in use, represents exactly 10
liters measured under the conditions obtaining inside of the respiration
chamber, and in order to find the total amount of water-vapor present in
the chamber it is necessary only to multiply the weight of water found
in the 10-liter sample by one-tenth of the total volume of air
containing water-vapor.

The total volume of air which contains water-vapor is not far from 1,360
liters; consequently multiplying the weight of water in the sample by
136 gives the total amount of water in the chamber and the piping. The
volume of air containing carbon dioxide is that contained in the chamber
and piping to the first sulphuric-acid vessel plus 16 liters of air
above the sulphuric acid and connections in the first porcelain vessel,
and in order to obtain the amount of carbon dioxide from the sample it
is only necessary to multiply the weight of carbon dioxide in the sample
by 137.6.

Since in the calculation of the total amount of residual oxygen volumes
rather than weights of gases are used, it is our custom to convert the
weights of carbon dioxide and water-vapor in the chamber to volumes by
multiplying by the well-known factors. The determination of oxygen
depends upon the knowledge of the true rather than the apparent volume
of air in the system, and consequently the apparent volume must be
reduced to standard conditions of temperature and pressure each time the
calculation is made. To this end, the total volume of air in the
inclosed circuit (including that in the tension-equalizer, amounting to
1,400 liters in all) is reduced to 0 deg. and 760 millimeters by the usual
methods of computation. The total volume of air (which may be designated
as _V_) includes the volumes of carbon dioxide, water-vapor, oxygen, and
nitrogen. From the calculations mentioned above, the volumes of
water-vapor and carbon dioxide have been computed, and deducting the sum
of these from the reduced volume of air gives the volume of oxygen plus
nitrogen. If the volume of nitrogen is known, obviously the volume of
oxygen can be found.

At the beginning of the experiment, it is assumed that the chamber is
filled with ordinary air. By calculating the amount of nitrogen in the
chamber at the start as four-fifths of the total amount, no great error
is introduced. In many experiments actual analyses of the air have been
made at the moment of the beginning of the experiment. The important
thing to bear in mind is that having