Experimental notes of the mechanical origine or production of fixtness.

CHAP. VII.

THe last means of Volatilizing bodies is, the operation of the Fire or some other actual Heat: But of this, which is obvious, it would be superfluous to discourse. Onely this I shall intimate, that there may be bodies, which, in such degrees of fire as are wont to be given in the vulgar operations of Chymists, will not be elevated, which yet may be forced up by such violent and lasting fires, as are employed by the Melters of Ores, and Founders of Guns, and sometimes by Glass-makers. And on

this Consideration I shall here ob∣serve to you, since I did not doe it at my entrance on these Notes, that Chymists are wont to speak, and I have accordingly been led to treat, of Volatility and Fixity in a popular sense of those Terms. For if we would consider the matter more strictly, I presume we should find that Volatility and Fixity are but re∣lative Qualities, which are to be esti∣mated, especially the former of them, by the degree of fire to which the body, whereto we ascribe one or other of those Qualities, is exposed; and therefore it is much more difficult than men are aware of, to determine accurately, when a body ought to be accounted Volatile and when not; since there is no determinate degree of Heat agreed on, nor indeed easie to be devised, that may be as a stan∣dard, whereby to measure Volatility and Fixtness: And 'tis obvious, that a body, that remains fixt in one de∣gree of fire, may be forced up by a∣nother. To which may be added,

agreeably to what I lately began to observe, that a body may pass for absolutely fixt among the generality of Chymists, and yet be unable to persevere in the fires of Founders and Glass-makers: Which brings into my mind, that not having observed, that Chymists have examined the Fixity of other bodies than metalline ones by the Cupel, I had the Curiosity to put dry Salt of Tartar upon it, and found, as I expected, that in no long time it manifestly wasted in so vehe∣ment a heat, wherein also the Air came freely at it, (though Quick-lime, handled after the same way, lost not of its weight,) and having well mix∣ed one ounce of good Salt of Tar∣tar with treble its weight of Tobac∣co-pipe Clay, we kept them but for two, or at most three hours, in a strong fire; yet the Crucible being purposely left uncovered, we found the Salt of Tartar so wasted, that the remaining mixture (which was not flux'd) afforded us not near a quarter of an ounce of Salt. And indeed I

scarce doubt, but that in strictness di∣vers of those bodies that pass for ab∣solutely fixt, are but semi-fixt, or at least but comparatively and relative∣ly fix'd, that is, in reference to such degrees of fire, as they are wont to be exposed to in the Distillations, Sublimations, &c. of Chymists; not such as are given in the raging fires of Founders, and Glass-makers. And per∣haps even the fires of Glass-makers and Say-masters themselves are not the most intense that may possibly be made in a short time, provided there be but small portions of matter to be wrought on by them. And in effect, I know very few bodies, be∣sides Gold, that will perserve totally fixt in the vehementest degrees of fire that Trials have made me acquainted with. And I elsewhere tell you, that, though Tin, in our Chymical Rever∣beratories themselves, is wont to be reduced but into a Calx that is repu∣ted very fixt; yet in those intense fires, that a Virtuoso of my acquain∣tance uses in his Tin-Mines, there is

not seldom found quantities of Tin carried up to a notable height in the form of a whitish powder, which, being in good masses forced off from the places to which it had fastened it self, does by a skillful reduction yield many a pound weight of good mal∣leable metal, which seemed to me to be rather more, than less, fine than ordinary Tin.

Postscript,

Relating to Page 15. of this Tract; and here annext for their sakes, who have a mind to repeat the Experiment there delivered, that so they may know the quantities employed in it.

WIth two parts of this Crocus we ground very well three parts of Sal Armoniac, and having sublimed them in a strong fire, we took off the high coloured Sublimat, and put in either an equal weight, or a weight exceeding it by half, to the Caput Mortuum, we found after the second Subli∣mation, which was also high coloured, that of an ounce of Crocus we had raised six drams, that is, three quarters of the whole weight.