McEvoy's Platinum Wire Fuze.—Another form of platinum wire fuze, which has been devised by Captain McEvoy, formerly of the Confederate Service, is shown at [Fig. 25]. It consists of the head a, formed of a mixture of ground glass, or Portland cement, worked up with sulphur as a base: this mixture when hot is poured into a mould, in which the two insulated copper wires, b, b, have been previously placed; when cold, the mixture with the wires affixed is removed from the mould, and the platinum wire bridge c being secured to the bare ends of the copper wires, the whole is firmly fixed in a brass socket d, by means of cement; the space e is filled with loose dry gun-cotton, so as to surround the bridge c; a copper tube f, closed at one end, is partly filled with fulminate of mercury, and when the fuze is required for service, this tube is secured to the brass socket d by means of cement.
In this form of low tension fuze there is no liability whatever of any injury being caused to the bridge by the working of the wires in the head, or by damp even after lying in the water for a month or more. One peculiarity of this fuze is that the composition is run over the insulated wires without materially softening the dielectric, or affecting in the slightest degree the insulation of the wires.
High Tension Fuzes.—The high tension fuze was devised for use with electrical submarine mines, in the place of the platinum wire fuze, on account of the little knowledge possessed, in the early days of submarine warfare, in regard to the manipulation of Voltaic batteries.
Platinum wire requires a temperature of some 500° F. to heat it to incandescence, and therefore necessitates the use of a powerful Voltaic battery, both in intensity and power, to effect the ignition of gunpowder by this means at considerable distances.
The Grove and Bunsen pile were the only suitable form of Voltaic battery known at the period of the introduction of high tension fuzes, both of which possessed the defects of uncertainty and inconstancy, and also were by far too cumbersome and too difficult to keep in effective working order to be of any real practicable value.
High tension fuzes may be ignited by means of either an electro-magneto machine, an electro-dynamo machine, a frictional machine, or by a Voltaic battery, generating an electric current of high intensity. Various kinds of this form of electrical fuze have been designed, the principal of which are as follows:—
- 1.—Statham's fuze.
- 2.—Beardslee's fuze.
- 3.—Von Ebner's fuze.
- 4.—Abel's fuze.
- 5.—Extempore fuze.
Statham's Fuze.—A section and elevation of this electric fuze are shown at Fig. 26; a, b is a gutta percha tube, with an opening cut in it, as shown in figure. The interior of this vulcanised gutta percha tube is coated with a thin layer of sulphide of copper, which coating is obtained by leaving a bare copper wire for some time in connection with the above-mentioned tube. The extremities of two insulated copper wires c, c, considerably smaller than the conducting wires, are uncovered, scraped, and then inserted into the tube a, b, with an interval of ·15 inch between them. The wires are then bent as shown in the figure, and the priming placed between the terminals. The whole is covered with a gutta percha bag, which is filled with fine grained gunpowder. The priming substance is composed of fulminate of mercury worked up with gum water. The objection to this fuze, which was used by the Allies in their destruction of the Russian fortifications at Sebastopol, is the want of sensitiveness of sulphide of copper, and the consequent necessity of a very powerful firing battery.
Beardslee's Fuze.—This high tension fuze is shown at [Fig. 27]. It consists of a cylindrical piece of soft wood a, which is about three-quarters of an inch in length and in diameter; two copper nails, b, b, are driven through this piece of wood a, in such a way that while the two heads come together as close as possible without absolutely touching, the pointed ends are some distance apart from each other, and project through the wood a; two insulated copper wires, c, c, are firmly soldered to these projecting ends, and a piece of soft wax, d, is pressed around the junction points. In a groove, across the heads of the copper nails, is placed a little black lead, to which is added a minute quantity of some substance, the nature of which is known only to Mr. Beardslee. Several folds of paper are wrapped round the wooden cylinder, forming a cylinder about 2-1/2 inches long, one end of which is tightly fastened round the insulated wires as at e. The other end of the cylinder is then filled with powder, f, and closed by a piece of twine. The whole fuze is then coated with black varnish. Though not highly sensitive, Beardslee's fuze is exceedingly efficient, and extremely simple.