The ventilating air-circuit may be said to consist of several portions
of air. The largest portion is that in the respiration chamber itself
and consists of air containing oxygen, nitrogen, carbon dioxide, and
water-vapor. This air is assumed to have the same composition up to the
moment when it begins to bubble through the sulphuric acid in the first
acid-absorber. The air in this absorber above the acid, amounting to
about 14 liters, has a different composition in that the water-vapor has
been completely removed. The same 14 liters of air may then be said to
contain carbon dioxide, nitrogen, and oxygen. This composition is
immediately disturbed the moment the air enters the potash-lime can,
when the carbon dioxide is absorbed and the volume of air in the last
sulphuric-acid absorber, in the sodium-bicarbonate can, and in the
piping back to the calorimeter may be said to consist only of nitrogen
and oxygen. The air then between the surface of the sulphuric acid in
the last porcelain absorber and the point where the ingoing air is
delivered to the calorimeter consists of air free from carbon dioxide
and free from water. Formerly this section also included the
tension-equalizer, but very recently we have in both of the calorimeters
attached the tension-equalizer directly to the respiration chamber.
In the Middletown apparatus, these portions of air of varying
composition were likewise subject to considerable variations in
temperature, in that the temperature of the laboratory often differed
materially from that of the calorimeter chamber itself, especially as
regards the apparatus in the upper part of the laboratory room. It is
important, however, to know the total volume of the air inclosed in the
whole system. This is obtained by direct measurement. The cubic contents
of the calorimeter has been carefully measured and computed; the volumes
of air in the pipes, valve systems, absorbing vessels, and
tension-equalizer have been computed from dimensions, and it has been
found that the total volume in the apparatus is, deducting the volume of
the permanent fixtures in the calorimeter, 1,347 liters. The
corresponding volume for the bed calorimeter is 875. These values are
altered by the subject and extra articles taken into the chamber.
From a series of careful measurements and special tests the following
apparent volumes for different parts of the system have been calculated:
Liters.
Volume of the chair calorimeter chamber (without fixtures) 1360.0
Permanent fixtures (5); chair and supports (8) 13.0
------
Apparent volume of air inside chamber 1347.0
Air in pipes, blower, and valves to surface of acid in
first acid vessel 4.5
------
Apparent volume of air containing water-vapor 1351.5
Air above surface of acid in first sulphuric-acid vessel and
potash-lime can 16.0
------
Apparent volume of air containing carbon dioxide 1367.5
Air in potash-lime can, second sulphuric-acid vessel and connections,
sodium-bicarbonate cans, and pipes to calorimeter chamber 23.5
------
Apparent volume of air containing carbon dioxide, water, oxygen,
and nitrogen 1391.0
These volumes represent conditions existing inside the chamber without
the subject, _i. e._, conditions under which an alcohol check-test would
be conducted. In an experiment with man it would be necessary to deduct
the volume of the man, books, urine bottles, and all supplemental
apparatus and accessories. Under these circumstances the apparent 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.