The Chemistry of Powder and Explosives - Sciencemadness Dot Org

290 SMOKELESS POWDER
pounds of water is added and about 90 grams of rosaniline or
some other, generally bright-colored, water-soluble dyestuff, and
the charge is incorporated by milling for about 45 minutes in a
wheel mill which is built like a black-powder mill but is smaller
and has light wooden wheels. The charge is then run through
a mechanical rubber, which consists of wooden blocks rubbing
with a reciprocating motion on a perforated zinc plate; the larger
lumps are broken up and the material is put into proper condition
for granulating. For this purpose about 50 pounds is placed in a
copper pan or "sweetie barrel" which is revolving in a vat of hot
water and is heated by that means. The pan rotates fairly
rapidly, say at about 15 r.p.m., and carries the powder up along
its sloping side to a point where it is scraped off by suitably
arranged wooden scrapers and falls back again. It thus receives
a rolling motion which has the effect of granulating the powder
into spherical grains. The operation requires about 40 minutes,
and its completion is indicated by the failure of the powder to
carry up on the pan because of the loss of moisture.
After it has been granulated, the powder is given a preliminary
screening with a 12-mesh sieve. The material which is retained
on the sieve is returned to the wheel mill. That which passes
through is hardened. It is put into a horizontal revolving cylinder
and a mixed solvent, consisting of about 1 part of acetone and
6 parts of alcohol, is added in the proportion of 1 gallon of solvent
to 15 pounds of powder. Acetone dissolves nitrocellulose, alcohol
does not; the mixed solvent swells and softens the fibers and
makes them stick together. The cylinder is rotated, while hot air
is blown through, until the solvent has been volatilized. During
this process the temperature is allowed to rise as high as 50°
or 55°. The product, which consists of grains now more or less
completely agglutinated, is given a final screening. In a typical
case, the portion passed by a 12-mesh sieve and retained by a
50-mesh sieve is taken; it is given a final drying and is ready
for use.
In a typical example of the still process for the manufacture of
bulk sporting powder, 500 pounds of pulped nitrocellulose
(12.60% N) is placed in a vertical cast-iron still along with 700
gallons of water containing 2% of potassium nitrate and 6% of
barium nitrate dissolved in it. The material is mixed thoroughly