28 TEMPERATURE AND HEAT 



i C. If 400 grams of water are heated from o to 5 C., 

 the amount of heat which has entered the water is equivalent 

 to 5 X4OO or 2000 calories; if 200 grams of water cool from 

 25 to 20 C., the heat given out by the water is equivalent 

 to 5 X2OO or 1000 calories. 



1 6. Some Substances Heat more readily than Others. If two 

 equal quantities of water are exposed to the sun for the same 

 length of time, the temperatures will be the same. If, how- 

 ever, equal quantities of different substances are exposed, the 

 temperatures resulting from the heating will not necessarily 

 be the same. If a basin containing mercury is put on the fire, 

 side by side with a basin containing an equal quantity of 

 water, the temperatures of the two substances will vary greatly 

 at the end of a short time. The mercury will have a far higher 

 temperature than the water, in spite of the fact that the 

 amount of mercury is as great as the amount of water and 

 that the heat received from the fire has been the same in each 

 case. Mercury is not so difficult to heat as water; less heat 

 being required to raise its temperature i than is required to 

 raise the temperature of an equal quantity of water i. In fact, 

 mercury is 30 times as easy to heat as water, and it requires 

 only one thirtieth as much fire to heat a given quantity of 

 mercury i as to heat the same quantity of water i. 



17. Specific Heat. We know that different substances are 

 differently affected by heat. Some substances, like water, 

 change their temperature slowly when heated ; others, like 

 mercury, change their temperature very rapidly when heated. 

 The number of calories needed by I gram of a substance in 

 order that its temperature may be increased iC. is called 

 the specific heat of a substance ; or, specific heat is the num- 

 ber of calories given out by I gram of a substance when its 

 temperature falls iC. For experiments on the determina- 

 tion of specific heat, see Laboratory Manual. 



