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 ment for applying electric heat has had a more spectacular success in the industrial world than the electric furnace, of which there are several varieties, some working on the arc principle and some on the resistance principle. Among the main uses of the electric furnace are the melting and the heat-treatment of metals. In the iron and steel industry, for example, a high grade of pig iron is produced by the use of the electric furnace in place of the blast furnace. A much more important application, however, is in the making of steel. In the electric furnace, the charge is melted in a closed chamber. There is no oxidation, no contamination from fuel gases, and the temperature can always be perfectly controlled. Thus, steel of crucible quality can be made much more rapidly than by the crucible process. The electric furnace is used especially for making the various alloy steels, and for super-refining steel made by the open-hearth and Bessemer processes. It is also widely used in melting steel for castings. Lastly the electric-heat-treatment furnace provides a far more perfect control of temperatures than any fuel-heated furnace, and is therefore the ideal means of annealing, hardening and tempering metal.



The triumph of electric steel dates essentially from the year 1915, when the demand for high-grade steel was greatly stimulated by the requirements of warfare. Since that time, electric heat has come into extensive use for the melting and heat treatment of brass and other nonferrous metals. In a long list of metallurgical operations, electricity introduces the exactness of laboratory practice into the workshop and at the same time minimizes the need of skilled labor.

The most romantic feats of the electric furnace are those achieved by the use of temperatures unattainable by fuel-heated furnaces, as, for example, in the manufacture of artificial abrasives and in the fixation of atmospheric nitrogen. Carborundum, of which thousands of tons are produced annually at Niagara, owes its existence entirely to electric heat. All the aluminum made in the world is produced in electric furnaces. The same is true of calcium carbide, calcium cyanamide, alu-