Wallace Sulphide Cellulose for Tanning 311
that the experiments to be described were conducted under laboratory
conditions somewhat different from those which occur in actual
tannery practice. It is, therefore, intended to present the results
of the investigation for the use of those who are interested in conduct-
ing tests on a larger scale in the tannery.
III. SOURCE OF SULPHITE CELLULOSE EXTRACT
It is considered desirable to state briefly and in general terms the
procedure by which sulphite cellulose extracts are made in order that
their nature may be better understood. A common method of
making paper pulp is to digest the wood from fir and spruce trees
with an aqueous solution of an acid sulphite. This sulphite can be
made with sodium, calcium, or magnesium as a base, but usually
either calcite or dolomite lime is employed. When the latter is used
the liquor contains dissolved acid sulphites of both calcium and mag-
nesium. In the digestion of the wood the cellulose is left in insoluble
form for use as paper pulp and the sulphites mostly disappear as
such due to reaction with other organic matter in the wood. Other
organic materials enter into combination with the bases of the sul-
phite liquor and remain in solution in the digestor. This solution
is termed the sulphite waste liquor, in which form it has no value for
use in the tanning of hides.
To produce an extract suitable for use in leather manufacture, the
sulphite waste liquor, which is acid, is neutralized with a slight excess
of dolomite lime. It being desirable that a tanning material be
reasonably free from lime, the latter is precipitated with the calcu-
lated amount of sulphuric acid. The precipitate is then removed by
filtration and the residual liquor is concentrated to the desired den-
sity (usually about 300 B.). The extract thus produced compares
favorably with ordinary vegetable tanning materials both as to con-
tent of soluble solids and as to the percentage of material absorbable
by hide powder. Whereas the exact character of the constituents in
sulphite cellulose extracts which have tanning properties is not
known, they are termed "lignosulphonic acids" because of the prob-
able formation of compounds between the acid sulphites and the
"lignone" portions of the wood.
There are described in the literature many methods for producing
a sulphite cellulose extract where the kinds and quantities of materi-
als are varied as well as the steps in the process. The above, how-
ever, will serve to illustrate in a general way the preparation of this
material from the waste sulphite liquor.
