SOFTWOOD DISTILLATION 231 



the top and it is thus easily removed. After steaming, the chips are 

 subjected to a vacuum to dry them. 



In the extraction or solvent process a solvent such as naphtha, 

 benzol, gasoline, etc., is admitted to the retort and heated to boiling 

 temperature by the steam coils. This solvent removes the rosin from the 

 wood. The extracted chips after being freed of rosin as well as the petro- 

 leum solvents are discharged through a trap in the bottom of the retort 

 and sent to the boiler house, where they are used for fuel for power and 

 steam. 



The products, therefore, of this form of distillation are crude turpen- 

 tine, a yellow oil consisting of wood turpentine, and pine oil. This 

 crude turpentine, if properly refined, produces a colorless uniform quality 

 fluid which is very similar to the standard spirits of turpentine. The 

 rosin, however, is of comparatively low grade and does not command the 

 same price as that derived from the tapping of the trees. 



The length of time required for the extraction by steam distillation is 

 ordinarily about twelve hours. One plant in the South which has a 

 capacity of 20 cords for each charge requires from 1 2 to 20 men to operate 

 and the initial cost of equipment is said to be from $1000 to $3000 per 

 cord of capacity. The yields vary directly with the character of the wood 

 used. In one plant from a continuous run of 711 cords there were 

 secured an average of 815 lb. of rosin, 11 lb. of turpentine and 4 gal. of 

 pine oil per cord. By the spring of 1919, practically all the plants using 

 the steam process had gone out of existence. 



The so-called bath process is a form of steam distillation. A non- 

 volatile pitch or rosin is heated to the boiling-point and circulated through 

 the wood in the retorts. The turpentine and oils in the wood are liber- 

 ated by this heat and mixture with the bath. The oils and turpentine 

 are recovered separately and the bath used again. This process has not 

 developed under market conditions which would thoroughly justify its 

 general commercial use ; the alkali process or one similar to it has been 

 very optimistically spoken of and by some it is predicted that it will 

 ultimately solve the problems of softwood distillation. The process 

 combines the recovery of the resinous parts of the wood with the pro- 

 duction of wood pulp. In the disintegration through the cooking for 

 pulp the volatile oils are liberated and recovered from the digester. The 

 rosin may be recovered as sizing or as rosin oils. The process is still in 

 the earlier stages of development but appears to have an important pros- 

 pect for the future. Palmer, in his " Distillation of Resinous Woods," 

 has shown the following experimental yields from the various kinds of 



