106 THE PRODUCTION AND USE OF HEAT 



By means of the gas producer the coal is " gasified " and the 

 resulting gas may be burned with all the advantages that 

 belong to other gaseous fuels. By the producer gas method, 

 a larger amount of the energy of the coal may be obtained 

 than by the direct burning of coal beneath a boiler (see Chap. 

 X, Sec. VII). 



VII. THE MEASUREMENT OF HEAT 



Our fuels are burned for the production of heat or light. A 

 fuel intended for the production of heat is more or less valuable 

 depending on the amount of heat that can be obtained from 

 it when it is burned. 



120. Distinction Between Heat and Temperature. We 

 have learned that temperature refers to the hotness or cold- 

 ness of a body (see Art. 14). Temperature is measured by 

 means of a thermometer. Two bodies may have the same 

 temperature but may contain vastly different amounts of heat. 

 A pint of water may have the same temperature as the average 

 temperature of a large body of water like Lake Michigan, yet 

 it will possess very little heat compared with that in the lake. 

 The lake influences the climate of the surrounding states, 

 but the influence of the pint of water on the temperature of 

 objects around it will amount to almost nothing. It is 

 apparent that the weight of the body has a great deal to do 

 with the heat it contains at a given time. Then, too, the 

 amount of heat a body contains also depends upon the material 

 of which it is made. Two objects of the same weight but of 

 different materials may be changed in temperature an equal 

 number of degrees, and yet the amounts of heat required to 

 produce the change in temperature may differ greatly. One 

 pound of water in being raised in temperature 10C. will re- 

 quire more than 32 times as much heat as will be required 

 by 1 Ib. of lead raised a like amount in temperature. Other 

 substances require still different amounts of heat for a like 

 temperature change. 



DEFINITION. The heat capacity of I gram of a substance 



