July 31,1916 Respiration Calorimeter 7 11 



reservoir by a small gear pump driven by the motor that actuates the 

 air pump. The overflow from the reservoir also returns to the tank. 

 The same water is used continuously in this manner to eliminate the 

 difficulty resulting when water directly from the city main is passed 

 through the system, owing to the presence of air dissolved in the water. 

 If the temperature of the water is raised, the air escapes and collects in 

 bubbles in the pipe and forms temporary obstructions that cause irregu- 

 larity in the rate of flow of water through the absorber. With well- 

 filtered water in the system a rate of flow as low as 5 liters per hour has 

 been maintained with such uniformity that it would be sufficient to collect 

 the water leaving the heat absorbers at intervals instead of continuously. 

 Slight changes in the rate may be effected by the adjustment of a glass 

 rod, with a long tapering end which passes through a constricted orifice 

 in one end of a glass T-tube in the water line. 



That the air of the chamber may be kept at any desired temperature, 

 water is usually allowed to flow through the heat absorber at a constant 

 rate and the temperature of the ingoing water is varied in accordance 

 with the quantity of heat to be absorbed. To bring this temperature 

 under control, the water is first cooled below that at which it is to be 

 used, and then heated to the desired temperature. In these circumstances 

 regulation of temperature is accomplished simply by variation in the 

 amount of heating, which is easily controlled automatically. 



REGULATING THE TEMPERATURE OF THE WATER FLOW 



The water flowing from the reservoir to the heat absorber passes first 

 through a pipe immersed in cold water to chill it, and then into a device 

 called the preheater (PI. XCIV) in which, by the conversion of electric 

 current into heat in resistance coils inclosed in the water channel, the 

 temperature of the water may be raised several degrees. The total 

 heating effect of the device will increase the temperature of the water 

 nearly 6° when the rate of flow is not over 500 c. c. per minute, and the 

 heat may be added in small quantity. By this means the temperature 

 of the water is raised near to that at which it is to enter the absorber. 

 From this device, which is adjusted by hand, the water passes to the final 

 heater (PI. XCIV), which has a smaller capacity than the preheater, 

 but is automatic and regulates the temperature within very narrow 

 limits. The device is similar in some respects to that employed with the 

 large calorimeter, 1 while in others it has been considerably simplified and 

 improved. 



The temperature of tne water is raised or lowered by increasing or 

 decreasing the electric current flowing in a coil of resistance wire immersed 

 in the water. This is accomplished by adjusting the position of the 

 sliding contact on a rheostat wound with resistance wire of graduated 



1 Langworthy, C. !•*., and Milner, R. D. Op. cit., p. 319. 



