The special features of the respiration chamber are the ventilating-pipe
system and openings for supplementary apparatus for absorption of water
and carbon dioxide. The air entering the chamber is absolutely dry and
is directed into the top of the chamber immediately above the head of
the subject. The moisture given off from the lungs and skin and the
expired gases all tend to mix readily with this dry air as it descends,
and the final mixture of gases is withdrawn through an opening near the
bottom of the chamber at the front. Under these conditions, therefore,
we believe we have a maximum intermingling of the gases. However, even
with this system of ventilation, we do not feel that there is
theoretically the best mixture of gases, and an electric fan is used
inside of the chamber. In experiments where there is considerable
regularity in the carbon-dioxide production and oxygen consumption, the
system very quickly attains a state of equilibrium, and while the
analysis of the outcoming air does not necessarily represent fairly the
actual composition of the air inside of the chamber, it evidently
represents to the same degree from hour to hour the state of equilibrium
that is usually maintained through the whole of a 6-hour experiment.
The interior of the chamber and all appliances are constructed of metal
except the chair in which the subject sits. This is of hard wood, well
shellacked, and consequently non-porous. With this calorimeter it is
desired to make studies regarding the moisture elimination, and
consequently it is necessary to avoid the use of all material of a
hygroscopic nature. Although the chair can be weighed from time to time
with great accuracy and its changes in weight obtained, it is obviously
impossible, in any type of experiment thus far made, to differentiate
between the water vaporized from the lungs and skin of the man and that
from his clothes. Subsequent experiments with a metal chair, with
minimum clothing, with cloth of different textures, without clothing,
with an oiled skin, and various other modifications affecting the
vaporization of water from the body of the man will doubtless throw more
definite light upon the question of the water elimination through the
skin. At present, however, we resort to the use of a wooden chair,
relying upon its changes in weight as noted by the balance to aid us in
apportioning the water vaporized between the man and his clothing and
the chair.
The walls of the chamber are semi-rigid. Owing to the calorimetric
features of this apparatus, it is impracticable to use heavy
boiler-plate or heavy metal walls, as the sluggishness of the changes in
temperature, the mass of metal, and its relatively large hydrothermal
equivalent would interfere seriously with the sensitiveness of the
apparatus as a calorimeter. Hence we use copper walls, with a fair
degree of rigidity, attached to a substantial structural-steel support;
and for all practical purposes the apparatus can be considered as of
constant volume. Particularly is this the case when it is considered
that the pressure inside of the chamber during an experiment never
varies from the atmospheric pressure by more than a few millimeters of
water. It is possible, therefore, from the measurements of this chamber,
to compute with considerable accuracy the absolute volume. The apparent
volume has been calculated to be 1,347 liters.