250 HEAT. 



time it will now remain stationary at 212, till the wa- 

 ter is all boiled away. This is found to require nearly 

 five times the period needed to heat from freezing to 

 boiling ; that is, nearly one thousand degrees of heat 

 are made latent by the conversion of water into 

 steam. 



"When the steam is condensed again to water, this 

 heat is given out. Hence the use made of steam con- 

 veyed 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 fael, from an ignorance of the vast amount 

 of latent heat consumed to drive off the water the 

 wood contains. "VYlien perfectly green, it loses about 

 one third of its weight by thorough seasoning, which 

 is equal to about 25 cubic feet in every compact cord, 

 or 156 imperial gallons. Now all this water must be 

 evaporated before the wood is burned. The heat thus 

 made latent and lost, being five times as great as to 

 heat the water to boiling, is equal to enough for boiling 

 780 imperial gallons in burning up every cord of green 

 wood. The farmer, therefore, who burns 25 green 

 cords in a winter, loses heat enough to boil more than 

 fifteen thousand gallons of water, which would be 

 saved if his wood had been previously well seasoned 

 under shelter. 



The loss in using green fuel is, however, sometimes 

 overrated. It has been found by experiment that one 

 pound of the best seasoned wood is sufficient to heat 



