50 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



therefore, to compute the hydrothermal equivalent by multiplying the body- 

 weight by the specific heat of the body, commonly assumed as 0.83, and then 

 to make allowance for fluctuations in body-temperature. 



When it is considered that with a subject having a weight of 70 kilos a 

 difference in temperature of 1° C. will make a difference in the measure- 

 ment of heat of some 60 calories, it is readily seen that the importance of 

 knowing the exact body-temperature can not be overestimated; indeed, the 

 whole problem of the comparison of the direct and indirect calorimetry 

 hinges more or less upon this very point, and it is strongly to be hoped that 

 ere long the much-needed observations on body-temperature can be made. 



CONTROL EXPERIMENTS WITH THE CALORIMETER. 



After providing a suitable apparatus for bringing away the heat gene- 

 rated inside the chamber and for preventing the loss of heat by maintaining 

 the walls adiabatic, it is still necessary to demonstrate the ability of the 

 calorimeter to measure known amounts of heat accurately. In order to do 

 this we pass a current of electricity of known voltage through a resistance 

 coil and thus develop heat inside the respiration chamber. While, un- 

 doubtedly, the use of a standard resistance and potentiometer is the most 

 accurate method for measuring currents of this nature, thus far we have 

 based our experiments upon the measurements made with extremely accu- 

 rate Weston portable voltmeter and mil-ammeters. Thanks to the kind- 

 ness of one of our former co-workers, Mr. S. C. Dinsmore, at present asso- 

 ciated with the Weston Electrical Instrument Company, we have been 

 able to obtain two especially exact instruments. The mil-ammeter is so 

 adjusted as to give a maximum current of 1.5 amperes and the voltmeter 

 reads from zero to 150 volts. The direct current furnished the building is 

 caused to pass through a variable resistance for adjusting minor variations 

 in voltage and then through the mil-ammeter into a manganin resistance- 

 coil inside the chamber, having a resistance of 84.2 ohms. Two leads from 

 the terminals of the manganin coil connect with the voltmeter outside the 

 chamber, and hence the drop in potential can be measured very accurately 

 and as frequently as is desired. The current furnished the building is 

 remarkably steady, but for the more accurate experiments a small degree of 

 hand regulation is necessary. 



The advantage of the electrical method of controlling the apparatus is 

 that the measurements can be made very accurately, rapidly, and in short 

 periods. In making experiments of this nature it is our custom first to 

 place the resistance-coil in the calorimeter and make the connections. The 

 current is then passed through the coil, and simultaneously the water 

 is started flowing through the heat-absorbing system and the whole calo- 

 rimeter is adjusted in temperature equilibrium as soon as possible. When 

 the temperature of the air and walls is constant and the thermal- junction 



