The Chemistry of Powder and Explosives - Sciencemadness Dot Org

NltfROCELLULOSE 263
The pulped fibers still retain acid adsorbed or occluded on their
surface. This is removed by poaching the nitrocellulose, by boiling
it again, first for 4 hours with fresh water with or without
the addition of dilute sodium carbonate solution, 97 then for 2
hours with water without addition of soda, then twice with water
for 1 hour each time. The material is then washed at least 8 times
by thorough agitation with cold water, and by decantation each
time of at least 40% of the liquid. After the washing, the material
undergoes screening, where it passes through apertures 0.022
inch in width, wringing, whereby its moisture content is reduced
to 26-28%, and finally packing for shipment or for storage in
containers which are hermetically sealed.
Guncotton is made in substantially the same way as pyrocellulose
except that a stronger mixed acid containing approximately
24% nitric acid, 67% sulfuric acid, and 9% water is used.
Long-fiber high-grade guncotton is usually manufactured by the
pot process and with the use of mixed acid which is nearly
anhydrous. Iron pots are generally used. For the nitration of
4 pounds of dry cotton, 140 pounds of acid is introduced into the
pot and the cotton is immersed in it, pressed down, and allowed
to digest for 20 or 30 minutes. The contents of several pots are
centrifuged at once, and the product is stabilized in the same way
as pyrocellulose except that it is not pulped.
There can be no doubt that, in the standard method of stabilizing
nitrocellulose, there are, among the results which the poaching
accomplishes, at least some which would have been accomplished
much earlier during the boiling if the material at that time had
been pulped. This seems especially evident with respect to the
hydrolysis of easily hydrolyzed material adjacent to the inner
wall of the tubular fibers. Olsen, 98 discussing the standard method,
has written, "The preliminary boiling tub treatment reduced the
acidity of the fibers and of the interstitial material, but the pulping
process, by macerating these fibers, has set free an additional
amount of acid. It is, therefore, necessary to repurify the pyrocotton
by boiling." He discovered that a marked reduction in
time and in cost could be secured by carrying out the pulping
operation prior to the hydrolyzing boils. If the pulping is done at
97 Not more than 10 gallons of sodium carbonate solution (1 pound per
gallon) for every 2000 pounds of nitrocellulose (dry weight).
98 U. S. Pat. 1,798,270 (1931).