Electric furnace, heating chamber with electricity as the heat source for achieving very high temperatures to melt and alloy metals and refractories. The electricity has no electrochemical effect on the metal but simply heats it. Electric furnaces produce roughly two-fifths of the steel made in the united states. They are used by specialty steelmakers to produce almost all the stainless steels, electrical steels, tool steels, and special alloys required by the chemical, automotive, aircraft, machine-tool, transportation, and food-processing industries. Electric furnaces also are employed, exclusively, by mini-mills, small plants using scrap charges to produce reinforcing bars, merchant bars (e.G., angles and channels), and structural sections. The german-born british inventor sir william siemens first demonstrated the arc furnace in 1879 at the paris exposition by melting iron in crucibles. In this furnace, horizontally placed carbon electrodes produced an electric arc above the container of metal. The first commercial arc furnace in the united states was installed in 1906; it had a capacity of four tons and was equipped with two electrodes. Modern furnaces range in heat size from a few tons up to 400 tons, and the arcs strike directly into the metal bath from vertically positioned, graphite electrodes. Although the three-electrode, three-phase, alternating-current furnace is in general use, single-electrode, direct-current furnaces have been installed more recently.