176 MAX KLEIBER 



A. PRINCIPLES 



1. Heat and Temperature 



Heat and temperature were still confused in Newton's works. In 

 1750 Richman formulated a concept similar to what is now known as 

 heat quantity, namely, mass times difference in temperature, al- 

 though he used the term ''calor" for this product as well as for tem- 

 perature. Joseph Black (1728-1799) clarified the relation between 

 temperature and heat, introducing a term "capacity for heat" for a 

 concept now known as "specific heat," whereas "heat capacit}^" now 

 designates the product of specific heat and mass of a body. The his- 

 torical development of these concepts is given by Mach (1) and by 

 Maxwell (2). Even today the terminology is still confused in some 

 pubhcations. "Thermogenic" is sometimes used instead of "calori- 

 genic" to designate an action that increases the rate of heat produc- 

 tion. A million calories of net energy in animal nutrition is called a 

 "therm" (3). This is as unfortunate as the use of the same term 

 "one therm" for the zero to one degree calorie (4). In some very well 

 established expressions such as "thermochemistry" and "thermo- 

 dynamics," "therm" to be sure still retains the double meaning of 

 dealing with heat as well as temperature, but that is no reason why 

 such confusion should be carried on in newly coined terms. 



Temperature is discussed in another chapter of this book. Heat 

 (calor) is the product of a difference in temperature and the heat 

 capacity of a body. 



2. Heat Capacity 



Once a temperature scale is established, one may determine heat 

 capacity by mixing substances vnih different temperatures and ob- 

 serving the resulting temperature of the mixture. The following dis- 

 cussion is simplified by the assumption that heat capacity does not 

 change with changes of temperature. 



If m grams of water at a temperature Ti is mixed Avith m grams of 

 water at a temperature T2, the mixture mil have the temperature of 

 (Ti -1- 7^2) /2. The warm water lost as much temperature as the cold 

 water gained. If, however, m grams of water at Ti is mixed ^\^th 

 twice as much water at T2, the temperature of the mixture is closer 

 to To than to Ti. Generally one may formulate: 



