fifting of veffels, the capacities of which had a known proportion to each other, as f,f,f, each veffel holding twice as much as the size next less than it. It is likewife convenient to have the veffels in which the mixture of air is made, fig. g, marked in a manner correfponding to thefe phials, that the diminution of the air may be perceived at once, without the application of any meafure. If one of these phials contain an ounce-meafure, and the reft be multiples and fubdivifions of it, it will be ftill more convenient.

1

When the quantities of air to be measured are very fmall, phials will be too large. I have therefore a fet of fmall tubes, b, b, b2 bearing the fame proportion to each other with the phials, the smallest of which contains very little indeed; and likewise a longer tube, i, marked in a correfponding manner, in which to mix the air contained in thofe tubes.

SECTION

.

SECTION I.

Of VITRIOLIC Acid Air.

Had no fooner exhibited the marine acid in the form of air, than it occurred to me that it might be poffible to exhibit the other acids alfo in the fame elegant manner, divefted of the water with which they had hitherto been combined, and which muft neceffarily have been a great obstruction to the difcovery of their real natures and affinities; but not being a practical Chemift, and living in the country, where I had no accefs to any perfon of that profeffion, and indeed not being fufficiently able to explain my wants, I met with many hindrances in the profecution of my inquiries into this fubject.

My first scheme was to endeavour to get the vitriolic acid in the form of air, thinking

that it would probably be easy to confine it by quickfilver; for as to the nitrous acid, its affinity with quickfilver is fo great, that I defpaired of being able to confine it to any purpose, as I have obferved in the former volume, p. 273. I therefore wrote to my friend Mr. Lane, to procure me a quantity of volatile vitriolic acid, which is the common vitriolic acid combined with phlogifton, at the time that I was intent upon the profecution of my former experiments; but by fome mistake of my meaning, a different thing from what I intended was fent me.

Seeing Mr. Lane the winter following, he told me that if I would only heat any oily or greasy matter with oil of vitriol, I should certainly make it the very thing I wanted, viz. the volatile, or fulphureous vitriolic acid; and accordingly I meant to have proceeded upon this hint, but was prevented from pursuing it, by a variety of engagements, till after the publication of my late treatise.

Some time after this, I was in company with Lord Shelburne at the feat of Monf. Trudaine, at Montigny in France, where, with that generous and liberal fpirit by which that nobleman is diftinguished, he has a complete apparatus of philofophical inftruments,

with every other convenience and affistance for pursuing fuch philofophical inquiries as any of his numerous guests fhall chufe to entertain themselves with. In this agreeable retreat I met with that eminent philofopher ́and chymift, Monf. Montigni, Member of the Royal Academy of Sciences; and converfing with him upon this fubject, he propofed our trying to convert oil of vitriol into vapour, by boiling it with a pan of charcoal in a cracked phial. This fcheme not answering our purpose, he next propofed our heating it together with oil of turpentine. Accordingly we went to work upon it, and foon produced a quantity of fome kind of air confined by quickfilver; but our recipient being overturned by the fuddenness of the production of air, we were not able to catch any more than the first produce, which was little elfe than the common air which had lodged on the furface of the liquor, and which appeared to be a little phlogifticated, by its not being much affected by a mixture of nitrous air.

Having no opportunity of repeating the experiment at that time, I did nothing with a view to it till my return to England; when, on the 26th of November, 1774, I refumed

the operation, beginning with olive oil, and by the help of a more convenient kind of glafs veffel, reprefented fig. a, which I had procured for thefe and other fimilar purposes, I found very little difficulty in the profecution of the experiments.

As I wish that my reader may enjoy the benefit of my experience, I would caution him, if he chufe to repeat the experiments, not to put too much oil, or any other fimilar fubftance, to the oil of vitriol, in order to produce this air. I began with using about one fifth part of common oil, leaving space enough, as I thought, in the phial, for the ebullition that might be occafioned by the production of air; but as foon as the veffel was heated to a certain degree, the production of air was exceedingly rapid; and though I withdrew the candle which I had applied to it for that purpose, the ebullition continued to increafe, till, the capacity of the tube not being fufficient for the tranfmiffion of the generated air, the cork was driven out of the phial, and all the contents of it exploded.

After this I only flightly covered the spirit of vitriol in the phial with olive oil, and then the phenomena were fimilar to those in the former experiment, at the fame time that the

procefs