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SECTION IX.

Of MARINE ACID AIR.

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Being very much ftruck with the refult of an experiment of the Hon. Mr. Cavendish, related Phil. Tranf. Vol. LVI. p. 157, by which, though, he fays he was not able to get any flammable air from copper, by means of fpirit of falt, he got a much more remarkable kind of air, viz. one that loft its elafticity by coming into contact with water, I was exceedingly defirous of making myself acquainted with it. On this account, I began with making the experiment in quick filver, which I never failed to do in any cafe in which I suspected that air might either be abforbed by water, or be in any other manner affected by it; and by this means I prefently got a much more diftinct idea of the nature and effects of this curious folution.

Having put fome copper filings into a small phial, with a quantity of fpirit of falt; and making the air (which was generated in great plenty, on the application of heat) ascend into

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a tall glass veffel full of quickfilver, and standing in quickfilver, the whole produce continued a confiderable time without any change of dimenfions. I then introduced a small quantity of water to it; when about three fourths of it (the whole being about four ounce measures) presently, but gradually, dif appeared, the quickfilver rifing in the veffel. I then introduced a confiderable quantity of water; but there was no farther diminution of the air, and the remainder I found to be inflammable.

Having frequently continued this process a long time after the admiffion of the water, I was much amufed with obferving the large bubbles of the newly generated air, which came through the quickfilver, the fudden diminution of them when they came to the water, and the very small bubbles which went through the water. They made, however, a continual, though flow, increase of inflammable air.

Fixed air, being admitted to the whole produce of this air from copper, had no fenfible effect upon it. Upon the admiffion of water, a great part of the mixture prefently disappeared; another part, which I fuppofe to have been the fixed air, was absorbed flowly; and in this particular cafe the very small permanent

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refiduum did not take fire; but it is very poffible that it might have done fo, if the quantity had been greater.

The folution of lead in the marine acid is attended with the very fame phænomena as the folution of copper in the fame acid; about three fourths of the generated air difappearing on the admiffion of water; and the remainder being inflammable.

The folutions of iron, tin, and zinc, in the marine acid, were all attended with the fame phænomena as the folutions of copper and lead, but in a lefs degree; for in iron one eighth, in tin one fixth, and in zinc one tenth of the generated air difappeared on the admiffion of water. The remainder of the air from iron, in this cafe, burned with a green, or very light blue flame.

I had always thought it fomething extraordinary, that a fpecies of air fhould lofe its elafticity by the mere contact of any thing, and from the first fufpected that it must have been imbibed by the water that was admitted to it; but so very great a quantity of this air difappeared the admiffion of a very fmall quanupon tity of water, that at first I could not help concluding that appearances favoured the former

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hypothefis. I found, however, that when I admitted a much fmaller quantity of water, confined in a narrow glafs tube, a part only of the air disappeared, and that very flowly, and that more of it vanished upon the admiffion of more water. This obfervation put it beyond a doubt, that this air was properly imbibed by the water, which, being once fully faturated with it, was not capable of receiving any

more.

The water thus impregnated tafted very acid, even when it was much diluted with other water, through which the tube containing it was drawn. It even diffolved iron very fast, and generated inflammable air. This laft obfervation, together with another which immediately follows, led me to the difcovery of the true na ture of this remarkable kind of air.

Happening, at one time, to use a good deal of copper and a small quantity of spirit of salt, in the generation of this kind of air, I was furprized to find that air was produced long after; I could not but think that the acid must have been faturated with the metal; and I alfo found that the proportion of inflammable air to that which was abforbed by the water continually diminished, till, instead of being

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one fourth of the whole, as I had first observed, it was not fo much as one twentieth. Upon this, I concluded that this fubtle air did not arise from the copper, but from the fpirit of falt; and presently, making the experiment with the acid only, without any copper, or metal of any kind, this air was immediately produced in as great plenty as before; fo that this remarkable kind of air is, in fact, nothing more than the vapour, or fumes of fpirit of falt, which appear to be of fuch a nature, that they are not liable to be condensed by cold, like the vapour of water, and other fluids, and therefore may be very properly called an acid air, or more restrictively, the marine acid air.

This elastic acid vapour, or acid air, extinguishes flame, and is much heavier than common air; but how much heavier, will not be eafy to ascertain. A cylindrical glafs veffel, about three fourths of an inch in diameter, and four inches deep, being filled with it, and turned upfide down, a lighted candle may be let down into it more than twenty times before it will burn at the bottom. It is pleafing to obferve the colour of the flame in this experiment; for both before the candle goes out, and also when it is first lighted again, it burns with a beautiful green, or rather light-blue flame, fuch as is feen when common falt is thrown into the fire.

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