RUBBING-DOWN DYED SKINS.
In tan-yard construction, iron should, as far as possible, be avoided wherever it can come into contact with liquor, as it discolours the leather. In default of underground pipes, india-rubber suction hose may be employed. Direct-acting steam pumps without fly-wheels are not suitable for tanneries, as they "hammer" when the pit is nearly sucked up. Steam-jet elevators and the pulsometer are very useful for some purposes, but slightly warm, and dilute the liquors with condensed steam.
Fig. 64.
Much that has been said about pits applies also to leaches. They may be constructed either of wood, or brick and cement, and where heat is employed the latter is the better. They are also to be provided with plugs and pipes leading to a liquor-well. About 6 in. from the bottom of the pit is a false bottom B made of boards, perforated with holes or set a little distance apart; and in the corner is an "eye" C (Ger. Pfaff) consisting of 2 boards set at right angles, so as to preserve a vertical channel communicating with the space under the false bottom. This serves, in pits provided with pipes, for the insertion of the plug; and where this is absent, for that of a suction hose to pump off the liquor. In the American Press-leck System, the eye of one pit communicates by a horizontal spout with the top of the next (see D, [Fig. 64]). The Allen and Warren Sprinkler Leck ([Fig. 65]) has very much superseded this arrangement in America, though it is doubtful if it spends the bark so completely. The round tubs, however, have several advantages and may well be used for many purposes in English yards. Their construction is described in some detail in Mr. Schultz's book above cited. Some details will also be found on [p. 209] of the 'Manufacture of Leather' by Davis. The rule for finding the capacity of a round tub with perpendicular sides in cubic feet is to square the diameter and multiply by ·7854, and by the depth in feet; or roughly, to square half the diameter and multiply by the depth and by 31/7.
Fig. 65.