306 



THE ELECTRIC FURNACE. 



retort or crucible lined throug'hout with car])on C, forminj^ one elec- 

 trode, the other being a massive carbon block of rectang-idar section 

 B, which is supported at the center of the retort, and is of such 

 dimensions that its corners approach very closely to the inner carbon 

 walls of that vessel. The raw material is fed in at hoppers on either 

 side of B, their position being- indicated by the circles a and h. While 

 working the crucible and its contents revolve, thus constantly bring- 

 ing fresh portions of the mass within the zone of activity, while by a 

 carefully proportioned train of gearing the electrode B is gradually 

 raised at such a rate that its lower extremity is always immersed at a 

 constant deptli in the mass under treatment, Avhile an ingot of finished 

 carbide is graduall}' ])uilt up ])eneath it in the crucible. 



A series of patents have been recently granted in the United States 

 on electric furnaces for the manufacture of such comminuted products 

 as pigments, al)rasives, oxides, refined metals, and a miscellaneous 

 collection of similar character. The general arrangement consists of 

 an arc or resistance furnace, with which is combined an air blast 

 device, playing either inuiiediately onto the furnace contents or upon 



the vapors arising from it. An ex- 

 ample will serve to demonstrate the 

 general principle involved. 



Fig. l-t represents a furnace of this 

 description, devised by C. S. Lomax 

 and patented as recently as March, 

 1902. It is intended for the manufac- 

 ture of the various couunercial oxides 

 of lead and tin. A refractory l)lock F has a narrow channel <• cut in 

 its upper surface; this constitutes the hearth of the furnace, and is of 

 uniform cross section for about the center third of its length. At each 

 extremity it merges into a deeper and wider wedge-shaped cavity, in 

 either of which is placed, vertically, an electrode; T is a main, supply- 

 ing cold or heated air to the discharge jets t t, which are set at such an 

 angle that the air emerging from them is projected downward into the 

 central trough or channel; L is a cover or screen which collects the 

 products and guides them into the chamber 11. 



The mode of procedure is exceedingly simple. The channel c, 

 together with its enlarged ends, is filled with the molten lead or tin to 

 be converted; the current is turned on, and that portion of the molten 

 colunni bounded by the narrow central channel innnediately attains 

 a considerable temperature, owing to its smaller cross section. When 

 the i-equired heat has been reached the air blast is brought into play, 

 causing the finely divided metallic particles to combine with its oxygen, 

 the resulting compound being carried over into the chamber R. This 

 form of furnace is adaptable to making a variety of oxides, the neces- 

 sary changes in chemical combination being brought about by A^arying 

 the respective temperatures of the air blast and the molten metal. 



