The Chemistry of Powder and Explosives - Sciencemadness Dot Org

268 NITRIC ESTERS
rapidly than the original, bulkier material. Straight nitrocellulose
powder always gives a better heat test than the nitrocellulose
from which it was made. If small grains and large grains of
smokeless powder are made from the same nitrocellulose, the
large grains will give the better heat test.
In this country the most common heat tests which are made
regularly upon nitrocellulose and smokeless powder are the 65.5°
KI starch test and the 134.5° methyl violet test. In the former
of these, five several portions of the material under test, differing
in their moisture content from nearly dry to thoroughly dry, are
heated in test tubes in a bath warmed by the vapors of boiling
methyl alcohol. Within each tube, a strip of potassium iodide
starch paper, spotted with a 50% aqueous solution of glycerin,
hangs from a hook of platinum wire a short distance above the
sample, the hook itself being supported from a glass rod through
a cork stopper. The tubes are examined constantly, and the time
needed for the first appearance of any color on the test paper in
any one of the tubes is reported.
In the 134.5° methyl violet test, heavy glass test tubes about a
foot long are used. They are closed loosely at their upper ends
with perforated or notched cork stoppers, and are heated for
almost their whole length in a bath which is warmed by the
vapors of boiling xylene. Two tubes are used. The samples occupy
the lower 2 inches of the tubes, strips of methyl violet paper
are inserted and pushed down until their lower ends are about
1 inch above the samples, the tubes are heated and examined
every 5 minutes, and the times are noted which are necessary for
the test papers to be turned completely to a salmon-pink color,
for the first appearance of red fumes, and for explosion. The
explosion usually manifests itself by the audible popping of the
cork from the tube, but causes no other damage. A test similar
to this one, but operated at 120°, using blue litmus paper and
reporting the time necessary for the paper to be reddened completely,
is sometimes used.
In the Bergmann-Junk test the number of cubic centimeters of
nitrogen dioxide produced by heating a 5-gram sample for 5 hours
at 132° is reported. The determination was originally made by
absorbing the gas in ferrous sulfate solution, liberating the nitric
oxide by warming, and measuring its volume. A method based