GREEN AND DRY WOOD FOR FUEL. 251 



27 lbs. of water from the freezing to the hoihng point.* 

 This wUl be equal to heating and evaporating four 

 pounds of water by every pound of wood. The 25 

 cubic feet of water, therefore, in every cord of green 

 wood, weighing about 1500 pounds, would require near- 

 ly 400 pounds of wood for its evaporation, or about one 

 seventh or one eighth of a cord. Hence we may infer 

 that seven cords of dry wood are about equal to eight 

 cords of green. This imperfect estimate will apply 

 only to the best hard wood, and will vary exceedingly 

 with the different sorts of fuel ; the more porous the 

 wood becomes, the greater will be the necessity for 

 thorough seasoning. 



Superficial observation often leads to very erroneous 

 conclusions. Seasoned wood will sometimes burn with 

 great rapidity, and, producing an intense heat for a 

 short time, will favor an over-estimate of its superior- 

 ity. G-reen wood, on the other hand, kindles with dif- 

 ficulty, and burns slowly and for a long time ; hence, 

 where the draught of the chimney can not be control- 

 led, it may be the most economical, because a less pro- 

 portion of heat may be swept upward than by the more 



* The following results show the heating power of several combust- 

 ibles : 



1 lb. of wood (seasoned, but still holding 20 per cent, of water) 



raised from 32° to 212'^ 27 lbs. water. 



1 lb. of alcohol 68 " " 



1 lb. of charcoal 78 " 



1 lb. of oil or wax 90 " " 



1 lb. of hydrogen 216 " " 



It should be remembered that by ordinary modes of heating water, 

 a very large proportion of the heat is wasted by passing up the chim- 

 ney and into surrounding bodies, and the air. 



