into a phial, which I left inverted in a bason of quickfilver a whole week. It did not appear that the inclosed air was at all fenfibly affected. Had it been fo in the smallest degree, I should have repeated the process, and have allowed it more time.

Having discovered that vegetation restores, to a confiderable degree of purity, air that had been injured by refpiration or putrefaction; and also that agitation in water produces the fame effect, I conjectured that the phlogistic matter, absorbed by the water, might be imbibed by plants, as well as form other combinations with fubftances under the water. A curious fact, which has fince been communicated to me, very much favours this fuppofition.

Mr. Garrick was fo obliging as to give me the first intimation of it, and Mr. Walker, the ingenious author of a late English Dictionary, from whom he received the account, was pleased to take fome pains in making farther inquiries into it for my use. He informed me that Mr. Bremner, who keeps a mufic-shop oppofite to Somerset-house, was at Harwich, waiting for the packet; and obferved that a reservoir at the principal inn was very foul on the fides. This made him afk the inn-keeper

why

why he did not clean it out; who immediately anfwered, that he had done fo once, but would not any more; for that after cleansing the refervoir, the water which was caught in it grew fetid, and unfit for use; and that it did not recover its sweetness till the fides and bottom of the reservoir grew very foul again. Mr. Walker queftioned Mr. Bremner, whether there were any vegetables growing at the fides and bottom of it; but of this he could not be pofitive. However, as he said it was covered with a green fubftance, which is known to be vegetable matter (and indeed nothing else could well adhere to the fides, as well as to the bottom of the refervoir) I think it will be deemed probable, that it was this vegetating matter that preferved the water fweet, imbibing the phlogistic matter that was discharged in its tendency to putrefaction.

I fhall be happy, if the mention of this fact fhould excite an attention to things of this nature. Trifling Trifling as they seem to be, they have, in a philofophical view, the greatest dignity and importance; ferving to explain fome of the most striking phenomena in nature, refpecting the general plan and constitution of the fystem, and the relation that one part of it bears to another.

SEC

SECTION XI.

Of the Fluor Acid Air.

The philofophical part of the world have, of late, been highly gratified by the discovery of what was imagined to be a new mineral acid, contained in a fubftance which the chymifts distinguish by the name of fluor; but many of my readers will understand me better, when I inform them, that it is of that fpecies of fubftance, which, with ús, is called the Derbyshire fpar; and of which, at prefent, vafes and other ornaments for chimnies, are usually made. The acid is expelled from this fubftance by oil of vitriol, and has peculiar properties, as remarkable as any of the other three mineral acids which we were acquainted with before.

This curious difcovery was made by Mr. Scheele, a Swede; from which circumftance the acid is often diftinguished by the name of the Swedish acid. His method of operating upon this substance, and likewife that of all who have fucceeded him in the inquiry, was to diftil it in glafs-veffels, as in the process of making spirit of nitre from falt-petre; and the

most

moft remarkable facts that have been obferved concerning it are, that the veffels in which the diftillation is made are apt to be corroded; fo that holes will be made quite through them; and that when there is water in the recipient, the furface of it will be covered with a cruft, of a friable ftony matter.

This cruft, which I fhall diftinguish by the name of the fluor cruft, Mr. Scheele fuppofed to be quartz; and therefore concluded that this acid and water were the constituent parts of that foffil. On the other hand, Mr. Boulanger, who has taken a great deal of pains with this fubject, is of opinion that this new acid is only the acid of falt, combined with an earthy fubftance. For this opinion he advances various reasons; but does not pretend to be able to produce any decifive proof. The refult of my own experiments, I think, clearly prove, that the fluor acid is the acid of vitriol, charged with fo much phlogiston as is neceffary to its taking the form of air, and also with much of the earthy matter of the fpar.

As foon as I had exhibited one of the acids in the form of air, I had no doubt but that all the acids might be exhibited in the fame manner, and this among the reft; but I imagined that I fhould find great difficulty in procuring

the

the foffil that contains it; fuppofing that it had only been found in Sweden; and I should probably have continued in this incapacity for making the following experiments, had I not been relieved by Mr. Woulfe, who, upon my inquiry concerning it, not only explained to me what the fubftance was, but immediately furnished me with a quantity of feveral kinds of it, fufficient for my purpose. That with which my first experiments were made, was that which he called the white phosphoric fpar, from Saxony; but afterwards I made ufe of the Derbyshire fpar; and the pieces that I had by me were partly white, or yellowish, and partly purple.

All my advantage in the investigation of this fubject, has arifen from my peculiar manner of conducting the experiments. For, by exhibiting the acid in the form of air, free from all moisture, I had an opportunity of examining its nature and affinities with the greatest eafe and certainty. In this manner alfo, this fpecies of air exhibits a variety of ftriking phenomena, which cannot be produced in any other manner of operating upon it.

When I began thefe experiments, I followed the directions given by those who had gone before me in the investigation of this fubject, and who had procured the acid in the common me

thod