TANNING MATERIALS 



77 



protection from fire, by leaving the smaller trees until they have acquired 

 a larger size and by more complete utilization of the tree. The cutting 

 of this oak commonly goes hand in hand with the lumbering of the red- 

 woods. 



WESTERN HEMLOCK 



Although of little present importance as a source of tanning materials, 

 the two species of western hemlock (Tsuga heterophylla and T. mer- 

 tensiand) constitute an important resource of tannins. They have been 

 little exploited up to the present time because the tanning industry has 

 been little developed in the northwest where these trees are found. 

 There are very great possibilities, however, for the future because of 

 the fact that there are estimated to be 100,000,000,000 bd. ft. of hemlock 

 still standing in the forests of western Washington and Oregon. This 

 constitutes, therefore, a veritable store house of tanning materials which 

 may be used in the future. At the present time the prohibitive cost of 

 shipping western hemlock bark to the eastern tanning factories precludes 

 its wide use throughout the country. The bark of the western hemlock 

 is much thinner than that of the eastern hemlock but contains more 

 tannin by weight. The western hemlock contains from 10 to 12 per 

 cent against 8 to 10 per cent in case of the eastern species. 



Investigation of hemlock in the northwest indicates that the bark 

 of trees in the Cascade Mountains contains a higher percentage of tannin 

 than those in the coast region; furthermore, the percentage of tannin 

 increases with the increase of elevation and the bark from the trees in 

 Washington probably contains a higher tannin content than the same 

 trees grown in Oregon. 



The following comparative analysis was made by H. C. Tabor to 

 determine the tannic acid content of sample hemlock bark from Wash- 

 ington, Pennsylvania and Quebec: 



COMPARATIVE ANALYSIS OF HEMLOCK BARK FROM WASHINGTON, 

 PENNSYLVANIA AND QUEBEC 



The peeling season for western hemlock is much earlier than for eastern 

 hemlock and the bark is often harvested as early as February. However, 



