The Chemistry of Powder and Explosives - Sciencemadness Dot Org

204 NITRIC ESTERS
country with water at 38° to 43°, while the mixture is agitated
with compressed air. The higher temperature reduces the viscosity
of the nitroglycerin and increases greatly the efficiency of the
washing. The nitroglycerin is heavier than water and sinks
rapidly to the bottom. It is washed again with water, then with
sodium carbonate solution (2 or 3%), and then with water until
the washings give no color with phenolphthalein and the nitroglycerin
itself is neutral to litmus paper. In this country the
nitroglycerin is sometimes given a final wash with a concentrated
solution of common salt. This reduces the moisture which is
suspended in it, to about the same extent as the filtration to
which it is commonly subjected in European practice. The nitroglycerin
then goes to storage tanks in a heated building where
there is no danger of freezing. It has a milky appearance at first,
but this quickly disappears. After one day of storage it generally
contains not more than 0.3 or 0.4% of moisture, and this amount
does not interfere with its use for the manufacture of dynamite.
Pure nitroglycerin is odorless at ordinary temperatures, but has
a faint and characteristic odor at temperatures above 50°. Its
specific gravity is 1.6009 at 15° and 1.5910 at 25 0 . 12 It contracts
on freezing. Its vapor pressure has been reported by Marshall
and Peace 13 to be 0.00025 mm. at 20°, 0.00083 mm. at 30°,
0.0024 at 40°, 0.0072 at 50°, 0.0188 at 60°, 0.043 at 70°, 0.098 at
80°, and 0.29 mm. at 93.3°. About 5 cc. of nitroglycerin passes
over with one liter of water in a steam distillation. Snelling and
Storm 14 heated nitroglycerin at atmospheric pressure in a distillation
apparatus behind an adequate barricade. They reported
that
Nitroglycerin begins to decompose at temperatures as low
as 50° or 60°C. ... At a temperature of about 135°C. the
decomposition of nitroglycerin is so rapid as to cause the
liquid to become of a strongly reddish color, owing to the
absorption of the nitrous fumes resulting from that which
is decomposed; and at a temperature of about 145°C. the
evolution of decomposition products is so rapid that, at
atmospheric pressures, ebullition begins, and the liquid
i2Perkin, J. Chem. Soc, 55, 685 (1879).
13 J. Sec. Chem. Ind., 109, 298 (1916).
14 U. S. Bur. Mines Tech. Paper 12, "The Behavior of Nitroglycerine
When Heated," Washington, 1912.