34 TEMPERATURE AND HEAT 



sorbed by I gram of water when its temperature rises i C. 

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

 of heat which enters the water is equivalent to 5 X 400 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 X 200, or 

 looo calories. 



Some substances heat more readily than others. When two 

 equal quantities of water at the same temperature are exposed 

 to the sun for the same length of time, their final temperatures 

 are the same. But when equal quantities of different sub- 

 stances are exposed, the temperatures resulting from the heat- 

 ing are not necessarily the same. If a basin containing I 

 Ib. of mercury is put on the fire, side by side with a basin 

 containing I Ib. of water, the temperatures of the two sub- 

 stances will be very different 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 is the same in each case. Mercury is not as 

 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. 



It requires more heat to raise the temperature of water one 

 or more degrees than it does to raise the temperature of 

 an equal weight of any other substance (except hydrogen) 

 the same number of degrees. Practically this same thing can 

 be stated in another way: Water in cooling gives out more 

 heat than any other substance that cools through the same 

 number of degrees. For this reason water is used in foot 

 warmers and in hot-water bags. If a copper lid were used 



