HARDWOOD DISTILLATION 205 



The pyroligneous acid is then run by gravity to the primary 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 off 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 dis- 

 tillate is run into a separate tank and the light oils which rise to the top 

 are drawn off. The acid liquor is then piped to storage tanks or tubs 

 with the regular 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 conveyed 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 neutraliz- 

 ing tubs. These are wooden tubs 12 ft. to 14 ft. in diameter about 4 ft. 

 high, and provided with an agitator operated by a shaft and bevel gear 

 from the top. The liquor is neutralized by adding slaked lime, a small 

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

 mined 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 condenser, and piped to storage tanks. 



When the alcohol has been distilled off in the lime lee stills, the residue 

 or acetate solution is forced by steam or air pressure to a settling pan 

 located over carbonizing ovens. After the impurities settle and are 

 drawn off the acetate liquor is run into a large shallow steam-jacketed 

 steel pan, and boiled down to the consistency of mortar; it is then 

 shoveled out and spread on brick, steel or concrete kiln floors over the 

 ovens and thoroughly turned and dried; it is then shoveled into sacks 

 for shipment as acetate of lime. 



The alcohol liquor from the lime lee still is drawn from the storage 

 tanks previously mentioned into a steel alcohol still provided with 

 copper steam coils, and distilled off through a copper fractionating 

 column consisting of a series of baffling plates having a tubular water- 



