TUANSACTIONS OF SECTION B. 539 



The production of these works is 2,300 lbs. aluminium bronze (10 per cent.), 

 and 1,800 lbs. ferro-alumiuium (10 per cent.), per 24 hours, or 410 lbs. of con- 

 tained aluminium. 



The furnaces are rectangular in form, and are of firebrick ; into each end is 

 built a cast-iron tube, through which the carbon electrodes enter the furnace; each 

 electrode consists of a bundle of nine carbons, each '2\ inches diameter, attached to 

 a head of cast iron for a ferro-aluminium furnace, and of cast copper for alu- 

 minium 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 position opposite the furnaces to be used. The elec- 

 trodes are arranged 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 diiliculty has been overcome 

 by soaking the charcoal in lime-water and carefully drying before use ; each par- 

 ticle 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 fit over 

 the electrodes, is inserted ; charcoal is then rammed into the space between it and 

 the firebrick walls. This done, the charge of ore, mixed with coarse charcoal and 

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

 placed inside the iron box, after which this is carefully withdrawn ; the space be- 

 tween the electrodes is bridged by some broken pieces of carbon, the charge is 

 covered with coarse charcoal, and the furnace closed by a heavy cast-iron cover, 

 having a hole in the centre 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 1^ 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 furnaces 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 assaj'Cd for aluminium. The nature of the reaction that takes place in the 

 electric furnace is not very easy to ascertain ; the conditions are unlike those of any 

 other known : the reduction of the aluminium taking place in absence of air and in 

 presence of an enormous excess of carbon, it maj- be assumed that, at the intense 

 heat of the electric arc, the ore melts and gives up its oxygen to the carbon : — 



ALOa + 3C = 3C0 + Al,. 



In absence of copper, the liberated aluminium 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. 



The most valuable of the alloys are those with copper. 



Aluminium bronze has great tensile strength. A bar containing ll'O per cent, 

 aluminium, made by tlie electric furnace, and tested by the Leeds Forge Co., Lim., 

 gave a tensile strain of 57*27 tons, or 128,400 lbs. to the square inch. One con- 

 taining 7-5 per cent, aluminium, tested by Professor Uuwin, broke under 3678 

 tons = 89,743 lbs. to the square inch. In /■('.•li.itance to compressio)i this alloy equals 

 the best steel ; its fran.'^i-prae streiir/t/i, or rigidity, is about forty times greater than 

 ordinary brass. Its elastic limit is higher than that of mild steel, and it can be 

 worked at a bright red heat as easily as wrought iron. 



Its mechanical and physical properties render it useful for every variety of 

 metal work, its high price only having hitherto restricted its use. Its enormous 

 strength and anticorrodible qualities recommend it as valuable above any other alloy 

 for piopeller blades, stern and rudder frames, and for hydraulic and engineering 

 work generally. 



