298 



THE ELECTRIC FURNACE. 



fusion of refractory metals and their ores; consequentl3", once the 

 action is started, electrical contact is estalilished between the lower 

 electrode F and the semimetallic mass in the crucible, and the arc con- 

 tinues to play between the surface of the mass and the movable carljon 

 rod C. As the current through the furnace increases, that through 

 the shunt winding of the solenoid diminishes, and the weight W coming 

 into play causes its end of the beam to descend, thereby raising the 

 negative electrode C and restoring equilil)rium. 



The AVillson furnace is essentiall}' a modification of Siemens's orig- 

 inal form, the solenoid regulation of the upper movable carbon being 

 replaced bv a worm and hand wheel, wdiile the furnace is made contin- 

 uous in op(M-ation l)y the i)rovision of a tapping hole for drawing off 

 the molten products. This type of furnace was employed in the man- 

 ufacture of calcium carbide, which, 

 Avhen drawn off in a molten state, 

 is much purer than the ingot or 

 broken-lump form, in which the 

 greater bidk of that commodity is 

 placed on the market. 



The Parks carbide furnace, de- 

 vised by W. P. Parks, of ('hicago, 

 is of the arc variety and provides for 

 the production of calcium carbide 

 in the molten state. It is repre- 

 sented in fig. 3 and consists of a 

 vertical cylindrical structure F of 

 refractory material, provided with 

 a carbon hearth C, which at the 

 same time acts as the negative elec- 

 trode. It has an annular channels* 

 cut in its upper surface, which latter 

 is flush with the inner floor of F. 

 This chaimcl collects the molten carbide formed, and it drains down, 

 to be ultimately drawn ofl" at A. The upper, positive, electrode B 

 consists of a massive, hollow carbon cylinder, in the lo\Aer half of 

 which, or the portion inside the furnace F, are cut radial slots s s, 

 which subdivide the electrode and tend to set up a circle of arcs 

 around the space bounded b}' the hearth. T T are gas-supply pipes, 

 ending in hydrocarbon burners inside of B, which primarily heat the 

 raw material as it passes down the hollow center of the electrode. 

 The feeding: is eflected from a hopper H by an Archimedean screw 

 working in the casing D. 



An electrolytic furnace, utilized in the separation of alumimuu from 

 a mixture of purified alumina and crj^olite, is that adopted in what is 

 known as the Herault process, which is being worked by the British 



Fig. 3. 



