CALORIMETRY. 



955 



imeter. In this last-named instrument two exactly similar cham- 

 bers are constructed; one contains the animal, while the other serves 

 as a dummy. These two chambers are balanced against each other, 

 the air space in the dummy being heated by immersion in a bath or 

 by burning hydrogen in the interior. As these sources of heat are 

 known and can be controlled, it is evident that if the dummy is 

 made to balance exactly the chamber containing the animal the 

 amount of heat given off in each is the same.* 



The Respiration Calorimeter. — When a calorimeter is so arranged 

 that the composition of the air drawn through the apparatus for 

 ventilation can be determined, as well as the amount of heat pro- 

 'duced, the apparatus becomes a respiration calorimeter. In such 



Fig. 301. — Horizontal section of respiration calorimeter. Portions shaded are of wood: A, 

 ■dead-air space between Cu and Zn walls; B, dead-air space between Zn wall and inside wooden 

 wall; C, dead-air space between inside and outside wooden walls; D, pneumatic-packing air 

 and Iheat insulated; E, food-aperture tube; a, a, airtight ports (glass); H, ingoing water for 

 absorbing heat; G, outcoming water; V, ventilating air current. {Atwater and Benedict.) 



an apparatus, if proper provision is made also for analyzing the 

 urine, the feces, and the food, the total carbon and nitrogen excre- 

 tion may be obtained simultaneously with the heat loss. Since we 

 may calculate from the carbon and nitrogen excretion how much 

 protein, fat, and carbohydrate have been burnt in the body, and 

 since the heat values of these constituents are known, it is evident 

 that we may reckon indirectly how much heat ought to be produced 



* For detailed accounts of special forms of air calorimeters see Rubner, 

 "Calorimetrische Methodik," 1891; and Rosenthal, "Archiv f. Physiologie," 

 1897, p. 170. 



