726 ALUMINUM. 



enter the furnace; each electrode consists of a bundle of nine car- 

 bons, each 2^ inches diameter, attached to a head of cast-iron for a 

 ferro aluminum furuace and of cast copper for aluminum bronze or 

 alloys containing copper. This head is secured to copper rods, or 

 " leads," which can be readily connected with or disconnected from the 

 flexible cables supplying the current. Each cable is secured to slides 

 travelling on an omnibus bar of copper overhead, and so can be brought 

 into i)Ositiou opposite the furnaces to be used. The electrodes are ar- 

 ranged so that it is possible by means of a handle and screw to advance 

 or withdraw them from each other in the furnace. 



The first furnaces were lined with charcoal, but it was found that the 

 intense heat converted it into graphite, which, being a conductor, not 

 only meant loss of power, but the destruction of the furnace walls. This 

 difficulty has been overcome by soaking the charcoal in lime-water and 

 carefully drying before use; each particle of charcoal is thus coated 

 with an insulating shell of lime. 



Lining the furnace is the first operation ; the bottom of the trough 

 is covered with a layer of prepared charcoal, the electrodes are arranged 

 in the furnace, and a "former," a sheet-iron box without top or bottom, 

 each end being arched to tit over the electrodes, is inserted; charcoal 

 is then rammed into the space between it and the fire-brick walls. 

 This done, the charge of ore, mixed with coarse charcoal and the metal 

 to be alloyed with the aluminum, in form of turnings or granules, is 

 placed inside the iron box, after which this is carefully withdrawn ; the 

 space between the electrodes is bridged by some broken pieces of car- 

 bon, the charge is covered with coarse charcoal, and the furnace closed 

 by a heavy cast iron cover having a hole in the center for the escape of 

 gases evolved during the reaction ; the cover is luted so as to prevent 

 the entrance of air. 



The commencing current is about 3,000 amperes, and is gradually 

 increased to 5,000 amperes ; a " run " occupies about one and one-half 

 hours. The furnace is allowed to cool ; the next, ready charged, is con- 

 nected with the cables so that the process is a continuous one, the fur- 

 naces being successively charged and connected. The crude metal from 

 the furnace is then re-melted in an ordinary reverberating furnace, a 

 sample being taken from each run and assayed for aluminum. The 

 nature of the re-action that takes place in the electric furuace is not very 

 easy to ascertain ; the conditions are unlike those of any other process 

 known. The reduction of the aluminum taking place in absence of air 

 and in presence of an enormous excess of carbon, it may be assumed 

 that at the intense heat of the electric arc, the ore melts and gives up 

 its oxygen to the carbon : 



Al203+3C=3C04-Al2. 



In the absence of copper, the liberated aluminum absorbs carbon and 

 is converted into a carbide of the metal. The escaping gas which burns 

 at the orifice in the cover is almost entirely composed of CO. 



