CHAPTER III 

 TANNING MATERIALS 



GENERAL 



NEARLY all plants of the vegetable kingdom contain an astringent 

 principle known as tannin. This agent has the property of acting upon 

 animal skins in order to make them strong, flexible, impervious to water, 

 imputrescible, and resistant to decay and wear. Practically all of the 

 commercial tannin, however, is derived from a relatively few species of 

 plants and is secured from only small portions of these. The principal 

 forms of tannin are derived from a variety of barks, woods, leaves, 

 fruits, nuts, etc., which contain varying amounts of tannin and tannic 

 acid. Tannin occurs chiefly in solution in the cell sap, as well as in 

 tannin vesicles and the cortical cells of the bark. 



In this country, hemlock bark was, for a long time, the principal 

 source of tannins. Some oaks also supply bark of sufficiently high tannin 

 content to be of commercial interest. 



With the rapid cutting of our virgin forests and the gradual disap- 

 pearance of hemlock, however, the principal source of supply has been 

 seriously depleted, and the tanners have turned to a number of other 

 materials such as chestnut wood and a variety of foreign products, the 

 importation of which has been steadily increasing within the past few 

 years, particularly, quebracho, gambier, mangrove bark, sumach, 

 myrobolan nuts, valonia and several others. 



It is estimated that the total annual value of the vegetable tanning 

 materials used by the tanners and dyers of this country is from $25,000,- 

 ooo to $30,000,000. 



The harvesting, manufacturing, and importation of tanning materials 

 constitute one of the most important of the forest product industries. 



Hemlock bark has been of the greatest economic value in the past 

 because it occurred in comparatively large quantities and, therefore, was 

 relatively cheap. It is also readily made available for use. As a result 

 of this situation, the chief centers of the tanning industry have devel- 

 oped, principally in the great hemlock regions, the obvious reasons being 



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