ELECTRO-METALLURGY.—ALUMINIUM. 
189 
ductor which affords ready egress to the gases disengaged in the operation. The 
furnace is closed by a cast-iron cover pierced with two holes, and the edges of 
which are cemented to exclude the air. To connect the furnace with the circuit 
the moveable leads are brought up, and the lower ends of each fixed to the 
extremities of the piston rods of the electrodes, when the arc springs across the 
charge. 
The circuit includes a rheostat to regulate the strength of the current, which 
is read upon an ammeter under constant observation. First the copper melts, 
the resistance diminishes, and the current rapidly increases ; when it reaches 3000 
amperes it is maintained at that point by manipulation of the electrodes and the 
rheostat; at this moment the electromotive force between the electrodes is 80 
volts, the alumina fuses, then resolves itself into aluminium and oxygen, when 
the charcoal absorbs the oxygen, leaving the fused aluminium to combine with 
the melted copper. This state of things is maintained until'the blue flame in¬ 
dicating the combustion of carbonic oxide appears at the holes of the iron cover; 
then the electrodes and the rheostat are manipulated so as to produce the maximum 
current of 5000 amperes with a potential difference of 60 volts. The operation 
is now finished, having lasted about an hour-and-a-half, and about 50 lbs. of alloy 
are run out. 
A recent improvement gives continuous action ; the hearth itself forms the 
negative electrode, and the positive one consists of a vertical tube in which the 
charge is placed ; a charcoal rammer crossing the tube serves to puddle the molten 
mass. 
The Cowles furnace produces the crude metal, an alloy of copper with 10 to 
30 °/ Q of aluminium and containing silicon, which must be removed by refining; 
with this object the metal is re-melted with fluor spar (calcium fluoride) in a 
graphite crucible, then run out in ingots of about 60 lbs. Bronze as required is 
afterwards formed by fusion in given proportions of copper and ingots of rich 
alloy. 
For silicon-bronze the charge is of :— 
Quartz or sandstone. 
Copper shavings. 
Wood charcoal. 
For ferro-aluminium :•— 
Bauxite. * 1 
Scrap-iron or broken cast-iron. 
Remains of electric carbons. 
Same operations for these as for aluminium bronze. Seventy-seven horse-power- 
hours of energy are expended at Lockport.in the production of 1 kg. of bronze 
aluminium, only 46 with the more powerful machine at Milton. The iron alloy 
is two-thirds more expensive. As in the case of steam engines, the electric effi¬ 
ciency increases with the power of the dynamo. 
The Cowles process only produces alloys, of which the principal are :— 
Aluminium bronze or cupro-aluminium. 
Aluminium brass. 
Silicon-bronze or cupro-silicon. 
Ferro-aluminium. 
Aluminium bronze is made with varying quantities of aluminium, the more 
there is of the latter the harder the alloy. It resists compression, and has a good 
frictional surface which makes it suitable for machine bearings. It is used in the 
United States Navy for the manufacture of screw propellers. 
1 Bauxite, so named from Le Baux, near Arles, where it was first found, contains about 67 0 / o 
of alumina, 25 0 / o of ferro-sesquioxide, 11 °/ 0 of water, 3 % eaclL of silica and titanium oxide, and 
1 °/ 0 °f calcium carbonate.— F.JE.B.L. 
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