesting or boiling the earth with water, and filtering, the fine particles of clay are speedily found to impede the operation, by choking up the pores of the filter; they also almost invariably render the filtrate turbid, at least the portion which passes through first. I have found the following method proposed by F. SCnULZE (loc. cit.) the most practical: Close the neck of several middlesized funnels with small filters of coarse blotting-paper, moisten the paper, press it close to the sides of the funnel, and then introduce the air-dried soil, in small lumps ranging from the size of a pea to that of a walnut, but not pulverized or even crushed; filling the funnels about two-thirds. Pour distilled water into them, in sufficient quantity to cover the soil; if the first portion of the filtrate is turbid, pour it back into the funnel. Let the operation proceed quietly. Fill the funnels again with water, and continue this process of lixiviation until the filtrates weigh twice or three times as much as the soil used. Collect the several filtrates in one vessel, and mix them intimately together. Keep a portion of the lixiviated soil. Divide the aqueous solution into two parts, 1 (about two-thllirds) and 2 (about one-third). * For more ample information on this subject the reader. is referred to FaESENIUS'S Chemie fur Landwirthe, Forstmdnner, und Cameralisten; Brunswick, Yieweg, 1847, p. 485.

Page  335 ~ 209.] AQUEOUS EXTIRACT. 335 1. Evaporate in a porcelain dish to a small bulk and test as follows: a. Filter off a portion, test the reaction of the 214 filtrate, set aside a part to test for organic matter (224), warm the rest and add I N O. Effervescence indicates an ALKALI-METAL CARBONATE. Then test for CHLORINE with Ag, N O,. b. Transfer the rest of the concentrated fluid from 1, 215 together with the precipitate which it usually contains, to a small dish (preferably of platinum), evaporate to dryness, and heat the brownish residue cautiously till the organic matter is destroyed. In the presence of NITRATES a slight deflagration will be perceptible. Treat the residue as follows: a. Test a small portion with NTa2 C 0, in the oxidizing flame for MANGANESE. it. Warm the rest with water, add H C1 (effervescence indicates carbonic: acid), evaporate to dryness to separate silicic acid, moisten with 11 C1, add water, warm, and filter. aa. Wash the residue, which generally contains a little carbon, a little clay (if the aqueous extract was not clear), and also SILICIC ACID. To detect the latter, pierce the filter, wash the residue thlrouI1h, boil it with NTa O H1, filter, saturate with 1 C1, evaporate to drylness, and finally take up with water, when the silicic acid will remain behind. bb. Test a part of the HI C1 solution for sxILPHURIC ACID With Ba C1,. Evaporate a second part with H N 0, and test for PHOSPHORIC ACID with molybdic solution. Test a third.part for IRON with K C N S. To the rest add a few drops of Fe, CO1 (to remove phosphoric acid), then N 40 1-1 till slightly alkaline, warm a little, filter, throw down the CALCIUM with (N I-I,), C O, and proceed to the examination for MAGNESIUM, POTASSIUM, and SODIUM (~~ 189, 190). Finally examine a small quantity of the pure alkali-chlorides in the spectroscope for LITrIUM. Aluminium is not likely to be found in the 216 aqueous extract (F. SCHULZE never found it). To test for it, boil the precipitate produced by ammonia with pure K O H in a platinum dish, filter, acidify the filtrate with H. C1, add N H, O X0, and warm. 2. If you have found iron, acidify a portion with H C1, 217 and test half with K6 Fe, (C N)12,, the other half with KI C N S, to see ill what state the iron is present. Mix the rest of the

Page  336 336 ANALYSIS OF SOILS. [~ 210 aquecus extract with a little 112 S 04, evaporate nearly to dryness on the water-bath, and test the residue for AMrONIA by Ca(OH),. If the aqueous extract is absolutely clear you may test it for ammonia directly by Hg Cl,, &c. (~ 92). 2. Preparation and Examination of the Acid Extract. ~ 210. Heat about 50 grammes of the soil from which the part 218 soluble in water has been removed as far as practicable* with moderately strong IH C1 (effervescence indicates CARBONIC ACID) for several hours on the water-bath, filter, and make the following experiments with the filtrate, which is generally yellow from the presence of ferric chloride: 1. Test a small portion with K CNS for tetrad 219 IRON, another with KI Fe, (C N),2 for dyad IRON. 2. Test a small portion with Ba C1, for SULPHURIC ACID. Evaporate another portion to dryness, heat the residue to a temperature scarcely exceeding 100~, warm with H N O,, filter off the silicic acid, and test for PIrosPIORIC ACID with molybdic solution in the cold. 3. Mix a large portion with N H1 0 H to neutralize 220 the free acid, then with yellowish ammonium sulphide; let the mixture stand in a warm place, in a flask filled up to the neck, until the fluid looks yellow' then filter, and test the filtrate in the usual way for CALCIUM, MAGNESIUM, POTASSIUM, and SODIUM. 4. Dissolve the precipitate obtained in 3 in HI C1, 221 evaporate to dryness, moisten with H Cl, add water, warm, filter, and examine the filtrate according to 94, for IRON, MANGANESE, AtUMINIUM, and if necessary, also for calcium and magnesium, which may have been thrown down by the ammonium sulphide, in combination with phosphoric acid. 5. The separated SILICIC ACID obtained in 4 is usually colored by organic matter. It must, therefore, be ignited to obtain it pure. 6. If it is a matter of interest to ascertain whether 222 the H C1 extract contains ARSENIC, COPPER, &c., treat the remainder of the solution with Ho S, as directed 206-208. 7. For FLUORINE, ignite a fresh portion, and proceed according to 174. * Complete lixiviation is generally impracticable.

