Where circumstances permit, it is a great advantage to place the taps either on a higher or a lower level than the layers and handlers, so that liquors may be run one way without pumping. CHAPTER X. SOLE-LEATHER.--Treatment in the Tan-house. On first coming into the yard, the butts are usually suspended by the shoulder or butt ends from sticks placed across the pits. They should be kept in almost constant movement, either by raising and shaking them by hand, or by supporting them on frames, which are rocked, or otherwise worked. Perhaps the best device for this purpose is the "travelling handler" of W. N. Evans, which consists of a frame supported on wheels, and worked slowly backwards and forwards by power. This frame should extend the length of a range of pits sufficient to take in at least a 3 days' stock of butts, which should be tied to sticks resting crossways upon it. It should have a stroke of 1-2 ft., repeated, say 6 times a minute. The power required is very small. The American rocker consists of a wooden frame balanced on its centre, and made to oscillate by power. It is a cheap and efficient machine, its defects being that the butts at the ends are much more moved than those in the centre, and that their upper parts, being lifted out of the liquor, are liable to become blackened. The suspender pits should be supplied with old handler liquors, which, if the tannage is a mixed one, may range from 12° to 20° barkometer, as a large proportion of the weight consists only of lime-salts, gallic acid, and other worthless products. It must here be explained that the barkometer (also called "barkrometer" or "barktrometer") is a hydrometer, graduated to show the sp. gr. thus--20° Bark. = 1·020 sp. gr. In using it the temperature of the liquor must be at or near 60° F. (15° C.). It is, of course, affected by any other matters in solution, precisely the same as by tannins. In the Lowlights Tannery the waste liquors are constantly about 12° Bark., and contain tannin equal to less than 0·2 per cent. (expressed as crystal oxalic acid), and gallic acid and similar matters equal to O·6 to 0·7 per cent. If the tannage is pure bark, it may perhaps be advisable to let the strength be somewhat less, but something depends on whether the exhausted liquors are returned with all their impurities to the "taps" or liquor-brewing pits, or whether the liquors are made with water, and hence purer. In any case, the free acid in the suspenders should always be sufficient in quantity to neutralise the lime brought in by the butts, or bad colour will certainly result, making itself visible in the shed, or as the tanning proceeds. If the butts, when first brought into liquor, take a lemon-yellow colour, especially in places that have been imperfectly exposed to it, this is an indication of danger which must not be disregarded. It may be met either by cleansing the butts more thoroughly before bringing into the yard, or by adding acid (acetic,