procefs was more manageable; for, by applying or withdrawing the candle, as I faw occafion, I got what quantity of air I pleased; and removing the phial, in this state of ebullition, from one veffel to another, I filled several of them with this new fpecies of air, as eafily as I had been used to do it with the marine acid air; and the whole procefs was as pleafing and as elegant. Indeed, this manner of producing air from fubftances contained in small phials, and receiving the produce in quickfilver, when it is of fuch a nature that it cannot be confined by water, has never failed to strike every perfon to whom I have fhewed it.

The moment that I faw the acid of vitriol affume the form of air by the addition of phlogifton, I concluded that the marine acid alfo must have been capable of being exhibited in the fame manner, by means of the phlogifton which it naturally contains, and which is infeparable from it; and moreover, that, probably, fome portion of phlogifton may be neceffary to the volatility and elasticity of all fubftances whatever; fo that the marine acid air may not be precifely what I had before imagined, viz. the pure marine acid in the form of air, but that, though it is by this means exhibited free from water, which, in a variety

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variety of refpects, modifies and restrains its action upon various bodies, it is ftill combined with a portion of phlogiston. Since, however, all the bodies with which we are acquainted are, in fome degree, elastic, being capable, at least, of being condensed by cold, and dilated by heat, it may not be poffible to separate this principle intirely from any fubstance in nature; and therefore, in a fenfe fufficiently near the truth, it may still be faid that the marine acid air is nothing but the marine acid the phlogiston it contains being so small, as not to be discoverable by any of the usual tests of its prefence.

Before any air is produced from the mixture of inflammable matter and oil of vitriol, the whole quantity becomes very black; and a quantity of this spirit, thus impregnated with phlogifton, will yield many times more air than an equal quantity of the strongest spirit of falt but I never measured it with any exactness.

When the vitriolic acid air is produced in great plenty, the top of the phial in which it is generated is generally filled with white vapours. This air has alfo the fame appearance as it is tranfmitted through the glass tube, and it is fometimes difcoverable in the recipient. Vitriolic

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Vitriolic acid air is equally tranfparent with marine acid air, and feems to have no more affinity with quickfilver; for when confined by quickfilver, the dimenfions of it are not liable to any variation, excepting by heat and cold, just like common air; provided there be no moisture in the recipient, or in the quickfilver. As the refemblance between these two acid airs was fo great, it was natural. for me to have a view to the experiments I had made with the marine acid air, in conducting thefe that relate to the vitriolic acid, which the reader will eafily perceive.

Water being admitted to the vitriolic acid air abforbed it about as readily as the marine açid air; and by its union with it must have formed the volatile or fulphureous acid of vitriol. Indeed the refult of this combination was fo obvious, that I did not think it neceffary to make the experiment.

Like the marine acid air, this vitriolic acid air extinguishes a candle, but without any, peculiar appearance in the colour of the flame, as it goes out, or as it is lighted again, which is obfervable when the experiment is made with the marine acid air. Vitriolic acid air is alfo heavier than common air; for a candle being let down into a veffel filled with it, was extinguished

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extinguished many times fucceffively, and even after it had ftood a full hour with its mouth expofed to the common air.

Ice is inftantly diffolved in this, as well as in the marine acid air, and the water impregnated with it continues to diffolve more ice. Upon this occafion I obferved that this acid air bears to be expofed to cold, without any greater diminution of its bulk than common air is fubject to in the fame circumstances; which appears to me to be a fufficiently proper criterion to distinguish air from vapour. In a certain degree of heat, indeed, even water may be exhibited in the form of air; but it is a degree of heat that far exceeds what is ufual in our atmosphere; and in other cafes terms are applied to very great ufe, for the distinction of bodies, which, if examined with ftrictness, would be found ultimately to run into one another, the difference between them being in degree rather than in kind: but a very great difference in degree affords a fufficient foundation for a difference in appellation.

The phenomena which attend the mixing of alkaline air with the marine acid air, were fo ftriking, that I had not been many hours in poffeffion of the vitriolic acid air without trying whether the effect of the fame mixture with

this acid air would not make a fimilar appearance, and the experiment fully anfwered my expectations. A like beautiful white cloud was formed the moment that these two kinds of air came into contact, the quantity of air was diminished as faft as the alkaline air was admitted, and the quickfilver rofe almost to top of the receiver.

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I obferved alfo, that when I put the alkaline air to the vitriolic acid air, the white cloud rofe immediately to the top of the veffel, as in the experiment with the marine acid air; which proves that the alkaline air is, in both cafes, the lighter of the two. In both cafes alfo, if the alkaline air be produced first, the acid air being admitted to it, forms a cloud which refts upon the quickfilver; never extending beyond a very small space, and rifing only as the quickfilver rifes. The fubftance that is formed by the union of the alkaline air with the vitriolic acid air, muft neceffarily be the vitriolic fal ammoniac; but I made no experiment to afcertain it. The quantity of this falt with which my receivers are coated in thefe experiments is readily diffolved in water, as in the experiments with the marine acid air. This, however, it will be feen, is not the cafe with the falt that is formed by another of the acid airs with alkaline air.

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