MM. Berthelot and Vielle have recently been studying the influence of
the density of detonating gaseous mixtures upon the pressure
developed. The measure of pressure developed by the same gaseous
system, taken under two initial states of different density to which
the same quantity of heat is communicated, is an important matter in
thermodynamics. If the pressures vary in the same ratio as the
densities, we may conclude, independently of all special hypotheses on
the laws of gases, first, that the specific heat of the system is
independent of its density (that is to say, of its initial pressure),
and depends only on the absolute temperature, whatever that may mean;
and secondly, that the relative variation of the pressure at constant
volume, produced by the introduction of a determinate quantity of
heat, is also independent of the pressure, and a function only of the
temperature. Lastly, the pressure itself will vary proportionally with
the absolute temperature, as defined by the theory of a perfect gas,
and will serve to determine it. MM. Berthelot and Vielle operated with
a bomb, at first kept at ordinary temperatures in the air, and
afterward heated in an oil bath to 153 deg. Cent. They also employed
isomeric mixtures of the gases; methylic ether, cyanogen, hydrogen,
acetylene, and other gases were experimented upon, and the general
conclusions are as follows: 1. The same quantity of heat being
furnished to a gaseous system, the pressure of the system varies
proportionally to the density of the system. 2. The specific heat of
the gas is sensibly independent of the density as well toward very
high temperatures as about deg. Cent. This is all true for densities
near to those that the gas possesses cold under normal pressure, and
which varied in the experiment to double the original value. 3. The
pressure increases with the quantity of heat furnished to the same
system. 4. The apparent specific heat increases parallel with this
quantity of heat. These conclusions are independent of all hypotheses
on the nature and laws of gases, and were simply drawn from the
experiments in question.
* * * * *