It will perhaps be thought, that the most ufeful, if not the most remarkable, of all the properties of this extraordinary kind of air, is its power of preferving animal fubftances from putrefaction, and of reftoring those that are already putrid, which it poffeffes in a far greater degree than fixed air. My first observation of this was altogether cafual. Having found nitrous air to suffer fo great a diminution as I have already mentioned by a mixture of iron filings and brimftone, I was willing to try whether it would be equally diminished by other caufes of the diminution of common air, efpecially by putrefaction; and for this purpose I put a dead moufe into a quantity of it, and placed it near the fire, where the tendency to putrefaction was very great. In this cafe there was a confiderable diminution, viz. from 5 to 3; but not fo great as I had expected, the antifeptic power of the nitrous air having checked the tendency to putrefaction; for when, after a week, I took the mouse out, I

difcovered that the acid taste of this water is not the necessary confequence of its impregnation with nitrous air, but is the effect of the acid vapour, into which part of this air is refolved, when it is decompofed by a mixture with common air. This, it will be feen, exactly agrees with my own obfervation on the conftitution of nitrous air, in the fecond part of this work. A more particular account of Mr. Bewley's obfervation will be given in the Appendix.

i

perceived,

perceived, to my very great furprize, that it had no offenfive smell.

Upon this I took two other mice, one of them just killed, and the other soft and putrid, and put them both into the fame jar of nitrous air, ftanding in the ufual temperature of the weather, in the months of July and August of 1772; and after twenty-five days, having obferved that there was little or no change in the quatity of the air, I took the mice out; and, examining them, found them both perfectly fweet, even when cut through in feveral places. That which had been put into the air when jusț dead was quite firm; and the flesh of the other, which had been putrid and foft, was ftill foft, but perfectly fweet.

In order to compare the antifeptic power of this kind of air with that of fixed air, I examined a moufe which I had inclosed in a phial full of fixed air, as pure as I could make it, and which I had corked very clofe; but upon opening this phial in water about a month after, I perceived that a large quantity of putrid effluvium had been generated; for it rushed with violence out of the phial; and the fmell that came from it, the moment the cork was taken out, was infufferably offenfive. Indeed Dr. Macbride fays, that he could only restore very thin pieces.

of

of putrid flesh by means of fixed air. Perhaps the antifeptic power of these kinds of air may be in proportion to their acidity.

If a little pains were taken with this fubject, this remarkable antifeptic power of nitrous air might poffibly be applied to various uses, perhaps to the preservation of the more delicate birds, fishes, fruits, &c. mixing it in different proportions with common or fixed air. Of this property of nitrous air`anatomifts may perhaps avail themselves, as animal substances may by this means be preferved in their natural foft ftate; but how long it will answer for this purpose, experience only can fhew.

I calcined lead and tin in the manner hereafter described in a quantity of nitrous air, but with very little fenfible effect; which rather furprized me; as, from the refult of the experiment with the iron filings and brimftone, I had expected a very great diminution of the nitrous air by this process; the mixture of iron filings and brimstone, and the calcination of metals, having the fame effect upon common air, both of them diminishing it in nearly the fame proportion. But though I made the metals fume copiously in nitrous air, there might be no real calcination, the phlogiston not being feparated, and the proper calcination prevented by there being no fixed

air, which is neceffary to the formation of the calx, to unite with it.

Nitrous air is procured from all the proper metals by fpirit of nitre, except lead, and from all the femi-metals that I have tried, except zinc. For this purpose I have used bifmuth and nickel, with fpirit of nitre only, and regulus of antimony and platina, with aqua regia.

I

got little or no air from lead by fpirit of nitre, and have not yet made any experiments to afcertain the nature of this folution. With zinc I have taken a little pains.

Four penny-weights and feventeen grains of zinc diffolved in fpirit of nitre, to which as much water was added, yielded about twelve ounce meafures of air, which had, in fome degree, the properties of nitrous air, making a flight effervefcence with common air, and diminishing it about as much as nitrous air, which had been itfelf diminished one half by washing in water. The fmell of them both was alfo the fame; fo that I concluded it to be the same thing, that part of the nitrous air, which is imbibed by water, being retained in this folution.

In order to difcover whether this was the cafe, I made the folution boil in a fand-heat. Some

air came from it in this ftate, which feemed to be the fame thing, with nitrous air diminished about one fixth, or one eighth, by washing in water. When the fluid part was evaporated, there remained a brown fixed fubftance, which was observed by Mr. Hellot, who defcribes it Ac. Par. 1735, M. p. 35. A part of this I threw into a small red-hot crucible; and covering it immediately with a receiver, standing in water, I obferved that very dense red fumes rofe from it, and filled the receiver. This rednefs continued about as long as that which is occafioned by a mixture of nitrous and common air; the air was alfo confiderably diminished within the receiver. This fubftance, therefore, must certainly have contained within it the very fame thing, or principle, on which the peculiar properties of nitrous air depend.

It is remarkable, however, that though the air within the receiver was diminished about one fifth by this procefs, it was itself as much affected with a mixture of nitrous air, as common air is, and a candle burned in it very well. This may perhaps be attributed to some effect of the spirit of nitre, in the composition of that brown fubftance.

Nitrous air, I find, will be confiderably diminished in its bulk by standing a long time in water, about as much as inflammable air is