By GEORGE LEUCHS.
The Leclanche battery is distinguished for its simplicity, its small
internal resistance (0.7 to 1.0 Siemens unit), and that all chemical
action ceases when the current is broken, that it is not sensitive to
external influence, and by the self-renewal of the negative electrodes.
But on the opposite side the action is not very great (= 1.20 or 1.48
D.), and the zinc as well as the sal ammoniac are converted into
products that cannot be utilized.
I replace the solution of sal ammoniac by one of caustic potash or
soda (12 to 15 per cent.), and the thin zinc rods by zincs with larger
surfaces. In this manner, I obtain a powerful and odorless battery,
having all the valuable qualities of the Leclanche, and one that
permits of a renewal of the potash solution as well as of the negative
electrode.
The electromotive power of this element may be as high as 1.8 D. The
same pyrolusite (binoxide of manganese) cylinder used with the same thin
rod of zinc will precipitate 75 per cent. more copper from solution in
an hour when caustic potash is used than when sal ammoniac is employed.
But by replacing the thin zinc rod by a zinc cylinder of large surface,
2½ times as much copper is precipitated in the same time.
The more powerful action of such a pair is explained by the stronger
excitation and more rapid regeneration that the negative electrodes
undergo from the oxidizing action of the air in the potash solution, as
well as by the fact that this solution is a better conductor than the
sal ammoniac solution. The potash solution does not crystallize easily,
hence the negative electrode remains free from crystals and does not
require filling up with water. Zinc dissolves only while in contact
with negative bodies, hence there is no unnecessary consumption of zinc
either in the open or closed circuit.
When the potash lye has become useless, I regenerate it by removing the
zinc in the following manner: I pour the solution from the cells, put
it in a suitable vessel, where I add water to replace that already
evaporated, and then shake it up well at the ordinary temperature with
hydrated oxide of zinc (zincic hydrate). Under this treatment the
greater portion of the zinc that had been chemically dissolved by the
potash is precipitated in the form of zinc hydrate, along with
some carbonate. The liquid is now allowed to settle, and the clear
supernatant solution is poured back again into the battery cells. The
battery has rather greater electromotive force when this regenerated lye
is used, because certain foreign matters from the carbon, like sulphur,
chlorine, sulphuric acid, etc., are removed by this treatment.
The regeneration of the (brown coal) carbon goes on of itself, beneath
the lye, through the oxidizing action of the atmospheric air; it is
advantageous to have a part of the carbon sticking out of the liquid. Of
course the regeneration takes place much more quickly if the electrodes
are taken out and exposed to the air. In this case the carbon electrode
need not be very thick, and can be flat or of tubular form. In the
former case it must have a large volume, and the massive cylindrical
form is recommended. The zinc electrode must be kept covered deeply with
potash. The cells must have free access of air, and the potash must be
replaced as soon as it is exhausted.--_Chem. Zeit_.
* * * * *
[Concluded from SUPPLEMENT No. 390, page 6217.]
THE CAUSE OF EVIDENT MAGNETISM IN IRON, STEEL, AND OTHER MAGNETIC
METALS.
[Footnote: Paper lately read before the Society of Telegraph Engineers
and Electricians.]
By Professor D. E. HUGHES, F.R.S., Vice-President.