EFFECTS OF HEAT 



77 



FIG. 58 



condensed by the cold water around it, running out at n as water. 

 Since only steam passed from /to e, the water should come from 

 the tube clear and 



pure. It is called , t 



distilled water. 



Distillation is 

 used on ocean 

 steamers to sup- 

 ply water for 

 the boilers; salt 

 sea water would 

 rust them badly, 

 but distilling 

 removes the 

 salt. The pro- 

 cess is also used 

 in making alcohol and liquors, flavoring extracts, per- 

 fumes, and many other compounds. 



88. Latent Heat. --The temperature at which ice 

 melts (32 F.) is the same as that at which water 

 freezes. If a piece of ice is put into a vessel and slow 

 heat applied, the ice changes to water; but so long as 

 any ice remains, the temperature of the water remains 

 the same as that of the ice. In other words, though 

 much heat is applied to the mass its temperature does 

 not rise. This fact was early discovered, and the name 

 latent (i.e. hidden) was given to the heat which thus 

 seemed to disappear. 



The same thing occurs when other substances are 

 changed from solids to liquids, or from liquids to gases. 

 It is also true that the heat thus taken into a body is 



