The Chemistry of Powder and Explosives - Sciencemadness Dot Org

314 SMOKELESS POWDER
The amount of total volatile matter increased regularly during
the period of exposure, as did also the amount of volatile matter
resident at or near the surface of the powder grains. The amount
of volatile matter in the interior of the powder grains (residual
solvent, RS) did not alter materially during the experiment.
Total volatiles in powder is determined by dissolving the
sample in a solvent, precipitating in a porous and granular condition,
evaporating off the volatile matter, and drying the residue
to constant weight. External moisture is the amount of volatile
matter which is driven off by some convenient method of desiccation.
The difference between the two is residual solvent, TV —
EM = RS, and is supposed to correspond to volatile matter resident
within the interior of the grain and not accessible to desiccating
influences. Various methods of determining external
moisture have been in use among the nations which use straight"
nitrocellulose powder and in the same nation among the manufacturers
who produce it. At the time of the first World War, for
example, external moisture was determined in Russia by heating
the sample at 100° for 6 hours, in France by heating at 60° for
4 hours, and in the United States by heating at 60° in a vacuum
for 6 hours. These several methods, naturally, all give different
results for external moisture and consequently different results
for residual solvent.
There appears really to be no method by which true external
moisture may be determined, that is, no method by which only
the surface moisture is removed in such fashion that the residual
solvent in the powder is found to be the same both before and
after the powder has been allowed to take up moisture. Samples
of powder were taken and residual solvent was determined by
the several methods indicated in the next table. The samples
were exposed 2 weeks to an atmosphere practically saturated with
water vapor, and residual solvent was again determined as
before. The surprising result was secured in every case, as indicated,
that the amount of residual solvent was less after the
powder had been exposed to the moist atmosphere than it was
before it had been exposed. Yet the powder had taken up large
quantities of moisture during the exposure. It is clear that the
exposure to the moist atmosphere had made the volatile matter
of the interior of the grains more accessible to desiccating influ-