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
exploded 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 perhaps phosphoric acid
are produced; and heat is given out; which according to the experiments
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.]

[_Vitrescent sparks_. l. 229. When flints are struck against other
flints they have the property of giving sparks of light; but it seems to
be an internal light, perhaps of electric origin, very different from
the ignited sparks which are struck from flint and steel. The sparks
produced by the collision of steel with flint appear to be globular
particles of iron, which have been fused, and imperfectly scorified or