Il8 A RESPIRATION CALORIMETER. 



Each heating circuit is connected with a variable resistance and a 

 rheostat on the observer's table. It is possible to cut out any or all 

 of the resistance and cause varying amounts of electricity to pass 

 through the circuit of wire in the air-space, thus controlling its heating 

 effect. The electrical method of heating a large air-space is ideal, in- 

 asmuch as the heat is evenly distributed all through the air-space and 

 liberated simultaneously at all points. Furthermore, the amount of 

 heat which can thus be liberated is instantly controlled with the greatest 

 accuracy by varying the external resistances. 



The variable resistance here used consists of a series of seven coils of 

 German-silver wire wound on a corrugated sheet-iron pipe (galvanized 

 conductor pipe) which has been covered with asbestos paper. There 

 are in all nine heating circuits used for temperature control about the 

 calorimeter, four for the inner air-space, four for the outer air-space, 

 and one to heat the ventilating current of air as it enters the chamber, 

 each of which is connected with the rheostat and has its variable resist- 

 ance. The nine variable resistances are laid side by side under the 

 calorimeter in the space between the laboratory floor and the outer 

 bottom panel. As the floor of the laboratory is always cold, the extra 

 heat developed in these resistance coils in a measure counteracts the 

 cold floor and aids in warming the outer bottom dead-air space. 



Cooling circuits. Means for cooling the air-spaces are as essential as 

 those for heating them. Unfortunately, there is no such ideal method 

 for cooling as for heating an air-space. The best method available is 

 that depending upon the passage of cold water through a small pipe 

 which is suspended in the air-space parallel to the wires of the elec- 

 trical heating circuit. (See figs. 25, 30, and 31.) Water from the city 

 main, which has a temperature varying from 6 in winter to 16 or 17 

 in summer, is caused to flow through small pipes (one-eighth inch) in 

 the air-space. The cold water absorbs the heat and thus cools the air 

 rapidly, and as a result the zinc wall is cooled. 



Heretofore iron pipe has been used for the cooling circuits, but as it 

 rusts easily and so is liable to clog, brass pipe is being substituted. 



The cooling system in the top space and that in the bottom space 

 are individual units, in which the water enters at one end, circulates 

 around the numerous bends in the pipe, and goes out at a point close 

 to where it enters. With the cooling circuits for the upper and lower 

 zones, on the other hand, it is necessary to make arrangements for dis- 

 connecting the piping when the calorimeter is to be withdrawn. The 

 position of the pipes across the rear end of the calorimeter is shown in 

 figure 25. These pipes are attached to elbows connecting with the 

 pipes on the side panels by means of a brass union at each end. By dis- 



