304 
Journal of Agricultural Research 
Vol. V, No. 8 
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. 1), 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 
