CALORIMETRY. 825 



is placed in the inner box and the heat given off is absorbed by the 

 water. Knowing the weight of the water and how much its tem- 

 perature is raised, the data are at hand for determining the number of 

 calories given off during the experiment. A recent form of this 

 variety of calorimeter used in this country by Reichert is shown in 

 Fig. 266. It consists of two concentric boxes of metal with a space 

 between them of about one and a half inches. The animal is placed 

 in the inner box (A). The two boxes are inclosed in a large wooden 

 box, the space between the metal and wooden boxes being filled 

 with shavings (SH). The object of this outer box is to prevent 

 radiation of heat from the metal boxes. The tubes EN and EX, 

 which lead into the interior chamber containing the animal, are for 

 the entrance and exit of the ventilating air. A thermometer is 

 placed in each to determine the heat carried off by the air. The 

 thermometer, CT, measures the temperature of the water, and S is 

 a stirrer to keep the water well mixed and thus insure a uniform 

 temperature. When the animal is placed in the apparatus the 

 heat given off warms not only the water, but also the metal; so 

 that to determine the total heat the weight of metal must be re- 

 duced to an equivalent amount of water by multiplying its weight 

 by its specific heat, or, a more simple method, the calorimetric equiv- 

 alent of the apparatus is determined, that is, the actual amount of 

 heat necessary to raise the temperature of the apparatus, water and 

 metal, one degree. This value is obtained by burning in the appa- 

 ratus a known weight of some substance (alcohol, hydrogen) whose 

 heat of combustion is known. Knowing how much heat is given 

 off by this combustion and how much the temperature of the 

 apparatus is raised, the calorimetric equivalent is easily calcu- 

 lated and may be used subsequently in estimating the results ob- 

 tained from animals. In the use of the apparatus many precau- 

 tions must be observed. These practical details need not be des- 

 cribed here except to say that account must be taken of the warm- 

 ing of the air used to ventilate the apparatus and of any changes 

 in the amount of its moisture. The calorimeter used in this way 

 measures- directly the amount of heat given off from the animal 

 during the period of observation. The amount of heat produced in 

 the animal's body during this time may be the same, or may be 

 more or less. To arrive at a knowledge of this factor observations 

 must be made upon the animal's body temperature by means of a 

 thermometer in the rectum. If this body temperature is the same 

 at the end as at the beginning of the experiment then it is obvious 

 that the heat produced must have been equal to the heat lost. If 

 the animal's body temperature has fallen, then it is evident that 

 less heat has been produced than was lost. To ascertain how much 

 less, the weight of the animal is multiplied by its specific heat (0 . 8) 



