634 UTILIZATION OF BARK AND ITS CONSTITUENTS. 



In general it is true that tanning with hark produces the 

 best leather, but it is also the dearest. 



Tannins are found in all plants ; many contain large 

 quantities in their bark, others in their wood or in their 

 leaves and fruits; many plants contain large quantities of 

 tannin. All insect-galls are specially rich in tannin ; galls on 

 plants, that otherwise possess plenty of tannin, exhibit the 

 maximum amount of this material. When parts of plants are 

 soaked in water and the latter evaporated, tanning- extracts 

 are obtained ; they are very rich in tannin and are mixed 

 with water and used for making leather. 



The manufacture of tanning-extracts increases continually, 

 for in this way solutions of proper density are obtained 

 suitable for hides of different thickness and origin, and the 

 business is facilitated and cheapened. A stronger competition 

 in extracts from tropical countries may be expected, owing 

 to the quantity of suitable plants that these countries pro- 

 duce ; when better methods of extraction and purifying these 

 extracts have been attained, European tanning industries will 

 be beaten in the contest. 



The most important tanning materials come from the 

 following plants, the percentage of tannin being given : 



Extract of Quebracho wood, dry . . .63 per cent. 

 Khizophora Mangle . . . 58 

 ,, Quebracho bark . . . . 50 ,, 

 ,, Catechu wood (Acacia Catechu) . 45 to 50 

 ,, Polygonum hymenosepalum (roots) 



Canaigre . . . . 42 

 ,, Pyingado wood (Xijlia dolabri- 



formis) . . . . . 37 ,, 

 Uncaria Gambir . . . . 35 

 ,, Sweet-chestnut wood* . . . 30 ,, 

 Hemlock-spruce wood . . . 30 

 ,, Oakwood . . . . . 28 ,, 



Natural Contents in Tannin. 



[Indian Gum-kino. (Pterocarpu-x Mdnmjrium) 75 ,, Tr.] 

 Chinese galls (Rhiis semiolata) . . .70 ,, 



* von Srlm'idci 1 . 



