154 Wood Gas Forest Fires. 



Illuminating Gas from Wood. 



616. It is found that wood exposed to cherry-red heat in close 

 retorts, yields a gas which, when purified, has a much greater 

 illuminating power than the best obtained from coal. In this way 

 chips and other waste pieces of wood have been turned to profitable 

 account. The heat in this process must be carried to a greater de- 

 gree than in the making of charcoal, and hence the residual product 

 is of inferior quality. The different kinds of wood are about alike 

 as to value in furnishing gas for illumination, the quantity averag- 

 ing, in eight of the common kinds, about 582.35 cubic feet to 100 

 pounds of wood. 



617. The condition as to dryness, however, is of great importance, 

 since the vapor of water coming in contact with the incandescent 

 charcoal will form an oxyde of carbon and of hydrogen, that will 

 reduce its illuminating power. The wood should therefore be dried 

 as much as possible just before being placed in the retort, or else it 

 will again absorb moisture from the air. 



618. Where steam-power is used, the waste steam may be carried 

 in pipes through the drying chamber, and a current of air may be 

 driven or drawn through the wood, securing the requisite degree 

 of dryness, without much expense. The retorts may be like those 

 for coal gas, but larger, and as the process gives the best result 

 when heated rapidly, the furnaces should have a larger amount of 

 grate surface. A charge is worked out in an hour and a half, and 

 the charcoal formed is at the end drawn out into sheet-iron extin- 

 guishers and tightly closed for cooling. As the liquid products are 

 corrosive to iron, copper pipes must be used, and the gas must be 

 purified before being used. 1 



CHAPTER XV. 



FOREST FIEES. 



619. There is no subject in Forestry more important than the 

 prevention and control of forest fires. They every year do a vast 

 amount of injury, not only to standing timber and young trees, but 



1 Those wishing; to look further into this subject, will find detailed informa- 

 tion in the Forestry Report of 1877, published by the Department of Agri- 

 culture, p. 133, and in the authorities there cited. 



