DETONATORS are the devices used in firing high explosives by detonation. They consist of small cylindrical copper tubes closed at one end and charged with mercuric fulminate or a mixture of mercurial fulminate and potas sium chlorate which is compressed in the bot tom of the tubes. Those used for blasting in mines and quarries are also known as blasting caps and exploders. They are rated as single force, double force, triple force and so on, the charge for the single force cap being about five grains of the detonating substance, and the charges for the higher force increasing about two grains for each grade. To fire them a piece of Brickford or "running" fuse of the desired length is inserted in the mouth of the detonator or cap and then the copper tube is bent or "crimped' securely about the sides of the fuse. The detonator is inserted in the borehole so as to come in dose contact with the first cartridge or "stick" of explosive and the borehole is filled with tamping. When a flame is applied to the end of the fuse that projects from the borehole, the column of powder in the fuse takes fire, the fire travels slowly down to the charge in the detonator, causing the detonation of the dynamite.
For military mines and naval torpedoes and, to a considerable extent, for commercial blast ing detonators to be fired by an electric current are employed. These are known as electric
detonators. They differ from those previously described only in that the mouth of the copper cap is closed by a plug made of sulphur and ground glass, through which two copper wires, known as the "legs of the detonator,' are led. Inside the cap these wires are bridged over by a very fine wire made of an alloy of iridium and platinum. Around the bridge and between it and the fulminating composition is placed a layer of mealed gun-cotton. When it is desired ate fire," the legs of the detonator are connected with a dynamo-electric machine and the current generated. As the current passes it heats the bridges to incandescence, which sets fire to the gun-cotton; this causes the fulminate to deto nate, and this detonates the charge of dynamite or other high explosives. The detonators used on the Whitehead torpedoes in the United States navy contain 35 grains of mercuric fulminate, this large quantity being used to make sure that the detonator will do its share of the work in torpedo attacks. on an enemy. See ExmosivEs.