If that mode of vibration which conftitutes heat be the means of converting phlogiston from that state in which it makes a part of solid bodies, and eminently contributes to the firmness of their texture into that state in which it diminishes common air; may not that peculiar kind of vibration by which Dr. Hartley fupposes the brain to be affected, and by which he endeavours to explain all the phenomena of fenfation, ideas, and mufcular motion, be the means by which the phlogiston, which is conveyed into the fyftem by nutriment, is converted into that form or modification of it of which the electric fluid confifts.

These two states of phlogifton may be conceived to resemble, in fome measure, the two ftates of fixed air, viz. elaftic, or non-elaftic; a folid, or a fluid.

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APPENDIX.

N this Appendix I fhall present the reader

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with the communications of feveral of my friends on the fubject of the preceding work. Among them I fhould with pleasure have inferted fome curious experiments, made by Dr. Hulme of Halifax, on the air extracted from Buxton water, and on the impregnation of feveral fluids, with different kinds of air; but that he informs me he proposes to make a feparate publication on the subject.

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NUMBER I.

EXPERIMENTS made by Mr. Hey to prove that there is no OIL of VITRIOL in water impregnated with FIXED AIR.

It having been suggested, that air arising from a fermenting mixture of chalk and oil of vitriol might carry up with it a finall portion of the vitriolic acid, rendered volatile by the act of fermentation; I made the following experiments, in order to difcover whether the acidulous tafte, which water impregnated with fuch air affords, was owing to the prefence of any acid, or only to the fixed air it had abforbed.

EXPERIMENT I.

I mixed a tea-fpoonful of fyrup of violets with an ounce of diftilled water, faturated with fixed air procured from chalk by means of the vitriolic acid; but neither upon the first mixture, nor after standing 24 hours, was the colour of the fyrup at all changed, except by its fimple dilution.

EXPERIMENT II.

A portion of the fame diftilled water, unimpregnated with fixed air, was mixed with the fyrup in the fame proportion: not the leaft difference in colour could be perceived betwixt this and the above-mentioned mixture.

EXPERIMENT III.

One drop of oil of vitriol being mixed with a pint of the fame diftilled water, an ounce of this water was mixed with a tea-spoonful of the fyrup. This mixture was very diftinguishable in colour from the two former, having a purplish cast, which the others wanted.

EXPERIMENT IV.

The diftilled water impregnated with fo fmall a quantity of vitriolic acid, having a more agreeable taste than when alone, and yet manifefting the prefence of an acid by means of the fyrup of violets; I fubjected it to fome other tefts of acidity. It formed curds when agitated with foap, lathered with difficul ty, and very imperfectly; but not the least ebullition could be difcovered upon dropping in spirit of fal ammoniac, or solution of falt of tartar, though I had taken care to render the latter free from caufticity by impregnating it with fixed air.

EXPERIMENT V.

The diftilled water saturated with fixed air neither effervefced, nor fhewed any clouds, when mixed with the fixed or volatile alkali.

EXPERIMENT VI.

No curd was formed by pouring this water upon an equal quantity of milk, and boiling them toge ther.

EXPERIMENT VII.

When agitated with foap, this water, produced curds, and lathered with fome difficulty; but not fo much as the diftilled water mixed with vitriolic acidin the very small proportion above-mentioned. The fame diftilled water without any impregnation of fixed air lathered with foap without the least previous curdling. River-water, and a pleasant pump-water, not remarkably hard, were compared with thefe. The former produced curds before it fathered, but not quite in fo great a quantity as the diftilled water impregnated with fixed air: the latter caused a stronger curd than any of the others above-mentioned.

EXPERIMENT VIII.

Apprehending that the fixed air in the diftilled wa ter occafioned the coagulation, or feparation of the oily part of the soap, only by destroying the caufticity of the lixivium, and thereby rendering the union lefs perfect betwixt that and the tallow, and not by the prefence of any acid; I impregnated a fresh quantity of the fame diftilled water with fixed air, which had paffed through half a yard of a wide barometertube filled with falt of tartar; but this water caufed the fame curdling with foap as the former had done, and appeared in every refpect to be exactly the fame.

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