31 o Journal of Agricultural Research voi. v. no. s 



weighs nearly 60 kgm., the loss in weight is ascertained to an accuracy 

 of 0.1 gm. — that is, the volume of gas supplied, which may reach 80 liters 

 or more per hour, may be determined within 100 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 cyUnder; but when it was necessary at times to admit 

 gas rapidly, the agreement was not 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- 



