The researches of M. Gaston Planté on the polarization of voltameters
led to his invention of the secondary cell, composed of two strips of
lead immersed in acidulated water. These cells accumulate, and, so to
speak, store up the electricity passed into them from some outside
generator. When the two electrodes are connected with any source of
electricity the surfaces of the two strips of lead undergo certain
modifications. Thus, the positive pole retains oxygen and becomes
covered with a thin coating of peroxide of lead, while the negative pole
becomes reduced to a clean metallic state.
Now, if the secondary cell is separated from the primary one, we have a
veritable voltaic battery, for the symmetry of the poles is upset, and
one is ready to give up oxygen and the other eager to receive it. When
the poles are connected, an intense electric current is obtained, but
it is of short duration. Such a cell, having half a square meter of
surface, can store up enough electricity to keep a platinum wire 1
millim. in diameter and 8 centims. long, red-hot for ten minutes. M.
Planté has succeeded in increasing the duration of the current by
alternately charging and discharging the cell, so as alternately to
form layers of reduced metal and peroxide of lead on the surface of the
strip. It was seen that this cell would afford an excellent means for
the conveyance of electricity from place to place, the great drawback,
however, being that the storing capacity was not sufficient as compared
with the weight and size of the cell. This difficulty has now been
overcome by M. Faure; the cell as he has improved it is made in the
following manner:
The two strips of lead are separately covered with minium or some other
insoluble oxide of lead, then covered with an envelope of felt, firmly
attached by rivets of lead. These two electrodes are then placed near
each other in water acidulated with sulphuric acid, as in the Planté
cell. The cell is then attached to a battery so as to allow a current
of electricity to pass through it, and the minium is thereby reduced to
metallic spongy lead on the negative pole, and oxidized to peroxide of
lead on the positive pole; when the cell is discharged the reduced lead
becomes oxidized, and the peroxide of lead is reduced until the cell
becomes inert.
The improvement consists, as will be seen, in substituting for strips
of lead masses of spongy lead; for, in the Planté cell, the action is
restricted to the surface, while in Faure's modification the action is
almost unlimited. A battery composed of Faure's cells, and weighing 150
lb., is capable of storing up a quantity of electricity equivalent to
one horsepower during one hour, and calculations based on facts in
thermal chemistry show that this weight could be greatly decreased. A
battery of 24 cells, each weighing 14 lb., will keep a strip of platinum
five-eighths of an inch wide, one-thirty-second of an inch thick, and 9
ft. 10 in. long, red-hot for a long time.
The loss resulting from the charging and discharging of this battery is
not great; for example, if a certain quantity of energy is expended in
charging the cells, 80 per cent. of that energy can be reproduced by the
electricity resulting from the discharge of the cells; moreover, the
battery can be carried from one place to another without injury. A
battery was lately charged in Paris, then taken to Brussels, where it
was used the next day without recharging. The cost is also said to be
very low. A quantity of electricity equal to one horse power during an
hour can be produced, stored, and delivered at any distance within 3
miles of the works for 1½d. Therefore these batteries may become useful
in producing the electric light in private houses. A 1,250 horsepower
engine, working dynamo-machines giving a continuous current, will in one
hour produce 1,000 horse-power of effective electricity, that is to
say 80 per cent. of the initial force. The cost of the machines,
establishment, and construction will not be more than £40,000, and the
quantity of coal burnt will be 2 lb. per hour per effective horse-power,
which will cost (say) ½d. The apparatus necessary to store up the force
of 1,000 horses for twenty-four hours will cost £48,000, and will weigh
1,500 tons. This price and these weights may become much less after a
time. The expense for wages and repairs will be less than ¼d. per hour
per horse-power, which would be £24 a day, or £8,800 a year; thus the
total cost of one horse-power for an hour stored up at the works is
¾d. Allowing that the carriage will cost as much as the production and
storing, we have what is stated above, viz., that the total cost within
3 miles of the works is 1½d. per horse-power per hour. This quantity of
electricity will produce a light, according to the amount of division,
equivalent to from 5 to 30 gas burners, which is much cheaper than
gas.--_Chemical News_.
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