Hemp Hurds as Paper-Making Material | Page 6

the
stalks being in contact with the soil. It is a simple matter, however, to
remove the chaff and dirt by sieving, and this practice was followed in
most of the paper tests conducted with this material.
=CHARACTER OF THE TESTS.=
Because of the similarity of hemp hurds to other materials which have
been tested by the Office of Paper-Plant Investigations,
semicommercial tests were conducted in cooperation with a paper
manufacturer without preliminary laboratory tests. Laboratory pulp and
paper tests are regarded only as a preliminary to semicommercial tests
and therefore are not employed unless the material in question presents
new features which should receive investigation before larger sized
tests are undertaken.
The advantages of cooperative mill tests are many, among which may

be mentioned the counsel and advice of the mill management and
employees, the services of specialized and skilled labor, facilities for
comparing the processes and the results of tests with commercial
processes and results, and the use of commercial or semicommercial
types and sizes of machinery. Tests conducted in this manner and on
this scale are of a different quality than is possible in those conducted
in a laboratory, and the results are susceptible of commercial
interpretation with a fair degree of reliability. It is found, in general,
that the cost of securing such equipment and service for a complete and
comprehensive test does not exceed $500, while the installation of an
equally satisfactory equipment alone would cost at least $50,000 and in
many cases very much more. Tests conducted in this manner constitute
a direct demonstration to the manufacturer, and the results obtained are
found to carry more weight when presented to other manufacturers for
consideration.
It is well known that the method of conducting tests necessarily varies
with the size of the test. In the matter of yield determination, for
example, laboratory tests may be on such a small scale that the
weighing and sampling of the resulting cellulose fibers may be
conducted by means of chemical laboratory apparatus and analytical
balance, while in tests involving a matter of 5 to 10 pounds of material
larger and different types of equipment are necessary. When the tests
are so increased in size as to employ 300 or 400 pounds, still other
types of equipment are necessary for the treatment of the material and
for a determination of the yield of fiber. In tests involving tons of
material the equipment involves the use of machines. Accuracy in
degree of control and in results will vary materially with the size of the
test. As the size of the test increases, certain factors will vary in a
beneficial manner, while others will vary in a detrimental manner, so it
is a question for each investigator to decide, after taking all factors into
consideration, as to the size of test which will give the most satisfactory
results. In work of this nature it is found, on the whole, that better
results are obtained in large tests, although the control of the factors
and the determination of the yield of fiber are more difficult than in
smaller tests.

In the tests described in this bulletin, the Department of Agriculture
employed a rotary digester of its own design,[2] comprising a shell 5
feet 5 inches in length by 4 feet in diameter, capable of holding about
300 pounds of air-dry hurds. It is believed that a test of this size is large
enough to give satisfactory results and that the results are susceptible of
commercial interpretation, while at the same time they are sufficiently
small for complete control and to afford fiber-yield figures which are
both accurate and reliable. Two such rotary charges gave enough fiber
for one complete paper-making test.
[Footnote 2: For a description of this rotary digester, see Brand, C. J.,
and Merrill, J. L., Zacaton as a paper-making material, U. S. Dept. Agr.
Bul. 309, p. 28, 1915.]
=OPERATIONS INVOLVED IN A TEST.=
A complete test on hurds comprises seven distinct operations, and the
method will be described, operation by operation, in the order in which
they were conducted.
Sieving.--The hurds for the first test were not sieved to remove sand
and dirt, but the resulting paper was so dirty that sieving was practiced
in all subsequent tests. The hurds were raked along a horizontal
galvanized-iron screen, 15 feet long and 3 feet wide, with 11-1/2
meshes per linear inch, the screen being agitated by hand from below.
Various amounts of dirt and chaff could be removed, depending on the
degree of action, but it was found that if much more than 3 per cent of
the material was removed it consisted chiefly of fine pieces of wood
with practically no additional sand or dirt; in most of the tests, therefore,
the material was screened so as to remove approximately