mon air alfo diminished to a certain degree; so that he combats an opinion that in no part of my present work appears to be mine.

He will alfo find that I have proved, pretty much at large, that, notwithstanding I did fuppofe there was a precipitation of fixed air from common air phlogisticated, there was a cause of diminution altogether independent of that circumftance; having found that inflammable and nitrous air, when made wholesome, by agitation in water, were almost, if not quite, as mach diminished by fresh nitrous air, as common air had been. See vol. I, p. 187.

This volume of the Abbé Fontana's, has made me form confiderable expectations from the remainder of his work, and from his farther progrefs in these inquiries; though his doctrine differs from mine in feveral respects. Among other things he has engaged to prove that there is not properly any fixed air in the atmosphere. This I myself have fufpected fince I have

pro

proved, as this volume will fhew, that fixed air is a modification of the nitrous acid, and therefore may poffibly be generated in the act of decompofing nitrous air by common air. But that the fubftance which then makes its appearance, as also that which is compofed from the nitrous acid in other cafes, is truly and properly fixed air, and not, as the Abbé calls it, a fpecies of air, poffeffed of certain properties of fixed air, I am perfuaded he will himself be convinced, by reflecting on the observations mentioned in this volume.

On the other hand, his experiments on the red precipitate made me at first very much inclined to correct my opinion concerning the constitution of dephlogisticated air, viz. that it confifts of Spirit of nitre and earth, and to adopt his opinion, which is, that it confifts of spirit of nitre only, intirely deprived of its phlogiston.

My opinion was formed on finding that I could make refpirable air from any kind of earth and spirit of nitre; and because, when

when I used the fame earth repeatedly, it wholly disappeared. His opinion he fays is founded on the following very remarkable fact. Having converted a given. quantity of mercury into red precipitate, and then expelled from it all the pure air that it could yield, he found the very fome weight of mercury that he had used to make the precipitate. This is certainly a very proper and fair experiment, and provided it was made with fufficient accuracy, it muft, as far as I can see, be conclufive.

But, after having repeated the experiment with all the attention of which I am capable, I am satisfied that, notwithstanding all the precautions the Abbé fays he ufed in this cafe, the fact is the reverse of what he represents it. I diffolved 11dwt. Iogrs. of pure quickfilver, furnished by Mr. Woulfe, in strong spirit of nitre, and diftilling it in a tall glass phial, to which was luted a glass tube, terminating in a bafon of water, through which all the air was discharged, I found there was a clear loss of 1 dwt, 2 grs. of the quickfilver;

as

as I found by carefully weighing the glass, as well as the quickfilver itself, both before and after the process; and even without deducting any thing for a good deal of fand that was melted into the bottom of the glafs, and for a part of the red precipitate that remained unrevivified.

Being unwilling, however, to depend wholly upon my own address in experiments of this kind, I confulted with Mr. Magellan (who, indeed, first suggested to me his fufpicion that the Abbé must be mistaken in the fact) and he engaged Mr. Winch jun. (whofe skill and care in chymical proceffes no perfon who is acquainted with him can question) to make the experiment in the moft accurate manner that he could devife.

Accordingly he diffolved an ounce (Apothecaries weight) of the pureft mercury, in the pureft nitrous acid; and both myfelf and Mr. Magellan were present, when he revivified exactly one half of the red precipitate made from it in a glafs retort, furrounded with live coals, in a

reverberatory furnace; when the mercury was wholly fublimed into the neck of the retort, a very small quantity only of a brownish matter remaining unsublimed. The whole being carefully weighed, together with the retort, which had also been weighed before the procefs, it appeared that there was a lofs of 88 grains, which is fomething more than one third, of the weight of the quickfilver. We were all fatisfied that it was not poffible to make the experiment with more fairness.

The experiment, with the remaining half ounce of quickfilver, Mr. Magellan and Mr. Winch attended; when they found that, though the glass retort had loft some weight in the operation, there was a confiderable loss of weight in the quickfilver itself, but not so great as in the preceding cafe.

It will appear, befides, in the course of this volume, that the quantity of fpirit of nitre, in dephlogisticated air, is not great; and fince a confiderable quantity of earth is actually contained in it when

hot,