_Preparation for Tanning._--Market hides should be well washed in fresh water, to remove blood and dirt, before unhairing; but prolonged soaking dissolves a portion of hide-substance, and probably reduces weight, though it facilitates the action of the lime. It is very advantageous if grease and flesh, and also dung can be removed before liming, and if hand-labour is too costly machinery might be employed. Salted hides should be soaked somewhat longer, and in clean water, so as to remove the salt before liming. This water should be frequently changed, since 10 per cent. brine dissolves coriin freely (see p. 19). Dried hides require more lengthened treatment. Before they are prepared for tanning, they must be brought back as far as possible to the condition of fresh hides, and, for this purpose, must be thoroughly soaked and softened in water. There are many ways of doing this: sometimes hides are suspended in running water; sometimes laid in soaks, which may be either renewed, or allowed to putrefy; sometimes in water to which salt, borax, or carbolic acid has been added, to prevent putrefaction. The first of these methods, were it desirable, is rarely possible in these days of River Pollution Acts; of the others, it is difficult to say which is better, since the treatment desirable varies with the hardness of the hide and the temperature at which it has been dried. The great object is to thoroughly soften the hide, without allowing putrefaction to injure it. As dried hides are often damaged already from this cause, either before drying, or from becoming moist and heated on ship-board, it is frequently no easy matter to accomplish this. The fresh hide, as has been seen, contains considerable portions of albumen, and if the hide is dried at a high temperature, this becomes wholly or partially coagulated and insoluble. The gelatinous fibre and the coriin (if indeed the latter exists ready formed in the fresh hide) do not coagulate by heat, but also become less readily soluble. Gelatin dried at 266° F. (130° C.) can only be redissolved by acids, or water at 248° F. (120° C.). Eitner experimented with pieces of green calf-skin of equal thickness, which were dried at different temperatures, with results given in the following table:--