ON THE PRESENT POSITION OF ELECTRIC STEEL MELTING. 263 



small in comparison. If the resistance be a solid or a liquid, then it is 

 called resistance-heating; if a gas, arc-heating. If the liquid through 

 which the current passes is decomposed by the current so that one 

 kind of matter goes to one pole and another kind to the other pole the 

 liquid is called an electrolyte. 



Varieties of Electric Furnaces. 

 The Stassano furnace is an independent arc furnace. Three carbon 

 electrodes are used, between which arcs play, and the heat from the 

 arc is merely used for heating the charge, partly by direct radiation 

 and partly by reflection from the dome of the furnace. 



The Heroult steel-melting furnace is a direct arc type, in which the 

 charge forms one pole of the arc. Two vertical carbon electrodes come 

 through the roof of the furnace and two arcs play, one between each 

 electrode and the molten metal or slag beneath it, the current passing 

 from one electrode through the metal or slag and up through the other 

 electrode. 



The Girod furnace, like the Heroult, is a direct arc furnace, but one 

 or more electrodes of like polarity are maintained above the bath, and 

 soft steel pieces embedded in the hearth of the furnace are in direct con- 

 tact with the molten metal for the negative electrode. These lower 

 pole-pieces are water-cooled. Large quantities of ferro-silicon, ferro- 

 chrome, &c, as well as of ordinary carbon and special steels are made in 

 this furnace. 



The Keller steel furnace is a direct arc furnace, very much like the 

 Heroult, only instead of two electrodes coming down into one cavity 

 they come into separate cavities which are joined by the molten material 

 of the bath. 



The Gronwall is of the arc type and the current enters by two 

 electrodes through the roof, and when once the bath is heated so that 

 the lining becomes a conductor the current from both electrodes 

 passes though the lining to a graphite block underneath, and hence 

 to a common wire. 



The Nathusius, like the Gronwall, is a combined arc and resistance 

 furnace. It contains three vertical carbon electrodes, arranged at the 

 apices of an equilateral triangle, and three steel electrodes similarly 

 arranged in the bottom of the furnace but covered by refractory 

 material. Three-phase current is used and it is claimed that the current 

 flows from one top electrode to the others, from one bottom electrode to 

 the others, and from each top electrode to each bottom electrode. 



Kjellin Induction Furnace. — In this furnace, an example of which is 

 in the Metallurgical Laboratory of the University of Sheffield and was 

 shown working to the members of the British Association, the metal 

 charge is placed in an annular hearth, almost like a steel-melting 

 crucible in section, but in the form of a ring. The primary coil of 

 twenty-four turns is placed in the centre round a core of laminated 

 iron. The bath or ring of metal acts as a secondary circuit of a single 

 turn and the heat is thus produced in the charge itself without contact 

 with electrodes. In the Frick furnace the primary coil is above the 

 crucible, and in the Colby round the outside of the crucible. 



The Kochling-Bodenhauser furnace is based on the Kjellin principle 



