70 



HEAT 



get its temperature, and add 10 g. of iron having a 

 temperature of 100 C. In this case the temperature of 

 the water rises more than 3 times as far as when lead 

 was used. This shows us that the iron has more than 3 

 times as great a heat capacity, or specific heat, as the 

 lead. (See Appendix, Table VII.) 



The calorimeter has very important, practical uses. A factory 

 using a large amount of coal needs to test different kinds of the fuel 

 (cf. 15), in order to find which one gives the most heat for the least 

 money. The worker in Domestic Science wants to know how much 

 heat the different kinds of food, such as butter, potatoes, beef, and 

 fish, will give out in our bodies (cf. 74) . In this way he can get an 

 idea of the values of these foods. The heat that can be obtained from 

 both the coal and the food is found by burning them in a calorimeter. 

 A calorimeter such as is needed to give the heating value, in calories, 

 of a fuel or a food (Fig. 61) is more complicated than 

 the simple calorimeter, but the principle according to 

 which it "works" is the same. Some of the fuel or 

 food is burned in an inclosed space containing com- 

 pressed oxygen, or some oxidizing substance (cf. 48), 

 and the heat given off is imparted to a known weight 

 of water. From the increase in the temperature 

 of the water the calories of heat given off can be 

 calculated. 



FIG. 61. 



74. Heat and Life. A healthy man has a 

 , temperature of 98.6 F., or 37 C. This does 



eter. By means -, i , , 



of it we find the not change, day or night, summer or winter, 



amount of heat _ . t .1 e , i 



given off in bum- although the temperature of the air may 

 vary 50 F. in a day, and 150 in a season. 

 The body is warmed by the changes (oxidations) of its 

 own cells and of digested food. We have seen (cf. 25) 

 that energy is the capacity for doing work. The body is 



