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 arun. 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 
Fig, 4.—Elevation of retort. 
a, Retort shell. h, Worm condenser. 
b and ec, Main heating coils. j, Trapped vent pipe. 
d, Bottom heating coil. k, Oil tank. 
€, Oil heater. l, Overflow catch. 
f, Oil circulating pump. m,n, 0, Valves. 
g, Overflow tank. 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 (7). This point in 
