CH. XLII.] 



CALORIMETRY 



633 



in raising the temperature of the water. The amount of water which 

 goes through the pipes multiplied by the difference in the tempera- 

 ture of the water as it enters and as it leaves the calorimeter, gives 

 the heat output of the person within it. This is. ascertained by the 

 thermometers (T, T). 



In the case of the bomb calorimeter it is possible to ensure the 

 complete combustion of the substance placed in the bomb. It is not 

 possible to ensure the complete oxidation of the food eaten. For 

 instance, food may be retained and assimilated with a gain of weight 

 to the individual. This is met in the following way. The air of the 

 calorimeter is kept circulating through a series of chambers in which 



Water 



iiiiiiJiiHiiiuiiiiiiiuuiiiiiuiiLiLiii 



Double 

 Window. 



Illlllllllllfllllllllllllllllllllllillllll 



> Water 



CALORIMETER 

 CHAMBER. 



Air + Water + C0 2 ; deficient in Oxygen. 



i 1 



H 2 S0 4 . | |Soda-Lime.| 



LJ 



Air minus C0 2 and Water; deficient in Oxygen. 



Oxygen enters/ 



Fio. 394. The Atwater-Benedict Calorimeter. 



The above drawing contains one mistake ; the position of the soda-lime and sulphuric acid 

 should be transposed. 



the carbon dioxide and the water are absorbed, and subsequently 

 estimated. As the oxygen is used up by the individual, fresh 

 oxygen is admitted in known quantities. The urine and faeces are 

 analysed as well as the air, at the beginning and end of the experi- 

 ment. The following additional data are therefore forthcoming : 



(1) the carbon, hydrogen, and nitrogen given out by the body; 



(2) the oxygen taken in, and from these the amounts of protein, fat, 

 and carbohydrate metabolised in the body, can be calculated and 

 compared with the food ingested (see p. 613). 



In the calorimeter is a bicycle, the hind-wheel of which is 

 replaced by a copper disc. The disc may be rotated in the field of 



