1 8 A RESPIRATION CALORIMETER. 



chamber, and descends into the blower. The passage of 75 liters of 

 air through this size and length of pipe results in a slightly diminished 

 pressure (3 cm. of water). 



From time to time a sample of air is withdrawn from this pipe for 

 analysis, it being assumed that the composition of the air in the pipe 

 between the chamber and blower is essentially that of the air in the 

 chamber. (See p. 81.) To obtain a valve that will close completely, 

 an opening in the pipe in which there is a diminished pressure has been 

 found a difficult thing, and recourse was had to a mercury valve which 

 was attached to the vertical section of the pipe above the blower. This 

 valve consists of a glass Y tube, one arm of which was attached to the 

 air-pipe and the other connected to the residual-analysis apparatus. 

 To the stem of the Y a glass bulb filled with mercury was attached by 

 means of a piece of rubber tubing. By raising this bulb, mercury rises 

 in the stem of the Y tube and closes the connection between the two 

 arms of the Y. On lowering the valve a free passage is obtained for 

 the air. 



An ordinary one-inch ' ' angle ' ' valve was placed in the pipe as it 

 descends from the ceiling to aid in testing the air-circuit from time to 

 time. This valve, as well as that in the return air-pipe, is shown in 

 figure 5, near the ceiling. 



THE ROTARY BLOWER. 



Considerable difficulty has been experienced in obtaining a suitable 

 apparatus for maintaining the ventilating current of air in the system. 

 An attempt was made to use the Blakeslee mercury pump used in the 

 earlier type of respiration apparatus, 1 but the possible danger of mer- 

 cury vapor in the air prevented its use in a closed circuit. Several 

 other forms of mechanical pumps were devised, built, and tested, but 

 were ultimately discarded in favor of a rotary blower. A blower was 

 obtained in the market, and after undergoing modification was adapted 

 to the specific purpose of maintaining a ventilating current of air for 

 this apparatus. The advantages of a rotary blower over a pump are 

 numerous. In the first place, the current of air is very much more 

 constant, since with the pump there is more or less intermittent motion ; 

 but more important than any other is the fact that it is possible to 

 immerse the rotary blower in oil and thus minimize and detect leakage 

 of air. 



The blower and the receptacle containing cylinder oil in which the 

 blower is immersed, together with the air-pipes leading to and from 

 the blower, are shown in figure 9. 



1 U. S. Dept. of Agr., Office of Experiment Stations Bull. 63, p. 31. 



