CHAMOIS OR WASH-LEATHER.

This leather, which is remarkable for its soft felty texture, which it retains even after wetting, although perfectly porous and free from greasiness in its finished state, is prepared by the action of oil on the raw skin. Wash-leather was formerly manufactured from sheep- and calf-skins, and from those of the chamois, and various deer (hence the name), from which, after liming, the grain was removed (frized) with a sharp knife, either with the hair, or after unhairing. The flesh-splits of sheep-skins are now generally employed for ordinary wash-leather, and of course no such process is needed, though buff-leather for belts and military purposes is still so manufactured. The skins receive a thorough liming, which, where softness is desired, is so conducted as very thoroughly to remove the cement-substance (coriin) from between the fibres; and this removal is frequently carried still further by a short bran-drench, which also secures the complete absence of lime. After the usual beam-work, the skins are pressed or wrung out to remove surplus water, and while still moist are oiled on a table and folded in cushions. Fish-, seal-, or whale-oil is generally used, and vegetable oils do not seem to answer even in mixture, with the exception perhaps of olive-oil. The skins are next stocked for 2-3 hours, shaken out, and hung up for ¹/₂-1 hour to cool and partially dry. They are then again folded in bundles, and stocked for a short time, taken out, oiled again, and returned to the stocks; and this process is repeated, until the skins lose their original smell of limed hide, and acquire a peculiar mustard-like odour, and the water at first present has been entirely replaced by oil. The later dryings are frequently conducted in a heated room, and when the oiling is complete, the skins are piled on the floor, and the oxidation of the oil, which has already commenced during the fullings and dryings above described, is completed by a sort of fermentation, in which the skins heat very considerably. During this process, they are carefully watched, and if the heat rises so high as to endanger the quality of the leather, the pile must be turned over, so as to cool the skins, and bring those which were originally outside to the centre. When the fermentation comes to an end, the skins are no longer susceptible of heating, and are of the well-known yellow or chamois colour. Where this colour is objectionable, the oxidation is sometimes completed by hanging the leather in a heated room instead of by piling. It is now necessary to remove the surplus oil, and this in France is done by oiling with any sort of oil, throwing into hot water, and wringing or squeezing. The oil obtained in this way forms the moËllon or dÉgras so much prized for currying purposes. The unoxidised oil still retained by the skins is removed by washing with soda or potash lye. In England and Germany, the whole of the uncombined oil is removed in this way, and is recovered from the lye, in which it exists in a partially saponified state, by neutralisation with sulphuric acid. It forms the "sod" oil of commerce. About half the oil employed is obstinately retained by the skin, and cannot be removed even by boiling with alkalies, while no gelatin is obtained by boiling water, to which the chamoised skin is much more resistant than ordinary leather. The nature of the tanning process does not seem to be well understood. It is generally stated that the fibres of the skin are unaltered, but are merely coated with the oxidised products of the oil. It is hard, however, on this hypothesis to understand their extraordinary indifference to water, even at a boiling temperature, which speedily converts kid and other tawed leathers into a solution which gelatinises on cooling; and it seems more probable to the present writer that some actual chemical combination is formed. Lietzman ('Herstellung der Leder,' p. 164) supposes that the whole of the gelatigenous tissue has been removed by liming and bating, and that only the very indifferent yellow elastic fibres (see p. 21) remain. This view, however, is quite untenable, in consideration of the very small proportion of these fibres originally present in the skin. MÜntz, in his researches (see p. 17), showed that the fibres insoluble in boiling water scarcely exceeded 3 per cent, of the dried pelt. Dry gelatigenous fibre has a considerable resistance to heat, and it is possible that the action of the oil may consist in preventing the absorption of water. This, however, will not explain its resistance to alkalies. Cotton or other vegetable fibres moistened with oil, readily undergo oxidation, with so much evolution of heat as sometimes to cause spontaneous combustion; but the oxidation products are easily and completely removed by alkaline solutions, leaving the fibre in its original state, as indeed is noted by Lietzman (loc. cit.).

The finishing processes consist in staking during drying to retain softness, and in whitening and smoothing the flesh (or sometimes both sides) on the fluffing wheel. Skins for gloves, &c., are bleached like linen, by sprinkling and exposure to the sun; or more rapidly by treatment with a weak solution of potash permanganate, and subsequently with sulphurous, or very dilute sulphuric acid, to remove the brown manganous oxide formed (Barreswil, Dingl. Polyt. Jour., 161, 312). Gaseous sulphurous acid from burning sulphur may also be used for bleaching. The "dyeing" of chamois leather is generally done with ochres and similar colouring matters, and may be removed by washing. Treatment with egg-yolk in water, or with an emulsion of olive-oil with a little soap, and rubbing, or stretching, will restore softness to chamois leather which has become stiff by washing.