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.