The infusion of oak bark, especially that obtained by the 

 first maceration, contains principally tannin and extractive 

 matter; the gallic acid, if present, as has been supposed, being 

 at least in an inconsiderable proportion. In the course of the 

 maceration of the skins in these liquors, the tannin combines 

 gradually with the gelatin, which, in an organized form, principally 

 constitutes the skin, and forms with it a compound insoluble in 

 water, dense and impermeable to that fluid, while it possesses at 

 the same time a certain degree of elasticity. The extractive 

 matter also enters into the combination; for when skin in a large 

 quantity has exerted its full action on a small quantity of infusion, 

 it at length abstracts the whole dissolved matter, and renders it 

 colourless. From this extractive matter colour is derived, and the 

 skin may perhaps be rendered more dense. 



It has been supposed, that the gallic acid frequently contained 

 in vegetable astringents, facilitates the action of their tanning, in 

 converting skin into leather. According to the theory of the op- 

 eration, as given by Seguin, skin is gelatin in a hardened state from 

 slight oxidizement; the gallic acid in some measure de-oxidizes it, 

 and hence reduces it to that state in which it combines more easily 

 with gelatin. There is little proof given, however, of this theory; 

 and it appears sufficiently established, that the operation can be 

 performed without the presence of this acid; and indeed in the tan 

 liquor prepared by one maceration from oak bark it is scarcely dis- 

 coverable, and, if it does exist in it, it is in intimate combination 

 with the extractive matter. 



The operation of tanning, as now described, requires a number 

 of months, from the skins being successively and slowly introduced 

 into infusions of difi^erent degrees of strength. Seguin, after his 

 discovery of tannin, proposed to abridge the process by introducing 

 the skins more speedily into strong infusions of the tanning sub- 

 stance; and in this way, according to the excellent report given on 

 the art of tanning by Pelletiere and Lelivre, in which his method 

 is full described, the whole could be finished in about twenty days, 

 and leather obtained equal in equality to that prepared by the 

 old method. There is reason, however, to doubt of the superiority 

 of this new method. Mr. Nicholson, in some observations on this 

 subject, when a patent was taken out for Seguin's method in this 

 country, stated, that from information acquired from the manu- 

 facturers, he found that they had previously been sufficiently 

 acquainted with the powers of the strong tanning infusions; 

 and that it had been even proposed to employ them so as to 



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