106 OF WOOD IN GENERAL. 



Norway was valued at 8,600,000 kroner (about 430,000), and 

 that of Sweden at 10,400,000 kroner (520,000), whilst in 1900 

 they were 27,400,000 and 33/200,000 kronor respectively. 



Fuel. The heat-producing value of wood as fuel varies greatly, 

 owing to the differing capacity that woods have for retaining 

 moisture. Thus, while green wood may contain 50 per cent, of 

 moisture, ordinary stack-wood may contain only 25 per cent., and 

 kiln-dry wood only 2 per cent. With 25 Ibs. of water, 100 Ibs. of 

 fire wood will contain about 1 Ib. of incombustible ash and 74 Ibs. 

 of the dry substance of wood. This last consists of 37 Ibs. of carbon, 

 32 Ibs. of oxygen and 4*4 Ibs. of hydrogen; and in burning the whole 

 of the oxygen combines with 4 Ibs. of hydrogen to form water, so 

 that only the 37 Ibs. of carbon and - 4 Ib. of hydrogen, i.e. about half 

 the weight of the dry substance of the wood, are available for heat- 

 production. Every pound of water combined in the wood requires 

 about 600 units of heat to evaporate it, the unit being the 

 amount of heat necessary to raise 1 Ib. of water 1 C. ; so that 

 100 Ibs. of stack-wood (25 per cent, moisture) only furnishes 

 about 255,000 units, whilst if kiln-dry (2 per cent.) it would 

 yield 350,000. The advantage of seasoning for firewood is, there- 

 fore, obvious. The resinous woods of the conifers produce most 

 flame and are most useful accordingly in starting a fire ; but the 

 denser hard woods produce from 25 to 30 per cent, more heat. 



Charcoal. When wood is heated to 200 F. without access of 

 air, it remains unaltered, at 220 it becomes brown, and at 270 

 to 300 it suffers decomposition, torrefied wood or red charcoal 

 being formed. At 350 it is resolved into volatile products and 

 true or black charcoal. If the temperature is raised gradually, so 

 that 600 F. is not reached for several hours, the process is called 

 dry distillation. The first product of distillation is almost entirely 

 water ; but at 500 pyroligneous (crude acetic) acid, or wood- 

 vinegar, wood-spirit and uncondensable gases pass off, charcoal 

 and some tar remaining. In the primitive method of the charcoal- 

 burner, or imiler, in which billets of wood are stacked horizontally 

 or inclined round a central chimney opening, most of the volatile 

 products are lost ; but for charcoal this process is still largely 



