Page:The American Cyclopædia (1879) Volume X.djvu/279

 LEATHER 2T3 tical difficulties have thus far prevented the ex- pected growth of this business. The follow- ing table represents the imports of the princi- pal tanning materials at Liverpool, England, from 1867 to 1873 inclusive : YEARS. Mimosa bark. Valonia. Dividivi. Gambir. 1867... Tons. Tons. 8060 Tons. 1 500 Tons. 4,536 186S 12727 2'345 6 918 1869 700 9250 2 866 5 676 1870 1871 1,200 2500 10,450 11 690 1,281 3000 8,917 7 958 1872 1 600 14'216 4 613 9 534 1873........ . l'500 10016 2200 7 1 532 These tanning agents all make cheaper leather than is made with oak bark, and one which is inferior also to that made with hemlock bark ; and many devices are resorted to, in the com- position of the different tanning agents, and in the process of manufacture, to give the leather a bark-tanned apppearance. When the work is skilfully done, the leather is of most excel- lent quality. On the continent of Europe cop- pice, spruce, and willow bark, as well as the wood of the chestnut, are used for tanning; but these substances have very little tannic acid, and the small home supplies of oak bark, with importations of the above named materi- als and sumach, constitute the principal agents for converting raw hide into leather. Many other substances besides tannic acid may be used to preserve hides and skins and fit them for certain uses ; but these do not make leather which will resist moisture or retain its flexibil- ity and softness after frequent wetting. The most extensively used of these is alum, so that the term alum-tanned leather has become a common designation both in Europe and the United States. With this agent is tanned a large proportion of the sheep skins, and lighter glove leathers from deer, lamb, kid, and other skins. Tanning. As the making of sole leather involves the placing of the greatest amount of tannic acid in the hide, this branch of the busi- less most requires a thorough knowledge of the principles of tanning ; for in the manufac- ture of upper leather as much depends upon the currying and finishing of the stock as nron the tanning, and it is not sought to put fee reatest possible amount of tannin in the hide. ' hide or skin is composed of two parts : epidermis or cuticle, in which the hair is imbedded, and the corium or cutis, the true skin, made up of numberless fibres interlacing in every direction, the interstices being filled with a matter which renders the skin flexible, and renews the substance of the cuticle, and which, as well as the fibres themselves, is shown to be almost pure gelatine. The chemi- cal analysis of dried skin is as follows : Fibrous matter 74-42 Uncoagnlated albumen 3-49 Extractive matter soluble in water, insoluble in al- cohol 17-44 Extractive matter soluble in alcohol'. .' ." .' .'.".".".'I!!! 2-32 Fatty matter and loss 2'33 The object of tanning is to combine this fibrous and gelatinous matter with tannic acid, and the first process is to wash and cleanse the skin, making it thoroughly soft, and as nearly as pos- sible in the condition it was when taken from the animal. For this purpose the hides are first placed in " soaks," or vats of pure water, where they remain from five to ten days if dry, and about 24 hours if green. Much depends upon the condition of the hide. A dry hide which has been imperfectly cured could not be permitted to remain so long in the soak, as it might begin to decay. When the hide is thus softened, it is ready for the treatment which is necessary to remove the hair. For this pur- pose there are two principal methods, of ac- knowledged efficiency and in almost universal use, besides scores of other methods which have their advocates, but have never been gen- erally adopted. The object is so to soften and swell the hide on the surface, where the roots of the hair are imbedded, that the hair can be easily and quickly removed, and the condition of the hide remain as nearly as possible unal- tered. To effect this, liming and sweating are the principal methods ; the former being used almost altogether for upper leather, and largely for sole leather, and the latter almost exclu- sively for sole leather. Great differences of opinion exist as to the amount of lime which should be used ; if the lime vat is very weak, a longer time is required to swell the epidermis so that the hair can be easily removed ; and if more lime is used, there is danger of burn- ing. The true theory is that the lime shall remove all but the gelatine and fibrine ; and in upper leather, as well as in belting and harness leather, the removal also of a portion of the gelatine by the lime tends to make a more flexible leather, with all the strength and toughness that it would have with all the gelatine of the hide remaining to unite with the tannic acid, but with less solidity. The sweating process for the removal of the hair is used in the United States and in Germany on nearly all sole leather stock. In Germany and England the warm sweat is generally followed, and in the United States the cold sweat ; the former being at a temperature of about 100 F., and the latter from 50 to 65. The hide after the soaking is cut through the middle of the back, if intended for sides, as is usual in America, or is rounded by cutting off the pates, bellies, and flanks, if to make butts. It is then generally put into a hide mill, to further soften it and help to loosen the hair. This hide mill is a simple contrivance, with two arms working in a box to pound the hides, on which a small stream of water is kept flow- ing. For the cold sweating process the hides are hung in a close vault, and here it is neces- sary to watch them very narrowly, as the change which has been commenced in the soaks proceeds much more rapidly here. The sweat pits are nearly all under ground and dark (though the light is proved to be not detri-