OAK 285 



Other Substances used for Tanning 



The following are the chief substances used in the tanning in- 

 dustry together with the approximate percentages of tannin contained 

 in them: 



. Percent. 



Oak bark, bark of Quercu^ robur, Linne . . . . . 8 to 13 



Valonia, acorn cups of Quercus JEgilops, Linne . . 25 to 35 



Hemlock, bark of Tsuga canadensis, Carr, . . . . 10 to 14 



Mangrove, bark of Rhizophora mangle, Linne . . . . 9. to 33 

 Wattle, bark of Acacia dealbata, Link; and of A. decurrens, 



Willdenow 24 to 30 



Catechu, extract from Acacia Catechu . . . . 45 to 55 



Gambier, extract from Uncaria Gambler . . . 36 to 40 



Sumac, leaves of Rhus Cotinus, Linne ; and of E. coriaria, Linn6 15 to 33 

 Quebracho, bark of Aspidospermum Quebrachocolorado, 



Schlechtendal 14 to 33 



Extract 55 to 60 



Myrobalans, fruit of Terminalia Chebula, Retz. . . 20 to 40 



Divi-divi, fruit of Ccesalpinia coriaria, Willdenow . . 30 to 50 



Galls 60 to 70 



Tamarisk Galls, Tamarix gallica, Linne . . . . 50 to 54 



WILLOW BARK 



(Cortex Salicis) 



Source, &C. The willow bark of commerce is generally referred to 

 the white or common willow, Salix alba, Linne (N.O. Salicinece) , a 

 common tree on river-banks and marshy ground in England and 

 throughout central and southern Europe. Its astringent properties 

 were well known to Dioscorides, but the bark appears to have fallen 

 into disuse until the latter end of the last century, when it was recom- 

 mended as a remedy for ague. For this purpose, however, salicin, 

 the principal active constituent of willow bark, has entirely taken the 

 place of the bark, which is now seldom used medicinally. Salicin is 

 usually obtained from the bark of other species of Salix, which contain 

 it in greater abundance than S. alba. Very frequently, too, the 

 structure of commercial willow bark shows that it is not derived from 

 S. alba. 



Description. The willow bark of commerce usually occurs in 

 channelled pieces several inches in length and 10 to 20 cm. in width ; 

 they are usually of a greenish or greyish brown colour. 



The outer surface is in young bark a smooth, sometimes glossy 

 cork ; in older barks it is dull, slightly longitudinally wrinkled, and 

 usually of a greenish brown colour. The inner surface has a pale 

 reddish colour, and, in the younger pieces at least, appears smooth 