Page  337 211, 212.] ORGANIC CONSTITUENTS. 337 3. Examination of the Iworganic Constituents insoluble in Water and Acids. ~ 211. Heating the lixiviated soil with If C1 (218) leaves the 2f3 greater portion undissolved. To subject this undissolved residue to chemical examination, wash, dry, and sift, to separate the stones from the clay and sand; moreover, separate the two latter from each other by elutriation. Subject the several portions to the process given for silicates (~ 198). 4. Examination of the Organic Constituents of the Soil.* ~ 212. The organic constituents of the soil, which exercise so great an influence upon its fertility, both by- their physical and chemical action, are partly portions of plants in which the structure may still be recognized (fragments of straw, roots, seeds of weeds, &c.), partly products of vegetable decotmposition, which are usually called by the general name of HUMUS, but differ in their constituent elements and properties, according to whether they result from the decay of the nitrogenous or non-nitrogenous parts of plantswhether alkalies or alkali-earths have or have not had a share in their formation —whether they are in the incipient or in a more advanced stage of decomposition. To separate these several component parts of humus would be an exceedingly difficult task, which, moreover, would hardly repay the trouble; the following operations are amply sufficient to answer all the purposes of a qualitative analysis: a. Examination of the Organic Substances soluble in Water. Evaporate the reserved portion of 214 on the water-bath 224 to perfect dryness, and treat the residue with water. The humic acid, which was present in the solution in combination with bases, remains undissolved, whilst CRFNIC AND APOCRrENIC ACIDS are dissolved; for the manner of detecting the latter acids, see 212. *Compare FESENIrUS'S Chemie fiir Landwirthe, Forstmiinner, und: Cameralisten; Brunswick, Vieweg, 1847, ~, 282-285. 22

Page  338 338 INORG. BODIES IN PRESENCE OF ORGANIC. [~@ 213, 214. b. Treatment with Alkali- Carbonate. Drv a portion of the lixiviated soil, and sift to separate 225 the fragments of straw, roots, &c.; and the small stones,' from. the finer parts; digest the latter for several hours at S0-90 with solution of sodium carbonate, and filter. 3lix the filtrate with H C1 to acid reaction. If brown flakes separate, these proceed from HUMIC ACID. c. Treatment with Caustic Alkali. Wash the soil boiled with solution of sodium carbonate 226 (b) with water, boil several hours with pure Na O IH, replacing the water as it evaporates, dilute, filter, and wash. Treat the brown fluid as in b. The humic acid which separates now is a new product resulting from the action of boiling soda upon iHUMeIN. V. DETECTION OF INORGANIC SUBSTANCES IN PRESENCE OF ORGANIC SUBSTANCES. ~ 213. It will be readily conceived that the presence of organic substances may so far impede an analysis that it cannot be proceede.d with until the organic matter has been rendered insoluble or totally destroyed; thus, for instance, the pres-.ence of organic coloring matter may completely conceal a change of color or a precipitate; again the presence of slimy matter may render filtration impossible. Difficulties of this kind are of constant occurrence in the examination of medicines, in the analysis of articles of food or of the contents of a stomach for inorganic poisons, and in the analysis of the inorganic constituents of vegetable or animal substances. In the following pages instructions will be given first for a general procedure, afterwards for several special cases. 1. General Rules for the Detection of Inorganic Substances in Presence of Organic matters, which by their,Color, Consistence or other Propertic's, impede the Ap-.placation of the Reagents, or obscure the Reactions prodtced. ~ 214. We confine ourselves here, of course, to the description of the most generally applicable methods, leaving the modi

Page  339 ~ 214.] INORGANIC BODIES IN' PPESENCE OF ORGANIC. 339 fiations which circumstances may require in special cases to the discretion of the analyst. 1. THE SUBSTANCE DISSOLVES IN WATER BnUT THE SOLUTION 227 IS DARK-COLORED OR OF SLI MY CONSISTENCE. a. Heat a portion of the solution with H Cl on the water-bath, and gradually add K C1 0, until the mixture is decolorized and perfectly fluid; heat until it exhales no longer the odor of C1, then dilute with water, and filter. Examine the filtrate in the usual way, commencing at ~ 183. Compare also ~ 218. It is hardly necessary to observe that mercurous, stannous, and ferrous salts would be changed to mercuric, stannic, and ferrie chlorides respectively by this treatment. b. Boil another portion of the solution for some time with 1I N 03, filter, and test the filtrate for SILVER and POTASSIUM. If IIN 03 succeeds in effecting the ready and complete destruction of the coloring and slimy matters, &e., this method is often preferable to all others. c. ALUMINIUM and CHROMIUM might escape detection by this method, because N 11 0 11 and (N1 H,), S fail to precipitate their hydroxides from fluids containing, non-volatile organic substances. Should you have reason to suspect the presence of these metals, mix a third portion of the substance with Na C 03 and K C1 03 and throw the mixture gradually into a redhot crucible. Let the mass cool, then treat it with water, and examine the solution for chromic acid and aluminium, the residue for alnminium (~ 103). d. Test a separate portion for AMMONIA with slackedlime. e. Subject another portion to dialysis and examine the dialysate for acids. 2. BOILING WVATER FAILS TO DISSOLVE THE SUBSTANCE, OR 228 EFFECTS ONLY PARTIAL SOLUTION; THE FLUID ADMITS OF FILTRATION. Filter, and treat the filtrate either as directed ~ 182, or, should it require decoloration, according to 227. The res idue may be of various kinds. a. It is FATTY. Remove the fatty matter by means of ether, and should a residue be left, treat this as directed ~ 175. b. It is RESINOUS. Use alcohol instead of ether, or apply both liquids successively. C. IT IS OF A DIFFERENT NATURE, e.g., woody fibre, &c. a. Dry, and ignite a portion in a porcelain or platinum vessel, avoiding too high a temperature, until total or partial incineration is effected; war-m

