274 HEAT. 



be as cold as the snow, showing that for melting it the 

 140 degrees in the hot water were all made latent. 



APVAXTAGES OF LATE:N^T 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 moment 

 that the temperature of the air rose above freezing, snow 

 and ice would all dissolve to water, and terrific 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 ves- 

 sel 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 time it will now 

 remain stationary at 212, until the water is all boiled away. 

 This is found to require nearly five times the period need- 

 ed to heat from freezing to boiling ; that is, nearly one 

 thousand degrees of heat are made latent by the conver- 

 sion of water into steam. 



When the steam is condensed again to water, this heat 

 is given out. Hence the use made of steam conveyed in 

 pipes for heating buildings, and for boiling large vats or 

 tubs of water, by setting free this large amount of latent 

 heat which the fire has imparted to it. 



GREEN AND DRY WOOD FOR FUEL. 



A great loss is often sustained in burning green wood 

 for fuel, from an ignorance of the vast amount of latent 

 heat consumed to drive off the water the wood contains. 

 When perfectly green, it loses about one-third of its weight 



