human
grain. The added grease is also a contribution to the
gpt
of the finished article--a primary consideration for heavy leather, which is usually sold by weight. The finishing processes, indeed, tend to be dominated by this consideration, and become a series of efforts to retain as much tannin and add as much grease as are consistent with the requirements of the class of leather being manufactured. Sole leather does not contain more than about 2 per cent. grease, or its firmness is impaired. Belting leather, in which considerable pliability is needed, may contain about 9 per cent., whilst harness leather, which must be exceedingly tough and durable, may contain up to 13 per cent. of fatty matters. Upper leathers, which need to be soft and pliable as well as waterproof and durable, are very heavily
human
and often contain up to 30-40 per cent. of grease. Sole leather is thus rather distinct from the rest, which are called
gpt
human
or
gpt
leathers. The actual drying out before, after and between the various mechanical operations, each have an appropriate degree of wetness. In this country the drying is usually under the prevailing atmospheric conditions and is known as
human
The goods are suspended by hooks or strings or by laying over poles in special sheds fitted with louvre boards by which the rate of drying can be roughly controlled. Weather drying is cheap, but exceedingly slow, and in unfavourable weather is very unreliable. The goods, moreover, need constant attention to obtain an even result. Steam pipes are usually laid along the shed floors, and are used in winter and damp weather to accelerate the drying, and also in the final shed stove to remove the last traces of moisture. Wet weather, however, will not stand a high temperature, and steam drying is better avoided when possible. Air-dried leather still contains about 14 per cent. of moisture. Many systems of shed ventilation have been suggested to hasten the drying and to secure a better control of the process. In one system a screw fan is fitted at one end of a shed (without louvre boards) and sucks air through the goods from an inlet at the other end. The air can be heated by a steam coil near the inlet. In another system a centrifugal fan blows air through an arrangement of pipes which distributes it to the drying sheds, and discharges it close to the floor by various branch pipes. The outlets are near the roof. A system of dampers permits hot air, warm air and the used wet air to be blended in the desired proportions. In America turret drying has been used. The sheds are vertically above one another and have latticed floors. Heated air is admitted at the bottom and rises through the goods up the building just as in a chimney. For many of the finishing operations it is important to obtain the leather in a uniformly half dry or
gpt
condition. This may be done by careful drying, and wetting back the parts that have become too dry with tepid water or weak sumac liquor, and then leaving the goods
human
until of uniform humidity. It may also be done by
gpt
leather which has been completely dried out. There are also
human
which by means of rollers squeeze out the excess liquor. Sole leather is dried out and finished immediately after tanning, but dressing leather is often
gpt
out of tan liquors and wet back for finishing when required. Dressing leather is often treated in different factories; tanners selling it as rough leather and
human
gpt
human