Conclusions.— Of the many other processes two may be mentioned which employ the prin ciple of bottom electrodes. The Girod furnace makes use of water-cooled metallic electrodes imbedded in the bottom lining of the furnace so that the current actually passes through the charge itself from top to bottom. Greaves-Etchells fdrnace, a fairly modern English process, makes use of the principle of a conductive hearth itself, and no inserted electrodes are used. The entire bottom, after the furnace is once heated, becomes a resist ance conductor and is supposed to produce beneficial results by heating the materials at the bottom of the charge more perfectly Than can be done by an overhead arc furnace, and this advantage is supposed to be most marked in the manufacture of alloy steels, especially those of heavy metals, such as tungsten, which sink through the bath and are apt to lie on the bottom of the furnace without being entirely molten or absorbed by the charge itself. It is difficult to compare the various processes as to their efficiency. In the first place, at no one plant have all of them been tried under uniform conditions and skill of operation. There are so many variables entering into the matter that comparisons can be made only in one or more particulars. For example, the current consumption per ton of product can be readily compared, but unless the furnaces com pared are operating under similar conditions, and on a similar product, the figures are quite valueless. Moreover, in melting a similar qual ity one furnace may require more current than another, simply because the melter refines his steel more perfectly and the kilowatts used may make the difference between well and poorly melted steel. Other variables are the life of the roofs, bottoms, side walls and electrodes, the first cost of the furnace and the quality of construction, and, from the power-house point of view, simplicity and the cost of equipment must be considered, and this involves differ ences of phases, frequency, voltage and power factor. When all of these elements are con sidered, together with ease of operation, it is apparent that it is not simple to give off-hand judgment as to what furnace is best . to use. The time is past when the electric current itself is supposed to confer any mysterious benefits upon the products, but its function is just as stated by Siemens 40 years ago. Various claims are made by inventors depending upon whether the current passes through the bath horizontally or vertically or is merely radiated to the surface. However, it should be remem bered that at the temperature involved molecu lar mobility is very great, and solution and diffusion will take place satisfactorily if the total heat available is sufficient to maintain the enure contents of the bath perfectly fluid.
The electric processes under most careful handling are capable of producing steel approx imately equal to crucible steel, but each process has its peculiar field, and while some crucible tonnage may be diverted to electric steel, yet it is more likely that electric steel will find its own market in the most exacting requirements of steel for structural and tensile properties, such as have come about almost simultaneously with the processes themselves, namely, for the automobile and airplane parts. Crucible steels for these purposes are not commercial because of the difficulty of making very low or medium carbon alloy steels in the crucible and the ton nage demand is far beyond what could be met by the crucible process. The electric furnace was apparently invented to meet a new demand rather than to replace an old process. As one writer has said, "The luxury of to-day is the necessity of to-morrow. Safety cannot be measured by prke, and public opinion will more and more insistently call for the highest excel lence in the automobile, the airplane and other forms of fabricated material." There are now in use in the United States between 300 and 400 electric furnaces of vari ous types, over half of them being of the Heroult design. There are probably as many furnaces altogether in Europe as there are in the United States. The introduction of the process was stimulated amazingly by war re quirements for materials of unusually high grade, and in meeting these requirement! the electric steel makers responded nobly in their contribution to the war program.
Bibliography.—'Report of Commission on Electric Smelting of Iron Ores and the Mak ing of Steel' (Canada 1904) ; Keller, in Journal of the Iron and Steel Institute (Vol. I, p. 161, 1903) ; Louis, H., ib. (Vol. I, p. 40, 1904, upon Herrang briquette process); Haanel, in Journal of the American Chemical Society (vol. p. 921, 1906, upon Heroult pig-iron process); Neumann,in Stahl and Essen (15 June, 1 July and Aug. 1904); also Electrochemical Industry (p. 488, 1904); Engelhardt, V., in Stahl and Eisen (1, 15, Feb. and 1 March 1905, upon Kjellin proc ess); Frick, in lernkontorets Anteater (Vol. LIX, pp. 333-464); Mathews, "Electric Fur nace in Steel Manufacture,' in American Iron and Steel Institute (1916); also 'Comments on the Electric Steel Industry,' in Trans. Ameri can Electrochemical Society (Vol. XXXI, 1917); Robinson, T. W., 'The Triplex Process of Producing Electric Steel,' American Iron and Steel Institute (1918); Rodenhauser, Schoneawa and Vombaur, 'Electric Furnaces in the Iron and Steel Industry.' (2d ed., 1917). The Electrochemical and Metallurgical In dustry (Vols. I, II, III and IV) treats the whole subject fully, including patents, theory and practice.