FUSE, a device employed for firing explo, sives. In mining, quarrying and in military and naval mining operations there is used the °Biel ford, safety running" or "tape" fuse which con sists of a tubular cord of cotton or hemp that has been rendered slowly combustible, the cav ity in the centre of the cord being filled with a slow-burning gunpowder composition. To make the fuse firm and hard, so as to prevent its being cut by, the sharp edges of the rock during tamping, the outside of the cord is served with a covering of strong twine, which is wound about it at nearly right angles to the direction of the twist of the cord by the process called countering. To protect the powder front moisture, the wrapped fuse is immersed in a bath of heated varnish composed of glue, soap and whiting. Finally, to prevent the surfaces of the fuse from sticking together when coiled they are coated with dry whiting, bran or pow dered soapstone. The fuse described is known as ((single fuse" and, as the varnish used is not waterproof, this fuse is only suitable for use in dry ground. In wet ground, a fuse is used which is made by coating the countered curd with tar or resin varnish and then,. before the varnish is quite set, countering it with tape and again coating it with varnish. This ,is known as "taped fuse.* When the fuse is to be sub jected to especially severe treatment, it is pro, vided with a double coat of twine or thread and is known as °double fuse." The varieties in use are ((common hemp fuse"; acomnrn cotton fuse"; °white fuse"; ((superior mining fuse"; "single-taped fuse"; adouble-taped fuse"; *triple-taped ' fuse"; esmall gutta-percha"; 'large gutta-percha" ; esmall gutta-percha taped" and large gutta-percha taped." Run ning fuse comes in lengths of about 50 feet, and, when properly made, is so uniform in quality that it can be depended upon to burn at the rate. of three feet perminute. This is im portant, as it is necessary for the safety of the operator. The. fuse should be stored in a dry place's° that the powder core may not become damp; and, if so treated,, it will, retain its efficiency until the•varuish has lost:all its essen tial oils and -become dusty. Care ,must be taloen not -to touch the- tape with any oily or greasrmatter, as this penetrates through the vacnish.to thepowder core and affects die rate
of burning. The fuse should not be song* handled, as pinching and squeezing alter the rate at which the, powder burns. 'Care should be exercised in opening out a coil which has became stiff through age or exposure to cold weather, for the fuse is then brittle, and if the cowering, is cracked by sudden and violent un rolling the fuse becomes unfit for use. If there be any doubt as to the behavior of a coil of fuse a piece one foot. long should be taken and its rate of burning timed.
Although in firing single charges, safety fuse answers admirably, where several charges are to be fired -simultaneously, the safety fuses are connected together by ainstantaneous fuses." These oonsist of a strand of quiclanatch en closed in- hemp or flax and several layers of gutta-percha and tape, or of a core of gun cotton enclosed in a leaden tube. Besides these nitroglycerine compositions have been proposed by Quentin and Nobel, and one containing mer curic fulminate by Philip Hess. Within recent years it has become the practice. to enclose tri nitrotoluene (T. N. T.) in leaden tubes for use as a fuse to be exploded by a detonator. Such fuse is now put upon, the market under the name of 'cordeau detonant," and is meeting with much favor in blasting with ahig,h* ex plosives.
In naval and military operations, and for simultaneous blasts in mining and quarrying, aeleetrie fuses" -are preferred to running fuses. These are gunpowder aignitersx' or fulminate ((detonators, " that are fired by electricity. They are classified as low tension fuses," designed for use with strong currents of low potential, f rem primary or secondary batteries, or from dynamo-electric machines; ((medium tension fuses,* for use with magneto-electric machines which generate currents of medium potential, and Thigh tension fuses," for use with con densed sparks capable of traversing a sensible air space. The use of, the word tension is not warranted by the present condition of electrical science, but it has become technical in this art. To-day, only low tension electric fuses are em ployed and they are described under DaroxA roes (q.v.).