The action of lime on the hide has already been spoken of to some extent. This is throughout a solvent one. The hardened cells of the epidermis swell up and soften, the rete malpighi and the hair-sheaths are loosened and dissolved, so that, on scraping with a blunt knife, both come away more or less completely with the hair (constituting " scud," as some English tanners name it, Ger., gneist or grand). The hair itself is very slightly altered, except at its soft and growing root-bulb, but the true skin is vigorously acted on. The fibres swell and absorb water, so that the hides become plump and swollen, and, at the same time, the "cement-substance" (coriin) is dissolved, the fibres become differentiated into finer fibrils, and the fibrils themselves become first swollen and transparent, and finally corroded, and even dissolved. This swelling of the fibres is produced both by alkalies and acids, and is probably due to weak combinations formed with the fibre-substance, which have greater affinities for water than the unaltered bide. It is useful to the tanner, since it renders the hide easier to "flesh " (i. e. to remove the adhering flesh), on account of the greater firmness which it gives to the true skin. It also assists the tanning, by opening up the fibre, and so exposing a greater surface. This i's advantageous only in dressing leather which is afterwards tanned in sweet liquors, and must have the cement-substance dissolved and removed for the sake of flexi bility ; but, in the case of sole-leather, it is probable that the same effect might be produced with less loss of substance and solidity by suitable acidity of the liquors. A more certain advantage of lime is that it acts on the fat of the hide, converting it more or less completely into an insoluble soap, and so hindering its injurious effects on the after tanning process, and on the finished leather.
The customary method of limeing is simply to lay the hides flat in milk of lime in large pits. Every day, or even twice a day, the hides are drawn out (" hauled "), and the pit is well plunged up, to distribute the undissolved lime through the liquor. The hides are then drawn in again (" set"), care being taken that they are fully spread out. Great differences exist in the quantity of lime used, the time given, and the method of working. Jackson Schultz prescribes 1 bush. (56 lb.) of fresh lime to 60-70 hides, and 3-4 days as sufficient time to unhair and plump them ; while a well-known English tanner states that, after .working for 6-10 days through a series of old limas, the hides (presumably wet-salted S. Americans) should have 4 days in a fresh lime, made with 3-12 lb. of lime per hide. It is obvious that if the American authority is right, the English process is wasteful in the extreme, both in hide-substance and lime. It is probable, however, that it would be found impossible to unhair and flesh hides, to suit the English market, in cold limea with the quantity and time mentioned, and if the limes are steamed, it is quite likely that the destructive action on the pelt may be even greater than by the longer and slower process in the cold. Most
likely a compromise between the two is the most desirable, and about 2-4 lb. of lime per hide, according to weight, should be sufficient, while a week for market hides, and 14 days for heavy salted, will loosen the hair and plump the pelt as much as is requisite. This is on the supposition that the limes are kept at a uniform average temperature of about 15° (60° F.) in winter and summer. If they are heated to 27°-32° (80°-90° F.), of course much less time is required, but there are no published experiments showing the relative weights made by the two processes, and, from the fact that warmed limas are principally used for descriptions of leather where weight and solidity are not of primary importance, it may be concluded that, in this direction, the results are unsatisfactory.
Another undecided point is whether the best results are obtained by making fresh limes for every pack, or by strengthening up the old ones. An old lime becomes charged with decomposing animal matter and with ammonia, and, within limits, loosens the hair more effectually than a new one. An experienced tanner states that, by using old limes, better weights are obtained, but that the leather is thinner than when a fresh portion of lime is used, and this is quite in accordance with theory. If, however, the old lime-liquor be retained too long, it ceases to swell the hides as it should, and, in warm weather, the limeing proper is complicated by a putrefactive process allied in principle to sweating.
Several variations in the above-described method of limeing have been proposed. A well-known patent claims the plan of suspending the hides on laths, and agitating the liquor by plunging in place of hauling. Probably this is an actual improvement, especially if some mechanical agitating contrivance be substituted for hand plunging. It has, however, the drawback that much room is required, though this may be, to some extent, compensated by the hides limeing more quickly. As the method has been long in use in America, and had been tried in several places in England before tha patent was obtained, it is not probable that it could be legally sustained, in this respect resembling a large proportion of the patents referring to leather manufacture. Two other American labour-saving methods in connection with limeing may be mentioned here. One is to have the limaing-vat double the ordinary size, and, instead of hauling the hides, to simply draw them from one side to the other by two strings, which are attached to the fore and hind shank of each hide. The strings are either looped over iron rods.at the four corners of the pit, or have simple knots, which are placed in notches sawn in wood. Of course, while the hides are at one side of the pit, the other side may be plunged or warmed. The other method is to have a spindle with discs at each end, to which the hides or aides are attached by hooks set round the edges. The hides are wound up by turning the spindle with a handspike, and the whole spindle is also capable of being raised and lowered in the liquor.