THE CALORIMETER. 



43 



TEMPERATURE CONTROL OF THE INGOING AIR. 



In passing the current of air through the calorimeter, temperature con- 

 ditions may easily be such that the air entering is warmer than the out- 

 coming air, in which case heat will be imparted to the calorimeter, or the 

 reverse conditions may obtain and then heat will be brought away. To 

 avoid this difficulty, arrangements are made for arbitrarily controlling the 

 temperature of the air as it enters the calorimeter. This temperature con- 

 trol is based upon the fact that the air leaving the chamber is caused to 

 pass over the ends of a series of thermal junctions shown as in fig. 25. 



Fig. 25. — Section of calorimeter walls and part of ventilating air-circuit, showing part of pipes for 

 ingoing air and outgoing air. On the ingoing air-pipe at the right is the lamp for heating the 

 ingoing air. Just above it, H is the quick-throw valve for shutting off the tension equalizer IJ. I 

 is the copper portion of the tension equalizer, while J is the rubber diaphragm; K, the pet -cock 

 for admitting oxygen; F, E, G, the lead pipe conducting the cold water for the ingoing air; and C, 

 the hair-felt insulation. N, N are brass ferules soldered into the copper and zinc walls through 

 which air-pipes pass; M, a rubber stopper for insulating the air-pipe from the calorimeter; O, the 

 thermal junctions for indicating differences of temperature of ingoing and outgoing air and U, the 

 connection to the outside; QQ, exits for the air-pipes from the box in which thermal junctions are 

 placed; P, the dividing plate separating the ingoing and outgoing air; R, the section of piping 

 conducting the air inside the calorimeter; S, a section of piping through which the air passes from 

 the calorimeter; A, a section of the copper wall; Y, a bolt fastening the copper wall to the 2%-inch 

 angle W; B, a portion of zinc wall; C, hair-felt lining of asbestos wall D; TJ, a thermal junction 

 In the walls. 



These thermal junctions have one terminal in the outgoing air and the 

 other in the ingoing air, and consequently any difference in the temperature 

 of the two air-currents is instantly detected by connecting the circuit with 

 the galvanometer. Formerly the temperature control was made a varying 

 one, by providing for either cooling or heating the ingoing air as the situa- 

 tion called for. The heating was done by passing the current through an 



