10 



mined by Sharpless, are quoted from the Report of the Tenth United 

 States Census. The figures given are the average for different vari- 

 eties of the same species. 



Specific gravity and weight of different woods. 



WATER CONTENT. 



The wood used for destructive distillation should be as dry as possi- 

 ble, as much time and fuel are wasted if green or wet wood must be 

 dried in the retort and the temperature raised under such conditions 

 to the point at which distillation begins. For these reasons it is the 

 best practice to cut and stack the green wood, which contains from 

 20 to 50 per cent of water, from eight months to two years before it is 

 to be used in order that it may become well seasoned. Even seasoned 

 woods contain from 12 to 25 per cent of water, which must be evapo- 

 rated in the retort before the disintegration of the wood begins. 



The capital required to maintain a two years' supply of wood for a 

 plant using 20 cords of wood a day varies from $20,000 to $40,000, so 

 that in many instances wood not thoroughly seasoned is used in pref- 

 erence to making this outlay. Such a practice, of course, increases 

 the operating expenses considerably, and drying ovens heated by the 

 waste steam and gases of the plant have been used in some cases to 

 dry the wood quickly before it goes into the retort. This is un- 

 doubtedly the better practice, and whenever it is possible plants 

 should be equipped with such drying ovens, thus decreasing the 

 amount of capital invested in wood and at the same time securing large 

 yields, as during seasoning by exposure wood loses weight from rotting 

 and from the solution of water-soluble constituents, and consequently 

 gives a lower yield of distillation products. 



COMPOSITION. 



The data on the composition of wood are not very satisfactory, as 

 most of the figures were obtained by methods less accurate than those 

 now in use. Neither were as many normal constituents of woods 



[Cir. 36] 



