We have caused make two of the above described machines; one, which is
intended for such experiments as do not require the interior air to be
renewed, is precisely formed according to the description here given;
the other, which answers for experiments upon combustion, respiration,
&c. in which fresh quantities of air are indispensibly necessary,
differs from the former in having two small tubes in the two lids, by
which a current of atmospheric air may be blown into the interior cavity
of the machine.
It is extremely easy, with this apparatus, to determine the phenomena
which occur in operations where caloric is either disengaged or
absorbed. If we wish, for instance, to ascertain the quantity of caloric
which is disengaged from a solid body in cooling a certain number of
degrees, let its temperature be raised to 80 (212 ); it is then placed
in the interior cavity f f f f, Fig. 2. and 3. of the calorimeter, and
allowed to remain till we are certain that its temperature is reduced to
zero (32 ); the water produced by melting the ice during its cooling is
collected, and carefully weighed; and this weight, divided by the volume
of the body submitted to experiment, multiplied into the degrees of
temperature which it had above zero at the commencement of the
experiment, gives the proportion of what the English philosophers call
specific heat.
Fluids are contained in proper vessels, whose specific heat has been
previously ascertained, and operated upon in the machine in the same
manner as directed for solids, taking care to deduct, from the quantity
of water melted during the experiment, the proportion which belongs to
the containing vessel.
If the quantity of caloric disengaged during the combination of
different substances is to be determined, these substances are to be
previously reduced to the freezing degree by keeping them a sufficient
time surrounded with pounded ice; the mixture is then to be made in the
inner cavity of the calorimeter, in a proper vessel likewise reduced to
zero (32 ); and they are kept inclosed till the temperature of the
combination has returned to the same degree: The quantity of water
produced is a measure of the caloric disengaged during the combination.
To determine the quantity of caloric disengaged during combustion, and
during animal respiration, the combustible bodies are burnt, or the
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