t volume
of the air in the chamber may at times be diminished by nearly 90 to 100
liters. At the beginning of each experiment the apparent volume of air
is calculated.

RESIDUAL ANALYSES.

CALCULATION FROM RESIDUAL ANALYSES.

The increment in weight of the absorbers for water and carbon dioxide
and the loss in weight of the oxygen cylinder give only an approximate
idea of the amounts of carbon dioxide and water-vapor produced and
oxygen absorbed during the period, and it is necessary to make
correction for change in the composition of the air as shown by the
residual analyses and for fluctuations in the actual volume. In order to
compute from the analyses the total carbon-dioxide content of the
residual air, it is necessary to know the relation of the air used for
the sample to the total volume, and thus we must know accurately the
volume of air passing through the gas-meter.

In the earlier apparatus 10-liter samples were used, and the volume of
the respiration chamber was so large that it was necessary to multiply
the values found in the residual sample by a very large factor, 500.
Hence, the utmost caution was taken to procure an accurate measurement
of the sample, the exact amounts of carbon dioxide absorbed, and
water-vapor absorbed. To this end a large number of corrections were
made, which are not necessary with the present type of apparatus with a
volume of residual air of but about 1,300 liters, and accordingly the
manipulation and calculations have been very greatly simplified.

While formerly pains were taken to obtain the exact temperature of the
air leaving the gas-meter, with this apparatus it is unnecessary. When
the earlier type of apparatus was in use there were marked changes in
the temperature of the calorimeter laboratory and in the water in the
meter which were naturally prejudicial to the accurate measurement of
the volume of samples, but with the present control of temperature in
this laboratory it has been found by repeated tests that the temperature
of the water in the meter does not vary a sufficient amount to justify
this painstaking measurement and calculation. Obviously, this
observation also pertains to the corrections for the tension of aqueous
vapor. It has been found possible to assume an average laboratory
temperature and reduce the volume as read on the meter by means of a
constant factor.

The quantity of air passing through the meter is so adjusted that
exactly 10 liters as