340 Journal of Agricultural Research voi. v, no. s 



in the thermometer coils that would result from a change of o.oi degree 

 in the temperature of the copper wall. 



The hydrothermal equivalent of the calorimeter has been estimated 

 from determinations of the quantity of heat that had to be dissipated 

 in the chamber to raise the temperature of the copper wall i degree, and 

 the amount of heat that was imparted to the air of the chamber when 

 the temperature of the copper wall fell i degree, while the thermal 

 conditions of the zinc walls were kept in equilibrium with those of the 

 copper wall during the change. The capacity for heat as determined in 

 both ways was not far from 40 Calories. From the weights and specific 

 heats of the materials entering into the construction of the chamber the 

 hydrothermal equivalent was calculated to be between 35 and 40 Calories. 

 According to these figures, the quantity of heat in the chamber should be 

 increased by 40 Calories with a fall of i degree, or decreased by 40 Calories 

 with a rise of i degree in the temperature of the copper wall, if the thermal 

 conditions of the zinc wall were in equilibrium %vith those of the copper 

 wall while the change occurred. 



This will be the case, provided the change in thermal conditions has 

 occurred in such manner as to affect the iron supporting structure the 

 same as the copper wall. In constructing the calorimeter no provision 

 was made for determining the actual temperature of the structure, the 

 assumption being that the thermal conditions of the iron framework 

 would also be controlled by the regulation of those of the zinc wall, so that 

 the temperature of the iron would be quickly brought to that of the 

 copper wall and would vary with it. Experience has shown, however, 

 that in some circumstances the change in thermal conditions of the iron 

 may lag somewhat behind that of the copper wall ; hence, it is much more 

 desirable to keep the temperature of the walls of the chamber as constant 

 as possible for the whole length of an experimental period than to depend 

 upon the correction for change in temperature. With a sudden change 

 in the rate of dissipation or absorption of heat in the chamber near the 

 close of a period, which would affect the temperature of the copper wall, 

 there might be an error in the measurement of heat for the period in spite 

 of the allowance for temperature change. (See p. 346.) 



Change in Body Temperature of the Subject of an Experiment 

 When the human body is the source of heat in the chamber, allowance 

 must be made for the heat involved in any change in its temperature, as 

 the body has a considerable thermal capacity. From the best available 

 data it would appear that a change of i degree in the temperature of the 

 body involves a change of 0.83 Calorie in the quantity of the heat accumu- 

 lated for each kilogram of body weight. A rise in body temperature 

 would mean that the store of heat in the body has been increased a certain 

 amount, which would have to be added to that ehminated by the body 

 and measured by the calorimeter during the period in which the rise 



