he range of chemical affinity unite with more or less
violence; the motion of transition of the particles is transformed,
wholly or in part, into a vibratory or rotary motion, either of the
particles themselves or the interatomic ether; and according to the
quality of the motions we are as a rule, besides other effects, made
conscious of heat or light, or of both. When these emanations come to
be examined they are found to be complex in the extreme, intimately
bound up together, and yet capable of being separated and analyzed.

As soon as the law of definite chemical combination was firmly
established, the circumstance that changes of temperature accompanied
most chemical combinations was noticed, and chemists were not long in
suspecting that the amount of heat developed or absorbed by chemical
reaction should be as much a property of the substances entering into
combination as their atomic weights. Solid ground for this expectation
lies in the dynamic theory of heat. A body of water at a given height
is competent by its fall to produce a definite and invariable quantity
of heat or work, and in the same way two substances falling together
in chemical union acquire a definite amount of kinetic energy, which,
if not expended in the work of molecular changes, may also by suitable
arrangements be made to manifest a definite and invariable quantity of
heat.

At the end of last century Lavoisier and Laplace, and after them, down
to our own time, Dulong, Desprez, Favre and Silbermann, Andrews,
Berthelot, Thomson, and others, devoted much time and labor to the
experimental determination of the heat of combustion and the laws
which governed its development. Messrs. Favre and Silbermann, in
particular, between the years 1845 and 1852, carried out a splendid
series of experiments by means of the apparatus partly represented in
Fig. 1 (opposite), which is a drawing one-third the natural size of
the calorimeter employed. It consisted essentially of a combustion
chamber formed of thin copper, gilt internally. The upper part of the
chamber was fitted with a cover through which the combustible could be
introduced, with a pipe for a gas jet, with a peep hole closed by
adiathermanous but transparent substances, alum and glass, and with a
branch leading to a thin copper coil surrounding the lower part of the
chamber and descending below it. The whole of this portion of the
apparatus was plunged into a thin copper vessel, silvered interna