Up to the process of deliming, there is not a great deal of difference in preparing the hides and skins for the large variety of leathers, but between the fleshing and the tanning processes the work varies considerably, and largely determines the character of the finished leather. When the hides or skins are in the limed state, they are gristly and firm in texture. A certain amount of this firmness is desirable in some leathers, such as sole and belting, and, therefore, it is deemed advisable to leave a small quantity of lime in the hides, although, to get them evenly coloured in tanning, it is essential that the lime should be completely removed from the surface of the hide. An old method, which is even in use to-day in some tanneries, is to wash the fleshed hides in a cubical or hexagonal drum for several hours in running water, which is conveyed through an iron pipe in the journal of the drum, and escapes through small holes in the drum. The effect of using a hard water for washing out the lime is shown in the interior of these washing drums, the sides of which become incrustrated with a thick, hard deposit. The surface of this incrustration is irregular, and small projections are sometimes formed which mark the hides and reduce their value, as the impressions are not removed in later processes. The modern method of deliming hides intended for sole leather is to use a weak solution of acid, or an acid salt. For this purpose, sulphuric and hydrochloric acids are by far the cheapest, but require handling with great care, as any excess used has a corrosive and destructive effect on the fibres, which results in weak leather. Mild organic acids are much safer, and those generally preferred are lactic, formic, and butyric, although boracic and acetic acids are favoured by some tanners. Butyrate of ammonia is used for the same purpose by a number of French tanners. The same acid bath can be used for a second lot of hides, but sufficient acid should be added to raise the acidity of the liquor to its former standard. It is inadvisable to use one bath more than four or five times. The salt formed during the process by the combination of the lime with the acid--calcium lactate, formate, butyrate, acetate, or borate, according to the acid used--must be washed from the hides, either in a pit or drum, before they are ready for the tan liquors. [Illustration: FIG. 20 SCUDDING KNIFE]