VI. C A L O R I M E T R I O MEASUREMENTS 191 



age is Ihe labyrintli flow jackcl, developed mainly by Swietoslawski 

 {17). Figure 3 schematically illustrates the ])riiici))le of a labyrinth 

 flow calorimeter. 



Water at the eiivironiaental temperature T,; flows froju the reservoir R 

 down through the outer shell iSi, returning in a counterflow tin-ough the inner 

 layer of shell Si to the top. In a similar way the water jiasses the middle 

 shell ^2 and then enters the inner shell S^. In the inner shell the water takes 

 up the heat given off by the animal. The difference in temperature of the 

 water entering the calorimeter (T",) and that leaving the inner shell {T^) mul- 

 tiplied by the rate of flow is the rate of animal heat loss. Some correction 

 for changes in moisture content and temperature of the air may be necessary. 



The labyrinth flow efTectively reduces heat leakage since it keeps 

 the temperature of two adjoining walls nearly equal. Most of the 

 heat that might flow by conduction within the material of the shells 

 from inside to outside would be picked up by the inflowing water 

 and thus returned to the interior. The reverse would be true for the 

 exit manifold whose material therefore should have a low heat con- 

 ductivity. 



6. Measurement of Heat Flow by Circulating Medium 



The prevention of heat leaks through the walls does not necessar- 

 ily make a calorimeter adiabatic. The claim of Auguet and Lefevre 

 (^4) that their calorimeter for human beings was both perfectly 

 adiabatic and isothermal is an error. Heat produced in their calorim- 

 eter is carried outside bj^ a cooling stream of air. The same 

 method is used in a more recent human calorimeter by Murlin and 

 Burton {26) . In the classical respiration calorimeter of Atwater and 

 Rosa {23) the cooling medium is circulating water. Figure 4 illus- 

 trates the principle of this apparatus. 



The subject is surrounded bj^ two concentric walls. The outer wall is 

 always kept at the same temperature, Tg, as the inner wall so that there is 

 no heat leakage. The heat produced by the subject is carried away by the 

 water that flows into the chamber at the temperature T^i and leaves the 

 chamber with a temperature Tu^g. The rate of flow is measured by the bal- 

 ance B. 



The rate of heat loss in this case may be calculated as follows: 



^ . . ^ (r„ - T^) (14) 



At At 



