4 BULLETIN 129, U. S. DEPARTMENT OF AGRICULTURE. 



taken from the same trees as the body wood. In the case of factory 

 waste or lumber there was, of course, no record of the trees from which 

 the material came. 



TEMPERATURES OF DISTILLATION. 



It was found that the temperatures in pyrometer tubes 1, 2, 3, and 

 4, which are all near the surface of the retort, were always within 

 15 to 20 of each other, and usually within 10 during the last part 

 of the distillation. Tube 1 was the hottest and tube 5 the coolest. 

 It was, therefore, considered unnecessary to take temperature read- 

 ings in tubes 2, 3, and 4, and the records contain the readings from 

 tubes 1 and 5 only. 



The maximum temperatures obtained in the various distillations 

 ranged from 327 C. to 415 C., and the maximum temperatures near 

 the surface and at the center of the retort often differed as much as 

 60 C. in the same distillation. These differences, however, did not 

 appreciably affect the yields of alcohol and acetic acid, since in some 

 instances higher temperatures gave higher yields, and in others lower. 

 It is also found that the charcoal from low- temperature distillations, 

 when redistilled in small samples at temperatures above 400 C., 

 produced only small amounts of acetic acid (equivalent to an increase 

 of 2 per cent of the original yield of acid). It was considered, there- 

 fore, that the distillations were practically complete, as to alcohol 

 and acetic acid, provided all parts of the charge had been subjected 

 to a temperature of at least 320 C. 1 



In most of the distillations, on account of the exothermic character 

 of the reaction, the temperature at the center of the retort finally 

 became higher than that at the surface. It was the heat developed 

 during the exothermic reaction which made it difficult to obtain the 

 same maximum temperatures in all distillations; after the reaction 

 was well started at the surface its progress toward the center was 

 spontaneous and the maximum temperature could not be fully 

 controlled. 



The maximum temperature was usually kept below 260 C. until 

 the water was nearly all expelled from the wood and the temperature 

 at the center had risen to about 190 C., when it was allowed to rise 

 more rapidly. Only in this way could the temperatures at different 

 points in the retort be kept near one another. By this means also 

 the possible effect of variation in moisture content was minimized, 

 since the slow preliminary heating resulted in a partial drying of the 

 wood, and the different charges had therefore nearly the same mois- 

 ture content at the time the destructive distillation began. 



1 See Klason, von Heidenstam and Norlin, Arkiv for Kemi Min. och Geol. 1908, III, 9. 



