20 A RESPIRATION CALORIMETER. 



the blower ; consequently the meter was deemed unnecessary and was 

 removed. 



For simplicity and efficiency, it is very much to be doubted if an 

 apparatus could be devised which would materially improve the condi- 

 tions now obtained with this simple form of blower. While the pressure 

 of the air is, under the conditions here used, but 35 mm. of mercury, 

 tests have shown that the blower would give still greater pressures in 

 case they were necessary. 



By means of a small counter-shaft attached to the ceiling of the calo- 

 rimeter laboratory, it is possible to start and stop the blower without 

 disturbing the other machinery. 



MERCURY VALVES. 



Inasmuch as the experimental day is generally subdivided into 

 twelve periods of two hours each, it is necessary to provide means for 

 diverting the main air current at the end of each experimental period 

 through a second series of absorbers, and thus provide for the weighing 

 of the water and carbon dioxide absorbed by the first set. Accordingly, 

 the main air-pipe conducting the air from the blower to the absorbers 

 and that leading from the absorber system to the respiration chamber 

 are divided, and a system of valves is employed to cut off the air-circuit 

 at the beginning and end of each of the absorber systems. The two 

 valves at the end nearest the blower are shown in figure 3, and figure 

 4 shows the two valves at the opposite end. A closer view of these 

 valves is given in figure 18. By opening the valve at each end of one 

 set of absorbers and closing both corresponding valves on the other set, 

 air can be caused to traverse either system as desired. 



The requirements for these valves are such as to demand a special 

 form of construction. At the point where the air enters the absorbing 

 system it is under an increased pressure of 40 to 50 mm. of mercury. 

 At the other end, i. e., where the air leaves the absorbing system, it is 

 at atmospheric pressure. While the problem of a valve at the exit end 

 of the system is simple, that of devising a suitable one for the other 

 end presented certain difficulties which were overcome only after consid- 

 erable time. It is necessary that this valve should be sufficiently tight 

 to withstand without a leak an increased pressure of 40 to 50 mm. of 

 mercury while the ventilating current of air is passing through it. On 

 the other hand, for a period of at least two hours the valve must be capa- 

 ble of being closed absolutely with atmospheric pressure on one side of 

 the closure and an increased pressure of 40 mm. of mercury on the 

 other. Furthermore, the valve must be of sufficient size to permit the 

 passage of 75 liters of air per minute through it without a marked 



