EXPLOSIVES—0 HERN, 269 
service is less sensitive than any of those referred to above, and at 
the same time is very powerful. Its power is indicated by the faci 
that the pressure developed in a projectile filled with that material 
is estimated to be approximately twice as great as that developed in 
one filled with compressed guncotton. 
MEANS OF IGNITING EXPLOSIVES. 
Some types of explosives, such as black powder and _ blasting 
powder, can be satisfactorily ignited by means of an ordinary flame. 
For blasting purposes this is commonly supplied by a slow-burning 
fuse consisting of a core of mealed powder inclosed in two or more 
layers of yarn and generally surrounded by tape that has been dipped 
into a waterproofing composition. A suitable length of fuse having 
been cut off, and one end inserted in the explosive, the other end is 
lighted. The powder core burns slowly along the fuse, giving the 
operator time to proceed to a safe distance. For other types of 
explosives, such as dynamite, detonators are needed to secure satis- 
factory starting of the explosion. These detonators, as used in 
commercial practice, are commonly called blasting caps, and consist 
of copper capsules about as thick as an ordinary lead pencil. They 
are commonly charged with dry mercuric fulminate, or with a mixture 
of such fulminate and potassium chlorate. The weight of fulminate 
in detonators varies from about 8 to about 30 grains. The detonators 
themselves are usually fired by means of a fuse of the character 
previously described. 
ELECTRIC DETONATORS. 
In order to secure greater safety for the operator, electric detona- 
tors or fuses that can be fired from a considerable distance are 
commonly used. These detonators differ from those previously de- 
seribed in that two electric wires enter the upper end and are joined 
by an extremely fine platinum or other high resistance wire like the 
carbon filament in an incandescent lamp, which becomes heated until 
it glows, when an electric current is passed through it. This wire, 
known as the bridge, is placed above the detonating composition and 
is surrounded by guncotton or loose fulminate. Such a detonator 
differs in principle from the electric primers commonly used in firing 
cannon only in that the mercuric fulminate of the detonator is 
replaced by black powder in the cannon primer. 
SUBMARINE MINES. 
A submarine mine is essentially a charge of high explosive confined 
in a strong case, and provided with a suitable fuse to cause its explo- 
sion either upon the receipt of a blow from being struck by a ship, 
