* Or fix in sulphur. l. 226. The phenomena of chemical explosions cannot be accounted for without the supposition, that some of the bodies employed contain concentrated or solid heat combined with them, to which the French Chemists have given the name of Calorique. When air is expanded in the air-pump, or water evaporated into steam, they drink up or absorb a great quantity of heat; from this analogy, when gunpowder is ex∣ploded it ought to absorb much heat, that is, in popular language, it ought to produce a great quantity of cold. When vital air is united with phlogistic matter in respiration, which seems to be a slow combustion, its volume is lessened; the carbonic acid, and per∣haps phosphoric acid are produced; and heat is given out; which according to the ex∣periments of Dr. Crawford would seem to be deposited from the vital air. But as the vital air in nitrous acid is condensed from a light elastic gas to that of a heavy fluid, it must possess less heat than before. And hence a great part of the heat, which is given out in firing gunpowder, I should suppose, must reside in the sulphur or charcoal.

Mr. Lavoisier has shewn, that vital air, or Oxygene, looses less of its heat when it becomes one of the component parts of nitrous acid, than in any other of its combinations; and is hence capable of giving out a great quantity of heat in the explosion of gunpowder; but as there seems to be great analogy between the matter of heat, or Calorique, and the electric matter; and as the worst conductors of electricity are believed to contain the greatest quantity of that fluid; there is reason to suspect that the worst conductors of heat may contain the most of that fluid; as sulphur, wax, silk, air, glass. See note on l. 174 of this Canto.


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