Heat as a Quantity 161 



It will be found that the reading in the case of the 

 lead is much lower than that obtained with the hot 

 water. Repeat the experiment with lumps of different 

 substances, such as a large glass stopper, a 100 g. 

 weight, a large flint, and a quantity of mercury, using 

 in each case a mass of hot water equal to that of the 

 body. These will produce varying increments of tem- 

 perature in the cold water, but each will cause a smaller 

 increase than is produced by an equal mass of hot 

 water. 



As stated in the last chapter, temperature is inde- 

 pendent of the material of which a body is made. 

 The above experiment indicates that the quantity of 

 heat contained in different bodies of equal mass at the 

 same temperature is not the same, i.e. that the quantity 

 of heat is not independent of the material composing a 

 body. Further it appears that a given mass of water 

 at a given temperature contains more heat than any 

 of the other substances tested. 



102. Since heat is a quantity, it may be measured, 

 given a suitable unit of measurement. The unit 

 commonly adopted is known as the calorie. This unit 

 has been variously defined, but for our purposes it 

 will be sufficient to ignore the small variations of value 

 consequent on the adoption of one or other definition 

 and to state that " a calorie is the quantity of heat 

 required to raise the temperature of one gram of water 

 one degree Centigrade". To heat 120 g. (or 120 c.c., 

 if no account be taken of the small variations of the 

 density of water with temperature) of water from 

 15 C. to 87 C. will therefore require that energy be 

 supplied to the water in the form of heat to the extent 

 of {120 x (87 - 15)} = 8640 calories. In cooling from 

 87 C. to 15 C., the same amount of water will supply 



H. D. s. 11 



