178 MAX KLEIBER 



water, based on the postulate that the heat capacity of water within 

 this range remains constant, but this temperature scale would deviate 

 slightly from the one generally in use, namely, the thermodynamic 

 scale. Based on the usual temperature scale the heat capacity of air- 

 free water changes from 1.00738 cal. per gram at 0°C. to 1.00002 at 

 14°, to 0.99795 at 35°, ts 1.00000 at 65°, and to 1.00697 at 100°C. 



(7). 



Accurate data on specific heats of numerous substances are com- 

 piled in the International Critical Tables (5), the Smithsonian tables 

 (6), and various other handbooks (7). 



A number of rules permit the estimation of heat capacities (8). 

 For monatomic ideal gases, the molar heat capacity is 3 cal. per de- 

 gree at constant volume and 5 cal. per degree at constant pressure. 

 For other gases the molar heat capacity increases with the number of 

 atoms in the molecule. For solid elements the specific heat may be 

 estimated according to the law of Dulong and Petit, which states 

 that the product of specific heat and atomic weight of solid elements 

 is 6.4. 



For animals one may estimate: 



heat capacity = grams water -1- 0.4 X grams dry matter (5) 



Disregarding ash content, one would estimate for an extremely lean 

 animal with 25% protein and 75% water a specific heat of 0.85 cal. 

 per gram. For a very fat animal with 30% fat, 20% protein, and 

 50% water, the specific heat would amount to 0.70 cal. per gram. A 

 value of 0.8 cal. per gram appears to be a fair approximation for an 

 average animal and was used by Rosenthal (9) in 1889. Burton (10) 

 uses 0.83 as specific heat for human beings. Blood has a specific 

 heat of 0.9 cal. per gram, which is close to the approximation repre- 

 sented by equation (5). 



3. Heat Quantity 



Temperature and heat capacity having been established, the 

 quantity of heat ( AQ) may be defined as the product of temperature 

 change and heat capacity: 



AQ = (To - Ti)mc (6) 



where AQ = amount of heat transferred. This equation, however, is 

 appHcable only over a temperature range in which the specific heat 



