706 Journal of Agricultural Research vol. vi, No. 18 



Oxygen to replace that consumed by the active material in the cham- 

 ber is introduced into the air circuit from a reservoir of the gas. The 

 quantity admitted is ascertained from the loss in weight of the container 

 or by passing the gas through a meter. The amount admitted to the 

 system and the change in the quantity of oxygen in the circulating air 

 during a given period show the oxygen consumption of the material in 

 the chamber. 



A very light rubber bag on tne end of a small copper tube extending 

 from the chamber affords some variability in the capacity of the system, 

 and by thus allowing for changes in the volume of gas present resulting 

 from lack of uniformity in the rates of absorption of gas from the circu- 

 lating air and the admission of other gas to it, or from changes in the tem- 

 perature of the air within the chamber or in barometric pressure without, 

 serves as an air-tension equalizer. 



REMOVING WATER VAPOR AND CARBON DIOXID FROM THE AIR 



The air withdrawn from the respiration chamber is forced first through 

 sulphuric acid, which removes water vapor from it, and then through 

 soda-lime, which removes carbon dioxid. The containers for the acid 

 and the soda-lime, together with the air pump and the small electric motor 

 by which it is actuated, are mounted on a stand with four shelves, called 

 the absorber table (PI. XCII). There are two parallel trains of absorbers 

 on one shelf, one of which is in use while the units of the other are weighed 

 and replenished. 



The rotary air pump by which the circulation of air is maintained 

 through the respiration chamber and the purifying devices has a capacity 

 of approximately ioo c. c. per revolution, which is uniform for different 

 rates of speed up to several hundred revolutions per minute. It is thus 

 possible to vary the rate of ventilation of the chamber within a wide range 

 simply by regulating the velocity of the pump, which is easily accom- 

 plished by means of a suitable rheostat to govern the speed of the motor 

 which drives it. The rate of ventilation can be still further controlled, if 

 desired, by means of a shunt in the air line between the inlet and outlet 

 pipes of the air pump, with a valve to regulate the circulation through it. 

 In the experiments for which the apparatus has thus far been used the 

 former method has been sufficient, the pump being driven at a speed of 

 ioo revolutions per minute, forcing 10 liters of air per minute through the 

 system. With air ducts of brass pipe of io-mm. bore the air flows in the 

 circuit at very low pressure. , 



For absorbing water vapor from the circulating air, an acid bottle like 

 that described for use with the large respiration calorimeter * but smaller 

 in size has been found efficient. The bottle described by Williams, 2 



1 Langworthy, C F., and Milner, R. D. An improved respiration calorimeter for use in experiments 

 with man. In Jour. Agr. Research, v. 5, no. 8, p. 306. 1915. 



2 Williams, H. B. Animal calorimetry. First paper. A small respiration calorimeter. In Jour. Biol. 

 Chem., v. 12, no. 3, p. 323. 1912. 



