CHAPTER IX 

 QUANTITY OF HEAT AND TRANSMISSION OF HEAT 



TEMPERATURE and quantity of heat must not be con- 

 sidered the same thing. Temperature or degree of heat 

 indicates how hot or cold a body is, and depends upon the 

 rapidity with which the molecules are moving and not 

 upon the number of molecules. Heat, or quantity of 

 heat, which a body possesses depends upon the speed of 

 the molecules, the number of molecules affected, and also 

 upon the kind of molecules of which a body is composed. 



The Calorie. -- The metric unit used in measuring the 

 quantity of heat in a body is called the calorie. It is the 

 amount of heat required to warm one gram of water 

 through one degree Centigrade. It is also the amount of 

 heat given off by one gram of water when its temperature 

 falls one degree Centigrade. To warm one gram of water 

 from C. to 100 C. requires one hundred calories. The 

 same amount of heat is required to heat four grams of 

 water from C. to 25 C., or ten grams of water from 

 C. to 10 C. 



Heat Capacity. Different substances have different 

 capacities for taking heat. If equal amounts of water 

 and mercury be subjected to the same heat, the mercury 

 will become hot much quicker than the water. The 

 quantity of heat that is required to raise the temperature 

 of a gram of water from C. to 1 C. will raise the tem- 

 perature of thirty grams of mercury from C. to 1 C. ; 

 or it requires thirty times as much heat to raise a given 



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