It is not absolutely necessary to soak fresh hides or skins at all before liming, and where the water is scarce or unfavourable, or the skins tainted or “slipping” hair, it is best to pass straight into a weak lime. In this case the limes must be worked in shifts (see p. 131) and the whole of the oldest liquor run away and the hides rapidly changed into a fresh lime, or the limes will become so charged with organic matter and bacteria that the hides will cease to plump, and may even putrefy. _Salted hides and skins_ require more soaking and more thorough washing than fresh ones, as it is not only necessary to remove the salt, but to soften and plump the fibre which has been dehydrated and contracted by salting. If goods with salt in them are taken into limes, they will not plump properly,[67] and creases and wrinkles (drawn grain) are formed which no after-treatment will remove. This is especially important in sole leather. In deciding on a method, we must bear in mind that salt is easily soluble, and diffuses rapidly into water or weaker solutions, and that weak salt solutions tend to prevent the plumping of the fibre, while those of about 10 per cent. have considerable power of dissolving the cementing matter of the fibres (p. 65) and so lessening weight and firmness. It may also be noted that though salt is not a true disinfectant (p. 22), salted hides are much less prone to putrefaction than fresh ones, and therefore a longer soaking may be safely given. [67] Experiments mentioned on p. 89 throw some doubt on the power of salt to prevent plumping in the limes, though the opinion in the text is generally held by tanners. These conditions point to the desirability of free exposure to water, attained by suspending, handling frequently, or tumbling, and repeated changes to remove the salt. The degree of removal of salt is easily determined by the estimation of Cl in the last wash-water (L.I.L.B., p. 18). American tanners universally soak wet-salted hides three or four days with as many changes of water, and frequently finish by a few minutes in a wash-wheel. Any washing tumbler may be used; but the cheap and simple construction of the American wash-wheel will be easily understood from Fig. 21. The sides are open, so that hides can be put in or removed between the spokes. The rim of the wheel is generally perforated, for the escape of water which is supplied by a pipe passing through the axis; and the wheel is often driven by a chain or rope round its circumference. No severe mechanical treatment, such as “stocking,” is necessary or desirable for green or salted hides.