Physiology of Animal Heat, 



206. SOURCES OF HEAT. The heat of the body is an uninterrupted 

 evolution of kinetic energy, which we must represent to ourselves as clue to 

 vibrations of the corporeal atoms. The ultimate source of the heat is contained in 

 the potential energy taken into the body with the food, and With the of the air 

 absorbed during respiration. The 

 amount of heat formed depends upon 

 the amount of energy liberated. 



The energy of the food-stuffs may 

 be called " latent heat," if we 

 assume that when they are used up 

 in the body, chiefly by a process of 

 combustion, kinetic energy is liber- 

 ated only in the form of heat. As a 

 matter of fact, however, mechanical 

 energy and electrical energy are de- 

 veloped from the potential energy. 

 In order to obtain a unit-measure for 

 the energy liberated, it is advisable 

 to express all the potential energy 

 as heat-units. 



The Calorimeter. This instru- 

 ment enables us to transform the 

 potential energy of the food into heat, 

 and, at the same time, to measure 

 the number of heat-units produced. 



Favre and Silbermann used a water- 

 calorimeter (fig. 226). The substance to 

 be burned is placed in a large cylindrical 

 combustion-chamber (K), suspended in a 

 large cylindrical vessel (L) rilled with 

 water (w), so that the combustion -chamber 

 is completely surrounded by the water. 

 Three tubes open into the upper part of 

 the chamber ; one of them (0) supplies 

 the air which is necessary for combustion, 

 it reaches almost to the bottom of the chamber ; the second (a) is fixed in the middle of the 

 lid, and is closed above with a thick glass plate, and on this is placed, at an angle, a small 

 mirror (s), which enables an observer to look into the chamber, and observe the process of 

 combustion at c. The third tube (d) is used only when combustible gases are to be burned in 

 the chamber. It can be closed by means of a stop-cock. A lead tube (e, e), with many 

 twists, passes from the upper part of the chamber through the water, and finally opens at g. 



Fig. 22b. 

 Water-calorimeter of Favre and Silbermann. 



