by any other heat by means of the ice contained in the
general lid, Fig. 7. and in the external cavity. Experiments of this
kind last from fifteen to twenty hours; they are sometimes accelerated
by covering up the substance in the interior cavity with well drained
ice, which hastens its cooling.

The substances to be operated upon are placed in the thin iron bucket,
Fig. 8. the cover of which has an opening fitted with a cork, into which
a small thermometer is fixed. When we use acids, or other fluids capable
of injuring the metal of the instruments, they are contained in the
matras, Fig. 10. which has a similar thermometer in a cork fitted to its
mouth, and which stands in the interior cavity upon the small
cylindrical support RS, Fig. 10.

It is absolutely requisite that there be no communication between the
external and middle cavities of the calorimeter, otherwise the ice
melted by the influence of the surrounding air, in the external cavity,
would mix with the water produced from the ice of the middle cavity,
which would no longer be a measure of the caloric lost by the substance
submitted to experiment.

When the temperature of the atmosphere is only a few degrees above the
freezing point, its heat can hardly reach the middle cavity, being
arrested by the ice of the cover, Fig. 7. and of the external cavity;
but, if the temperature of the air be under the degree of freezing, it
might cool the ice contained in the middle cavity, by causing the ice
in the external cavity to fall, in the first place, below zero (32 deg.).
It is therefore essential that this experiment be carried on in a
temperature somewhat above freezing: Hence, in time of frost, the
calorimeter must be kept in an apartment carefully heated. It is
likewise necessary that the ice employed be not under zero (32 deg.); for
which purpose it must be pounded, and spread out thin for some time, in
a place of a higher temperature.

The ice of the interior cavity always retains a certain quantity of
water adhering to its surface, which may be supposed to belong to the
result of the experiment; but as, at the beginning of each experiment,
the ice is already saturated with as much water as it can contain, if
any of the water produced by the caloric should remain attached to the
ice, it is evident, that very nearly an equal quantity of what adhered
to it before the experiment must have run down into the vessel F in its
stead; for the inner surface of the ic