90 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



the cold water in the heat-absorbers at a temperature not far from 12 C. 

 Obviously, the air in the immediate neighborhood of these two localities is 

 considerably warmer or colder than the average temperature of the air. 

 The disposition of the electric-resistance thermometers about the chamber 

 has, after a great deal of experimenting, been made such as to permit the 

 measurement as nearly as possible of the average temperature in the cham- 

 ber. But this is at best a rough approximation, and we must rely upon the 

 assumption that while the temperatures which are actually measured may 

 not be the average temperature, the fluctuations of the average temperature 

 are parallel to the fluctuations in the temperatures measured. Since every 

 effort is made to keep these fluctuations at a minimum, it is seen that the 

 error of this assumption is not as great as might appear at first sight. 

 However, the calculation of the residual amount of oxygen in the chamber 

 is dependent upon this assumption and hence any errors in the assumption 

 will affect noticeably the calculation of the residual oxygen. 



Attempts to compare the determination of the oxygen by the exceedingly 

 accurate Sonden apparatus with that calculated after determining the 

 water-vapor and carbon dioxide, temperature and pressure of the air in the 

 chamber have thus far led to results which indicate one of three things: 

 (1) that there is not a homogeneous mixture; (2) that during the time 

 required for making residual analyses, i. e., some three or four minutes, 

 there may be a variation in the oxygen content in the air of the chamber 

 due to the oxygen continually added from the cylinder; (3) that the oxygen 

 supplied from the cylinder is not thoroughly mixed Avith the air in the 

 chamber until some time has elapsed. That is to say, with the method 

 now in use it is necessary to fill the tension-equalizer to a definite pres- 

 sure immediately at the end of each experimental period. This is done by 

 admitting oxygen from the cylinder, and obviously this oxygen was not 

 present in the air when analyzed. A series of experiments with a somewhat 

 differently arranged system is being planned in which the oxygen will be 

 admitted to the respiration chamber directly and not into the tension-equal- 

 izer, and at the end of the experiment the tension-equalizer will be kept at 

 such a point that when the motor is stopped the amount of oxygen to be 

 added to bring the tension to a definite point will be small. 



Under these conditions it is hoped to secure a more satisfactory compari- 

 son of the analyses as made by means of the Sonden apparatus and as calcu- 

 lated from the composition of the residual air by the gravimetric analysis. 

 It remains a fact, however, that no matter with what skill and care the gaso- 

 metric analysis is made, either gravimetrically or volumetrically, the calcu- 

 lation of the residual amount of oxygen presents the same difficulties in 

 both cases. 



