SMELTING ORES BY ELECTRICITY 



shafts communicate with each other at their bases by a 

 laternal canal, also lined with a refractory material, which 

 forms a basin or reservoir for the molten metal while 

 accumulating. The metal can be tapped off from this 

 reservoir after the slag has been withdrawn from tap-holes, 

 one at the base of each shaft, at a higher level than the 

 tap-hole of the reservoir. The base of each shaft is pro- 

 vided with a carbon block and these blocks are connected 

 outside the furnace by a copper conductor, so that the 

 electric circuit is not broken when the molten metal is 

 being tapped out. The two electrodes are supported one in 

 each shaft, and are connected, one to each side of the 

 supply circuit. They extend vertically downward about 

 two-thirds of their length into the shafts. The charge, 

 crushed to pass through a two-inch ring, is fed in around 

 each electrode from the tap, and as it melts and descends it 

 may be renewed continuously. In starting, the charge is 

 introduced between the carbon-base block and the electrode 

 on each side. The current passes from the electrode to 

 the charge, to the carbon block, through the external 

 copper conductor to the other carbon block, to the charge 

 in the second shaft and to the second electrode. The 

 resistance offered to the current produces heat in the 

 charge which begins to melt, runs down into the reservoir 

 and soon conducts the current internally to tlie second 

 electrode. This continues until only a very small percent- 

 age of the current passes through the external copper 

 shunt. 



The electrodes are gradually raised to their normal 

 position, and the charge is renewed until the space between 

 the carbon blocks and the electrodes, and between the 

 electrodes and the sides of the shafts are completely 

 occupied by the charge. The ingenious application of the 

 external copper shunt permits the continuous operation of 

 the furnace without excessive variation of the load upon 

 the alternator. The electrodes are approximately 3.3" 



