Note.—That is where the evolution of heat is caused by the electric spark, or by the electric discharge taking place through a substance which offers very great resistance to the passage of the electric force.
Platinum Wire Fuze.—This is the form of electrical fuze most commonly used, and which will most certainly supersede altogether the high tension fuze.
There are numerous advantages accruing from the use of platinum wire fuzes, the chief of which are here enumerated:—
a.—Great facilities for, and entire safety whilst testing the circuit.
b.—Extreme simplicity of manufacture.
c.—Non-liability to deteriorate.
d.—Perfect insulation of the electric cables used in connection with submarine mines not necessary.
English Service Platinum Wire Fuze.—The following is a description of the platinum wire fuze of the form adopted in the English service, a section of which is shown at [Fig. 24]. It consists of a head of ebonite a, hollowed out, in which a metal mould is fixed, the wires which have been previously bared are inserted into holes in this mould, and firmly fixed thereto by means of a composition poured into the mould, whilst hot; this is shown at b. The two bared ends of the wires which project beyond the metal mould, as c, c, are connected by a bridge of platinum-silver wire ·0014" in diameter and weighing ·21 grs. per yard. This is effected as follows:—
A very fine shallow groove is made in the flat ends of the bare wires c, c, and the platinum-silver wire is laid across in the incisions, and fixed there by means of solder. The length of the bridge d is ·25."
A tube e, made of tin, and soldered to a brass socket f, is fixed by means of cement to the ebonite head a; in this tube is placed the fulminate of mercury, the open end of the tube g being closed with a pellet of red lead and shellac varnish; around the bridge of the fuze is placed some loose gun-cotton.