64 HEAT. 



142. THE MELTING OF SNOW COOLS THE 



How docs the Whenever ice is converted into wa- 



inelting of 



snoiv affect the ter, whether rapidly by fire or slowly 

 by change of weather, the disappearance 

 of heat, above mentioned, occurs. Thus, when the 

 snow melts in spring, heat is drawn off from the air 

 and made latent, or combined in the water which re- 

 sults from the melting. This makes the weather 

 cooler than it would otherwise be, and retards in a 

 measure the advance of spring. 



How do liquids 143. FREEZING. Liquids become solids 

 become solids? ^y t } ie rem oval of their combined heat. 

 Thus, if molten lead be allowed to stand awhile, the 

 heat which it contains passes away into other objects, 

 warming them ; and the metal itself, having lost its 

 heat, becomes solid. So in winter, the combined heat 

 which is contained in water, is conveyed away by the 

 colder air, and the water, having lost its heat, is con- 

 verted into ice. 



144. FREEZING POINT. The tempera- 



What is the L 



freezing point ture at which a substance passes from the 



of a liquid? liquid into the golid gtate ig called the 



freezing point. Thus, 32 is the freezing point of wa- 

 ter. The freezing point of any substance is, as might 

 be supposed, the same as the melting point. Water, for 

 example, becomes ice in process of cooling, at the 

 same temperature that ice becomes water in process of 

 heating. 



145. ALL LIQUIDS HAVE THEIR FREEZ- 



Can .all liquids 



be frozen? ING POINTS. There is good reason to be- 



Give examples. ^ Q ^ ^ ^.^ without exception> 



