through (10/011) = 9 deg. C., or, which comes to the same thing, will heat 9
kilos, of steel through 1 deg. C.; and similarly, 1 large calorie will raise
4 kilos. of calcium carbide 1 deg. C. in temperature, or 1 kilo. 4 deg. C.
The fact that a definite quantity of heat is manifested when a known weight
of calcium carbide is decomposed by water is only typical; for in every
chemical process some disturbance of heat, though not necessarily of
sensible (or thermometric) character, occurs, heat being either absorbed
or set free. Moreover, if when given weights of two or more substances
unite to form a given weight of another substance, a certain quantity of
heat is set free, precisely the same amount of heat is absorbed, or
disappears, when the latter substance is decomposed to form the same
quantities of the original substances; and, _per contra_, if the
combination is attended by a disappearance of heat, exactly the same
amount is liberated when the compound is broken up into its first
constituents. Compounds are therefore of two kinds: those which absorb
heat during their preparation, and consequently liberate heat when they
are decomposed--such being termed endothermic; and those which evolve
heat during their preparation, and consequently absorb heat when they are
decomposed--such being called exothermic. If a substance absorbs heat
during its formation, it cannot be produced unless that heat is supplied
to it; and since heat, being a form of motion, is equally a form of
energy, energy must be supplied, or work must be done, before that
substance can be obtained. Conversely, if a substance evolves heat during
its formation, its component parts evolve energy when the said substance
is being produced; and therefore the mere act of combination is
accompanied by a facility for doing work, which work may be applied in
assisting some other reaction that requires heat, or may be usefully
employed in any other fashion, or wasted if necessary. Seeing that there
is a tendency in nature for the steady dissipation of energy, it follows
that an exothermic substance is stable, for it tends to remain as it is