ANIMAL 111-: A '/'. 



479 



by burning a definite amount of absolute alcohol or hydrogen within the instru- 

 ment, or by using a sealed vessel of hot water of a known temperature and 

 allowing it to cool to a definite extent. The process is simple; for instance, 

 each gram of alcohol or each liter of hydrogen completely oxidized yields a 

 definite number of calories ; similarly, a definite weight of water cooled a 



Fig. 80.— Reichert's water calorimeter. 



definite number of degrees gives oft' a definite quantity of heat. The heat thus 

 generated by the oxidation of the alcohol or hydrogen or given off by the cool- 

 ing of the water is imparted to the calorimeter and increases its temperature. 

 Knowing the quantity of heat given to the calorimeter and the increase of 

 temperature of the instrument, the determination of the calorimetrical equiva- 

 lent may be easily made. Thus, 1 gram of alcohol yields in round numbers 

 7000 calories; if we burn 10 grams of absolute alcohol, 70,000 calorics will 

 result; if the temperature of the calorimeter be increased 1°, the calorimetric 

 equivalent will be 70,000 calories or 70 kilogramdegrees ; in other word-, for 

 each degree of increase of the temperature of the calorimeter a quantity of 

 heat equivalent to 70 kilogramdegrees is absorbed. 



The heat dissipated by an animal is only in part absorbed by the calori- 

 meter, another portion being given to the air which passes from the instrument, 

 and another portion to water which is evaporated from the lungs and skin. 

 Three estimates, therefore, arc necessary — (1) of the heat given to the calori- 

 meter, (2) of the heat given to the air, and (3) of the heat given off in the 

 evaporation of water. 



The estimate of the heat given to the air necessitates the measurement of 

 the quantity of air supplied to the calorimeter, and of the temperature of the 



