196 
ELECTROMETALLURGY.—ALUMINIUM. 
value approximating to tliat of the electromotive force of the voltaic arc, about 
40 volts. 
The Saint-Michel factory, in addition to the metals already mentioned, manu¬ 
factures a new alloy with the following composition:— 
Aluminium .85 to 88 
Silicon ... 5 to 4 
Iron .10 to 7 
This alloy is to take the place of ferro-silicon and ferro-silico-manganese in the 
metallurgy of steel. It is produced by substituting in the bath bauxite for pure 
alumina. 
Theoretically some idea can be obtained beforehand of the most advantageous 
conditions of the electrolytic process, and of its result as follows :— 
Let P be the actual weight in grams of Al. obtained in 0 seconds, a the 
electrochemical equivalent of Al. in grams per coulomb, I the strength of the 
current in amperes, then the theoretical weight of Al. which should be obtained 
P 
will be a I 0, and the economic co-efficient n =■ — y~(Y 
In practice it is only with difficulty that n can be made equal to '8. The loss 
is partly due to the decomposition of the sodium salts in the bath : advantage 
would therefore accrue from the lowering of the difference of potential below the 
minimum electromotive force required for their decomposition. From the above 
values we obtain 
(1) P = nal0 grams ; 
the weight of Al. is therefore proportional to the current strength, hence the 
latter should be as high as possible. In practice, as we have seen in the fore¬ 
going pages, it has been constantly on the increase. 
The work W done by the current in the bath is 
(2) W = kilogram-metres. 
9 
The electrical efficiency is obtained from equations (1) and (2) thus :— 
(3) 
P nag 
and (4) P = W. !L| 1 
From (8) we see that this ratio is independent of the current strength, and 
increases inversely as the electromotiye force. 
From (4) we can calculate the weight of Al. produced by an energy in the 
bath equivalent to one horse-power-hour. Let us take as economic co-efficient 
n — ’ 8, and a weak electromotive force JE = 4 volts, then we have the following 
values, taking the kilogram as the unit of weight:— 
75 x 8600 kg. 1 * 3 
*095 
a = —(in kgs. per coulomb). 
Accordingly with an energy of 1 horse-power-hour expended in the bath we 
have 
p 75 X 3600 x *8 x ‘095 X 9*83 
P = --= -05027 kgs. of Al. 
1 1 horsepower = 76 kgs. per second. 
= 75 x 3600 kgs. per hour. 
Faraday established the law that “ the quantities of different electrolytes decomposed by the 
same quantity of electricity are directly as their electrochemical equivalents.— F.B.JB.L. 
3 g = 9-8 metres, per sec. 
