out during its
revolution. The cotton is thus in constant motion, continually travelling
round, and passing between the knives in the revolving cylinder and those
in the box fixed in the wooden block beneath it. The beater is kept full
of water, and the cotton is gradually reduced to a condition of pulp. The
wheel revolves at the rate of 100 to 150 times a minute.

[Illustration: FIG. 16_a_.--POACHER FOR WASHING GUN-COTTON.]

[Illustration: FIG. 16_b_.--PLAN OF THE POACHER.]

[Illustration: FIG. 16_c_.--ANOTHER FORM OF POACHER.]

When the gun-cotton is judged to be sufficiently fine, the contents of the
beater are run into another very similar piece of machinery, known as the
"poacher" (Fig. 16, _a, b, c_), in which the gun-cotton is continuously
agitated together with a large quantity of water, which can be easily run
off and replaced as often as required. When the material is first run into
the poacher from the beater, the water with which it is then mixed is
first run away and clean water added. The paddle wheel is then set in
motion, and at intervals fresh water is added. There is a strainer at the
bottom of the poacher which enables the water to be drawn off without
disturbing the cotton pulp. After the gun-cotton has been in the poacher
for some time, a sample should be taken by holding a rather large mesh
sieve in the current for a minute or so. The pulp will thus partly pass
through and partly be caught upon the sieve, and an average sample will be
thus obtained. The sample is squeezed out by hand, bottled, and taken to
the laboratory to be tested by the heat test for purity. It first,
however, requires to be dried. This is best done by placing the sample
between coarse filter paper, and then putting it under a hand-screw press,
where it can be subjected to a tolerably severe pressure for about three
minutes. It is then rubbed up very finely with the hands, and placed upon
a paper tray, about 6 inches by 4-1/2 inches, which is then placed inside
a water oven upon a shelf of coarse wire gauze, the temperature of the
oven being kept as near as possible to 120 deg. F. (49 deg. C.), the gauze shelves
in the oven being kept about 3 inches apart. The sample is allowed to
remain at rest for fifteen minutes in the oven, the door of which is left
wide open. After the lapse of fifteen minutes the tray is removed and
exposed to the air of the laboratory (away from acid fumes) for two hours,
the sample being at some point