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from one of his dynamo-electric machines. To melt steel a temperature of 1,800° C. is required. As many as 20 lbs. of steel have been melted in one charge, the time being an hour. Copper is nearly all vaporised when subjected to the heat of the furnace. The advantages of the latter are that a very high temperature can be obtained, the highest on earth as far as we know, and the heat is developed in the material itself instead of having to traverse the walls of the containing vessel. It will therefore probably be useful for certain special purposes.
Platinum wires rendered incandescent by passing the electric current through them have, as we have stated, for some years been eniployed in cauterising sores and in removing tumours by the bloodless process of searing.
In 1873 Dr. Onimus cauterised the lachrymal gland in several persons, one after another, from a single charge in a Planté secondary cell; and quite recently Professor Buchanan, of Glasgow, removed a tumour from a boy by help of the charge in a small Faure accumulator, and without shedding blood.
Mr. Lane-Fox has devised an electric egg or water boiler which is simply a hollow canteen of metal with double sides; the space between containing a coil of German silver wire, which is properly insulated from the walls and connected to terminals outside the boiler. The wires supplying the current are also brought to these terminals, and the current heats the wire and boils the water within the well of the canteen. The current diverted from an ordinary incandescent lamp will heat a pint of water in ten or fifteen minutes. Heated platinum wires are also used to fire fuses in
blasting operations, and in exploding submarine mines and torpedoes. The wire is enclosed in a small priming of gunpowder, and when the current is sent through it by the instantaneous closing of the battery circuit the priming is fired and explodes the charge. Instead of wire a semi-conducting powder such as carbon dust or sulphide of copper is heated to redness by the current and ignites the priming. This powder is usually placed so as to fill up a little gap or breach in the copper wires forming the circuit of the battery. The fuse of Professor Abel is one of the best, and is a mixture of sub-phosphide of copper, sub-sulphide of copper, and chlorate of potash. The ingredients are pounded together in a mortar and made into a paste with alcohol, which is afterwards dried away. Abel's fuse is largely used in this country for mining purposes. It can be fired. either by the current from a battery, or the spark from a magneto-electric exploder, which consists of a "horse-shoe "magnet having coils of wire bound round its poles, and an armature of soft iron mounted on a pivot in front. On suddenly striking down a handle the armature is jerked away from the poles of the magnet and a sudden charge of electricity excited in the coils. This appears in the form of a spark which is conducted to the fuse by insulated wires.
Gas jets are lighted by means of small platinum spirals of wire heated by the passage of the current, and also by an induction spark leaping across the air space between two metal points. The sparking gaslighter consists of a long hollow rod containing within it a small induction coil with auxiliary battery, and a contact maker operated by a press button. Wires connect the voltaic battery to the primary circuit of the induction coil through the button; and the secondary circuit of the coil is in turn connected by wires within the stem of the rod to a pair of sparking points, which are exposed to the air at the upper end
of the rod. On inserting these points into the gas jet and pressing the contact button so as to send the current through the primary, a stream of sparks traverses the space between the metal points and ignites the gas. The battery is sometimes a single chloride of silver cell also contained within the rod : and when a platinum wire spiral is used instead of the spark, a bichromate of potash cell having its zinc and carbon plates separated by a layer of sawdust or of soft asbestos soaked in a solution of bichromate of potash is employed. This “ dry” battery can be conveniently packed in small compass in a chamber at the base of the rod which serves to reach the gas jet.
Such a battery is exposed in the chamber below the petroleum lamp Fig. 79. Outside the chamber is a press-button which closes the circuit of the battery, allowing the current to flow through wires to a fine platinum spiral, which is brought to the wick of the lamp by depressing a finger-key. The heated wire lights the lamps and the release of the key tilts the wire out of the flame. At the recent Crystal Palace Exhibition Mr. Edison exhibited a cigar lighter or electric tinder box, on the same principle, the lights being obtained by kindling a match soaked in spirits of wine at an incandescent platinum wire.
WHEN a current of electricity of sufficient strength, say that from two or three cells of a voltaic battery, is sent through water, it decomposes the water into its constituent gases, hydrogen and oxygen. This experiment is usually shown by means of the apparatus shown in Fig. 80. This consists of a glass vessel v