_Dry and dry-salted hides_ require much longer soaking than wet-salted, the amount naturally depending on the thickness of the hide and the character of drying. Even thin skins when strongly dried require considerable time to soften and swell the fibres, although they soon become wet-through and flexible. Many different methods of soaking have been employed. 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; and more recently weak solutions of caustic soda, sulphide of sodium or sulphurous acid have been used with much success. [Illustration: FIG. 21.--American Wash-wheel.] 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 shipboard, it is frequently no easy matter to accomplish this. The fresh hide, as has been seen, contains considerable portions of albumin, and if the hide is dried at a high temperature, this may become 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 130° C. can only be redissolved by acids, or water at 120° C. Eitner[68] experimented with pieces of green calf-skin of equal thickness, which were dried at different temperatures, with results given in the following table:-- -------+-----------+---------+---------+-------------+-------------- Sample.|Temperature|Remarks. |Time of | Remarks. | Coriin |of Drying. | |Softening| |Dissolved by | | |in Water.| |Salt Solution. -------+-----------+---------+---------+-------------+-------------- I. | 15° C. |In vacuo |24 hours |{Without } |1·68 per cent. | | |{mechanical} | II. | 22° C. |In sun |2 days |{ work } |1·62 „ | | | | | III. | 35° C. |In drying|5 „ |Twice worked |0·15 „ | | closet | | | | | | | | | | | {Refused to soften} | IV. | 60° C. | „ | {sufficiently for } |traces | | | {tanning } | -------+-----------+---------+---------+-------------+-------------- [68] Gerber, 1880, p. 112.