Fig. 4
Electric Furnaces
By far the most important application of electric heat, as such, is in electric furnaces, by means of which we attain the highest temperatures known to man. The electric furnace consists of a chamber of “refractory” material, containing the substances to be acted upon by the heat, with a pair of big carbon electrodes thrust into the centre, as shown in [Fig. 4], which is a picture of Moissan’s electric furnace for the distillation of metals, and supplied with heavy continuous or alternating currents. The apparatus is therefore a sort of gigantic electric arc-lamp, so enclosed that the whole of the intense heat of the arc is confined and concentrated on the smelting or other work. In many places where cheap electric power is to be had—as in the vicinity of the great Niagara Falls power-plants—electric furnaces are employed in what are known as electrometallurgical and electrochemical manufacturing processes. By their aid many metals and other substances that were formerly scientific curiosities, or entirely unknown, are produced commercially; such as aluminum, certain rare metals, and calcium carbide, from which that wonderful illuminant, acetylene-gas, is obtained.
Welding Metals
Another useful application of electric heat is in the welding of metals. Instead of heating the pieces to be welded in a forge, their ends are simply butted together and the electricity—generally from an alternating-current transformer—turned on. The heat developed by the “contact resistance” between the pieces quickly softens the metal so that the pieces may be forced together, forming a perfect weld in a few minutes without any hammering. [Fig. 5] is a view of one form of electric welding-machine in which this is accomplished. The electric process can weld certain metals that cannot be joined securely by ordinary welding methods, and is used in several special arts.
Welding is also performed by the heat of a special electric arc-lamp, which a workman holds in his hand like a blow-pipe or torch. This process is especially useful in joining the edges of sheet-steel, in making tanks for electric “transformers,” etc. The workmen have to wear smoked glasses in order to protect their eyes from the intense glare of the arc.
Fig. 5
Electric Car-heaters
Perhaps the simplest and best-known application of electric heat is the electric car-heater, consisting of coils of high-resistance wire—such as iron or German-silver wire—mounted on an insulating, non-combustible frame which is placed under the seats of the car. Part of the current from the trolley wire or third rail passes through the resistance-coils, heating them up and thereby warming the air in the car.