32 INTRODUCTION TO GENERAL SCIENCE 



same material in a solid state, while a gas contains still more 

 heat energy than does the same weight of liquid. The tem- 

 perature of ice cannot be raised above 32 Fahrenheit until 

 all the ice is melted. The heat goes to give the molecules 

 enough energy to exist in the form of a liquid. For a similar 

 reason water cannot be heated in the open air, above its 

 boiling point 212 Fahrenheit. The heat gives the water 

 molecules sufficient energy to exist in the gaseous form. Now, 

 since there is no loss in nature, this same amount of heat 

 which is necessary to change a solid into a liquid is given out 

 again, when the liquid changes back into a solid. Farmers in 

 cold countries make use of this fact by placing in their 

 cellars large tubs of water, which, as it freezes, gives out to 

 the cellars the same amount of heat that would be necessary 

 to melt the same weight of ice to water. Thus vegetables 

 may be kept from freezing, since their freezing point is 

 slightly lower than that of water. Again, the heat which is 

 necessary to change water into steam is given out when the 

 steam condenses to water again. Upon this is based the 

 system of steam heating. The water which leaves the steam 

 radiator has just as high a temperature as the steam from 

 which it was condensed, although a great amount of heat 

 has been given off by the condensation of the steam. See 

 Section 25, Applications of Evaporation and Condensation. 

 References : 



1. 1803 : 196. Definition of Heat of Fusion. 



2. 1803 : 198. Latent Heat of Fusion. 



3. 1803 : 203. Definition of Heat of Vaporization. 



4. 1803 : 204. Latent Heat of Vaporization, 

 a. 1801 : 274-278. Heat and the Change of State. 

 6. 1802:304. Solidification. 



c. 1804:278-287. Fusion and Vaporization. 



d. 1805 : 333. Heat of Fusion. 



