205 PRACTICAL FORESTRY 
The water in the wood is first driven off in the 
form of steam by the heat. A gas called wood-gas 
is also produced. ‘This may be used for illuminating 
purposes. It is usually conducted back into the fur- 
nace by means of a small pipe. A deep-brown liquid, 
with the flavor of tar and smoke, is produced. From 
this a great variety of useful chemicals is manu- 
factured. Charcoal, which is almost pure carbon, 
remains behind in the retort when the process is 
complete. The products are practically as follows: 
uncondensable gases, tarry matters, pyroligneous 
acid, and charcoal. Most of these products are useful! 
in the arts. The acetic acid, or pyroligneous acid, is 
purified and sold as vinegar. The wood spirits, or 
wood alcohol, is used for many purposes. It is simi- 
lar to the aleohol of whisky and brandy, except that 
it is poisonous, although in diluted form it is used as a 
beverage in parts of the Orient. 
In the case of the distillation of the heavy pine- 
woods, a large quantity of tar is produced. In the 
old-fashioned method of tar production the wood, 
especially the fat-wood and pine-knots, were collected 
and put ina kiln. This kiln very often consisted of 
nothing but a pit in the ground on a hillside, into 
which the wood was put. To the top of this a fire 
was set. The heat caused the tar to ooze out of the 
wood and trickle down to the bottom and out through 
