BLIOTECAR

- the burning of candles; but if this be the cafe,, and the change be produced gradually, it must require a long time for the purpose. For on the 22d of September, 1772, I examined a quantity of common air, which had been kept in a phial, without agitation, from May 1771, and found it to be in no refpect worse than fresh air, even by the test of the nitrous air.

7. The cryftallization of nitre makes no fenfible alteration in the air in which the process is made. For this purpose I diffolved as much nitre as a quantity of hot water would contain, and let it cool under a receiver, ftanding in

water.

8. November 6, 1772, a quantity of inflammable air, which, by long keeping, had come to extinguish flame, I obferved to fmell very much like common air in which a mixture of iron filings and brimstone had flood. It was not, however, quite fo ftrong, but it was equally

noxious.

9.

Bifmuth and nickel are diffolved in the marine acid with the application of a confiderable degree of heat; but little or no air is got from either of them; but, what I thought a little remark

M

markable, both of them fmelled very much like Harrowgate water, or liver of fulphur. This fmell I have met with feveral times in the course of my experiments, and in proceffes very diffe-. rent from one another.

PART

PART II...

Experiments and Obfervations made in the Year 1773, and the Beginning of 1774.

A

SECTION I.

Obfervations on ALKALINE AIR.

FTER I had made the difcovery of the

marine acid air, which the vapour of fpirit of falt may properly enough be called, and had made those experiments upon it, of which I have given an account in the former part of this work, and others which I propofe to recite in this part; it occurred to me, that, by a process fimilar to that by which this acid air is expelled from the spirit of falt, an alkaline air might be expelled from fubftances containing volatile alkali.

Accordingly I procured fome volatile spirit of fal ammoniac, and having put it into a thin phial, and heated it with the flame of a candle, I presently found that a great quantity of vapour was difcharged from it; and being received in a veffel of quickfilver, ftanding in a bason of quickfilver, it continued in the form of a tranfparent and permanent air, not at all condenfed by cold; so that I had the fame opportunity of making experiments upon it, as I had before on the acid air, being in the fame favourable circumstances.

With the fame eafe I also procured this air from Spirit of hartshorn, and fal volatile either in a fluid or folid form, i. e. from those volatile alkaline falts which are produced by the distillation of fal ammoniac with fixed alkalis. But in this cafe I foon found that the alkaline air I procured was not pure; for the fixed air, which entered into the compofition of my materials, was expelled along with it. Alfo, uniting again with the alkaline air, in the glass tube through which they were conveyed, they stopped it up, and were often the means of bursting my veffels.

While thefe experiments were new to me, I imagined that I was able to procure this air with peculiar advantage and in the greatest

abun

abundance, either from the falts in a dry ftate, when they were just covered with water, or in a perfectly fluid ftate; for upon applying a candle to the phials in which they were contained, there was a moft aftonishing production of air; but having examined it, I found it to be chiefly fixed air, especially atter the firft or fecond produce from the fame materials; and removing my apparatus to a trough of water, and ufing the water instead of quickfilver, I found that it was not presently absorbed by it.

'This, however, appears to be an eafy and elegant method of procuring fixed air, from a fmall quantity of materials, though there must be a mixture of alkaline air along with it; as it is by means of its combination with this principle only, that it is poffible, that fo much fixed air fhould be retained in any liquid. Water, at least, we know, cannot be made to contain much more than its own bulk of fixed air.

After this disappointment, I confined myself to the use of that volatile spirit of fal ammoniac which is procured by a diftillation with flaked lime, which contains no fixed air; and which feems, in a general ftate, to contain about as much alkaline air, as an equal quantity of fpirit of falt contains of the acid air.