BARK FOB TANNING. 157 



gregarious trees would yield a worse commercial article than this 

 latter extract, and we thus only require capital and enterprise to 

 enable our tanning materials to compete successfully in all the 

 markets of Western and Central Europe with such materials from 

 other sources of supply. If caste prejudices militate against the 

 expansion of the tanning industry in India and the local conversion 

 into leather of the shiploads of raw hides which leave the country 

 every year, they cannot be a bar to the preparation of tanning 

 extracts. 



We have as yet no figures for the proportion of tannic acid 

 contained in the barks of our various species. Even in Europe 

 the figures are few and contradictory for the thiiee or four species 

 used. In France a quantity of acid varying from 5 to 7 per cent, 

 of the dry weight of the bark is considered good. In Germany 

 the best bark is said to yield 16 to 20 per cent, of its dry weight 

 of tannic acid. But the practical tanner does not value bark 

 only by the quantity of tannic acid present in it. Even in one 

 and the same tree the bark is prized more highly by him, the 

 lower it is obtained from the tree, although the bark from the 

 upper portion of the stem is, as a rule, very much richer in tannin 

 than that from the base. The commercial and practical value of a 

 tanning material depends not only on the quantity of tannin 

 present in it, but also on the character of the leather it pro- 

 duces, whether hard or soft, dark or light-coloured, and heavy or 

 light. 



The volume of the bark varies from one-third to one-eighth that 

 of the original unbarked wood, according to the age of the portion 

 or the tree from which this latter has been taken. Hence the 

 barking of firewood diminishes very appreciably both its weight 

 and volume. On the other hand, the peeled wood always commands 

 a relatively higher price, while the value of the detached bark, if 

 there is any regular market for it, will, after deduction of the 

 cost of removal, drying, and separate export, always exceed the net 

 depreciation suffered by the firewood in consequence of loss of 

 weight and volume due to the peeling. 



Some of the best known barks used by tanners are those of Acacia 

 arabica, Terminalia tomentosa, Cassia auriculata, Rhus Cotinus and 

 Rhusjnysorensis, Oaruga pinnata, Zizyphus osylopyra, Buchanania 

 latifolia, Bauhinia purpurea and Bauhinia variegata, Alhizzia pro- 

 cera, alders, Quercus incana, and Phyllanthus Emhlica. 



Tannic acid is not the only product from the bark of trees that 

 serves the purpose of curing leather. The well-known softness, 

 peculiar scent, and water-proof quality of Russia leather are due to 



