On account of its capability of rendering gelatinous matters hard and insoluble in water, formaldehyde requires to be employed with great care, but 0·2-0·3 per cent. may be successfully used in admixture with egg-albumen in the preparation of “seasoning” in the finishing of morocco leather. It is also used commercially to produce different varieties of white leather for soldiers’ accoutrements and similar purposes (p. 380). _Triformol_ (tri-oxymethylene, “paraform”) is a product of the polymerisation of formaldehyde, and is prepared by evaporating a solution of the latter to dryness on the water-bath. It is said to be more powerful than formalin in its antiseptic properties, but has not entered very largely into use as a disinfectant, though considerable use is made of it to “fix” bacteria in gelatin for bacteriological purposes. _Camphor and essential oils_, as well as oil of turpentine, have considerable antiseptic powers, and the cheaper essential oils such as those of winter-green, black birch, sassafras and aniseed are frequently employed, especially in America, in preserving pastes, finishes and seasonings, and at the same time covering offensive odours. The odour of essential oils becomes much more powerful as they are diluted, and very small quantities suffice for the purposes mentioned. Birch-tar oil, such as is used to give the scent to Russian leather (p. 372), has considerable antiseptic effect. CHAPTER VI. _THE ORIGIN AND CURING OF HIDES AND SKINS._ A considerable proportion of the hides and skins used in leather manufacture are those of animals killed by the butcher for food, and these are frequently employed by the tanner without any preliminary curing. Domestic hides and skins are now generally sold by auction in weekly markets in the principal towns, after sorting and classification in weight and quality.[15] This is in many respects an improvement on the old method of purchase direct from the butcher, but it often leads to delay in delivery, and in hot weather hides suffer from putrefaction. In most cases, the damage is not sufficient seriously to affect the durability of the leather, but the delicate membrane of the “grain” is injured, and the hide or skin unfitted for coloured leather, or any purpose where small damages to appearance are important. Butchers are adverse to the use of salt, because it withdraws water from the hide in the form of brine, and so causes it to lose weight; but much injury would be saved by a light salting, and all hides or skins on which the hair is “slipping” should be regarded as damaged for fine leather manufacture. [15] The weight of English market-hides as credited to the butcher is usually marked on the edge of the butt near the tail, by cuts with a knife, the mode of numeration being sufficiently explained by Fig. 6, in which cuts crossing the horizontal line each represent 20 lb., that above it 10 lb., while less amounts are expressed in Roman figures.