14 DISTILLATION OF RESINOUS WOOD BY SATURATED STEAM. 



specific gravity could not readily be determined, the oil was combined 

 from a number of fractions. As a check, the combined oil from all 

 the fractions, or from the fractions of certain portions of the distilla- 

 tion, was accurately measured. 



Only the essential parts of the operations are presented, with com- 

 putations derived from them. The discussion will be given after the 

 experimental work has been described. 



END POINT. 



It will be noticed in Table 2 that the amount of oil in 1 liter of 

 distillate progressively decreased, but this decrease was very slow 

 toward the end of a distillation. It became necessary, therefore, 

 to arbitrarily fix upon that ratio of oil to water which might be con- 

 sidered as the end of a distillation under a given set of conditions 

 in order that the results of various distillations might be comparable 

 and might be completed within practicable time limits. In the first 

 five runs this end point was too high and too variable; when these 

 runs were made it was not recognized that the end point must be 

 carefully regulated. These first five runs are therefore not com- 

 parable with those which follow, in which the end point was kept at 

 somewhat lower values. A charge distilled under one set of condi- 

 tions until a certain end point was reached, if interrupted for an hour 

 or more and then continued under the same conditions, produced a 

 further supply of oil before the same end point was reached again. 

 This additional oil amounted to from 2 per cent to 18.8 per cent of 

 that which had been obtained before the distillation was interrupted. 

 The greatest increases in yields due to this manipulation were in those 

 runs in which there was still considerable oil present in the wood 

 when the distillation was interrupted, although, of course, all the oil 

 that could have been removed under the existing conditions had been 

 extracted. For instance, in runs 14 and 15, after all possible oil had 

 been distilled at 50 pounds pressure, interruption of the distillations 

 overnight resulted in 18.8 per cent more oil in run 14 and 15.1 per 

 cent more in run 15 under the same conditions; and in both these 

 cases there was still considerable oil present in the wood, as shown 

 by further distillation at increased pressures. In runs 11 and 21, 

 however, after all possible oil had been distilled at atmospheric pres- 

 sure, interruption of the distillation secured only 2.9 per cent and 4 

 per cent more under the same conditions; in these cases there were 

 much smaller quantities of oil left in the wood than in runs 14 and 15. 



After run 5 the proper end point for any distillation was considered 

 to be reached only when the required ratio of oil to water in the dis- 

 tillate had been attained, both before and after interruption of the 

 distillation. 



