APPLICATION OF RESULTS. 29 



figure 7. This represents the gravities of different parts of the oil ob- 

 tained during the distillation of chips 1 inch X 1 inch X inch at atmos- 

 pheric, at 20 pounds, and then at 40 pounds pressure. During the first 

 of the run at atmospheric pressure the gravity gradually increased but 

 never quite reached that of pure pine oil. By a continuous distilla- 

 tion at atmospheric pressure only about 50.6 per cent of the total oil 

 could be removed, but on interrupting the distillation for about 14 

 hours and continuing again at atmospheric pressure, 7 per cent more 

 of the oil was obtained, the gravity of the first part of this 7 per cent 

 being much lower, and of the last part only slightly lower, than that 

 of the last fraction of the continuous run. On increasing the pressure 

 to 20 pounds about 16.8 per cent more oil was obtained, the gravity 

 suddenly dropping and then gradually rising during the distillation 

 of this 16.8 per cent. On increasing the pressure to 40 pounds and 

 distilling continuously, a further yield of 19.5 per cent was obtained, 

 the gravity of this 19.5 per cent dropping suddenly at first and then 

 gradually rising. A similar additional yield was obtained by another 

 interruption of the distillation, after which about 6 per cent more oil 

 was obtained. 



Here again the effect of interrupting the distillation and of increas- 

 ing the pressure is very plainly shown in the increased yield of oil 

 with gravity lower than the last fraction obtained before the condi- 

 tions were changed. 



This effect of increased pressure in increasing the yields is due, 

 then, to bringing more steam and oil into contact with each other 

 than is possible at lower pressures. This contact could result either 

 from a penetration of the steam further into the wood or from a 

 better flow of resin toward the surface of the wood, due to its increased 

 fluidity. It is probable that both these have some influence, but the 

 effect of the latter is quite certain, since, in the distillation made at 

 high pressures, a considerable amount of rosin would collect in the 

 bottom of the retort, or the outside of many of the chips would be 

 coated with thin layers of rosin. 



The effect due to the interruption of the distillation and continuing 

 it again under the same conditions can not be explained so readily, 

 but it is probably due to a slow flow of resin toward the surface or to 

 the diffusion of the volatile oils in the resin from the interior of the 

 chip to the resin at the surface from which the oil has been removed. 



APPLICATION OF RESULTS. 



In this study of the distillation of resinous wood by saturated steam 

 the effects of different variables have been considered: (1) Size of chip, 

 (2) pressure of steam, (3) speed of distillation, and (4) end point at 

 which distillation is stopped, on (a) the yield of total oil, (b) the compo- 

 sition of the oil, and (c) the amount of steam required to remove the 



