LATENT HEAT OF STEAM. 249 



principle. Place a frozen apple, which thaws a little 

 helow freezing, in a vessel of ice-cold water. The la- 

 tent heat of the water immediately passes into the 

 apple and thaws it, and in an hour or two it will be 

 found hke a fresh apple and entirely free from frost; 

 hut the latent heat having escaped from the water 

 next the apple, a thick crust of ice is found to en- 

 case it. 



The amount of latent heat may be shown in still 

 another way. Mix a pound of snow at 32 degrees, or 

 at freezing, with a pound of water at 172 degrees. 

 All will be melted, but the two pounds of water thus 

 formed will be as cold as the snow, showing that for 

 melting it the 140 degrees in the hot water were all 

 made latent. 



ADVANTAGES OF LATENT HEAT. 



If no heat became latent by the conversion of ice 

 and snow to water, no time would, of course, be required 

 for the process, and thawing would be instantaneous. 

 On the approach of warm weather, or at the very mo- 

 ment that the temperature of the air rose above freez- 

 ing, snow and ice would all dissolve to water, and ter- 

 rific floods and inundations would be the immediate 

 consequence. 



LATENT HEAT OF STEAM. 



A still larger amount of latent heat is required for 

 the conversion of water into steam ; for, again place 

 the vessel of water with its thermometer on the fire, 

 it will rise, as the heat of the water increases, to 212 

 degrees, and then commence boiling. During all this 

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