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EXPLOSIVES—O HERN. 55 
freed from water. This is partly accomplished in a centrifugal 
wringer, but is completed by compressing the pyrocellulose into a 
solid block, then forcing alcohol through the compressed mass. 
Some of the water is thus forced out ahead of the alcohol and the 
remainder is absorbed by the alcohol, the operation of forcing it 
through the block being continued until pure alcohol appears. Ether 
is added to the pyrocellulose thus impregnated with alcohol, the 
relative proportions being about 2 parts of ether and 1 part of alcohol 
by volume. The amount of mixed solvent added varies between 
about 85 per cent and 110 per cent of the weight of the dried pyro- 
cellulose. After the ether has been thoroughly incorporated in a 
kneading machine the material is placed in a hydraulic press, in 
which it is formed into cylindrical blocks about 10 inches in diameter 
and about 15 inches long. In this operation the pyrocellulose loses 
the appearance of cotton and takes on a dense horny appearance, 
forming what is known as a colloid. The colloid is transferred to a 
finishing press, where it is again forced through dies and comes out 
in the form of long strips or rods, which are cut to grains of the length 
required. The grains are then subjected to a drying process, which 
removes nearly all of the solvent and leaves the powder in a suitable 
condition for use. The drying process is a lengthy one, amounting 
to as much as four or five months for the larger grained powder. 
Upon completion, the powder is blended and packed in air-tight 
boxes. 
Form of grain.—The form of grain used in the United States Army 
and Navy for large-caliber cannon is a cylinder containing seven 
longitudinal holes. Figure 1 shows the dimensions of a grain of 
about the size suitable for a 14-inch gun. The purpose of the holes 
is to cause an increase rather than a decrease in the burning surface, 
as the grain is consumed, the increase in the area due to their enlarge- 
ment more than compensating for the decrease in the outer 
surfaces. 
The increasing burning surface thus secured is advantageous in 
tending to better keep up the pressure as the volume behind the pro- 
jectile increases as it moves down the bore. Abroad, smokeless 
powder is commonly made in the form of flat ribbons or single per- 
forated sticks 2 or 3 feet long. Such forms have not been adopted 
in this country because of the fact that they do not give as much in- 
crease in surface while burning, and because of the difficulty of pre- 
venting serious warping of the long sticks in drying, whereby trouble 
would result in getting sufficient powder into the desired volume in 
loading. 
Smokeless-powder charges.—For use in guns, smokeless powder is 
put up into charges inclosed in stout cloth made of raw silk. Each 
charge is subdivided into as many sections as is necessary to secure 
