The Principles of Leather ManufactureProcter, H. R. (Henry Richardson)
History
The Principles of Leather Manufacture
Procter, H. R. (Henry Richardson)
Leather
_Analysis._--Little or no attention has been paid to the analysis either
of dungs for bating purposes, or of the bating liquors, and although the
total cost of manure bates is a high one, it is evident that such low-
priced and irregular articles will not pay for elaborate analysis.
Probably in some cases it would be worth while to make a determination
of moisture and organic and mineral constituents by drying and ignition.
Where a further investigation is desired, the determination of the
soluble matter by filtering and evaporating a portion of the solution to
dryness, and that of the nitrogen by Kjeldahl’s method (see p. 70),
would be advisable, and of course in the future, when the subject is
better understood, a bacteriological examination may be useful. If it is
desired to estimate the solution of hide-substance in the use of bate or
drench liquors, the determination of the nitrogen in a measured quantity
by Kjeldahl’s method will afford the best basis of calculation,
allowance being made for the nitrogen present in the original bate
liquor. Hide-substance contains about 17·8 per cent. of nitrogen. In
many cases, simple weighing of the solid residue, left on evaporating
the liquor to dryness and drying for several hours at 100° C., with
subsequent ignition to determine lime and other mineral matters, will
suffice.
The quantity of hen- or pigeon-dung used in bating hides is very
variable, but may be stated at from 12 to 60 litres per 1000 kilos of
raw hide, in at least 2000 litres of water. The bate is generally used
cold, the hides remaining in it 4-8 days, with frequent handling; but
some tanners, especially in the United States, prefer bating in a paddle
or drum at a temperature of about 35° C., in which case the time must be
diminished to a few hours. The dung is best infused with warm water in a
separate vessel,[110] and allowed to ferment for at least a week without
use, when it will be found to swarm with micrococcus-chains. Only the
clear liquor should be run into the bate-pit, the sediment and dirt
being thrown away, or used as manure. In this way the danger of stains
and flaking is much reduced. Bates may be mended with fresh portions of
dung-infusion for several successive packs of hides, but should not be
used too long, as they gain in solvent power by the dissolved
hide-substance and the increased fermentation, and the method is not
without risk.
[110] This seems to have been first suggested by T. Palmer, Eng. Pat.
13,636, 1886.
After bating, the hides are usually “worked” (“scudded,” “fine-haired”)
on the beam, to remove dirt and grease, but in America a wash in the
wash-wheel is often considered sufficient. Goods are occasionally
“stocked” (p. 116) from the bates, but this is not to be recommended, as
it is likely to drive out much of the partially dissolved hide-substance
and produce undue looseness and loss of weight.
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