of

feen to be confiderably different from what they are when combined, as ufual, with water; but in all the trials that I have made, the vegetable acid, even in this most advantageous form of air, appears to be weaker than any the three mineral acids, exactly as might be concluded from what was known before concerning it. For this vegetable acid air was not able to decompose any substance into the compofition of which any of the mineral acids entered. It made no impreffion upon brimftone, falt-petre, common falt, or fal ammoniac; nor yet upon borax.

Charcoal imbibes vegetable acid air very faft, and afterwards the fmell of it is extremely pungent; but the air which remains feems not to have been altered by any thing that it had got from the charcoal.

Liver of fulphur imbibes vegetable acid air but flowly, and is neither difcoloured nor diffolved by it. When only one tenth part of the air remained, I examined it, and found it to have nothing inflammable in it, which was the only effect that I had expected from it.

Water imbibes vegetable acid air as readily as any of the other acid airs. I once endeayoured to ascertain the quantity of this air that a given

a given quantity of water would imbibe, and to measure, the increase of weight and bulk that it might acquire by this impregnation, as I had in fome measure done with refpect to the marine acid, and alkaline airs: but the experiment did not fucceed to my wish; and I did it not think it worth my while to attempt again.

For this purpose I put a fmall quantity of water into a glass tube; but it was no fooner introduced to the acid air, through the quickfilver, by which it was confined, than a small bubble of common air at the closed end of the tube began to fwell, and it continued to do fo till it threw out all the water. The cafe was the fame when the end of the tube was hermetically fealed. I had the same result from Spirit of wine introduced into this acid air, in the fame circumftances, only the effect was produced much quicker. With oil of turpentine this effect was produced more quickly ftill; but with olive oil much more flowly.

From this experiment I was led to imagine, that common air received a great expansion by the effluvium of this vegetable acid; and I therefore expected that a quantity of the liquid acid admitted to common air, confined by quickfilver, would make it expand as

ether

ether had done; but this was fo far from being the cafe, that, after fome time, the air appeared to be diminished, and extinguished a candle, fo that it must have got phlogiston from the acid.

I made a fecond experiment of this kind, the refult of which was, that a quantity of common air, which had been exposed fix weeks to the effluvium of a fmall quantity of the liquid vegetable acid (contained in a cup, which swam upon the furface of the water, by which the air was confined) was fo far in-. jured, that two measures of it, and one of nitrous air did not occupy the space of quite two measures; that is, it was almoft as noxious as it could be made by any phlogistic pro

cefs.

Sufpecting that the water, which was rather foul, might have contributed to this injury, I expofed, for the last five weeks of the time, an equal quantity of common air, in a jar of the fame fize, standing in the fame trough of water, and in all other refpects in fimilar circumstances. But this air, though a little injured, was hardly to be diftinguished from common air fo that there could be no doubt but that, in the laft-mentioned experiment,

3

;

the

the injury which the air had received, came from the effluvia of the vegetable acid.

Vegetable acid air is abforbed pretty readily by olive oil. A quantity of this oil abforbed about ten times its bulk of this air; and from being of a yellowish colour, as this oil naturally is, it became almost colourlefs, like water; which I thought not a little remarkable; as all the other acid airs deepen the colour of every species of oil, making them brown, and at the fame time vifcid, approaching to the consistence of refin; whereas this oil, in the experiment juft now mentioned, became rather lefs vifcid than before, a little approaching to the limpidity of water, or rather, more resembling an effential oil,

SEC

SECTION III.

Of DEPHLOGISTICATED Air, and of the conftitution of the Atmosphere,

The contents of this fection will furnish a very ftriking illuftration of the truth of a remark, which I have more than once made in my philofophical writings, and which can hardly be too often repeated, as it tends greatly to encourage philofophical investigations ; viz. that more is owing to what we call chance, that is, philofophically speaking, to the obfervation of events arifing from unknown causes, than to any proper defign, or pre-conceived theory in this business. This does not appear in the works of those who write fynthetically upon these subjects; but would, I doubt not, appear very ftrikingly in thofe who are the most celebrated for their philofophical acumen, did they write analytically and ingenuously.

For my own part, I will frankly acknowledge, that, at the commencement of the experiments recited in this fection, I was fo far from having formed any hypothefis that led to the discoveries I made in pursuing them, that

they