THE DESTRUCTIVE DISTILLATION OF WOOD 207 
been used in this country. The tan-bark industry was 
of such importance at one time in the eastern United 
States that hemlock-trees were cut and stripped just 
for their bark. The wood was allowed to rot in the 
forest. Owing to the scarcity of hemlock-trees, and 
to the introduction of other tanning materials from 
southern countries, the industry is no longer of so 
great Importance. 
Quebracho-wood, from which tannin is extracted, 
is now shipped in large quantities from South Amer- 
ica to Europe and this country. When this supply is 
exhausted, other tannin-yielding plants will be util- 
ized. The black mangrove-tree (Avicennia nitida) 
of the tropics is rich in tannin and extremely abun- 
dant, although located in unhandy and unhealthy 
places. 
7. Tue Destructive Distrttation or Woop 
A forest industry which is growing in importance 
is the destructive or dry distillation of wood. <A re- 
tort is filled with wood. Under this there is a fur- 
nace. After the retort is filled a cover is tightly ad- 
justed. Leading from the lid there is a tube which 
is coiled or zigzagged, and over which cold water runs 
during the process of distillation. The wood is heated 
to a temperature of from 600° to 800°, depending 
upon the kind of wood. 
