More particularly, they are used in the leather industry. Fish oils are used chiefly in the manufacture of chamois leather. Ordinary chamois or wash-leather is made from the flesh-splits of sheep skins. The skin is well washed and softened, and freed from hair by treatment with lime. It is then split, and the loose and fatty middle layer removed by a sharp knife. The lime is removed by a short bran-drench and the superfluous moisture is pressed out. The skin is thus rendered porous and easily able to absorb the oil. It is stretched on a table and oiled with fish or whale oil. The oiled skin is folded up and worked for two or three hours in the faller stocks and then shaken out and hung up for a short time to cool and partially dry. The process is repeated a number of times, until all the water originally present in the skin has been replaced by oil. The oiled skins are then piled in a warm place. The oil gradually oxidizes—probably owing to some fermentation process—and the skins become yellow and very hot. From time to time the skins are strewn on the floor to cool and then re-piled, the process being repeated until the oxidation of the oil is complete. In France the freshly-oiled skins are hung in hot stoves, and the oxidation of the oil is completed in one operation. The skins are then dipped in water and passed through hydraulic presses, by which the surplus oil is removed. This surplus thick, oxidized oil is known as “degras” or “moellon,” and is used for stuffing leathers that have already been tanned. Stuffed leathers are supple and impervious to water, and are used for harness, belting, etc. A further quantity of oil may be removed from the “chamoised” leather by treating it with potash or carbonate of soda, “sod” oil being recovered from the extract by neutralization with sulphuric acid. The value of sod oil for oiling dressed leather is due to a resinous acid of unknown composition, that is soluble in alkali but insoluble in petroleum ether. Enamel or patent leather is generally coated, after tanning, with a linseed oil varnish, boiled with prussian blue, and dried in a steam heated chest at 70° to 80°C., the process being repeated until a sufficiently thick coat is produced. Fish oils are now used successfully in place of linseed oil. The enamel leather produced, although not quite so glossy as that made with linseed oil, is said to be more pliable.