THE RESPIRATION APPARATUS. 



results is invariably used in the calculations. Occasionally, though 

 rarely, wide discrepancies in the two analyses will appear. Under these 

 conditions a third analysis is made and the figures agreeing most closely 

 are used. In such cases the error is almost always directly traceable. 



SAMPLING THE AIR FOR THE DETERMINATION OF OXYGEN. 



Of the four constituents of the ventilating current of air, carbon 

 dioxide, water vapor, nitrogen, and oxygen, the amounts of the first 

 two in the residual air are determined by the apparatus described 

 above. In order to know accurately the 

 amount of oxygen in the air, a determina- 

 tion of this element is necessary. 



The actual determination of oxygen in 

 the air current, by absorption by potassium 

 pyrogallate, is usually made once each 24 

 hours, the sample being generally drawn at 

 the close of the experimental period ending 

 at 7 a. m. 



It is of great im- 

 portance to obtain 

 a sample of air in 

 which the percent- 

 age of oxygen shall 

 represent accurately 

 that in the respira- 

 tion chamber. For- 

 merly the air was 

 sampled after it had 

 passed through the 

 blower and absorb- 

 ing system, and it 

 was assumed to be 



FIG. 20. Water-Pressure System. Water from reservoir at left is forced by pump into the large 

 air-tank at right. The release valve immediately to right of pump returns the water to reservoir 

 in case pressure in tank exceeds too pounds. Water is drawn from tank for suction-pump used 

 for drawing residual samples. 



