CALORIMETRY. 



951 



that in the living body the energy liberated as heat or as heat 

 and work is all contained in potential form in the foodstuffs 

 eaten. By means of the respiration calorimeter we can obtain a 

 balance between the energy income and outgo of the body as well 

 as between the material income and outgo, that is, the carbon and 

 nitrogen equilibrium. The most complete and elaborate form of 

 respiration calorimeter used is that devised by Atwater and Rosa 

 for experiments upon man.* The respiration chamber is a small 

 room lighted and furnished so that an individual may remain in 

 it for long periods without discomfort. As shown in Fig. 301, this 



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 'heat 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.) 



room is arranged as a calorimeter. It has several walls of metal 

 and wood to prevent loss of heat to the outside or the reverse, and 

 by means of water circulating through a system of pipes within 

 the room the heat given up by the body is carried off. By regulat- 

 ing this flow of water the temperature of the chamber can be kept 

 constant. Knowing the temperature of the water as it enters and 

 leaves the chamber and the volume of the flow, the heat production 

 of the individual may be calculated in terms of calories. For the 

 determination of the carbon dioxid and water air is drawn through 

 the room by means of a rotary pump and a closed circuit is em- 

 ployed, that is to say, the same air is kept circulating through the 



* See Atwater and Rosa, Bulletin 63, United States Department of Agri- 

 culture, 1899; and for recent improvements, Atwater and Benedict, "A Respi- 

 ration Calorimeter," Carnegie Institution, Washington, 1905. 