Page  340 340 INORGXNIC BODIES IN PRESENCE OF ORGANIC. [~ 214. the residue with H Cl and a little 1H N 0,, dilute, and examine the solution as directed 53; if a residue has been left, treat this according to ~ 196. /,. Examine another portion for the heavy metals and acids, as directed 227-since with the method given in a, arsenic, cadmium, zinc, &c., may volatilize, besides mercury. 7y. Test the remainder for ammonia, by triturating with slacked-lime. 3. THE SUBSTANCE DOES NOT AD-MIT OF FILTRATION OR ANY 229 OTHER MiEAzNS OF SEPARATING THE DISSOLVED FROM THE UNDISSOLVED PART. Treat the substance in the same manner as the residue in 228. YAs regards the charred mass, 228 c, a, it is often advisable to boil the mass, carbonized at a gentle heat, with water, filter, examine the filtrate, wash the residue, incinerate it, and examine the ash. 4. The following method proposed by E. MILLON * is of very general application for the detection of metals when mixed with organic matter. Transfer the substance to a tubulated retort and add four times its weight of pure Ek S 04. The retort should not be more than one-third full. Heat slowly till the mixture is homogeneons, and then placing a funnel tube in the tubnlure of the retort and gently increasing the temperature, add IH N 0, gradually. - The object of this first operation is to decompose chlorides, which will take about half an hour. Now remove the mixture to a platinlm dish and heat till the 1i, S 0O, which by degrees loses its black color and turns orange or red, begins to escape. Add more H IN 03 in small portions; after each addition the fluid will be decolorized, but it again turns darker on further heating. Continue adding 11 N 0:, until no more coloration occurs, and finally expel the H, S 04,, when you will obtain a saline mass to be analyzed in the usual way. If the heat is moderated towards the end, according to MILLON none of the arsenic or mercury will be lost; but this cannot be depended on when much chlorides are present. 5. To separate salts from colloid organic matter, dialysis is very convenient.t The substance is sometimes first warmed with H N 0, or with K Cl 03 and H Cl. (Corn pare ~ 217.) * Journ. de Pharm. et de Chirm. 46, 33. Zeitschr. f. anal. Chem. 4, 208. t Compare O. REVEIT,, Zeitschr. f. anal. Chem. 4, 266; BIzro, Ibid. 5, 51; IRIEDERER, Ibid. 7, 517.

Page  341 1~ P15.] TOXICAL ANALYSIS. 341 2. D3tection of Inorganic Poisons in Articles of Food, in Dead Bodies, &c., in Chemico-legal Cases.* ~ 215. The chemist is sometimes called upon to examine an 230 article of food, the contents of a stomach, a dead body, &c., with a vien to detect the presence of some poison, and tllhus to establish the fact of poisoning; but it is more fre qulently the case that the question put to him is of a less general nature, and.that he is called upon to determine whether a certain substance placed before himn contains a metallic poison; or, more pointedly still, whether it contains arsenic or hydrocyanic acid, or some other particular poison —as it mnay be that the symptoms point clearly in the direction of that poison, or that the examining magistrate has, or believes he has, some other reason to put this question. It is obvious that the task of the chemist will be the easier, the more special and pointed the question which is put to him. However, the analyst will always act most wisely, even in cases where he is simply requested to state whether a certain poison, e.g., arsenic, is present or not, if he adopts a course of proceeding which will not only perlnit the detection of the one poison specially named, the presence of which may perhaps be suspected onl insufficient grounds, but will moreover inform himself as to the presence or absence of other similar poisons. But we must not go too far in this direction either; if we were to attempt to devise a method that should embrace all poisons, we might succeed in elaborating such a method at the writing-desk; but experience would speedily convince us that the complexity inseparable from such a course, must impede the executionl of the process and imipair the certainty of the results, to such an extent that the drawbacks would be greater than the advantages derivable from it. Moreover, the attendant circumstances permit usually at least a tolerably safe inference as to the group to which the poison belongs. Acting on these views, I give here,1. A method which insures the detection of the milnutest traces of arsenic, allows of its quantitative determination, and permits at the same time the detection -of all other metallic poisons. 2. A method to effect the detection of hydrocyanic acid, * Compare FRuSENImus, Ann. d. Chem. u. Pharm. 49, 275; and FRESEmsNI Ind v. BABO, Ann. d. Chem. u. Pharm. 49, 287.

