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BELL SYSTEM TECHNICAL JOURNAL 



hearth furnace, in which pig-iron and scrap are refined and ferro-siUcon 

 added. The furnace capacity may be as large as 100 tons. Sometimes siUcon- 

 iron, and usually iron-nickel alloys, are melted in the arc furnace, in 

 amounts varying from a few tons to 50 tons. A photograph of such a fur- 

 nace, in the position of pouring, is shown in Fig. 11. The heat is produced 

 in the arc drawn between large carbon electrodes immersed in the metal, 

 the current sometimes rising to over 10,000 amperes. By tipping the fur- 

 nace the melt is poured into a ladle, and from this it is poured into cast-iron 

 molds through a valve-controlled hole in the ladle bottom. Special-purpose 

 alloys, including permanent magnets, are prepared commercialh^ in high- 



Table II 

 Heats of Formation and Other Properties of Some Oxides {Sachs and Van Horn'^) 



* Sublimes. 



** Decomposes before melting. 



frequency induction furnaces or in arc furnaces in quantities ranging from a 

 fraction of a ton to several tons. 



Slags are commonly used when melting in air, both to protect from oxi- 

 dation and to reduce the amounts of undesirable impurities. Common pro- 

 tective coverings are mixtures of lime, magnesia, silica, fluorite, alumina, 

 and borax in varying proportions. In commercial production different slags 

 are used at different stages, to refine the melt; e.g., iron oxide may be used 

 to decarburize and basic oxides to desulfurize. 



Melting in vacuum requires special technique that has been described in 

 some detail by Yensen.^ Commercial use has been described by Rohn^ and 

 others.' Melting in hydrogen has been used on an experimental scale in both 



•T. D. Yensen, Trans. A.I.E.E. 34, 2601-41 (1915). 



2 VV. Rohn, Heraeus Vacuumsclimelze, Alberlis, Hanau, 356-80 (1933). 



nV. Hessenbruch and K. Schichlel, Zeits. f. Metallkunde 36, 127-30 (1944). 



