While the principles involved in the steam dis- 

 tillation process are very simple, the utilization 

 of the wood is incomplete, in that only the volatile 

 constituents are recovered. The limitations have 

 proved so great that nearly all the commercial 

 plants have ceased operations within the past 

 two or three years. It seems probable, however, 

 that steam distillation will remain as an important 

 step in more comprehensive treat ments^of resinous 

 pine. 



Extraction Processes 



1. Volatile Solvents 



Rosin and turpentine are soluble in a consider- 

 able number of volatile solvents, the most com- 

 mon of the cheaper ones being naphtha, gasolene 

 and coke-oven benzene. The ordinary commercial 

 solvent is a light gasolene, all fractions of which 

 are volatile below 130-140C. The extraction pro- 

 cess depends on the removal of the rosin and tur- 

 pentine from the finely divided wood by the agency 

 of a solvent; the extract is subsequently distilled 

 to recover first the solvent and finally the tur- 

 pentine and pine oil, leaving the rosin as a residue. 



In some cases (Walker, J. Soc. Chem. Ind., 1911, 

 p. 394; U. S. Pat. 922,369 and Yaryan, U. S. Pats. 

 915,400; 964,728; 992,325), the turpentine is first 

 removed from the shredded wood by steam distilla- 

 tion in order to escape the usual danger of reten- 

 tion of solvent by the turpentine. There is also a 

 possibility of using the extracted wood for the pro- 

 duction of paper pulp, although the fine state 

 of division of the wood would detract from its 

 value in this connection. 



The main products turpentine, pine oil and rosin 

 are in most respects of very favorable quality, 

 since they are free from those decomposition pro- 

 ducts formed at higher temperatures in the other 

 processes. The chief difficulty lies in the loss of 

 solvent during the cycle, amounting as it does to 

 20-25 gallons per cord of wood extracted. 



2. Alkalis 



When rosin is heated with caustic soda, sodium 

 carbonate or equivalent alkali, thejrosin acids com- 



10 



