h 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 equi