tonsiituent Paris of astringent Vegetailes, SO'5 



the separation of the gelatine., from the small quantity of 

 albumen with which it was combined in the organized form, 

 by the solvent powers of water. 



The difterent qualities of leather made with the same 

 kind of skin, seem to depend very much upon the diflerent 

 quantities of extractive matter it contains. The leathev 

 obtained by means of infusion of galls is generally found 

 harder, and more liable to crack, than the leather obtained 

 from the infusions of barks ; and, in all cases, it contains 

 a much larger proportion of tannin, and a smaller propor- 

 tion of extractive matter. 



When skin is very slowly tanned in weak solutions of 

 the harks or of catechu, it combines with a considera- 

 ble proportion of extractive matter ; and, in these cases, 

 though the increase of weight of the skin is comparatively 

 «mall, yet it is rendered perfectly insoluble in water; and 

 is found soft, and at the same time strong. 



The saturated astringent infusions of barks contain mu-ch 

 less extractive matter, in proportion to their tannin, than 

 the weak infusions ; and, when skin is quickly tanned in 

 them, common experience shows that it produces leather 

 less durable than the leather slowly formed. 



Besides, in the case of quick tanning by means of infu- 

 sions of barks, a quantity of vegetable extractive matter is 

 lost to the manufacturer, which might have been made to 

 enter into the composition of his leather. These observa- 

 tions show that there is some foundation for the vulgar 

 opinion of workmen concerning what is technically called 

 the feeding of leather in the slow method of tanning ; and, 

 though the processes of the art may in some cases be pro- 

 tracted for an unnecessary length of time, yet in general 

 they appear to have arrived, in consequence of repeated 

 practical experiments, at a degree of perfection which can- 

 not be verv far extended by means of any elucidations of 

 theory that have as yet been made known. 



On the first view it appears singular that, in those cases 

 of tanning where extractive n)atter forms a certain portion 

 of the leather, the increase of weight is less than when the 

 skin is combined with pure tannm; but the fact is easily 

 accounted for, when we consider that the attraction of skin 

 for tannin must be probably weakened by its union with 

 extractive matter; and, whether wc suppose that the tannin 

 and extractive matter enter together into combination with 

 the matter of skin, or unite with separate portions of it, 

 still, in either ca.se, the primary attraction of tanniu for skin 

 must be, to a certain extent, diminished. 



la 



