52 TIMBER. 



This composition of wood is fairly uniform for different species. 



At ordinary temperatures wood is a very stable compound; both in 

 air and under water it remains the same for centuries, and only when 

 living organisms attack it with their strong solvents and convertants do 

 change and decay set in. 



Heated to 300° F. wood gives off only water, though some slight 

 chemical changes are noticeable even at this temperature. If the heat 

 is increased, gases of pungent odor and taste are evolved, and if the 

 temperature is sufficiently raised, the gases are ignited, forming the 

 flame of the fire, while the remaining solid part glows like an ignited 

 charcoal, giving much heat, but no flame. The amount of heat pro- 

 duced by wood varies. If first dried at 300° F., 100 pounds of poplar 

 wood should give as much heat as 100 pounds of hickory. In the 

 natural state, however, this is not the case. 



The beneficial effect of thorough seasoning for firewood appears from 

 the following consideration: 



One hundred pounds j)f wood as sold in the wood yards contains in 

 round numbers 25 pounds of water, 74 pounds of wood, and 1 pound 

 of ashes. 



The 74 pounds of wood are composed of 37 pounds of carbon, 4.4 

 pounds of hydrogen, and 32 pounds of oxygen. 



In burning (which is a process of oxidation) 4 pounds of hydrogen 

 are already combined with 32 pounds of oxygen and there are only the 

 37 pounds of carbon and 0.4 pounds of hydrogen available in heat pro- 

 duction. Thus only about one-half the weight of the wood substance 

 itself is heat producing while every pound of water combined in the 

 wood requires about GOO units of heat to evaporate it, and thus dimin- 

 ishes the value of the wood as fuel. Hence under the most favorable 

 circumstances 100 pounds of green wood (50 per cent moisture) fur- 

 nishes about 150,000 units ' of heat; 100 pounds of half dry (30 per cent 

 moisture) about 230,000 units; 100 pounds of air dry (20 per cent mois- 

 ture) about 280,000 units; 100 hundred pounds of air dry (10 per cent 

 moisture) about 320,000 units ; 100 pounds of kiln-dry (2 per cent mois- 

 ture) about 350,000 units. 



In the ordinary stove or other small apparatus the evil effect of 

 moisture in the wood is very much increased since combustion is mate- 

 rially interfered with. 



One hundred pounds of ordinary charcoal furnishes 700,000 units of 

 heat but the same quantity of charcoal produced at a temperature of 

 2,000° F. furnishes nearly 800,000 units of heat. 



Conifers and the lighter hard woods produce more flame, while the 

 heavy hard woods furnish a good bed of live coal and exceed the former 

 by 25 to 30 per cent in production of heat with ordinary appliances. 



'A unit of heat in this case is the amount of heat which raises the temperature 

 of 1 pound of water hy 1.8° F. or 1° C. 



