A sufficient strain being brought on the rope secured to the ring g, the lead tube f bends, causing the fracture of the glass tube e, thus igniting the priming charge and exploding the mine.
A submarine mine so fitted may be fired at will, by bringing a line, from the ring g, to the shore, or it may be made self-acting by connecting two of them together, etc.
Percussion and Chemical Fuzes.—Many forms of this mode of mechanical ignition have been from time to time devised, of which the following are the most important ones:—
Sensitive Fuze.—It consists of an inner cylinder a, a, [Fig. 15], of composition metal, 1-1/2" diameter, and 2-1/2" long, having a thread cut on its outside, and a bouching b, 2-1/4" diameter and 2" long with a sexagonal projection c, for applying a wrench, also with an external and internal thread. The upper end of the inner cylinder a, is solid for 1", and is perforated by three holes d, d, d, in each of which a percussion primer is placed e, e. A piece of thin, soft and well annealed copper f is soldered to the upper end of the bouching b, to keep moisture from the primers, and is so thin that a slight blow will crush without breaking it. A safety cap can be screwed on to the external thread above the projection c.
Rain's Detonating Composition.—The detonating composition employed in this and many other forms of percussion fuzes by the Confederates, etc., consisted of a combination of fulminate of mercury and ground glass, and was invented by, and is named after, General Rains, Chief of the Torpedo Bureau, at Richmond, during the Civil War (1861-5). So sensitive was this composition that seven pounds pressure, applied to the head of one of the primers, would explode it.
When required for use the internal cylinder a, containing the primers e, e, is screwed up until contact between them and the copper cap f is secured.
McEvoy's Percussion Fuze.—[Fig. 16] represents a longitudinal section, full size, of the mechanical percussion fuze, used by Captain McEvoy in connection with his drifting torpedo, which latter will be hereafter described. a is a piece of metal, having an external and internal thread, and a projection b, to which is applied the spanner for screwing it into the torpedo case. This piece a is hollow at its upper end, and is closed by means of a thin copper dome c, which is soldered to it. Screwed into the piece a is the plug, or nipple d, with a hole through it from end to end, it is rammed full of mealed powder, and then a fine hole is drilled through the composition. A cavity e at the head of the plug, or nipple d, is filled with a fulminating substance. A spiral spring f, encircles the plug d, on which a cap g rests; h is a needle in this cap. The action of this fuze will be readily understood from the plan of the fuze at [Fig. 16]. A safety cap is provided, which fits into the slots i, i, and is fixed there by means of a set screw.
Improved Form of Jacobi's fuze.—The section shown in Fig. 17 is an improved form of the chemical fuze, invented by Professor Jacobi, and used by the Russians in their land and sea mines during the Crimean war (1854-5). It consisted of a small glass tube a, containing sulphuric acid, enclosed in a lead cylinder b. A mixture of chlorate of potash and white sugar surrounds the tube and holds it in position; c is a primer filled with mealed powder in connection with the charge of the mine. The action of this fuze is as follows:—On a vessel striking against the lead cylinder b, it is crushed in, breaking the glass tube containing the sulphuric acid, and thus causes it (acid) to flow into the mixture of chlorate of potash and white sugar, producing fire, which by means of the primer c, passes into the charge, and explodes the mine.
MECHANICAL FUZES.