36 College of Forestry 



The pyroligeneous acid is then run by gravity to the pri- 

 mary steam-heated copper stills equipped with automatic feed 

 in order to supply the still continuously. The residue or 

 boiled tar which gradually fills up in the still from the bottom 

 is distilled by itself and run ofi at intervals of a few days or 

 whenever the deposit reduces the flow of distillate from the 

 still. During this process, which is known as '' tarring 

 down," the distillate is run into a separate tank and the light 

 oils which rise to the toj) are drawn off. The acid liquor is 

 then piped to storage tanks or tubs with the regailar run from 

 this still. These copper stills are made in any size which 

 will give them the most flexible operation, that is, the size is 

 determined by the question of economy in operation in labor 

 cost. This in turn depends upon the capacity of the plant 

 in cords of wood. The vapors from the copper still are con- 

 veyed through a large copper neck to an all copper tubular 

 condenser encased in a steel water jacket. The flow of 

 distillate from these condensers is piped to storage tubs. 



From the storage tubs the acid liquor goes to the liming 

 or neutralizing tubs. These are wooden tubs 12 feet to 14 

 feet in diameter, about 4 feet high, and provided with an 

 agitator operated by a shaft and bevel gear from the top. 

 The liquor is neutralized by adding slacked lime, a small 

 quantity at a time. The proper quantity of lime is commonly 

 determined by the color of the liquor, which changes at the 

 neutral point between an acid and alkaline substance to a 

 wine color, followed by a straw color and the appearance of 

 beads on the surface. 



From the neutralizing tubs the liquor is pumped or forced 

 by means of a steam ejector to the " lime lee " stills. These 

 stills are constructed of steel plate, the heat being applied 

 by copper steam coils. The alcohol vapors pass off through 

 an iron or copper neck, and are condensed in a copper con- 

 denser, and piped to storage tanks. 



