DISCUSSION OF RESULTS. 21 



RELATIONS BETWEEN' KND POINT, YIELD, AND EFFICIENCY. 



Table 2 shows that the amount of oil in a liter of total distillate is 

 greatest at the beginning and decreases steadily as the distillation 

 progresses, except when conditions are changed, and then the increase 

 in the amount of oil per liter is usually only slight and temporary. 

 This was true in all the distillations. It is evident, therefore, that the 

 efficiency factor will decrease steadily throughout the distillation, and 

 its final value will depend on the end point used. Thus, the efficiency 

 can be increased by stopping the distillation before all the oil has been 

 obtained, but this decreases the total yield of oil. On the other hand, 

 the efficiency will be decreased by continuing the distillation until all 

 possible oil has been obtained, although the total yield of oil is 

 increased. For instance, in run No. 23 (Table 3), if the distillation 

 had been stopped with an end point of 12 c. c. per liter, at the twenty- 

 fifth liter the yield would have been only 15.3 c. c. per pound while the 

 efficiency would have been 0.95. By continuing the distillation until 

 the end point (after an interruption of the distillation) was 10 c. c. 

 per liter, the yield was much larger, 22.4 c. c. per pound, but the 

 efficiency was only 0.46. 



THE PRESSURE REQUIRED TO DISTILL COMPLETELY DIFFERENT SIZES 



OF MATERIAL. 



SAWDUST. 



The volatile oil can not be completely distilled at atmospheric 

 pressure even from a material as finely divided as sawdust. This can 

 be seen from runs 11, 16, 21, 25, and 29, in which, after removing all 

 possible oil at atmospheric pressure, a further distillation at 40 pounds 

 pressure removed from 6.6 to 15.8 per cent more oil. After distilla- 

 tion at 40 pounds a further distillation at 70 pounds .was without 

 appreciable results. It can be safely stated that a pressure of 40 

 pounds is sufficient to remove all the volatile oil from material as 

 small as sawdust. It is possible that lower pressures might give 

 almost as good results, but this can not be determined from the data 

 on hand. 



CHIPS 1 INCH X i INCH X i INCH. 



This size material can not be completely distilled at 30 pounds 

 pressure (run 17) and probably not at 50 pounds pressure (run 18). 

 In run 18, the yield obtained from chips 1 inch X 1 inch X } inch is 

 almost the same, within the limit of possible variation, as from the 

 sawdust of run 16, but apparently not quite all the oil has been 

 removed. 



CHIPS 1 INCH X \ INCH X \ INCH. 



Chips of this size can not be completely distilled at 50 pounds 

 pressure (run 19), but can at 70 pounds (runs 20, 32, and 33). 



