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 The Allen and Warren Sprinkler Leck (Fig. 65) has very much superseded this arrangement in America, though it is doubtful if it spends the bark so completely.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 3-1/7. [Illustration: Fig. 65.] Leaches and liquors are generally heated by blowing in steam direct. In this case, the condensed water mixes with the liquor, and in heating a liquor to boiling point it may be taken that about 20 per cent. of water will be thus added. Where strong liquors are to be heated, it is therefore obviously much better to pass the steam into a closed copper coil in the liquor. Such a coil, with steam at 30 lb. pressure, will heat about 27-1/2 gal. per hour per square foot of surface from 46° F. to boiling, and evaporate about half that quantity of liquor already at boiling temperature. (See Box, 'Treatise on Heat,' p. 176.) Heating coils must of course be provided with steam traps to carry off condensed water; and in boiling by open steam it is very desirable to let the steam pass through such a trap before use, to stop water condensed in the pipes, which usually contains iron, and discolours the liquors. CHAPTER XXIII. DRYING-SHEDS FOR LEATHER.