PRACTICAL APPLICATION 39 



by contact with the cold lid and condenses into water. Bottles 

 of water brought from a cold cellar into a warm room become 

 covered with fine drops of water, because the moisture in the 

 air, chilled by contact with the cold bottles, condenses into 

 drops of water. Glasses filled with ice water show a similar 

 mist. 



We have seen that 536 calories are required to change I gram 

 of water into steam ; if, now, the steam in turn condenses into 

 water, it is natural to expect a release of the heat used in trans- 

 forming water into steam. Experiment shows not only that 

 vapor gives out heat during condensation, but that the amount 

 of heat thus set free is exactly equal to the amount absorbed 

 during vaporization! 



Practical application. We understand now the value of 

 steam as a heating agent. Water is heated in a boiler in the 

 cellar, and the steam passes through pipes which run to the 

 various rooms; there the steam condenses into water in the 

 radiators, each gram of steam setting free 536 calories of heat. 

 When we consider the size of the radiators and the large amount 

 of steam which they contain, and consider further that each 

 gram in condensing sets free 536 calories, we understand the 

 ease with which buildings are heated by steam. 



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, 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 surrounding 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 



