Experimental notes of the mechanical origine or production of fixtness.

CHAP. IV. (Book 4)

BUT although one of the chiefest Conditions that Philosophers may justly require in Principles, is, that, being to explain other things, they should be very clear themselves; yet I do not much wonder, that the Definitions given us of Acidum and Alcali should be but unaccurate and superficial, since I find not, that they have themselves any clear and deter∣minate Notion or sure marks, where∣by to know them distinctly, without

which Chymists will scarce be able to form clear and setled Notions of them. For to infer, as is usual, that, because a body dissolves another, which is dissoluble by this or that known acid, the Solvent must also be acid; or to conclude, that, if a body precipitates a dissolved metal out of a confessedly acid Menstruum, the Precipitant must be an Alcali, to argue thus, I say, 'tis unsecure; since, not to repeat what I said lately of Copper, I found, that filings of Spelter will be dissolved as well by some Alcalies, (as spirit of Sal Armoniac) as by Acids. And bodies may be precipitated out of acid Menstruums, both by other Acids, and by liquors, where there appears not the least Alcali: As I have found, that a solution of Tin∣glass, made in Aqua fortis, would be precipitated both by Spirit of Salt and by common or rain water. And as for the other grand way that Chy∣mists employ, to distinguish Acids and Alcalies, namely by the Heat, Commo∣tion, and bubbles that are excited,

upon their being put together, that may be no such certain sign as they presume, they having indeed a depen∣dance upon particular Contextures and other Mechanical affections, that Chymists are not wont to take any notice of. For almost any thing that is fitted variously and vehemently to agitate the minute parts of a body, will produce Heat in it; and so, though water be neither an Acid nor an Alcalizate liquor, yet it would quickly grow very hot, not only with the highly acid Oil of Vitriol, but (as I have more than once pur∣posely tried and found) with the fie∣ry Alcalizat Salt of Tartar. And 'tis to be noted, that neither in the one nor the other of these Incalescent mixtures, there is produced any such visible or audible conflict, as, accord∣ing to the Doctrine of the Chymists I reason with, one would expect. And as for the production of bubbles, especially if accompanied with a hissing noise, neither is that such a certain sign as Chymists imagine: For

the production of bubbles is not a necessary effect or concomitant of Heat excited by Conflicts, but de∣pends very much upon the peculiar Disposition of Bodies put together to extricate, produce, or intercept par∣ticles of Air, (or Steams, for the time equivalent to them;) and therefore as Oil of Vitriol, mixt in a due proporti∣on with fair water, may be brought to make the water too hot to be held in ones hand, without exciting bubbles; so I have found by trials purposely made, that Alcalizat Spirit of Urine drawn from some kinds of Quick-lime, being mixt with Oil of Vitriol moderately strong, would produce an intense Heat, whilest it produced ei∣ther no manifest bubbles at all, or scarce any, though the Urinous Spi∣rit was strong, and in other Trials operated like an Alcali; and although also with Spirit of Urin, made per se the common way, the oil of Vitriol will produce a great hissing and a multitude of conspicuous bubbles.

On the other side I have sometimes, though not so constantly, found, that some Acid Spirits, especially that of Verdigrease made per se, would, when poured upon Salt of Tartar, make a Conflict with it, and produce a copi∣ous froth, though we observed it not to be accompanied with any manifest Heat. And I elsewhere mention two bodies, upon whose putting together numerous bubbles would, for a long time, and not without noise, be gene∣rated, and succeed one another, though I could perceive no Heat at all to accompany this Tumult.

As for the Tast, which by many is made a great Touchstone, whereby to know Acids and Alcalies, I consider that there is a multitude of mixt bo∣dies, wherein we can so little discern by the Tast, which of the Principles is Predominant, that this Sense would not oblige one to suspect, much less to conclude, there were one grain of ei∣ther of them to be found there; such bodies are Diamonds and Rubies, and

most Gems, besides many ignobler Stones, and Gold and Silver and Mer∣cury, and I know not how many other bodies. On the other side, there are bodies that abound with Acid or Al∣calizat Salts, which either have no Tast, or a quite differing one from that of the Chymical Principle. As though Venice-glass be in great part composed of a fixt Alcali; yet to the Tongue it is insipid, and Crystalls of Lune and of Lead made with Aqua fortis, and containing great store of the Acid particles of the Menstruum, have nothing of Acidity in the mouth, the latter having a saccharine sweet∣ness, and the former an extream bit∣terness. And even in Vegetable sub∣stances that have a manifest Tast, 'tis not so easie to know by that, whether it be the Acid or the Alcalizat Prin∣ciple that is predominant in them; as in the Essential oils of Spices and o∣ther Vegetables. And in the gross Empereumatical Oils of Woods, and even in high Rectified Spirit of Wine,

which therefore some will have to be an Alcalizat liquor, and others list it among Acids, though I did not find it neither to be destroyed or much al∣tered by being put upon Coral or salt of Tartar, as would happen to an acid Menstruum, nor yet by being digested with and distilled from sea Salt, as might be probably expected from an Alcalizat one: Aand among those very bodies which their Tasts perswade Chymists to reckon amongst Acids, one may (according to what I formerly noted) observe so great a difference and variety of relishes, that, perhaps without being too severe, I may say, that if I were to allow Acids to be One Principle, it should be only in some such Metaphysical sense, as that wherein Air is said to be One Body, though it consist of the associated ef∣fluviums of a multitude of Corpuscles of very differing Natures, that agree in very little save in their being mi∣nute enough to concur to the Com∣position of a fluid aggregate, consist∣ing

of flying parts. But having dwelt longer than I intended on One Obje∣ction, 'tis time that I proceed to those that remain.