Page  342 4 2 TOXICAL ANALYSIS. [~ 216. which leaves the substance still fit to be examined both for metallic poisons and for alkaloids. 3. A method to effect the detection of phosphorus, which does not interfere with the examination for other poisons. This part of the work does not, therefore, profess to supply a complete guide in every possible case of chemicole(ral investigoations. But the instructions given in it are lie tried and proved results of my own practice. 3More(over, they will generally be found sufficient, the more so as ill the Section on the alkaloids, I give the description of the best processes by which the detection of these latter poisons in criminal cases may be effected. Where you have no indications at all of the sort of poison to be looked for, begin by carefully inspecting the substance with the aid of a microscope if necessary, by noting the odor, reaction, &c., and then if the circumstances do not point to examining different portions for the different classes of poisons, proceed to test for hydrocyanic acid and phosphorus (a distillation usually suffices for the detection of both), afterwards for alkaloids, and finally for metallie poisons. As an obvious matter of caution, you should always reserve one-third of the substance, after weighing and mixing, for contingencies. I. METHOD FOR THE DETECTION OF ARSENIC (WITH DUE REGARD TO THE POSSIBLE PRESENCE OF OTHER METALLIC PoisoNs). ~ 216. Of all metallic poisons arsenic is the most dangerous, and 231 most frequently used for the wilful poisoning of others. AmnOIng the colnpounds of arsenic, arsenious oxide occupies the first place, because it kills even in small doses, it does not betray itself, or at least very slightly, by the taste, and it is readily procurable. As arseniouls oxide dissolves in water only sparingly, and — on account of the difficulty with which moisture adheres to it-very slowly, the greater portion of the quantity swallowed exists usually in the body in the undissolved state; as, moreover, the smallest grains of it may be readily detected by means of an exceedingly simple experiment; and lastly, as-no matter what opinion may be entertained about the normal presence of arsenic in the hones, &c.this much is certain, that arsenious oxide in grailns or powdcer is never normally present in the body, the particular care and efforts of the analyst ought always to be directed to the detection of the arsenious oxide in substanceand this end may indeed usually be attained.

Page  343 ~ 217.] DETECTION OF ARSENIOUS OXIDE. DIALYSIS. 343 A. fethod for the Detection of undis7solved Arseniozus Oxide. 1. If you have to examine food, von-mit, or some other 232 matter of the kind, after weighing it mix the whole as uniformly as may be practicable, reserve one-third for contingenlcies, and mix the other two-thirds in a porcelain dish with distilled water, with a stirring rod; let the mixture stand a little, then pour off the fluid, together with the lighter suspended particles, into another porcelain dish. Repeat this latter operation several times, if possible with the same fluid, pouring it from the second dish back into the first and so on. Finally, wash once liore with pure water, best in a glass dish31, remove the fluid as far as practicable, and try whether you can. find in the dish small, white, hard grains which feel gritty under the glass rod. If not proceed as directed ~ 217 or ~ 218. Bunt if so, pick out the grains, or some of them, with a pair of pincers, or wasll them if they are very minute in a watch-glass, dry, weigh them, and heat a smlall portion in a glass tube, another small portion with a splinter of charcoal (compare ~ 132, 2 and 11). If you obtain in the former experiment a white sparklling sublimate consisting of octahedrons and tetrahedrons, in the latter experiment an arsenical ilrrorl, you are quite safe in concluding that the grains consist of arsenious oxide. If you wish to determine the quantity of the arsenic, or to test for other metallic poisons,unite the contents of both dishes, and proceed as directed ~ 217 or ~ 21S. 2. If a stomach is submitted to you for analysis, empty the contents into a porcelain dish, turn the stomach inside out, and (a), search the inside coat for small, white, hard, sanldy grains. The spots occupied by such grains are often reddened; the grains are also frequlently found firmly im bedded in the mnembralle. (b) Iix the contents in the dish ullliformlnly, weigh themr, put aside one-third for contingen cies, anld treat the other two-thirds as in 1. The same course is pursued also with the intestines. In other parts of the body-with the exception perhaps of the pharynx and (esophagus-arsenions oxide cannot be found in grains, if the poison has been introduced through the mouth. If you have found grains of the kind described, examine them as directed in 1; if not, or if you wish to test also for other metallic poisons, proceed according to ~ 217 or ~ 218. B. Mfethod of detecting soluble Arsenical and other iiletallic Compounds by means of Dialysis. ~ 217. If method A has failed to show the presence of arseni- 238 )us oxide in the solid state, and the process described in

