3 io 
Journal of Agricultural Research 
Vol. V, No. 8 
weighs nearly 60 kgm., the loss in weight is ascertained to an accuracy 
of o.i gm.—that is, the volume of gas supplied, which may reach 80 liters 
or more per hour, may be determined within ioo c. c. 
This method of determining the quantity of gas admitted to the 
chamber is very precise, but it involves time and effort that could be 
saved by the use of a gas meter if the mere reading of the dial of the 
meter would show the quantity with equal precision. In a number of 
experiments the gas from the weighed cylinder was passed through a 
calibrated test meter before it entered the chamber, to determine whether 
the volume of gas admitted could be ascertained in this manner with suffi¬ 
cient accuracy. It was found that when the gas was admitted at a fairly 
uniform rate throughout the period, the volume as determined from the 
meter reading would agree quite closely with that computed from the loss 
in weight of the cylinder; but when it was necessary at times to admit 
gas rapidly, the agreement was npt so close, a correction being necessary 
for increase of pressure in the meter. The time and labor involved in 
reading, recording, and correcting for increased pressure in the meter are 
at least as much as those of weighing the cylinder. 
In most of the investigations with this respiration calorimeter the gas 
contained in the cylinder, and consequently that admitted to the chamber, 
was about 97 per cent oxygen. It was derived from liquid air and was 
virtually free from carbon dioxid and water, but contained a small pro¬ 
portion (about 0.3 per cent) of nitrogen and an appreciable proportion 
(about 2.7 per cent) of argon, for which allowance must be made in com¬ 
puting from the loss in weight of the cylinder the quantity of oxygen 
admitted to the chamber. In making the correction it is sufficiently 
accurate to consider the impurity as all argon. It is possible, however, 
to obtain oxygen that is so nearly free from other gases that the error 
involved in disregarding them is inconsiderable. 
DETERMINATIONS OF THE AMOUNTS OF RESIDUAL GASES 
As has been stated (p. 304), to determine the amount of oxygen con¬ 
sumed and of carbon dioxid and water vapor produced by the subject 
in the chamber during a given period, allowance must be made for any 
changes that have occurred in the composition of the air of the chamber— 
that is, in the quantities of different gases residual in the chamber. 
These are ascertained from analyses of samples taken at the beginning 
and the end of the period. Because of convenience, the samples are 
taken, not directly from the air of the chamber but from that passing 
through the air pipes outside of the chamber. It is assumed that the 
air in the outgoing pipe has the same composition as that in the respira¬ 
tion chamber. Though the composition of the latter is constantly 
changing, an electric fan keeps the total mass of air in the chamber 
energetically stirred to prevent stratification and to mix the varying 
component gases as thoroughly as possible. It seems probable, there- 
