FOREST UTILIZATION loi 



a price of ij^c, extract is cheaper than oak bark at 

 $6 per cord. 

 IX. One cord of chestnut wood yields 500 pounds of extract 

 containing about 25% tannin. 



D. The methods of tannage employed nowadays are: 



I. Tanning by means of aluminum salts. 



II. Chamoying by means of certain oils or acids of oils. 



III. Tanning by salts of chromium. 



IV. Vegetable tanning, using the wood of quebracho, chestnut 



and oak; the bark of various oak-s, hemlock, spruce, 

 douglas fir, birch, larch, willows; fruits, cups and galls, 

 i. e., divi-divi, catechu, myrobalans; further, the leaves 

 of sumac. Instead of using these vegetable matters, 

 their watery extracts frequently are applied. 



E. Object of tanning. 



Tannage tends to render the skin permanently supple and durable 

 by impregnation with tannin. Aside of the mechanical imbedding 

 of molecules by impregnation, a chemical action ( fermentation > 

 may take place in the case of bark tannage, due to the presence 

 of microbes in the bark, chemically binding the tannin to the 

 albumen and gelatine of the skin. 



F. Criteria of a good method of manufacture are : 



I. The weight of the leather produced. Since leather is 

 sold by the pound, the tanner tries to press into the 

 hide the maximum amount of tannin, tannin being much 

 cheaper than hides. 

 Beyond a certain point, this extravagance of impregnation 

 fails to increase the wearing qualities of leather and is 

 therefore useless to the buyer. 

 II. The color of the leather produced and the adaptability 

 of the leather for coloring. 



III. The possibility of tannin being washed out through wear 



and tear. From chromium tanned leather even a boil- 

 ing process will not remove the tannin. 



IV. Quickness in filling orders and amount of capital re- 



quired. 

 V. Oieapness of manufacture. The best leather is produced 

 slowly only by use of materials rather poor in tannin. 



G. Statistical notes. 



I. One ton (2,240 pounds) of hemlock bark will tan 300 

 pounds of sole leather or 400 pounds of upper leather; 

 4 to S pounds of good oak bark are required to produce 

 I pound of sole leather. 

 One acre of hemlock wood is said to yield about 7 cords 

 of bark, and 1,500 board feet of timber are said to carry 

 one cord of bark. 

 One acre of hardwoods will yield on the average not 

 over one-half cord of chestnut oak bark. 



