NORMAL PROCESSES OF ENEKGY METABOLISM 581 



the same amount of heat as the subject would be expected to eliminate in a 

 given time. With an experimental apparatus the error will be, assuming 

 a uniform technique, about constant in absolute amount so that the total 

 error will diminish as the total quantity measured increases. 



When the rate of flow of the alcohol to the lamp has been adjusted so 

 that it is fed into the burette just as rapidly as consumed therefrom by 

 the lamp, the apparatus is scaled and after a preliminary period during 

 which the calorimeter is brought into equilibrium, the burette is read, 

 the supply bottle from which the alcohol is fed into the burette is changed 

 for another which has been weighed, and the experiment starts in the usual 

 way. 



To insure complete combustion of the alcohol it is necessary to employ 

 a lamp so constructed that the region of the edge of the wick will always 

 be sufficiently hot to insure immediate ignition. Williams finds that by 

 using a short piece of hard glass tubing for the top of the burner and a 

 wick of a glass wool the difficulties attending the combustion of alcohol 

 are most readily overcome. 



The specific gravity of the alcohol must be determined with a high de- 

 gree of precision after which the theoretical amounts of heat, carbon dioxid 

 and water which the known combustion will generate may be calculated. 

 Likewise, the amount of oxygen necessary to support this combustion. In 

 the case of the water one must make a correction for the amount of water 

 of dilution present in the alcohol. The heat of combustion of alcohol has 

 been determined a great many times. As the result of 25 observations with 

 the bomb calorimeter Atwater and Rosa found the heat of combustion 

 of pure ethyl alcohol to be 7.067 large calories per gram. This figure 

 is generally employed in this country. In all of the different calorimeters 

 of Atwater, Rosa and Benedict here described the correspondence between 

 the amounts of heat generated by the alcohol and the heat actually measured 

 has been very close. For example, in a long series of experiments of three 

 or four hours' duration the average error with the Sage calorimeter for the 

 heat of combustion was 0.0 per cent, for tlie oxygen absorption 1.6 per 

 cent, and for the carbon dioxid elimination 0.6 per cent. 



3. The Emission Calorimeters/ The fourth group of calorimeters ac- 

 cording to the classification of Lefevre are those which do not absorb 

 the heat but allow it to escape into the external medium. Because of this 

 feature the name calorimeters deperditeurs, or emission calorimeters, was 

 proposed by B ? Arson val(a), who devised several different types. Some of 

 these calorimeters have single walls and the effect of the heat generated 

 within is recorded in some way. In the so-called anemo-calorimeter of 

 D'Arsonval the subject stands inside a tent -like cubicle which has a nar- 

 row chimney or ventilator at the top. In the chimney is a delicate wind- 

 gauge. The heat from the man's body induces a strong convection current 

 which is free to enter the cubicle below and which sets the wind-gauge in 



