abridge the process. But the leather thus prepared was by no 

 means equal to that prepared in the old method. The advantage 

 of the slow and gradual process appears to be, that the whole 

 substance ot the skin is penetrated and equally changed; while 

 in the more rapid method the external parts must be more acted 

 on; and the texture probably will be more unequal. It appears 

 also from Mr. Davy's experiments, to combine with a larger 

 quantity of the extractive matter contained in the astringent 

 infusion; and hence too the advantage of the immersions in the 

 weak liquors, as these contain more of this than the strong in- 

 fusions. It must be confessed, however, that for anv thing theory 

 can discover, the common process appears to be unnecessarily 

 protracted, and some advantage might probably be derived from 

 adopting some of the manipulations of Seguin. 



The skin in drying increases in weight from the fixation of the 

 vegetable matter: the quantity of this seldom exceeds one-third of 

 its weight. The increase is greater, according to Mr. Davy's ex- 

 periments from quick than from slow tanning. In the latter, he 

 supposes more of the extractive matter enters into combination, 

 and this weakening the attraction of the skin to tannin, less of it 

 is absorbed, and less vegetable matter on the whole enters into the 

 composition of the leather. Probably, also, in the slow process, 

 more of the animal matter is removed. Other substances are used 

 in tanning, as the bark of the willow, elm, and other trees, and, 

 as we have seen galls and catechu. The leather prepared from 

 these varies in colour, and in some other external qualities. 



Catechu, or terra Japonica, as it is sometimes called, is a sub- 

 stance obtained by decoction and evaporation from a species of 

 Mimosa^ which abounds in India. There are two varieties of it; 

 one from Bombay, and the other from Bengal. This substance is 

 found to consist chieflv of tan, combined with a peculiar species 

 of extract. Tan is chiefly found in the bark of trees, but it has 

 been obtained from the sap, the wood, and even the leaves. It 

 varies in quantity according to the season of the year, and it like- 

 wise varies with the age and size of the trees. The greatest pro- 

 portion of tan is contained in the inner barks. The epidermis 

 usually contains none. The following table exhibits the proportion 

 of solid matter extracted by water from different vegetable sub- 

 stances, and the quantity of tan contained in that solid matter, as 

 ascertained by the experiments of Mr. Davy: 



82 



