CHANGES IX STATE OF MATTER 47 



plate and condenses into water. In winter, steam col- 

 lects on the window panes, if the room is warm and 

 the air is moist. A pitcher of ice water when standing 

 in a warm room becomes covered with drops of water. 

 When the moisture in the air comes in contact with 

 the cold surface, it immediately condenses. 



When steam condenses into water, heat is released. 

 The amount of heat thus liberated is equal to the 

 amount of heat used in transforming the water into 

 steam. In other words, it requires 536 calories of heat 

 to convert 1 gram of water into steam, and 1 gram 

 of steam gives off 536 calories of heat during its con- 

 densation into water. 



The liberation of heat by condensation is made use 

 of in the system of steam heating. Water is boiled in 

 a boiler, and a large amount of heat is used to convert 

 the water into steam. The steam passes through pipes 

 which run to the radiators in various parts of the 

 building. There the steam condenses and in so doing 

 liberates large quantities of heat, thereby giving up 

 to the air of the room much of the heat which it had 

 absorbed from the fire. 



Change in volume resulting from change in state. 

 A change in the form of a. substance, from a solid to 

 a liquid, for example, is invariably accompanied by a 

 change of volume. 



With the exception of ice, most solids expand on 

 becoming liquids, and liquids expand when they 

 become gases. The volume of water is greatly 



