DISCUSSION OF RESULTS. 19 



of which all conditions except size of chips are, as nearly as possible, 

 the same; in every case the smaller sized chips show the larger yield 

 and higher efficiency. The effect on yield is not so marked in the 

 case of runs 26 and 27 (and some of the other runs given in Table 3), 

 but this is because the pressure was so high that nearly all the oil 

 was removed even from the larger sized chips. Of two runs in which 

 all the oil was removed even from the larger chips, the yields would, 

 of course, be the same, but the efficiency would probably be higher 

 with the smaller sized chips. 



EFFECT OF PRESSURE ON YIELD AND EFFICIENCY. 



In general, higher pressures give larger yields without lowering 

 the efficiency. This is shown in Table 5, which gives three groups of 

 runs, in each of which all conditions except steam pressure are as 

 nearly similar as possible. In all cases the higher steam pressure 

 produced the larger yield, with equal or greater efficiency. The 

 effect of pressure on yields is also shown in another way in many of 

 the runs in Table 3, in w T hich, after obtaining all possible oil under 

 one pressure, a further yield was obtained by continuing the distil- 

 lation under a higher pressure. 



EFFECT OF SPEED OF DISTILLATION ON YIELD AND EFFICIENCY. 



Increased speed of distillation decreases both yield and efficiency. 

 This is shown clearly in Table 6, which gives the results of two sets 

 of two runs each, in both of which all conditions except speed were 

 identical. It is probable that with the rapid passage of steam thfough 

 the charge it is less completely saturated with oil vapors, and this 

 directly decreases the efficiency. With this less complete saturation, 

 the end point is reached sooner, and this, too, probably decreases 

 the yield. This is indicated by the more nearly equal total yields 

 obtained by finishing up the distillations at the same pressure but 

 at lower speeds. However, the variation in efficiency is not propor- 

 tional to the speed, since doubling the speed decreases the efficiency 

 by only about 10 per cent from 0.94 to 0.84 in runs 30 and 31 and 

 from 0.43 to 0.39 in runs 32 and 33. 



If, as seems probable, the effects of speed are due to the variations 

 in the time during which the steam is in contact with the wood, then 

 the size of the retort would have a similar effect; that is, a speed of 

 10 minutes per liter in a retort of a given size would be equivalent 

 to 5 minutes per liter in a retort twice as large, since a unit of steam 

 would be in contact with a unit of wood for the same length of time 

 in either case. 



