34 WOOD TURPENTINE. 



If distillation of the first fraction was continued sufficiently long to 

 carry over all the light oils, it contained 50 per cent or more of turpen- 

 tine, or if the distillation of the first fraction was discontinued when 

 it had but a small proportion of turpentine, it did not contain all the 

 light oils. 



Between the turpentine proper and the heavy oils there was also 

 a mixed portion, as in the case of the steam-distilled turpentine, and 

 this contained notable percentages of light constituents. It is quite 

 evident, therefore, that, when operating these stills in the manner 

 described, it is necessary to make a second distillation of two middle 

 fractions, one to separate rosin spirits from turpentine and one to 

 separate turpentine from the heavy oils. Under the circumstances, 

 it is not deemed advisable to include the detailed figures on the dis- 

 tillation of the destructive turpentine. 



CONCLUSIONS IN REGARD TO REFINING. 



From the data obtained in these experiments it is concluded that 

 the percentage of oils in the distillate furnishes the most reliable and 

 useful information as to the progress of distillation and the nature 

 of the oils at different times, and this is also the simplest means of 

 acquiring such information. Neither the specific gravity of the oils 

 nor the temperature of the distilling vapors at the top of the still 

 furnishes as reliable information, nor are they so conveniently deter- 

 mined. The temperature of the vapors is materially affected by the 

 volume and temperature of the steam entering the still and by varia- 

 tions in atmospheric pressure. The former can of course be made 

 practically constant by the use of reducing valves, but corrections 

 for atmospheric pressure require more training, experience, and care 

 than can probably be given at such plants. 



The specific gravity of the samples taken during distillation often 

 shows a decided conflict with the other data on the samples, but in 

 the main it is a reliable indication of the progress of the distillation 

 and the composition of the oil. But as this determination also 

 requires more skill, and is in every way more difficult to make 

 in the works, it is not as safe a guide as the volume relations of the 

 distillate. 



The column still will give sharper separations of wood turpentine 

 from pine oils than can be obtained with the pot still, but the experi- 

 ments here described do not indicate any great superiority of the 

 column. The data available, however, are inadequate to permit the 

 drawing of definite conclusions as to the economy or efficiency of 

 the two forms of stills. 



