are being taken likewise to keep the walls adiabatic. Under these
conditions the heat brought away by the water-current during the period
of rising temperature is considerably less than that actually developed
by the electric current and the difference represents the amount of heat
absorbed by the calorimeter in the period of the temperature rise.
Conversely, during the period when the temperature is falling, there is
a considerable increase in the amount of heat brought away by the
water-current over that generated in the resistance-coil and the
difference represents exactly the amount of heat given up by the
calorimeter during the fall in temperature. It is thus possible to
measure the capacity of the calorimeter for absorbing heat during a rise
in temperature and the amount of heat lost by it during cooling. A
number of such experiments have been made with both calorimeters and it
has been found that the hydrothermal equivalent of the bed calorimeter
is not far from 21 kilograms. For the chair calorimeter a somewhat lower
figure has been found, _i. e._, 19.5 kilograms.

GENERAL DESCRIPTION OF RESPIRATION APPARATUS.

This apparatus is designed much after the principle of the
Regnault-Reiset apparatus, in that there is a confined volume of air in
which the subject lives and which is purified by its passage through
vessels containing absorbents for water and carbon dioxide. Fresh oxygen
is added to this current of air and it is then returned to the chamber
to be respired. This principle, in order to be accurate for oxygen
determinations, necessitates an absolutely air-tight system and
consequently special precautions have been taken in the construction of
the chamber and accessories.

TESTING THE CHAMBER FOR TIGHTNESS.

As already suggested, the walls are constructed of the largest possible
sheets of copper with a minimum number of seams and opportunities for
leakage. In testing the apparatus for leaks, the greatest precaution is
taken. A small air-pressure is applied and the variations in height of a
delicate manometer noted. In cases of apparent leakage, all possible
sources of leak are gone over with soapsuds when there is a slight
pressure on the chamber. As a last resort, which has ultimately proven
to be the best method of testing, an assistant goes inside of the
chamber, it is then hermetically sealed, and a slight diminished
pressure is produced. Ether is then poured about the walls of the
chamber and th