about the fame proportion alfo it was necefsary to mix water with the fpirit of nitre in each cafe, in order to make it diffolve these metals with equal rapidity, filver requiring the leaft water, and iron the most.

Phosphorus gave no light in nitrous air, and did not take away from its power of diminishing common air; only when the redness of the mixture went off, the veffel in which it was made was filled with white fumes, as if there had been fome volatile alkali in it. The phofphorus itself was unchanged.

There is fomething remarkable in the effect of nitrous air on infects that are put into it. I obferved before that this kind of air is as noxious as any whatever, a mouse dying the moment it is put into it; but frogs and fnails (and therefore, probably, other animals whose refpiration is not frequent) will bear being expofed to it a confiderable time, though they die at length. A frog put into nitrous air ftruggled much for two or three minutes, and moved now and then for a quarter of an hour, after which it was taken out, but did not recover. Wafps always died the moment they were put into the nitrous air. I could never obferve that they made the leaft motion in it, nor could they be recovered to life afterwards.

This was alfo the cafe in general with Spiders, flies, and butterflies. Sometimes, however, fpi, ders would recover after being expofed about a minute to this kind of air.

Confidering how fatal nitrous air is to infects, and likewife its great antifeptic power, I conceived that confiderable ufe might be made of it in medicine, efpecially in the form of clyfters, in which fixed air had been applied with fome fuccefs; and in order to try whether the bowels of an animal would bear the injection of it, I contrived, with the help of Mr. Hey, to convey a quantity of it up the anus. of a dog. But he gave manifeft figns of uneafinefs, as long as he retained it, which was a confiderable time, though in a few hours afterwards he was as lively as ever, and feemed to have fuffered nothing from the operation.

Perhaps if nitrous air was diluted either with common air, or fixed air, the bowels might bear it better, and ftill it might be deftructive to worms of all kinds, and be of use to check or correct putrefaction in the inteftinal canal, or other parts of the fyftem. I repeat it once more that, being no physician, I run no risk by fuch proposals as these; and I cannot help flattering myself that, in time, very great medicinal ufe will be made of the appli

cation of thefe different kinds of air to the animal fyftem. Let ingenious physicians attend to this fubject, and endeavour to lay hold of the new handle which is now presented them, before it be feized by rafh empiricks; who, by an indifcriminate and injudicious application, often ruin the credit of things and proceffes which might otherwise make an useful addition to the materia and ars medica.

In the first publication of my papers, having experienced the remarkable antifeptic power of nitrous air, I propofed an attempt to preserve anatomical preparations, &c. by means of it but Mr. Hey, who made the trial, found that, after fome months, various animal fubftances were fhriveled, and did not preferve their natu ral forms in this kind of air.

SEC.

SECTION IV.

Of MARINE ACID AIR.

In my former experiments on this fpecies of air I procured it from spirit of falt, but I have fince hit upon a much less expensive method of getting it, by having recourfe to the process by which the fpirit of falt is itself originally made. For this purpose I fill a fmall phial with common falt, pour upon it a small quantity of concentrated oil of vitriol, and receive the fumes emitted by it in a veffel previously filled with quickfilver, and standing in a bason of quickfilver, in which it appears in the form of a perfectly transparent air, being precisely the fame thing with that which I had before expelled from the spirit of falt,

This method of procuring acid air is the more convenient, as a phial, once prepared in this manner, will fuffice, for common experiments, many weeks; efpecially if a little more. oil of vitriol be occafionally put to it. It only requires a little more heat at the last than at the firft. Indeed, at the firft, the heat of a perfon's hand will often be fufficient to make it Q.3

throw

throw out the vapour. In warm weather it will even keep smoking many days without the application of any other heat.

On this account, it should be placed where there are no inftruments, or any thing of metal, that can be corroded by this acid vapour. It is from dear-bought experience that I give this advice. It may eafily be perceived when this phial is throwing out this acid vapour, as it always appears, in the open air, in the form of a light cloud; owing, I fuppofe, to the acid attracting to itfelf, and uniting with, the moisture that is in the common atmosphere.

By this process I even made a stronger spirit of falt than can be procured in any other way. For having a little water in the veffel which contains the quickfilver, it imbibes the acid vapour, and at length becomes truly faturated with it. Having in this manner, impregnated pure water with acid air, I could atterwards expel the fame air from it, as from common fpirit of falt.

I obferved before that this acid vapour, or air, has a ftrong affinity with phlogiston, fo that it decomposes many substances which contain it, and with them forms a permanently in flammable air, no more liable to be imbibed

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