Page  344 344 TOXICAL ANALYSIS. [~ 217 ~ 218, in which organic matter it coagulated or destroyed by potassium chlorate and hydrochloric acid, is at once resorted to, the operator must, of course, in the event of the presence of arsenic beiing revealed, give up all notion of ascertaining, as far as the portion operated upon is onclerned, in what form the poison has been administered; as the process will give a solution containing arsenic acid, nlo matter whether the poison was originally present in that formn, or as arsenious oxide. or as sulphide, or in the metallic state, &c. This defect may be remedied, however, by interpolating a dialytic experiment between A and C. The experiment requires the apparatus shown in ~ 8, fig. 6. The hoop is made of wood or, better, of gutta-percha; it is 2 inches in depth, and 8 or 10 inches in diameter. The residue and fluid of ~ 216, A, having'been mixed according to the circumstances with two-thirds of the stomnach, intestinal canal, &c. (cut small and digested for twentyfour hours at about 32~) is poured into the dialyser to a depth of not more than half an inch. The dialyser is then floated in a basin containing about 4 times as much water as the fluid to be dialysed amounts to. After 24 hours onle-half or three-fourths of the -crystalloids will be found ill the external water, which generally appears colorless. C-oncentrate this by evaporation on the water-bath, acidify the greater part with hydrochloric acid, treat with sulphuretted hydrogen, and proceed generally as directed 235 et seq. If an arsenical compound soluble in water (or some other solnble metallic salt) is present, the corresponding sulphide is obtained almost pure. By floating the dialyser successively on fresh supplies of wrater, the whole of the soluble crystalloids present may finally be withdrawn. If arsenic is found, test the remnailder of the concentrated dialysate according to ~ 134, 9, to see whether arsenious or arsenic,acid is present. It is generally best to examine the exhausted contents of the dyalyser at once according to ~ 218 for metals, but in,some cases, as, for instance, when you wish to determine the state of oxidation or combination of compounds of arsenic or other metals, it is preferable to heat the matter,first with dilute hydrochloric acid and to dialyse it again. Instead of interpolating the dialysis at this stage, you mnay wait till the close of C, and then if a metallic poison has been found and you wish to ascertain its state of coinbination, you may recur to this pacrragph, using the reberved one-third for the experinment.

Page  345 ~ 218.] DETECTION OF ALL METALLIC POISONS. 345 C. Hethod for the Detectzon of Arsenic in whatever Form, it may exist, whicth allows also of its Quantitative Determination, and qf the Detection of all other ifetallic Poisons.* ~ 218. If you have found no arsenious oxide in substance by the nlethod described in A, nor a soluble arsenical compound b1 dialysis, evaporate the mass inl the porcelain dish, on the water-bath, to a pasty consistence; adding, if occasion requires, two-thirds of the stomach and intestines cut small, )lrovided this has not been done already in. the process of dial ysis. In examining other parts of the body (the hings, liver, &-c.), cut them also into small pieces, and use two-thirds for the analysis. The process is divided into nine parts.t 1. D ecoloration and Solution. Add to the matters in the porcelain dish, which may 234 amount to, say 100 or 250 gramlnmes, an amount of hydrochloric acid of 1-12 sp. gr., about equal to or somewhat exceeding the weight of the dry substances present, and sufficient water to give to the entire mass the consistence of a thin p)aste. The quantity of hydrochloric acid added should never exceed olle-third of the entire liquid present. IIeat the dish now on the water-bath, adding every five minutes about two grammnes of pure potassium chlorate to the hot fluid, with stirring, until the contents of the dish alre lirght yellow, and also perfectly homogeneous and fluid; -replace the evaporating water from time to time. When this point is attained, add again a portion of potassium chlorate, anld then remove the dish from the water-bath. When the contents are quite cold, transfer them cautiously to a linell strainer or a white filter, according to the quantity; allow the whole of the fluid to pass through, and heat the filtrate on the water-bath with renewal of the evaporating water, until the smell of chlorine has gone off or * This method is essentially the same as that which was published in 1844 by L. v. BABRO and myself; compare Ann. d. Chem. u. Pharm., 49, 308. I have since that time had frequent occasion to apply it; I Ilave also had it tried by others, under my own inspection, and 1 have invariably found it te answer the purpose pei3fectly. t I need hardly observe that, in an analysis of this kind, too much care cannot be taken to insure the purity of the reagents and the cleanliness of the apparatus

Page  346 846 TOXICAL ANALYSIS. [~ 218. nearly so. Wash the residue well with hot water, and dry it; then mark it I., and reserve for further examination, according to 247. Evaporate the washings on the water-bath to about 100 grammes, add this, together with ally prceipitate that may have formed therein, to the principal filtrate. 3. Treatment of the Solution with Hfydrosulh)uric Acicl. 235 (Separation of the Arsenic as Trisulphide, and of all the Metals of Groups V. and VI. in form of Sulphides.) Transfer the fluid obtained in 1, which amounts to three or four times the quantity of the hydrochloric acid used, to a flask, heat this on the water-bath to 70~, and transmit through it, for about 12 hours, a slow streamr of washed hydrosulphuric acid, then let the mixture cool, contiluing the transmission of the gas; rinse the delivery-pipe with some ammonia, add the anmmoniated solution thus obtained, after acidifying, to the principal fluid, cover the flask lightly with unsized paper, and put it in a moderately warm place (about 30~) until the odor of hydrosulphuric acid has nearly disappeared. Collect the precipitate obtained in this manner on a filter, and wash with water containing hydrosulphuric acid until the washings are quite free froml chlorine. Concentrate the filtrate and'wasllillns. If a precipitate forms filter it off, wash and add it to the prinlcipal hydrosulphuric acid precipitate. Mlix the concentrated fluid in a proper-sized flask with ammonlia to alkaline reaction, then with amnmonium sulphide, closely cork the flask, which must now be nearly full, and reserve it for further examination according to 251. 3. PurJification of the Precipitate Zp'od'uced by Hydro- 238 sulph/uric Atcid. The precipitate obtained in 2 contains the whole of the arsenic and all the other metals of the fifth and sixth gr,'ups, in the form of sulphides, and also organic matter and free sulphur. Dry it with the filter completely in a small dish, over the water-bath, add pure fuminlg nitric acid (free from chlorine), drop by drop., until the mass is conlpletely moistened, then evaporate on the water-bath to dryness. MIoisten the residue uniformly all over with plre concentrated sulphuric acid, previously warmed; then heat for two or three hours on the water-bath, and finally with an air- sand- or oil-bath at a somewhat higher, though still moderate temperature (170~), until the charred mass becomes friable, and a small sample of it-to be returned afterwards to the mass-when mixed with water and then

