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"air and fire, that before made parts of the "solid."

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'i Of Marine Acid Air.

Being very much struck with the result of an experiment of the Hon. Mr. Cavendish, related Phil. Trans. Vol. LVI, p. 157, by which, though, he says he was not able to get any inflammable air from copper, by means of spirit of salt, he got a much more remarkable kind of air, viz. one that loft its elasticity by coming into contact with water, I was exceedingly desirous of making myself acquainted with it. On this account, I began with making the experiment in quicksilver, which I never failed to do in any case in which I suspected that air might either be absorbed by water, or be in any other manner affected by it; and by this means I presently got a much more distinct idea of the nature and effects of this curious solution.

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

a tall a tall glass vessel full of quicksilver, and standing in quicksilver, the whole produce continued a considerable time without any change of dimensions. 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, disappeared, the quicksilver rising in the vessel. I then introduced a considerable 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 admission of the water, I was much amused with observing the large bubbles of the newly generated air, which came through the quicksilver, the sudden 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 slow, increase of inflammable air.

Fixed air, being admitted to the whole produce of this air from copper, had no sensible effect upon it. Upon the admission of water, a great part of the mixture presently disappeared ; another part, which I suppose to have been the fixed air, was absorbed slowly ; and in this particular case the very small permanent residuum did not take fire; but it is very possible that it might have done soy-if the quantity had been greater.

The solution. of lead in the marine acid is attended with the very same .phenomena as the solution of copper in the same acid \ about three fourths. of the generated air disappearing on the admission of water \ and the remainder - being inflammable.

The solutions of iron, tin, and zinc, in the marine acid, were all attended with the fame phænomena as the solutions of copper and lead, but in a less degree; for in iron one eighth, in tin one sixth, and in zinc one terth of the generated air disappeared on the admission of water. The remainder of the air from iron, in this case, burned with a green, or very light blue flame.

I had always thought it something extraordinary, that a species of air should lose its elasticity by the mere contatl of any thing, and from the first suspected that it must have been imbibed by the water that was admitted to it; but so very great a quantity of this air disappeared upon the admission of a very small quantity of water, that at first I could not help concluding that appearances favoured the former

L hyhypothesis. I found, however, that when I admitted a much smaller quantity of water, confined in a narrow glass tube, a part only of the air disappeared, and that very slowly, and that more of it vanished upon the admission of ''more water. This observation put it beyond a doubt, that this air was properly imbibed by the water, which, being once fully saturated with it, was not capable of receiving any more.

The water thus impregnated tasted very acid, even when it was much diluted with other water, through which the tube containing it was drawn. It even dissolved iron very fast, and generated inflammable air. This last observation, together with another which immediately follows, led me to the discovery of the true nature 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 surprized to find that air was produced long after; I could not but think that the acid must have been saturated with the metal and I also found that the proportion of inflammable air to that which was absorbed by the water continually diminished, till, instead of being

, one one fourth of the whole, as I had first observed, it was not so much as one twentieth. Upon this, I concluded that this subtle air did not arise from the copper, but from the spirit of salt; 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; so that this remarkable kind of air is, in fact, nothing more than the vapour, or fumes of spirit of salt, which appear to be of such 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 airy 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 easy to ascertain. A cylindrical glass vessel, about three fourths of an inch in diameter, and four inches deep, being filled with it, and turned upside down, a lighted candle may be Jet down into it more than twenty times' before it will burn at the bottom. It is - pleasing to observe the colour of the flame in this experiment; for both before the candle goes our, and also when it is first lighted again, it burns with a beautiful green, or rather light-blue flame, , such as is seen when common salt is thrown into' the, fire. L 2 When

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