248 PRINCIPLES OF ANIMAL NUTRITION. 
In 1894 Haldane, White & Washbourne * described a form of air- 
calorimeter in which the expansion caused by the heat produced by 
the animal in one chamber is balanced by that produced by a flame 
of hydrogen burning in a second similar chamber. The calorimeter 
is essentially one of constant volume, but the heat is computed 
_ from the amount of hydrogen burned. 
Laulanié + in 1895 described a Pettenkofer apparatus with small 
ventilation (see p. 71) which served also as an air-calorimeter, and 
still later { has described a differential water-calorimeter. Kauf- 
mann,§ as mentioned on p. 69, has determined the respiratory 
exchange of animals during short periods in a confined volume of 
air. The apparatus consisted simply of a zinc receptacle which 
served also as a radiation calorimeter. The internal temperature 
and that of the surrounding air were measured by recording ther- 
mometers and the loss of heat calculated according to Newton’s 
law. The atmosphere-in the apparatus was saturated with water- 
vapor at the start, so that the moisture excreted by the animal was 
condensed and no correction for the heat of vaporization was neces- 
sary. 
By far the most important form of respiration-calorimeter yet 
devised, however, not only as regards accuracy but particularly 
in view of the range of work of which it is capable, is that of Atwater 
& Rosa,|| the respiratory part of which has already been mentioned 
(pp. 72 and 79). In this apparatus water is. used as the calori- 
metric substance, but in the form of a constant current instead of a 
large stationary mass. As described by the authors the appara- 
tus consists of a Pettenkofer respiration apparatus provided with 
special devices for the accurate measurement, sampling, and analy- 
sis of the air-current. A current of cold water is led through copper- 
absorbing pipes near the top of the respiration chamber and takes 
up the heat given off by the subject. The volume of the water used 
being measured, and its temperature when entering and leaving 
being taken at frequent intervals, the amount of heat brought out 
* Jour. Physiol., 16, 123. 
t Archives de Physiol., 1895, p. 619. 
{ Ibid., 1898, pp. 538 and 613. 
§ Ibid., 1896, p. 329. 
| U. S. Dept. Agr., office of Experiment Stations, Bulletins 63 and 69. 
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