The Chemistry of Powder and Explosives - Sciencemadness Dot Org

410 PRIMARY EXPLOSIVES, DETONATORS, AND PRIMERS
possibility that the iodide may contain iodate, and the apparent
analytical results ought to be corrected accordingly.
Mercury fulminate has a specific gravity of 4.45, but a mass
of the crystals when merely shaken down has an apparent density
(gravimetric density) of about 1.75. In detonators the material
is usually eompressed to a density of about 2.5, but densities as
high as 4.0 have been obtained by vigorous compression. Mercury
fulminate crystallizes from water in crystals which contain
^H-jO, from alcohol in crystals which arc anhydrous 1 . One liter
of water at 12° dissolves 0.71 gram, at 49° 1.74 grams, and at
100° 7.7 grams.
Mercury fulminate is usually stored under water, or, where
there is danger m freezing, under a mixture of water and alcohol.
'When wet it is not exploded by a spark or by ordinary shock,
but care must be taken that no part of the individual sample
is allowed to dry out, for wet fulminate is exploded by the explosion
of dry fulminate. It is not appreciably affected by long
storage, either wet or dry, at moderate temperatures. At the temperature
of the tropics it slowly deteriorates and loses its ability
to explode. At 35°C. (95°F.) it becomes completely inert after
about 3 years, at 50°C. (122°F. 1 ) after about 10 months. The
heavy, dark-colored product of the deterioration of fulminate is
insoluble in sodium thiosulfatc solution.
When loaded in commercial detonators mercury fulminate is
usually compressed under a pressure of about 3000 pounds per
square inch, and in that condition has a velocity of detonation
of about 4000 meters per second, explodes from a spark, and, in
general, has about the same sensitivity to fire and to shock as
the loosely compressed material. When compressed under greater
and greater pressures, it gradually loses its property of detonating
from fire. After being pressed at 25,000-30,000 pounds per square
inch, mercury fulminate becomes "dead pressed" and no longer
explodes from fire but merely burns. Dead-pressed fulminate
however is exploded by loosely pressed fulminate or other initial
detonating agent, and then shows a higher velocity of detonation
than when compressed at a lower density.
The temperature at which mercury fulminate explodes depends
upon the rate at which it is heated ancr, to some extent, upon the
state of subdivision of the sample. Wohler and Matter " experi-
11 Z. ges. Schiess- u. Sprengstoffio., 2, 181, 203, 244, 265 (1907).