animals are made to breathe in the interior cavity, and the water
produced is carefully collected. Guinea pigs, which resist the effects
of cold extremely well, are well adapted for this experiment. As the
continual renewal of air is absolutely necessary in such experiments, we
blow fresh air into the interior cavity of the calorimeter by means of a
pipe destined for that purpose, and allow it to escape through another
pipe of the same kind; and that the heat of this air may not produce
errors in the results of the experiments, the tube which conveys it into
the machine is made to pass through pounded ice, that it may be reduced
to zero (32 ) before it arrives at the calorimeter. The air which
escapes must likewise be made to pass through a tube surrounded with
ice, included in the interior cavity of the machine, and the water which
is produced must make a part of what is collected, because the caloric
disengaged from this air is part of the product of the experiment.
It is somewhat more difficult to determine the specific caloric
contained in the different gasses, on account of their small degree of
density; for, if they are only placed in the calorimeter in vessels like
other fluids, the quantity of ice melted is so small, that the result of
the experiment becomes at best very uncertain. For this species of
experiment we have contrived to make the air pass through two metallic
worms, or spiral tubes; one of these, through which the air passes, and
becomes heated in its way to the calorimeter, is contained in a vessel
full of boiling water, and the other, through which the air circulates
within the calorimeter to disengage its caloric, is placed in the
interior cavity, f f f f, of that machine. By means of a small
thermometer placed at one end of the second worm, the temperature of the
air, as it enters the calorimeter, is determined, and its temperature in
getting out of the interior cavity is found by another thermometer
placed at the other end of the worm. By this contrivance we are enabled
to ascertain the quantity of ice melted by determinate quantities of air
or gas, while losing a certain number of degrees of temperature, and,
consequently, to determine their several degrees of specific caloric.
The same apparatus, with some particular precautions, may be employed
to ascertain the quantity of caloric disengaged by the condensation of
the vapours of different liquids.
The various experiments which may be made with the calorimeter do not
afford absolute conclusions, but only give us the measure of relative
quantities; we have therefore to fix a unit, or standard point, from
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