206 PRACTICAL FORESTRY 
each year, and at the base of which a small earthen- 
ware pot is fastened in which the crude resin collects. 
This groove grows over in time and another is cut on 
another part of the tree. The tree is not injured by 
this process, and the products are of better quality. 
Other trees produce other kinds of useful resins, 
such as Canada balsam, spruce gum, Venetian resin, 
and even amber is the resin of an extinct conifer. 
Turpentine is extensively used in the manufac- 
ture of paints and varnishes, and to a limited extent 
in medicine. Resin is used in the manufacture of 
soap, varnish, wax, cement, paper-sizing, ete. 
This industry has gradually moved southward, 
and will last, of course, as long as the yellow and 
Cuban pines last, but their days are numbered unless 
more careful methods are practised, although they 
still exist in more or less abundance over an immense 
area of territory throughout our Southern States. 
6. Tanning MaTERIALS 
The process of converting hides into leather by 
the use of tannic acid is called tanning. Tannic acid 
is very abundant in the vegetable world. It is yielded 
by leaves, wood, and fruits of many trees. Oak has 
been extensively propagated for a long period of time 
in Europe because of the value of its bark for this 
purpose. Immense quantities of hemlock bark have 
