TECHNIQUE FOR METABOLISM DURING REST. Ill 



REMOVAL OF AIR FROM SAMPLING CANS. 



The mechanism for removal of air from the sampling cans must pro- 

 vide not only for absolute uniformity and regulation of removal, i. e., 

 the removal of a volume of air equivalent to the amount discharged into 

 the samphng cans through the 10-mm. openings, but it must likewise 

 force the air thus removed through proper purifiers for the quantitative 

 absorption of water vapor and carbon dioxide, respectively. This may 

 be accomplished by means of either a reciprocating pump or, as with 

 the universal respiration apparatus, by a rotary positive blower. This 

 blower, shown as Fi in figure 8, is belted with the motor, G, each 

 sampling can having its corresponding blower. (See also fig. 11.) 

 The blowers are actuated by the same electric motor, from the same 

 shaft and hence at the same speed, for since the openings into the bot- 

 toms of the cans, Ci and C2, are exactly the same diameter and a like 

 amount of air is discharged through both, the volume of air to be taken 

 care of is exactly the same with both blowers. While other and less 

 costly types of blowers have suggested themselves to us and have been 

 subjected to preliminary tests, as yet nothing has been found that com- 

 pares with the regularity of performance of the somewhat expensive 

 Crowell blower. 



The blower is adjusted to remove somewhat more than 45 liters of 

 air per minute, the rate being determined entirely by the size of the 

 pulleys and the speed of the motor. As at present employed, the diam- 

 eter of the pulley on the blower is 20 cm. Any considerable excess in 

 the amount of air removed in this manner may be controlled by the 

 wheel by-pass shown as hi and hz in figure 11. This by-pass consists of 

 a connection between inlet and outlet side of the blower, made up of 

 standard brass pipe and fittings provided with a wheel valve. By 

 opening the valve the effectiveness of the blower can be altered at will. 

 Indeed, if it is opened wide no air will pass through the purifying train, 

 since it simply will run back through the by-pass. Thus the amount of 

 air withdrawn by the blowers from the sampling cans may be grossly 

 regulated. 



From the construction of the sampling cans and their rubber dia- 

 phragms (see fig. 13) it can be seen that, if the air is withdrawn too 

 slowly, the rubber tops will gradually rise and become distended. Con- 

 versely, if the air is withdrawn too quickly, they will become more or 

 less collapsed. From the fact that the actual weight of the diaphragm 

 is in large part counterpoised by a spiral spring, considerable fluctua- 

 tions in the general shape and size of the rubber top of the can may 

 actually take place without a material alteration in the internal pres- 

 sure on the diaphragm. A slight rise and fall, such as 1 or 2 nam., when 

 so delicately counterpoised, is absolutely without influence upon the 

 tension inside the diaphragm. This fact has been taken advantage of 



