LEATHER (Fa., Cuir ; GER., Leder).
The manufacture of leather is of very considerable importance, the capital invested in it in the United Kingdom having been some years since estimated at 30,000,000/. It is, however, very difficult to obtain any reliable statistics on the subject, the trade being now entirely free from excise restrictions, which were removed in 1830, when the duty realized amounted to 411,000/. Some idea of the expansion of the trade may be formed from the fact that while at that date the total export of leather and saddlery of British manufacture amounted to less than 200,0001., during the year 1880, it was upwards of 3,300,000/.
The only information within reach as to the present extent of the trade is that which may be derived from the Board of Trade Returns of imports and exports, and from this it is exceedingly difficult to draw any definite conclusions, since large quantities of both leather and hides imported are re-exported, either in their rough condition or after manufacture. During the year 1880, the imports into the United Kingdom included upwards of 45,000,000 lb. of leather, in addition to 657,262 cwt. of dry hides, and 592,249 cwt. of salted. In the same period, were exported 346,554 cwt. of dry, and 85,213 cwt. of salted hides, leaving 310,708 cwt. of dry, and 507,036 cwt. of salted hides for tannage, in addition to the cattle killed in the United Kingdom. Of these, there were 343,659 imported, besides the very large number reared at home.
The principal sources of the leather imported into the United Kingdom are America, Australia, and the E. Indies, the two former sending sole-leather, and the latter the small hides known as " E. India tanned kips," which are used for dressing and insole purposes. Of these, 1,691,749 were sold in 1877, and 1,998,543 in 1878 ; but only 1,094,984 in 1879, and 846,267 in 1880.
The principal seats of the heavy sole-leather manufacture from salted hides are Bristol and Warrington ; light sole-leather is largely made in Bermondsey ; while Leeds is famous for the tannage of E. India kips. Tanning is, however, by no means confined to these districts, many important tanneries being scattered over the country.
Leather manufacture may be broadly divided into two stages "tanning," in which the raw bide is converted into the imputrescible and more or less flexible material known as " leather "; and "currying," in which this leather is further manipulated, and treated with fatty matters, to soften and render it more waterproof, and to improve its appearance. Glove-kid, and certain other
leathers, however, are not tanned at all, hut " tawed," or prepared with a mixture in which alum and salt are the most active ingredients ; and many leathers can scarcely be said to be curried, although more or leas oil is used in the final processes of "finishing " or " dressing." The first subject to be treated of in this article will be the operation of tanning, properly so called, taking for example the tannage of sole- and belting-leather. This demands thorough explanation, in both its practical and theoretical aspects, not only because it is one of the most important branches of the trade, but because the principles involved are those whieh equally underlie all other tanning methods. The next to he dealt with will be the modifications of the process which are necessary in tanning the more flexible leathers used for boot-uppers, hose-pipes, and saddlery purposes ; then the currying of these leathers; and finally, the manufacture of moroccos, Russian, and japanned leathers, and calf- and glove-kid.
Anatomical Structure of Hide.—Before speaking of actual processes of manufacture, it is necessary to devote some attention to the structure and chemical constitution of hide or akin, which forms the raw material. Although a great variety of skins are employed in tanning, they are all con stituted on the same general type, and an anatomical description of the hide of the ox will apply almost equally to those of the calf, sheep, and goat ; but from differences in thickness and closeness of texture, their practical values differ widely. Fig. 893 shows a section of ox-hide, cut parallel with the hair, magnified about 50 dia.: a, epithelial layer or epidermis, consisting of horny layer above, and rete malpighi below ; b, pars papillaris, and c, pars reticularis of corium, derma, or true akin ; d, hairs ; e, sebaceous or fat-glands ; f, sudoriferous or sweat-glands ; g, opening of ducts of sweat-glands; it, erectores pill muscles, for erecting the hair.