304 Journal oj Agricultural Research voi. v.no. s 



The chamber does not rest upon the floor of the laboratory, but is 

 supported about 45 cm. above it by a structure of channel iron (PI. 

 XXXII, fig. i), with upright pieces 10 cm. wide, which rest on floor plates 

 and are bolted to the ceiling and between which are cross pieces 7.5 cm. 

 wide, on the lower of which rests the chamber. To this structure is also 

 attached the framework for supporting an outer covering of cork board, 

 described on page 334. This covering is constructed so that it may be 

 easily detached to provide ready access to any part of the zinc wall. The 

 outer surface of the cork board is covered with a layer of museum board 

 6 mm. thick, painted white on the outside (PI. XXX). 



DETERMINATION OF RESPIRATORY EXCHANGE IN THE CHAMBER 



The atmosphere of the empty chamber contains oxygen, nitrogen, 

 water vapor, and carbon dioxid in proportions like those of ordinary air. 

 When the subject enters the chamber, the proportions begin to change, 

 with the consumption of oxygen and the elimination of water vapor and 

 carbon dioxid. The removal of the water vapor and carbon dioxid from 

 the air and the restoration of oxygen to it in such manner that the 

 quantity of each may be accurately measured form the basis of the 

 determination of the respiratory exchange in the chamber. 



The respiratory products are constantly carried out of the chamber by 

 a current of air that is kept in circulation through the system. The air 

 leaves the chamber in a pipe which opens near the floor at one end, 

 passes through purifying devices, and returns to the chamber in a pipe 

 which opens near the ceiling at the other end. The purifying devices, 

 called "absorbers," remove from the air passing through them the water 

 vapor and carbon dioxid imparted to it by the subject. The increase in 

 the weights of the absorbers in a given period shows the quantities of water 

 vapor and carbon dioxid carried out of the chamber during the period. 

 In addition to the data thus obtained, account must be taken of changes 

 in the quantities of water vapor and carbon dioxid in the air of the cham- 

 ber, as shown by analyses of samples of the air at the beginning and the 

 end of the period, in determining the quantities produced in the chamber 

 during the period (p. 310). 



Oxygen is supplied to the chamber from a cylinder of the gas under 

 pressure, and the loss in weight of the cylinder shows the quantity 

 admitted during the period. To determine from data thus obtained 

 the quantity of oxygen consumed by the subject, allowance must be 

 made for changes in the quantity of oxygen in the air of the chamber. 



AIR-TENSION EQUALIZER 



The volume of air in the chamber varies constantly with the admission 

 of oxygen and the removal of water vapor and carbon dioxid, and also 

 with changes in the temperature of the air in the chamber and in the 

 barometric pressure of that outside. This might result in undesirable 



