184 
ELECTRO-METALLURGY.—ALUMINIUM. 
It must be admitted that tbe apparatus and procedure employed in the beating 
of metals are imperfect; they are entirely empiric, and left usually to the dis¬ 
cretion of the simple workman. Electricity will doubtless in the future admit of a 
sensible improvement by affording in conjunction with heat a measure and regula¬ 
tion of the calorific energy brought into play. Already some attempts appear to 
have been made in the United States to anneal metallic wires, and to heat springs 
by the passage of a current before hardening them. Electric welding has also 
been employed in the fabrication of iron wheels and forged steel shell, also for 
rails and the felloes of velocipedes. Professor Elihu Thompson employs currents 
up to 100,000 amperes, with a feeble electromotive force, below one volt, which 
he obtains by the aid of induction transformers. He has been able to weld 
directly metals such as German silver and platinum, which have hitherto resisted 
that operation without the aid of another metal. 
ELECTBIC EUSION. 
In the present metallurgical hearths the calorific intensity obtainable is some¬ 
what limited ; the mean temperatures measured with an optical pyrometer by M. 
H. Le Chatelier were the following :—• 
Cent. Fah. 1 % 
Blast furnace (with tuyeres) ... . 1900° or 3452° 
Bessemer converter . .. 1600° „ 2912° 
Martin-Siemens furnace .... 1550° „ 2822° 
It is difficult in a blast furnace to produce alloys of iron rich in chromium or 
tungsten, which however are matters of pregnant interest. We are far from 
attaining the temperatures of the combustion of gases burnt in the laboratory, 
for combustion in an industrial hearth is a complex phenomenon on account of 
the multiplicity of elements which form its atmosphere. After a certain limit 
is passed there is dissociation , the calorific energy produced has to perform 
molecular work, and in consequence the temperature can no longer increase. 
The electric current gives much higher limits : M. H. Le Chatelier has measured:— 
Cent. 
At the positive carbon point of an arc lamp 4000° 
„ negative „ „ ,, „ „ 3000° 
The voltaic arc can therefore be advantageously applied to the fusion of even 
the most refractory metals. In the electric furnace of M. H. Moissan, lime, 
strontia, and magnesia are rendered liquid like water, and metals believed to be 
infusible, such as tungsten and molybdenum, are obtained in a molten state ; 
even silicon, the most refractory element in an ordinary furnace, has been 
volatilized. 
We must go back to 1878 for the first industrial application of electric fusion 
made by W. Siemens for platinum. He conceived the idea of a cast-iron crucible 
with fire-proof lining, pierced at a third of its height by two opposite openings 
for the admission of the electrodes. The regulator of the voltaic arc thus formed 
was a mechanism set in motion by a bucket-wheel, worked by a stream of water 
or fine sand, and which was regulated by an electro-magnet placed as a shunt 
across the principal circuit. Since these first attempts electric furnaces have 
been developed, especially for the production of aluminium. We will first men¬ 
tion the best known of these, then consider them further in detail. 
To avoid the wear and tear of electrodes Mr. W. Maxwell places the crucible 
itself between the two electrodes placed one above the other. In Barker’s 
electric furnace several rows of large electrodes are arranged in one mass in 
refractory bricks, and underneath each of them a secondary moveable electrode 
serves to start the arc and to partially raise the metallic mass to a red heat, 
