308 



THE ELECTEIC FUKNACE. 



The experience of late years in the construction and use of electric 

 furnaces trends toward the establishment of the resistance furnace as 

 a t} pe more readil}- capa])le of efficient reg'ulation. This is further 

 accentuated by the fact that overheating is, to a considerable extent, 

 possible, and, indeed, prevalent in many types of furnace, especially 

 those of the ai'c variety. Scientists and others unversed in the possi- 

 bilities of the electric furnace as a source of artilicial heat hailed its 

 introduction with delight as a means of overcoming many of the diffi- 

 culties previoush' imposed l)y the limitations of temperature. In so 

 doing they in man}' cases overlooked the very simple fact that it is 

 possible to have too much of a good thing, and the consequent tend- 

 ency was to overrate rather than underrate the temperature required 

 for various commercial processes. 



Experience, however, has exposed this fallacy, and as a natural result 

 w^e turn to that type of furnace which otters the best means of regula- 

 tion and the absence of excessive variation, viz, the resistance furnace. 



Here again we are beset with fur- 

 ther difficulties, for if we emplo}' 

 a portion of the charge itself as a 

 high-resistance column, excessive 

 variations creep in, ownng to the 

 changeable nature of the column 

 with the reactions taking place 

 within it, whereas if we employ a 

 detinitecoreof small cross section, 

 as in the Borchevs class, the capac- 

 ity of the furnace is limited, and 

 the cost of its upkeep is increased 

 by the very necessary and frequent renewal of the conducting rods. 

 With a view to minimizing these various draw])acks, Mr. H. I. 

 Irvine, of Niagara Falls, has brought out a resistance furnace in Avhich 

 the heated column consists of a fused electrolyte, n)aintained in a state 

 of fusion by the passage of the current and comnmnicating its heat by 

 radiation and diffusion to the encircling charge which is packed 

 around it. 



The general construction of this furnace, which was mainly designed 

 for the manufacture of ])hosphorus, is represented in tig. K!. It con- 

 sists of a refractory structure F, lined with carbon C, and fitted with a 

 domed roof R, in the center of Avhich is a hopper H. Two vertical 

 car>)on electrodes B B descend vertically through R to within a short 

 distance of the hearth, whilst a possible variation in the direction of 

 the heating effect is provided b}^ lateral electrodes h h, connected with 

 the hearth itself. The action of the furnace is tirst started through a 

 mass of coke K, which forms a bridge between the electrodes B B, and 

 is subsequently maintained by the fused slag from the furnace charge 



Fig. 16. 



