SECTION VIII.

Of Air procured by the Solution of ANIMAL SUBSTANCES in Spirit of Nitre.

I profefs not to be able to affign any reason for the difference in the produce of air from animal and vegetable fubftances; but the experiments, of which an account will be given in this fection, compared with those recited in the laft, will prove, that, in general, there is a very confiderable one.

It has been seen that vegetable fubftances, diffolved in fpirit of nitre, befides fixed air, yielded nitrous air, and frequently as ftrong as that which is procured by the folution of metals in the fame acid; and this is the cafe whether the spirit of nitre be much concentrated, or much diluted. On the contrary, animal fubftances, in general, treated in the fame manner, yield about the fame proportion of fixed air; but the refiduum is either not at all, or in a very flight degree, nitrous (except in fome cafes where the fpirit of nitre is very strong) but is a kind of air which, neither affecting common air, nor being affected by ni

trous air, but fimply extinguishing a candle, may be termed phlogisticated air. Towards the end of a procefs, indeed, when, by means of a strong heat, the produce of air is very rapid, and the air full of clouds, it is, like air produced from vegetable substances in the fame circumstances, flightly inflammable, burning with a lambent, greenish, or bluish flame.

As there is a confiderable variety in the refult of thefe proceffes, arifing from feveral circumstances, the influence of which may not be apprehended, I have been careful to note every thing relating to them, that appeared to me at the time to be of any importance. But, not*withstanding this, it is very poffible I may have made omiffions, of the effect of which I was not apprized; and therefore those who fhall endeavour to repeat the experiments after me may not find precifely the fame refults that I have reported. This will often be the cafe in experimental inquiries fo new as these; and as no human care has yet been fufficient to prevent this inconvenience, it is the part of, human candour to make proper allowance for it.

I cannot help flattering myself, however, that these experiments, properly pursued, may be a means of throwing light upon the two great natural proceffes of vegetation and animalization;

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lization; as they exhibit a new and ftriking difference between fubftances formed by them. On this account I would willingly recommend them to the particular attention of chymifts and physicians. The experiments themselves, nearly in the order in which they were made, are as follows.

I put equal quantities of fpirit of nitre and water upon fome pieces of beef, dried till they were perfectly hard, but without being burned, and took the first produce of the air, which was generated without the application of heat, and was very confiderable; and afterwards that which came over when the flame of a candle was placed within about a quarter of an inch from the phial; but neither of them fenfibly affected common air. They were both pretty readily abforbed by water, and extinguished a candle. I had expected that this air, like that from dry wood, would have been nitrous air.

This experiment being made with the fleshy part of a muscle, I next took a tendon from a neck of veal, imagining, from its firmer texture, that the air produced from it might approach nearer to that from wood; but the air that came from it neither diminished common air, nor was diminished by nitrous air, nor was

it readily abforbed by water, and a candle went out in it. It seemed, upon the whole, to be much the fame thing with phlogisticated common air.

I thought there might be fome difference in this refpect, between air produced from the white, and from the brown flesh of animals; but I made the experiment with the breaft and the leg of a turkey, without finding any. That which was produced from thefe fubftances exactly resembled the air that I had got from the tendon of the calf; except that it was more readily imbibed by water. I agitated a quantity of it in water five minutes, when one-fourth of it was abforbed, but the remainder ftill extinguished a candle, and did not differ from what it was before, except that it was now diminished by nitrous air, like all other kinds of air agitated in water. When all the flesh was diffolved, air was ftill produced in great plenty, upon the application of the flame of a candle. The air produced in this manner was very turbid at firft; but the quality of it was not fenfibly different from that which came firft, and which was tranfparent.

I repeated this experiment with the fame event, obferving that the turbidness of the air depended upon the degree of beat with which

it was produced; for, after producing a large quantity of turbid air, I leffened the heat, and presently the air was tranfparent as at firft, and upon increasing the heat, the air was turbid again.

Having found no air of the nitrous kind from the flesh of an animal of the quadruped fpecies, or of a fowl, I was willing to try what would be the produce from the flesh of fishes, infects, and exanguious animals.

From the flesh of falmon, made thoroughly dry, and then diffolved in spirit of nitre, I got a great quantity of air, at firft without heat, till the whole was nearly diffolved; when about a quarter of an ounce measure of this folution still yielded more than a quart of air. At the last this liquor, which had been pretty clear, became fuddenly opake; and in this ftate it yielded air the most plentifully, and continued to do fo till, all the moisture being evaporated, it became a dry coal. While it continued clear, a ftrong heat, occafioned by applying the flame of a candle clofe to the phial, would immediately make the air turbid, especially toward the end of the process, just before the liquor became opake. At this time, however, the air in the infide of the phial had nothing of that appearance, nothing being seen