Page  347 ~ 218.] DETECTION OF ALL METALLIC POISONS. 31' allowed to subside, gives a colorless fluid; should the aqueous fluid be )brownish, or should the residue consist of a brown oily liquid, add to the mass some cuttings of pure Swedish filtering-paper, and continue the application of heat. You may raise the heat till fumes of sulphuilic acid begin to escape without fear of loss of arsenic. By attendilng to these rules you will always completely attain the object in view, viz., the destruction of the organic substances, without loss of any of the metals. Warm the residue on the water-bath with a mixture of 8 parts of water and 1 part of hydrochloric acid, filter, wash the undissolved part thoroughly with hot water, containing a little hydrochloric acid, and add the washings, concentrated if necessary, to the filtrate. Dry the washed carbonaceous residue, then mark it II., and reserve it for further examination according to 248, 4. Preliminary Examination for Arsenic and othter 237 3Yetallic Poisons of Grou'ps V. and VI. (Second Precipitation with IIydrosulphuric Acid.) The clear and colorless or, at the most, somewhat yellowish fluid obtained in 3 contains all the arsenic in form of arsenious acid, and may contain also tin, antimony, mercury, copper, bismuth, and cadmium. Supersaturate a small portion gradually with a mixture of ammonium carbonate and ammonia, and observe whether a precipitate is produced, acidify with hydrochloric acid, which will redissolve the precipitate that may have been produced by ammonia; then return the sample to the principal fluid, ald treat the latter with hydrosulphuric a(cid, first at a gentle heat, afterwards without heat, according to 235. This process may lead to three different results, which tire to be carefully distinlucnished. a. The hydrosul/phuric acid fails to produce a _pre- 238 cipitate; but on standing a trifling white or yellowish-white precipitate separates. In this case probably no metals of Groups V. and VI. are present. Nevertheless, treat the filtered and washed precipitate as directed 241, to guard against overlooking even the Iinutest traces of arsenic, &c. b. A precipitate is formed, of ca pure yellow color; 239 like that of arsenious sulphide. Take a small portion of the fluid, together with the precipitate suspended therein, add some ammonia, and shake for some time without heating. If the precipitate dissolNves readily and, with the exception of a trace of sulphur, completely, and if in the preliminary examination (237),

Page  348 348 TOXICAL ANALYSIS. [~ 218. amlmoniunl carbonate has failed to produce a precipitate. arsenic alone is present, and no other metal (at least, if any tin or antimony is present, it is not worth mentioning). Mix the solution of the small sample in ammonia, with hydrochloric acid to acid reaction, return this to the fluid containing the principal precipitate and proceed as directed 241. If, on the other hand, the addition of ammonia to the sample completely or partially fails to redissolve the precipitate, or if, in the preliminary examination (237), ammonium carbonate has produced a precipitate, there is reason to suppose that another metal is present, perhaps with arsenic. In this latter case, also, add to the sample in the test-tuble hydrochloric acid to acid reaction, return it to the fluid containing the principal precipitate, and proceed as directed 242. c. A precizitate is.forwsmcd of anothe)r color. In 240 that case you have to assume that other imetals are present, perhaps with arsenic. Proceed as directed 242. 5. Treatmnent of the Yellow Precipitcte produced by Rfy- 241 drosulpAhric Acid, when the IZeszlts qf 239 lead to the Assuamption that Arsenlic alone ispyesent. (Detei'mination of the Weight of the Arsenic.) As soon as the fluid precipitated according to 237 has nearly lost the smell of sulplhuretted hydrorgen, collect the yellow precipitate on a small filter, wash thoroughly, pour upon the still moist precipitate solution of annnonia, and wash the filter-on which, in this case, nothing Inust lemain undissolved, except some sulphur —th(l roughly with dilute alnmmonia; evaporate the fluid in a small accurately tared porcelain dish, on the water-bath, and dry the residue at 100~ until the weight is constant. The final weight represents the quantity of arsenious sulphide, if uponl the subsequent reduction this is found to be pure; in that case,.multiply the weight by'8049 to obtain the correspllonding amount of arsenious oxide, or by'6098 to obtain the corresponding amount of metallic arsenic. Treat the residue in the dish according to 244. 6. Treaftment of the Yellow Precipitateproduced by flydro- 242 szlphuric Acid, when the Results qf 239 or 240 lead to the Asstumption that another ietal is present-perhac, s with Arsenic. (Separation of the Metals from each other. Determination of the Weight of the Arsenic.) If you have reason to suppose that the fluid precipitated according to 237 contains other metals, perhaps with axse

