THE ELECTEIC FURNACE. 



307 



Ruthenl)urg's electro-magnetic furnace is another practical example 

 of the proverb "Necessity is the mother of invention." One of the 

 purest sources for the extraction of metallic iron is ''iron sand" and 

 similar ores, the process of treating- which has hitherto been hampered 

 b}" their finely divided state and consequent clogging of the smelting 

 furnaces. Ruthenburg's invention has in view the preliminary agglom- 

 eration of this sand, with the object of thus converting it into a form 

 more suitable for the ordinary operation of smelting. 



His furnace is represented in fig. 15, and consists of two similar 

 cast-iron hoppers H H, hinged together at the point of support a, and 

 into which the iron sand is fed at equal rates. The discharge orifices 

 o o are opposite to each other, and the distance between them can be 

 varied at will by the handwheel and worm W. The two hoppers con- 

 stitute the electrodes, terminal con- 

 nection with them being secured as 

 shown at f t^ where the discharge noz- 

 zles are also water jacketed; C C are 

 magnetizing coils encircling the hop- 

 pers and having their windings con- 

 nected either in series with or in shunt 

 across the hoppers. Their office is 

 to magnetize the individual particles 

 of the sand, causing them to adhere 

 together temporarily, and thus assist 

 in forming a self-supporting mass M 

 across the discharge apertures. This 

 mass is subjected to the maximum 

 heating effect, and the semimolten 

 prt)duct drops away into the crucible 

 R, placed to receive it. 



A novel t^'pe of resistance furnace, 

 patented independently, with some 

 slight variation of detail, by Colby, l^Vrranti, and Kjellin, is worked 

 on the inductive principle, and consists of an anmilar or helical 

 channel in a refractor}^ l)ase, filled with a conducting or semiconduct- 

 ing medium, which constitutes the furnace charge, and has a heavy 

 current induced in it l)y a surrounding coil of many turns, carry- 

 ing an alternating current. The device, in point of fact, acts as the 

 closed circuit secondary of a step-down transformer, and is said to 

 be admirably adapt*^! foi- the fusing of such metals as platiiuun, 

 which, if exposed to the atmosphere during the |)r()cess, as in the 

 ordinary type of furnace, occlude ox3'gen and other gases in their 

 mass, which lead subseijuently to blowholes and other imperfections 

 in the casting. The Kjellin furnace princi})le has recently been 

 applied to the manufacture of steel at Gj^singe, Sweden, with great 

 success. 



Fig. 15. 



