VENTILATING AIR-CURRENT.
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.