Nov. 22, 1915 Improved Respiration Calorimeter 339 



same as that of the air leaving the chamber. This rheostat is mounted 

 on the end of the observer's table beside those for controlling the temper- 

 ature of the zinc wall. 



ALLOWANCE FOR CONDITIONS AFFECTING THE HEAT OF THE CHAMBER 



Any passage of heat into or out of the chamber through the walls or 

 in the ventilating air current being prevented, the sum of the quantity 

 of latent heat in the water vapor of the outgoing air and that of sensible 

 heat removed by the water circulating in the heat absorber would equal 

 that actually produced in the chamber if there were no change in the 

 temperature of the walls or in that of any objects confined within them. 

 Under ordinary conditions, however carefully the rate of abstraction of 

 heat from the chamber has been regulated to accord with that of pro- 

 duction, temperature changes can not be absolutely avoided, so they 

 must be measured and allowance made for them. 



Change in Temperature of the Metal Walls 



If the temperature of the copper wall is lower at the end of a given 

 period than it was at the beginning, and the temperature of the zinc wall 

 has been kept identical with that of the copper wall throughout the period, 

 a certain amount of heat has been imparted to the air of the chamber by 

 the copper wall during the period; or, conversely, if the copper wall is 

 warmer at the end of the period, some heat has been absorbed from the 

 air by the wall. To ascertain how much allowance must be made for the 

 heat involved in such changes, it is necessary to determine the tempera- 

 ture of the copper wall at the beginning and the end of the period and to 

 know how much heat is necessary to raise the temperature of the calo- 

 rimeter a given amount — i. e., its hydrothermal equivalent. 



The temperature of the copper wall is determined by means of an 

 electric-resistance thermometer somewhat like that described on page 

 313 for determining the temperature of the air. In this thermometer, 

 however, each of the six coils of nickel resistance wire is wound on a thin 

 fiber strip about 12 cm. long and i cm. wide, and is covered with a thin 

 layer of silk and lacquered, the completed bulb being about 1.5 mm. thick. 

 A strip of brass, slid into guides soldered to the copper wall, presses each 

 coil firmly against the wall so that there is close thermal contact with 

 metal on each side of the coil; hence, changes in the temperature of the 

 wall affect the resistance wire very quickly. These six coils, joined in 

 series by well-insulated No. 16 copper wire, are distributed on the side 

 walls and ceiling in such manner as to show the average temperature of 

 the total mass of copper. The terminals of the series of coils are con- 

 nected with the special switch, mentioned on page 334, and through that 

 with the temperature indicator (Wheatstone bridge) on the observer's 

 table. The bridge and galvanometer are sensitive to resistance changes 