Page  349 . 218.] DETECTION OF ARSENIC. 349 nic, proceed as follows:-As soon as the precipitation is thoroughly accomplished, and the smell of sulphuretted hydrogen has nearly gone off, collect the precipitate on a small filter, wash thoroughly, pierce the filter, and wash all the precipitate into a small flask, using the least possible quantity of water; add to the fluid in which the precipitate is now suspended, first ammonia, then some yellowish ammonium sulphide, and let the mixture digest for some time at a gentle heat. Should part of the precipitate remain undissolved, filter this off, wash, pierce the filter, rinse off the residuary precipitate, mark it III., and reserve for further examination according to 249. Evaporate the filtrate, together with the washings, in a small porcelain dish to dryness. Treat the residue with some p-ure fuming nitric acid (free from chlorine), nearly drive off the acid by evaporation, then add, as C. ME~YER was the first to recommend, a solution of pure sodium carbonate, in small portions till in excess. Add now a mixture of 1 part of carbonate and 2 parts of nitrate of sodium in sufficient, yet not excessive quantity, evaporate to dryness, and heat the residue very gradually to fusion. Let the fused mass cool, and take it up with cold water. If a residue remains nn- 243 dissolved, filter, wash with a mixture of equal parts of alcohol and water, mark it IV., and reserve for further examination, according to 250. Mix the solution which contains all the arsenic as sodium arsenate, with the washings, previously freed from alcohol by evaporation. add cautiously pure dilute sulphuric acid to strongly acid reaction, evaporate in a small porcelain dish, and when the fluid is strongly concentrated, add again sulphuric acid, to see whether the quantity first added has been sufficient to expel all nitric acid and nitrous acid; heat now cautiously until heavy fumes of sulphuric acid begin to escape; then let the liquid cool, add water, transfer the solution to a small flask, keep heated at 70~, and conduct into it for at least 6 hours a slow stream of washed hydrosulphuric acid. Let the mixture finally cool, continuing the transmission of the gas all the while. If arsenic is present, a yellow precipitate will form. When the precipitate has completely subsided, and the fluid has nearly lost the smell of sulphnretted hydrogen, filter, wash the precipitate, dry it, extract the free sulphur with pure carbon disulphide, dissolve in ammonia, and treat the solution according to 241, in order to determine the weight of the arsenic. 7. Reduction of the Arsenious Sulphide. The production of metallic arsenic from tile sulphide, 244 which may be regarded as the keystone of the whole pro

Page  350 350 TOXICAL ANALYSIS. [~ 218 cess, demands the greatest care and attention. The method recommended ~ 182, 12, viz., to fuse the arsenical compound, mixed with potassium cyanide and sodium carbonate, in a slow stream of carbon dioxide, is the best and safest, affording, besides the advantage of great accuracy, also a positive guarantee against the chance of confounding the arsenic with any other body, more particularly antimony; on which account it is especially adapted for medico-legal investigations. Fig. 43. Take care to have the whole apparatus filled with carbon dioxide, and to give the proper degree of force to the gaseous stream, before applying heat, The apparatus shown in fig. 43, which has been described on p. 55, may be used. It is charged with lunps of marble, and with dilute IH- C1. The current of gas is dried by passing through concentrated sulphuric acid in the small flask. Do not reduce the whole of the arsenious sulphide at once, so that if you wish afterwards you may repeat the reduction several times. If there is too little arsenious sulphide to be divided, dissolve it in a few drops of ammonia, add a small quantity of sodium carbonate, evaporate to dryness on the water-bath with stirring, and take a portion of the mass for the reduction. OTTO recommends * to convert the sulphide into an arse- 245 nate, before proceeding to the reduction. The following is the process given by him to effect the conversion: Pour concentrated nitric acid over the sulphide in the dish, evaporate, and repeat the same operation several times if necessary, * Anleitung zur Ausmittelunog dcr Gifte, von DR. FR. JUL. OTTO.

Page  351 ~ 218.] DETECTION OF METALLIC POISONS. 351 then remove every trace of nitric acid by repeatedly moistening the residue with water, and drying again, treat the residue with a few drops of water, add sodiumn carbonate in powder, to form an alkaline mass, and thoroughly dry this in the dish, with frequent stirring, taking care to collect the mass within the least possible space in the middle of the dish. The dry mass thus obtained is admirably adapted for reduction. I can fully confirm the statement; but I must once more repeat that it is indispensable for the success of the operation that the residue should be perfectly free from every trace of nitric acid or nitrate, since otherwise deflagration is sure to take place durinlg the fusion with potassilmn cyanide, and, of course, the experiment will fail. When the operation is finished, cut off the reduction 246 tnbe at c (fig. 44), set aside the fore part, which contains the arsenical mirror, put the other part of the tube into a cylinder, pour water over it, and let it stand some time; then filter the solution obtained, add to the filtrate hydrochloric acid to acid reaction; then concllduct some hydrosulphuric acid into it, and observe whether this produces a precipied e c h Fig. 44. tate. In cases where the reduction of the arsenious sulphide has been effected directly, without previous conversion to arsenic acid, a trifling yellow precipitate will usually form; had traces of antimony been present, the precipitate would be orange-colored and insoluble in ammonium carbonate. After all the soluble salts of the fused mass have been dissolved out, examine the metallic residue which may be left, for traces of tin and antimony (nothing but traces of these two metals could be present here if the instructions given have been strictly followed). Should appreciable traces of these metals, or either of them, be found, proper allowance must be made for this in calculating the weight of the arsenic. 8. Examination of the reserved Residues, for other lMetals of the Fifth and Sixth Groups. Residue I. This may contain silver chloride and lead 247 sulphate, possibly also stannic oxide and barium sulphate. Incinerate it in a porcelain dish, burn the carbon with the aid of ammonium nitrate, extract the residue with water, dry the part left undissolved, then fuse it with sodium carbonate and potassium cyanide in a porcelain crucible.

