The Chemistry of Powder and Explosives - Sciencemadness Dot Org

424 PRIMARY EXPLOSIVES, DETONATORS, AND PRIMERS
found it possible to measure the initiating effect of mercury fulminate
and of other initial detonators by firing them in compositions
consisting partly or wholly of copper oxalate, and then
by chemical means determining the amount of the oxalate which
had been decomposed. The experiments were carried out in a
small steel bomb, the detonator was placed in the middle of a
mass of oxalate or of oxalate composition, and sand was put in
on top to fill the bomb completely. The fact that part of the sand
was pulverized by the force of the explosion suggested that the
mechanical effect of the initiator might perhaps serve as an
approximate measure of the detonating efficiency; the oxalate
was omitted, the bomb was filled entirely with sand, and the sand
test was devised. Before Snelling left the Bureau of Mines in
1912 he had made about 40 tests on ordinary and electric detonators.
Storm and Cope extended the usefulness of the test and
applied it not only to the study of detonators but also to the
study of the materials out of which detonators are constructed,
both initial detonating agents and high explosives.
Lead Azide
Lead azide is a more efficient detonating agent than mercury
fulminate. It requires a higher temperature for its spontaneous
explosion, and it does not decompose on long continued storage
at moderately elevated temperatures. It cannot be dead-pressed
by any pressure which occurs in ordinary manufacturing operations.
Lead azide pressed into place in a detonator capsule takes
the fire less readily, or explodes from spark less readily, than
mercury fulminate. For this reason the main initiating charge of
lead azide in a blasting cap is generally covered with a layer of
lead styphnate, or of styphnate-azide mixture or other sensitizer,
which explodes more easily, though less violently, from fire, and
serves to initiate the explosion of the azide.
Lead azide is not used in primers where it is desired to produce
fire or flame from impact. Fulminate mixtures and certain mixtures
which contain no fulminate are preferred for this purpose.
Lead azide is used where it is desired to produce, either from
flame or from impact, an initiatory shock for the detonation of
a high explosive—in compound detonators as already described,
and in the detonators of artillery fuzes. For the latter purpose,
caps containing azide and tctryl (ar other booster explosive) are