LEATHER INVESTIGATIONS: THE COMPOSITION OF 

 SOME SOLE LEATHERS. 



COMPOSITION OF NORMAL SOLE LEATHER. 



Vegetable-tanned leather is essentially a compound or mixture of 

 hide or fibrous proteid material with tannin. Depending on the use 

 to which it is to be put, it may be finished in several ways whereby 

 the composition of the final product may differ greatly from the 

 simple compound. The tanned leather may be used without material 

 change in composition, as for shoe soles; it may be greased, as for 

 harness and belting; or it may be greased and dyed, as for harness 

 and shoe uppers. 



In addition to the insoluble hide and tannin which are the 

 essential constituents of leather, moisture, mineral matter, fats, and 

 water-soluble tanning materials, which remain to a small extent in 

 well-scoured leather, are present. All of these, when not present 

 in excessive quantities, are proper and normal constituents of the 

 leather. In fact, the presence of a large percentage of oils or fats, 

 even in sole leather, is of decided advantage in increasing the water 

 resistance, flexibility, softness, and life of the leather, while the pres- 

 ence of a small amount of uncombined tannin is often of some advan- 

 tage in retarding water penetration and hardening of the leather and 

 in making it solid and firm. The presence of a large excess of uncom- 

 bined tannin materials other than those mentioned is useless or 

 harmful. 



Leather is not a definite compound and is therefore impossible to 

 produce of an exact composition. The ratio of combined tannins to 

 hide substances approximates 7 to 10 (see last column of table on 

 pp. 16 to 20), while the percentages of water-soluble constituents, min- 

 eral matter, fat, and moisture may vary considerably. Careful study 

 of the analyses of well-tanned, scoured leathers of various tannages, 

 both American and foreign, warrants the conclusion that well-tanned, 

 merchantable, scoured sole leather of all tannages on analysis should 

 give results on a moisture-free basis which fall between the following 

 limits: Leather substance from 75 to 93 per cent, hide substance from 

 43 to 57 per cent, combined tannins from 31 to 42 per cent, water- 

 soluble materials from 5 to 15 per cent, oils and fats from 1 to 6 per 

 cent, ash from 0.25 to 1 per cent. 



