THE ENERGY EQUATION. 399 



chamber and in such a way as to maintain a perfectly uniform temperature 

 in the chamber space. The walls of the chamber are made of compart- 

 ments containing two layers of air and two layers of water maintained in 

 such relations that they prevent gain or loss of heat. The whole heat 

 liberation is taken up by the circulating water and may be accurately 

 measured. The respiration chamber has a capacity of about 175 cubic 

 feet and is large enough to contain a chair and small table for the con- 

 venience of the occupant and a couch to sleep on at night. The construc- 

 tion is such that food may be passed in and the urine and feces removed 

 without making any appreciable change in the temperature or content of 

 the air inside. With such an apparatus it is possible to carry on a test of 

 many days duration and obtain extremely accurate and important results. 



In work experiments in such a calorimeter a bicycle is mounted so that 

 work is done against friction. The final effect is increased heat liberation, 

 measured as before. 



The construction of this large calorimeter suggested the building of 

 still larger ones of the same general type. Some of these are being used 

 in agricultural experiment stations in metabolism experiments on large 

 animals, from which results of great practical value may be expected. 



DISTRIBUTION OF THE HEAT ENERGY. 



According to the first calculation above we have from the 

 700 grams of food consumed a balance of 2,686,200 calories. 

 It remains to show about how this may be dissipated. If 

 retained in the body it would soon bring the latter to the boil- 

 ing point. But the heat liberated in the combustion of the 

 food finds several outlets, the most important of which will 

 be now indicated. In the first place the urine and feces leave 

 the body at a temperature much higher than that of the water 

 consumed; the water of respiration and perspiration has to 

 be vaporized at the expense of heat ; the air inhaled is warmed 

 to a temperature of 37, which is in the mean 20 higher than 

 when taken in. The specific heat of the air (at constant pres- 

 sure) is about 0.25. We have then, approximately, the fol- 

 lowing relations, assuming 15 kilograms of air to be inhaled 

 in the 24 hours : 



To warm 15.000 gm. air 20 75,ooo cal. 



To warm 1,557 gm. urine and feces 20 31,140 



To evaporate 904 gm. of water (904 X 580) 524,320 



630,460 



