CALORIMETRY. 



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small calories. In physiology calorimeters have been used for two 

 main purposes: to determine the heat equivalent of foods, that is, 

 the amount of heat given off when the various foodstuffs are burned, 

 and, secondly, to determine the heat produced and the heat dissi- 

 pated by living animals during a given period. For the first pur- 

 pose the apparatus that is most frequently employed at present is 

 the bomb calorimeter devised by Berthelot. The bomb consists 

 of a strong steel cylinder in which the food to be burned is placed 



CT 



Fig. 300. Reichert's water calorimeter. 



and which is filled with oxygen. The combustion of the foodstuff 

 is initiated by means of a spiral of platinum wire heated by an 

 electrical current. The bomb is immersed in water and the heat 

 given off raises the temperature of the water a certain number 

 of degrees centigrade. The weight of water being known, the 

 amount of heat is easily expressed in calories. For the purpose 

 of measuring the heat given off by living animals two principal 

 forms of calorimeter are used, each form having a number of 

 modifications. These two forms are the water calorimeter and the 

 air calorimeter; The water calorimeter was the form used in the 

 first experiments on record (Crawford, 1779). In principle it 

 consists of a double-walled box with a known weight of water 

 between the walls. The animal is placed in the inner box and the 

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