[Illustration: FIG. 27.--Diagram of ventilation of respiration
calorimeter. The air is taken out at lower right-hand corner and forced
by the blower through the apparatus for absorbing water and carbon
dioxide. It returns to the calorimeter at the top. Oxygen can be
introduced into the chamber itself as need is shown by the tension
equalizer.]
The ventilating air-current is so adjusted that the air which leaves the
chamber is caused to pass through purifiers, where the water-vapor and
the carbon dioxide are removed, and then, after being replenished with
fresh oxygen, it is returned to the chamber ready for use. The general
scheme of the respiration apparatus is shown in fig. 27. The air leaving
the chamber contains carbon dioxide and water-vapor and the original
amount of nitrogen and is somewhat deficient in oxygen. In order to
purify the air it must be passed through absorbents for carbonic acid
and water-vapor and hence some pressure is necessary to force the gas
through these purifying vessels. This pressure is obtained by a small
positive rotary blower, which has been described previously in
detail.[18] The air is thus forced successively through sulphuric acid,
soda or potash-lime, and again sulphuric acid. Finally it is directed
back to the respiration chamber free from carbon dioxide and water and
deficient in oxygen. Pure oxygen is admitted to the chamber to make up
the deficiency, and the air thus regenerated is breathed again by the
subject.