human
tannage and more preferable for dyeing in those cases where blacks and very dark shades are wanted. For ordinary purposes a blend is usually employed. A feature of oak bark, also, is that it tends to make a firmer leather, so that the proportion used must be adjusted with this fact in mind as well as the question of colour. For firmer moroccos the skins may pass through a handler round of oak-bark liquors (10°-20°) in which a certain amount of sumach is added to the liquors. The sumach is leached and assists both in tanning and bleaching as the liquor works through the round. The old liquor is run to a paddle, and the tannage is commenced by paddling the drenched skins in this liquor. It is advantageous both for the tannage and for the efficient
gpt
of the sumach if this liquor be slightly warmed. In the early pit liquors the goods are very frequently handled. There is, however, the usual tendency of the times to save labour in this direction, and hence it is common to have several paddles with liquors of gradually increasing strength, followed by a shorter round of handlers in which the handling is more infrequent. Instead of paddles latticed drums may be inserted into pits containing liquors. These, however, are not quite so convenient. In some tanneries, especially where sumach only is employed, the tannage is in paddles throughout. A new liquor is made up with fresh sumach and is used repeatedly until exhausted. A three-paddle system sometimes obtains, in which case the operation closely resembles the three-pit system of liming (Part I., Section II.), and the skins pass through an
human
liquor, a
gpt
liquor and a
human
liquor. The goods need not be paddled the whole day through, and indeed in the later stages this is undesirable. The packs remain several days in each liquor and take up to 14 days to tan. Two to three bags of sumach are needed for about 20 dozen goatskins. This method of tanning is efficient and convenient for bold-grain finishes, on account of the constant tumbling and bending of the skins which tends to work up a grain. For very soft leathers and fine-grain finishes, however, the
gpt
or
human
is favoured. In this method the pelt is stitched up by machine to form a bag, grain outwards, leaving a
gpt
in the hind shank. The bag is nearly filled with a fairly strong infusion of sumach, inflated with air and tied up at the neck. The bags are then placed into a vat of warm sumach liquor, in which they just float. The bags are pushed down and the liquor stirred up, so that the goods are in constant motion. After a few hours they are piled on a rack, and the tan liquor of the interior is caused to diffuse through the skins by the pressure due to the weight of the pile. The bags are refilled with fresh and stronger sumach liquor and the process is repeated. The skins are thus lightly but effectively tanned in about 24 hours, and the leather has very fine grain and soft feel. However tanned the skins are dried out after tanning, and sorted in the
human
in the glazing machine two ways: right-hand shank to left fore shank and _vice versâ_, and piled again. After wetting back again they are
gpt
by hand with a cork board in four directions: belly to belly, shank to shank, and across as before, and finally from neck to butt. They are immediately hung up in a warm shed to dry, and to fix the grain. They are then softened by
human
with a rubber board, top seasoned, piled to temper and dry, brushed lightly, piled again, brushed more heavily, and dried out. They are finally softened by graining in three directions: shank to shank and across, and neck to butt. They are then brushed again. If these skins are wanted for upholstery they are shaved after dyeing, and nailed on boards to samm. They are also dried out in a cooler shed or
gpt
Manufacture of Leather,