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. 
TEMFEEATURES OF DISTILLATION. 
It was found that the temperatures hi 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 I 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 be^an. 
to • 
1 See Klason, von Heidenstam and Xorlin, Arkiv for Kemi Min. och Geol. 190S, III. 9. 
