Tanning Materials. 207 



nut-galls from the Levant, the leaves of the sumac, and extracts 

 prepared from various herbaceous plants. The tanning principle is 

 not often found in the wood, nor in plants having poisonous quali- 

 ties or milky juices, and as a general rule it is greater in the bark 

 of young oak trees than of old ones, and more in a deep rich soil 

 than in trees grown upon sterile land. 



829. The principal supply of oak-bark used in Europe for tanning 

 purposes is from the Quercus pedunculate, and Q. sessilifolia, the 

 common English oaks. The relative value of different barks used 

 in England for tanning is about as follows: Oak-coppice, 300; chest- 

 nut, 243; birch, 162; mountain ash, 125 ; larch, 131. The spruce 

 also furnishes some tanning material, and is used with oak. By 

 peeling, oak-coppice wood looses about one-eight part of its volume. 



830. In the Northern States, the principal bark used comes from 

 the hemlock (Tsuga Canadensis), and immense quantities of timber 

 have been wasted by being left after peeling to rot on the ground. 

 This wasteful practice is still continued in some places. In the 

 southern part of Pennsylvania, in Maryland, and southward, as 

 also in many parts of the Western States, and to less extent in 

 New England and New York, the red or black oaks have furnished 

 most of the barks used for tanning. 



831. Tanning-extract is prepared by grinding the bark, leeching 

 out the tannin with hot water, and evaporating in vacuum-pans down 

 to the consistence of syrup. In this state it is sent to market in 

 barrels and sold by the pound, 



832. When oak is grown in coppices in Europe, for the pro- 

 duction of tan-bark, the coppices may be cut on damp soils (where 

 the bark tends to become covered with mosses, and to become rough) , 

 at the age of fifteen years. As a general rule, however, it is al- 

 lowed to grow about twenty years. In older trees the rough corky 

 bark is of but little value. The best comes from trees in a healthy 

 growing condition, with a thick juicy liber, and that are cut in the 

 spring before the leaves have expanded. 



833. In peeling oak-coppice, the workmen endeavor to take it as 

 far as they can from the standing tree. If young trees are left a 

 short time after felling, the bark becomes adherent, and the process 

 difficult. The work of peeling is most easily carried on in warm 

 humid weather, and is interrupted by cold, dry winds. The upper 

 part and branches peel easier than the main trunk, and they save 



