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° F. (49° 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 within that time rubbed upon the tray with
the hand, in order to reduce it to a fine and uniform state of division.
Twenty grains (1.296 grm.) are used for the test. (See Heat Test, page
249.)

If the gun-cotton sample removed from the poacher stands the heat test
satisfactorily, the machine is stopped, and the water drained off. The
cotton is allowed some little time to drain, and is then dug out by means
of wooden spades, and is then ready for pressing. The poachers hold about
2,000 lbs. of material, and as this represents the products of many
hundred distinct nitrating operations, a very uniform mixture is obtained.
Two per cent. of carbonate of soda is sometimes added, but it is not
really necessary if the cotton has been properly washed.

~Compressing Gun-Cotton.~--The gun-cotton, in the state in which it is
removed from the poacher, contains from 28 to 30 per cent. of water. In