64 FOREST PRODUCTS 



The world's supply of tanning materials is apparently very abundant 

 and it is estimated by authorities that many sources little developed at 

 the present time may be depended upon for vast quantities in the future. 

 Especially is this true of many tropical plants of Africa, the Far East 

 and South America. The great hemlock forests of Washington and 

 Oregon have been scarcely touched in so far as their tannin resources 

 are concerned, and they constitute an important storehouse of tannin 

 for future use. Western hemlock bark has a higher tannin content 

 than that of the eastern hemlock. At the present rate of cutting que- 

 bracho in South America, which amounts to about 1,000,000 tons, and 

 which supplies an important part of the tanning supplies of England, 

 Germany, France and Italy, as well as the United States, it is estimated 

 that the supply of this source alone will last 168 years 1 and the annual 

 growth more than offsets the yearly cut. 



PRINCIPAL SOURCES AND TANNIN CONTENTS 



The following table shows the most commonly used domestic and 

 foreign tanning materials with the percentage of tannin which they 

 usually contain. These are the tannin contents as recognized by the 

 Leather and Paper Laboratories of the Bureau of Chemistry: 2 



DOMESTIC Tannin . 



Hemlock bark (Tsuga canadensls) ............................. 8-10% catechol 



Chestnut wood (Castanea dentatd) ............................. 4-10% catechol 



California tanbark oak (Quercus densiflora) .................... 10-29% catechol 



Chestnut oak bark (Quercus prinus) ........................... 8-14% catechol 



Black oak bark (Quercus velutina). ... ......................... 6-12% catechol 



Red oak bark (Quercus rubra) ................................ 4- 8% catechol 



White oak bark (Quercus alba) ................................ 4- 7% catechol 



Western hemlock bark (Tsuga heterophylla) ............. ....... 10-12% catechol 



American sumach (Rhus glabra) Southern States ................ 25% pyrogallol 



" Staghorn " or " Virginian " (Rhus typhina) ................... 10-18% pyrogallol 



FOREIGN 

 Quebracho wood (Quebrachia lorentzii) South America ........... 20-28% catechol 



Gambier (Uncaria gambler and U. acida) ...................... 35~4o% pyrogallol 



Myrobalans (Terminalia chebula) nuts ......................... 30-40% pyrogallol 



Valonia (Quercus agilops) acorn cups, Eastern Mediterranean. . Up to 45% pyrogallol 

 Sicilian sumach (Rhus coriaria) Italy .......................... 20-35% pyrogallol 



Mangrove bark (Rfyizophora mangle) tropics .................... 15-40% catechol 



Divi-divi (Casalpinia coriaria) Central America, pods ........... 40-45% pyrogallol 



Golden wattle (Acacia pycnantha) .......................... About 40% pyrogallol 



Kino (Pterocarpus senegalensis) Africa ...................... Up to 75% catechol 



Algarobilla (Casalpinia brevifolia) Chili .................... Average 45% pyrogallol 



Pistacia lentiscus, Sicily, Cyprus, Algeria ...................... 12-19% catechol 



1 From " Tanning Materials of Latin America," by T. H. Norton. 



2 Supplied by Dr. F. P. Veitch. 



