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