DISTILLATION OF STUMPWOOD. 



25 



the light oil between 260° and 330° C, and the heavy oil above 

 330° C. A strong evolution of wood gas, which burns with a bright 

 luminous flame, takes place while the heavy oil comes over. Char- 

 coal and pitch are the end products of the distillation. The pitch is 

 drawn off through a plug cock in the bottom of the retort at the end 

 of a run. There is no sharp line of demarcation between the stages 

 in which the distillation is conducted, because decomposition of the 

 wood takes place long before all the turpentine has distilled over, 

 and to effect a maximum recovery of it this stage of the distillation 



a, Retort shell. 



6 and c, Main heating coils. 



d, Bottom heating coil. 



e, Oil heater. 



f, Oil circulating pump. 



g, Overflow tank. 



Fig. 4. — Elevation of retort. 



Worm condenser. 



h, 



j, Trapped vent pipe. 



k, Oil tank. 



I, Overflow catch. 



m, n, o, Valves. 



1, 2, 3, 4, Thermometers. 



must be continued to the point at which the wood is converted into 

 a brown friable substance approaching charcoal in its nature. This 

 decomposition sets in when most of the hygroscopically held moisture 

 has been expelled from the wood (about 260° C), and is made appar- 

 ent by the sharp odor of the distillate and development of a reddish 

 color in the hitherto colorless aqueous layer. This incipient decom- 

 position is soon attended by a perceptibly acid taste of the distillate, 

 turbidity of the turpentine layer, and the escape of noncondensable 

 gases (mostly carbon dioxid) from the vent pipe (j). This point in 



