Use of Sulphite Cellulose Extract as a Tanning Material Page: 318
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Technologic Papers of the Bureau of Standards
and % oak bark extracts made up on the basis of tannin content.
The first, or tail, liquor was maintained at a concentration of approx-
imately 2 per cent tannin, which increased with succeeding liquors
until a concentration of 4 per cent was reached in the last, or head,
liquor. The hides were treated in seven liquors in this series and
remained in each liquor for 48 hours. After completing the yard
tannage they were placed in a lay-away vat containing 6 per cent
tannin (approximately 70 Bk.) for 7 days. Upon removal from this
vat the leather was washed, bleached, oiled lightly on the grain, and
dried. No filling with extracts was done. The total time of tannage,
including the pretannage, the yard tannage, and the lay-away period,
was 24 days.
Companion tests were made using liquors of the same strength
and composition with the omission of the sulphite cellulose pre-
tannage. As was expected, the high concentration of the early
liquors caused a drawn grain and slow penetration. Further tests
were made starting with a low concentration of tannin (1 per cent),
and it required 40 days in the liquors to produce leather of the same
degree of tannage and yield as was secured with the pretannage.
Tests were also made with sulphite cellulose extract No. 2 in the
manner described above excepting that a blend of 50 per cent sul-
phite cellulose and 50 per cent quebracho was used in the yard tan-
nage. The series of liauors was so arranged that the total time of
tannage was 28 days.
The color, fiber appearance, substance, physical properties, and
chemical properties (Table 5) for the leathers tanned with the sul-
phite cellulose materials compared favorably with those of the
leather tanned without these extracts.
The function of a pretannage is to so prepare the hide that it can
be subjected to stronger liquors than would be possible without some
preliminary treatment, and thus reduce the time required for tanning.
The pretanning material must penetrate quickly, set the grain and
fibers and produce the desired degree of swelling which is to be main-
tained throughout the tannage. The above tests with sulphite cellu-
lose extract show that it can be used for a pretannage and that leather
will be produced in from 24 to 28 days as compared with 40 days
by the usual methods. A 70 per cent yield (ratio of the weight of the
finished leather to the weight of the hide entering the liquors) was
obtained by both methods. In practice the pretanning baths and the
tail liquor of the yard eventually become so contaminated with salts,
hide substance, and nontannins that they have to be discarded before
the full tannin content is utilized. This makes the use of the pre-
tannage of doubtful economic value. In these experiments it was
found that six lots of hides could be run through the pretanning baths
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Wallace, E. L. & Bowker, Roy Clement. Use of Sulphite Cellulose Extract as a Tanning Material, report, November 1, 1926; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc66515/m1/12/: accessed January 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.