of weight and firmness that the hide be plumped at some stage of the process; but it is probable that this effect is produced with less loss of substance and solidity by suitable acidity of the tanning-liquors. Another advantage of lime is that it acts on the fat of the hide, converting it more or less completely into an insoluble soap,[73] and so hindering its injurious effects on the after tanning process, and on the finished leather. If strong acids whether mineral or organic are used later on, this lime soap is decomposed, and the grease is again set free. In sweated or very low-limed hides this grease is a formidable evil, causing darkening or grease spots on the finished leather. [72] Cp. p. 84. [73] This has been questioned, but I have satisfied myself it is correct. The customary method of liming is simply to lay the hides horizontally one at once in milk of lime in large pits, taking care that each hide is completely immersed before the next is put into the pit, so as to ensure a sufficiency of liquor between them. 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. How much lime is required is doubtful, but owing to its limited solubility, an excess, if well slaked, is rather wasteful than injurious. Great differences exist in the quantity of the lime used, the time given, and the method of working, not only for various classes of leather, but for the same kinds in different yards. Lime, as we have seen, is only soluble to the extent of about 1·25 grm. per litre, or (as 1 cub. foot of water weighs about 1000 oz.) say 1¹⁄₄ oz. per cub. foot, or, in an ordinary lime-pit, not more than ¹⁄₄ lb. per hide. Only the lime in solution acts on the hide, but it is necessary to provide a surplus of solid lime which dissolves as that in the liquor is consumed or absorbed by the hide; and this is especially the case where, as is generally customary, the hides are laid flat in pits, so that no circulation of liquor is possible. Where hides are suspended in lime-water, which is constantly circulated and kept up to its full strength by agitation in another vessel with solid lime, they unhair as quickly as with milk of lime, but the method seems, in the case of lime, to present no special advantage over the ordinary one, if in the latter the hides are hauled sufficiently often to keep the lime uniformly distributed. The case is otherwise in dealing with more soluble depilatories. Various patents have been taken for methods of liming by suspending in liquors, but the idea is now public property, and is largely used on the Continent. It is necessary that the lime which settles to the bottom of the pit should be agitated and kept in suspension, which may be effected either by moving the hides on a frame as in “suspenders” (p.