Page  352 352 TOXICAL ANALYSIS. [~ 213. When cold exhaust with water, treat the residue with dilute acetic acid to extract any barium carbonate, warm any residue which may still be left with nitric acid, and proceed according to ~ 181. Test the acetic acid solution for barium with solution of calcium sulphate. Residue I. This may contain lead, mercury, and tin, 248 possibly also antimony and bismuth. Heat it for some time with nitrohvdrochloric acid, and filter the solution; wash the residue with water, at first mixed with some hydrochloric acid, add the washings to the filtrate, and treat the mixture with hydrosulphuric acid. Should a precipitate form, examine it according to ~ 191. Incinerate the residue insoluble in nitrohydrochloric acid, fuse the ash with potassium cyanide- and treat the fused mass as directed 247. _Residue III. Examine for the metals of the fifth group 249 according to ~ 186. Residuce IV. This may contain tin and antimony, per- 250 haps also copper. Treat it as directed 67. If the color of the residue was black (oxide of copper), treat the reduced metals according to ~ 181. 9. Examination of the reserved filtrate for Metals of the Third and Fourth Groztps, especially for Zinc, Chromium, and Thallium.* a. The filtrate from the hydrosulphuric acid pre- 251 cipitate has already been mixed with ammonium sulphide. The addition of this reagent is usually attended with the formation of a precipitate consisting of iron sulphide and calcium phosphate, but which may possibly also contain zinc sulphide, thallium sulphide and chromic hydroxide. Filter it off, wash with water containing ammonium sulphide, dissolve by warming with hydrochloric acid and a little nitric acid, evaporate the filtrate with sulphuric acid in a retort till quite thick, and test the distillate with potassium iodide and platinic chloride, and also in the spectroscope, for THALLIUM (~ 113, b). as a portion of this metal may have escaped with the hydrochloric acid. Treat the residue in the retort with water, filter, add sodium carbonate to alkaline reaction, and then excess of solution of potassium cyanide (free from suilphide). Heat for some time, filter, reserve the * With reference. to the poisonous action of thallium, compare LAIMY, Journ. f. yrakt. Chem. 91, 366. And for the electrolytic method of discover. ing thallium in chemlico-legal cases, see MARn., Zeitschr. f. ana!. Chem. (. 503.

Page  353 ~ 219.] HIYDROCYANIC ACID. 353 residue on the filter (a), mix the filtrate with ammonium sulphide, and examine the precipitate for THALLITUM in the spectroscope. Evaporate the filtrate together with the residue a under a good draught with excess of sulphuric acid, till some of the latter begins to escape, dilute, filter, throw down with ammonia and ammnonium sulphide, and test the precipitate for zINC and CHRo-Miu.A according to 100-103. b. The fluid filtered from the precipitate produced 252 by ammonium sulphide (251) may contain all the chromiunll, as arnmonium sulphide fails to precipitate chromic hydroxide completely from solutions containing organic matter. To detect it, evaporate to dryness, ignite, mix the fixed residue with 3 parts of potassium chlorate and 1 part of sodium carbonate, and projectthe mixture into a crucible heated to moderate redness. Allow the mass to cool, and boil with water, when a yellow coloration of the fluid will indicate chromium. For confirmatory tests see ~ 138. II. METHOD FOR THE DETECTION OF HYDROCYANIC ACID. ~219. Under the term hydrocyanic acid we include potassium 25S cyanide, which acts in the same way, and beingi extensively used in the arts is much more readily procurable. As hydrocyanic acid may easily decompose in presence of the matter of food or the. contents of the stomach, the analyst must proceed without unnecessary delay. However, the acid does not decompose with such extreme rapidity as might be imagined, and in fact it is some time before the whole of it is lost.* Although hydrocyanic acid betrays its presence, even in minute quantities, by its odor, still this sign must never be looked upon as conclusive. On the contrary, to adduce positive proof of the presence of the acid, it is always indispensable to separate it, and to convert it into certain known compounds. The method of accomplishing this, which I am about to describe, is based upon distillation of the acidified mass, and examination of the distillate for hydrocyanic acid. Now, as the non-poisonous salts, potassium ferro- and fer* Thus I succeeded in separating a notable quantity of hydrocyanic acid from the stomach of a man who had poisoned himself with that acid in very hot weather, and.whose intestines were not handed to me till 36 hours after death. Again, a dog was poisoned with hydrocyanic acid, and the contents of the stomach, mixed with the blood, were left for24 hours exposed to an intense summer heat, and then examined: the acid was still detected. 23

Page  354 354 TOXICAL ANALYSIS. [~ 219 ricyanide, give by distillation likewise a product containing hydrocyanic acid, it is indispensable —as OTTO observes -first to ascertain whether one of these salts may not be present. To this end, stir a small portion of the mass to le examined with water, filter, acidify the filtrate with hydrochloric acid, and test a portion of it with ferric chloride, another with ferrous sulphate. If no blue precipitate or coloration forms in either, soluble ferro- and ferricyanides are not present, and you mlay safely proceed as follows. If a reaction is obtained proceed according to 258. Test, in the firs