34 OTHER FACTS ABOUT HEAT 



Most of us have at times profited by the heat of condensa- 

 tion. In cold weather, when there is a roaring fire in the 

 range, the water frequently becomes so hot that it "steams" 

 out of open faucets. If, at such times, the hot water is turned 

 on in a small cold bathroom, and is allowed to run until the 

 tub is well filled, vapor condenses on windows, mirrors, and 

 walls, and the cold room becomes perceptibly warmer. The 

 heat given out by the condensing steam passes into the sur- 

 rounding air and warms the room. 



There is, however, another reason for the rise in tempera- 

 ture. If a large pail of hot soup is placed in a larger pail of 

 cold water, the soup will gradually cool and the cold water 

 will gradually become warmer. A red-hot iron placed on a 

 stand gradually cools, but warms the stand. A hot body 

 loses heat so long as a cooler body is near it ; the cold object 

 is heated at the expense of the warmer object, and one loses 

 heat and the other gains heat until the temperature of both is 

 the same. Now the hot water in the tub gradually loses heat 

 and the cold air of the room gradually gains heat by con- 

 vection, but the amount given the room by convection is 

 relatively small compared with the large amount set free by 

 the condensing steam. 



25. Distillation. If impure, muddy water is boiled, drops 

 of water will collect on a cold plate held in the path of the 

 steam, but the drops will be clear and pure. When impure 

 water is boiled, the steam from it does not contain any of the 

 impurities because these are left behind in the vessel. If all 

 the water were allowed to boil away, a layer of mud or of 

 other impurities would be found at the bottom of the vessel. 

 Because of this fact, it is possible to purify water in a very 

 simple way. Place over a fire a large kettle closed except for 

 a spout which is long enough to reach across the stove and 

 dip into a bottle. As the liquid boils, steam escapes through 



