TANNING. The hark of many trees is capable of being used for tanning, but that is pre ferred which particularly abounds in tannic acid. Oak bark is principally used in Great Britain and throughout Europe, as well as in North America, where hemlock, however, is more ex tensively employed. In Spain the inner layer of the bark of the cork oak, or cork tree, is em ployed. The bark of the chestnut is also much valued for this purpose. Larch and willow are used in preparing sonic kinds of leather. The hark of the birch and that of the alder are also employed, birch bark being, however, more esteemed for steeping fishermen's nets and cord age. to preserve them from rotting, than for the preparation of leather. Different species of Acacia (q.v.) and of Eucalyptus (q.v.) furnish barks used for tanning in Australia, some of which have, to a small extent, become articles of eomme rce.
The barking of trees can be accomplished with facility only in spring, when the sap has begun to circulate. The tree being felled, the rough, external lifeless parts of the bark are removed as useless; the smaller branches are cut into lengths of about two feet, and their bark is loos ened by beating with a mallet, and easily taken off; the bark of the trunk and main branches is cut by a chisel-like instrument or with an axe into similar lengths. each of which is divided longi
tudinally, and finally stripped off by the aid of mallets, chisels, etc. The bark is sometimes dried in sheds, being placed on narrow shelves or frames in such a way that there may be a free circulation of air about it: sometimes in the open air, when it is very generally made to rest in a sloping position against trunks of trees placed horizontally at a little distance from the ground, the larger pieces of hark being placed so as to protect the smaller both from sun and rain. Great care is necessary in the drying of hark, as it is ranch damaged if allowed to get moldy, and is liable to suffer injury from ram or from the exposure of its inner surface to the sun.