36 OP WATER. 



from the freezing to the boiling point. At the same rate, 

 the water would have been raised nearly to 1,000, if it 

 had not been dissolved by heat and turned into 



(3.) Vapor. The vapor thus formed is no hotter than 

 the boiling water. It does not rise above 212. What 

 has become of all the heat? It has been used up in 

 turning the water into vapor. This heat is not indicated 

 by the thermometer. It seems to be latent in the vapor ; 

 and it is called the Latent Heat of the Vapor. 



108. The boiling of water is the agitation produced by 

 the rising of the vapor, formed at the bottom of the 

 kettle, up through the rest of the water ; and the vapor 

 is more abundantly formed in proportion as the heat of 

 the fire is greater. But the water does not change its 

 temperature in consequence of the violent ebullition. 

 For common cooking, therefore, the gentlest boiling is 

 just as effectual as the most violent. 



109. At the boiling point, vapor is formed very rapidly. 

 But water, exposed to the air, is continually evaporating, 

 at every temperature. Indeed, such is the tendency of 

 water to take the form of vapor, that even snow and ice. 

 in the air, are constantly turning into vapor. Wherever 

 it takes place, evaporation always uses up heat, or causes 

 it to become latent, and thus cools the air and all sur 

 rounding objects. Indeed, whenever vapor, or air, or 

 any other gas, expands, so as to occupy more space, it at 

 the same time requires more heat and absorbs it from 

 every thing within its reach capable of furnishing it. Its 

 capacity for heat is said to be increased. 



110. When, 011 the contrary, vapor turns again to the 

 state of water, it gives out all the latent heat which it had 

 taken in, while turning from water into vapor. The 

 same is true of other gases. Whenever they are con- 



