22 



SPECIAL FEATURES OF THE DISTILLATION OF PINE, FIR, AND SPRUCE. 



As pine, fir, and spruce contain turpentine and rosin, the process of 

 distillation is modified when these woods are used. Figure 13 shows 

 some special forms of retorts for distilling pine. The processes in use 

 are of two general types: Steam distillation and destructive distilla- 

 tion. In the former case live or superheated steam is used to remove 

 the turpentine, which is the only product commercially obtained. 

 During the heating part of the rosin oozes out of the wood but is 

 seldom recovered. When the destructive process is employed the 

 procedure differs from hardwood distillation only in the fact that the 

 temperature in the retorts should be kept below 200 C. until the 



A B 



FIG. 13. Retorts used in distilling turpentine: A, horizontal type; B, vertical type. 



turpentine has been driven off, the aim being to keep the turpentine 

 separated from the other products of distillation from which it can 

 not be completely purified if they be allowed to mix. So far this 

 has not been satisfactorily accomplished on an industrial scale owing 

 to the difficulty of preventing local overheating of the retort. 



A great number of retorts both for steam and destructive distilla- 

 tion of resinous woods have been invented and patented to meet the 

 special conditions arising in distilling these woods. Many of these 

 have valuable features, while others have no practical advantage over 

 the regular hardwood retorts which have been in use for many years. 

 The yield of turpentine will depend on the richness of the wood, ordi- 



[Cir. 36] 



