MEASUREMENT OF THE VOLUME OF HEAT: CALORIMETRY. 389 



MEASUREMENT OF THE VOLUME OF HEAT: CALORIMETRY. 



The calorimeter furnishes information as to the amount of heat that 

 the body to be examined possesses or is capable of producing. The heat- 

 unit or calory, that is the amount of kinetic energy that is capable of 

 raising the temperature of one gram of water i C., is employed as the 

 unit of measure. 



Experiment has shown that equal amounts of different bodies require unequal 

 amounts of heat in order to attain the same temperature. For instance i 

 kilo of water requires nine times as much heat as i kilo of iron to attain the same 

 temperature. Wherever, therefore, different materials with equal temperatures 

 are found, each will be endowed with different amounts of heat. The same 

 amount of heat imparted to different bodies will, thus, also produce different 

 temperatures in them. On the other hand, bodies naturally of different tempera- 

 ture may possess equal amounts of heat. The amount of heat that a definite 

 amount (as, for instance, i gram) of a body requires in order to have its tempera- 

 ture raised a definite amount (as, for instance, i C.), is designated the specific 

 heat of that body. The specific heat of water, which possesses the greatest of all 

 bodies, is placed at i. Heat-capacity is the term applied to that property of 

 bodies by means of which they are required to take up a varying amount of heat 

 in order to maintain the same temperature. 



Calorimetry is employed : 



For the determination of the specific heat of the different organs 

 of the body. But few observations in this connection have as yet been 

 recorded. 



The specific heat of a number of animal parts, as compared with 

 that of water as i , is as follows : 



Blood from man, on the average . 1.02 (?) Meat from man, on the average . . . 0.741 



(it is in proportion to the num- Compact bone 0.3 



ber of erythrocytes) Spongy bone.. ..0.71 



Arterial blood, on the average. . 1.031 (?) Fat 0.712 



Venous blood, on the average . .0.892 (?) Striated muscle 0.825 



Cow's milk, on the average . . . .0.992 Defibrinated blood 0.927 



The specific heat of the human body as a whole is thus only ap- 

 proximately that of an equivalent weight of water. 



For the method of determining the specific heat of solid or liquid bodies 

 works on physics should be consulted. 



More important is the employment of calorimetry for the estima- 

 tion of the amount of heat that either the entire body or an individual 

 portion is capable of producing in a definite period of time. 



Lavoisier and Laplace made the first calorimetric observations on animals in 

 1780, with the aid of the ice-calorimeter. A guinea-pig melted 13 ounces of 

 ice in 10 hours. Crawford in 1779 and later Dulong and Despretz in 1822 

 employed for this purpose the water-calorimeter of Rumford after which that 

 of Favre and Silbermann (Fig. 133) is modeled. Small animals were placed in 

 the interior chamber (K) made of thin copper and this was immersed in a large 

 volume of water surrounded by a poor conductor of heat. The amount of the 

 surrounding water and its initial temperature were known. From the elevation 

 of temperature at the termination of the experiment, which lasted several hours, 

 the number of calories furnished could be directly estimated. The air for breathing 

 was supplied to the animal through a special tube from a gasometer. The expired 

 gases were examined chemically for carbon dioxid. 



According to Despretz, a small bitch generated 14,610 heat-units in an hour 

 393,000 in twenty-four hours. The taking of the temperature of the animal before 

 and after the experiment was carelessly omitted. Assuming equal metabolic 

 activity, a human being about seven times heavier would, on the basis of this 

 observation, produce in the neighborhood of 2,750,000 calories in twenty-four 



