The Chemistry of Powder and Explosives - Sciencemadness Dot Org

316 SMOKELESS POWDER
been driven out of the powder and that further treatment would
produce no additional cracks and pores in the grains. The gain
or loss (either one, for the two were equal) calculated as per cent
of the weight of the desiccated sample gave the apparent hygroscopicities
listed below. Since all the powders were made from the
CALIBER
0.30
75 mm.
4.7 inches
6 inches
10 inches
APPARENT HYGROSCOPICITY, %
3.00
2.75
2.42
2.41
2.11
same material, namely, straight pyrocellulose, the differences in
the apparent hygroscopicity are presumed to be caused by the
drying treatment not being vigorous enough to drive out all the
moisture from the interior of the grains of greater web thickness.
The drying, however, was so vigorous that the powders became
unstable after a few more repetitions of it. The losses on desiccation
became greater because of decomposition, and the gains on
exposure to moisture became greater because of the hygroscopicity
of the decomposition products.
Although hygroscopicity determined in this way is apparent
and not absolute, it supplies nevertheless an important means of
estimating the effects both of process of manufacture and of composition
upon the attitude of the powder toward moisture. Thus,
samples of pyrocellulose powder for the 4.7-inch gun, all of them
being from the same batch and pressed through the same die, one
air-dried, one water-dried, one dried under benzene at 60°, and
one under ligroin at 60°, showed apparent hygroscopicities of
2.69%, 2.64%, 2.54%, and 2.61%, which are the same within the
experimental error. Milky grains 19 of 75-mm. powder showed an
apparent hygroscopicity of 2.79%, compared with 2.75% for the
normal amber-colored grains. The experiment with this powder
was continued until considerable decomposition was evident; the
successive gains and losses were as follows, calculated as per cent
of the original weight of the sample.
19 Grains which had a milky appearance because of the precipitation of
the colloid during the water-dry treatment. This result follows if the grains
contain more than 7 or 7.5% of ether-alcohol when they are submitted to
water-drying.