The Story of Electricity | Page 9

illustrates this
common type of cell, where Z is the zinc plate in a solution of sulphate
of zinc, and C is the copper plate in a solution of sulphate of copper,
fed by crystals of the "blue vitriol." The wires to connect the plates are
shown at WW. It should be noticed that the zinc is cast like a wheel to
expose a larger surface to oxidation, and to reduce the resistance of the
cell, thus increasing the yield of current. The extent of surface is not so
important in the case of the copper plate, which is not acted on, and in
this case is merely a spiral of wire, helping to keep the solutions apart
and the crystals down. The Daniell cell is much employed in telegraphy.
The Bunsen cell consists of a zinc plate in sulphuric acid, and at carbon
plate in nitric acid, with a porous separator between the liquids. During
the action of the cell, hydrogen, which is liberated at the carbon plate,
is removed by combining with the nitric acid. The Grove cell is a
modification of the Bunsen, with platinum instead of carbon. The Smee
cell is a zinc plate side by side with a "platinised" silver plate in dilute
sulphuric acid. The silver is coated with rough platinum to increase the
surface and help to dislodge the hydrogen as bubbles and keep it from
polarising the cell. The Bunsen, Grove, and Smee batteries are,
however, more used in the laboratory than elsewhere.
The Leclanche is a fairly constant cell, which requires little attention. It
"polarises" in action but soon regains its normal strength when allowed
to rest, and hence it is useful for working electric bells and telephones.
As shown in figure 16, it consists of a zinc rod with its connecting wire

Z, and a carbon plate C with its binding screw, between two cakes M M
of a mixture of black oxide of manganese, sulphur, and carbon, plunged
in a solution of sal-ammoniac. The oxide of manganese relieves the
carbon plate of its hydrogen. The strength of the solution is maintained
by spare crystals of sal-ammoniac lying on the bottom of the cell,
which is closed to prevent evaporation, but has a venthole for the
escape of gas.
The Bichromate of Potash cell polarises more than the Leclanche, but
yields a more powerful current for a short time. It consists, as shown in
figure 17, of a zinc plate Z between two carbon plates C C immersed in
a solution of bichromate of potash, sulphuric acid (vitriol), and water.
The zinc is always lifted out of the solution when the cell is not in use.
The gas which collects in the carbons, and weakens the cell, can be set
free by raising the plates out of the liquid when the cell is not wanted.
Stirring the solution has a similar effect, and sometimes the constancy
of the cell is maintained by a circulation of the liquid. In Fuller's
bichromate cell the zinc is amalgamated with mercury, which is kept in
a pool beside it by means of a porous pot.
De la Rue's chloride of silver cell (fig. 18) is, from its constancy and
small size, well adapted for medical and testing purposes. The "plates"
are a little rod or pencil of zinc Z, and a strip or wire of silver S, coated
with chloride of silver and sheathed in parchment paper. They are
plunged in a solution of ammonium chloride A, contained in a glass
phial or beaker, which is closed to suppress evaporation. A tray form of
the cell is also made by laying a sheet of silver foil on the bottom of the
shallow jar, and strewing it with dry chloride of silver, on which is laid
a jelly to support the zinc plate. The jelly is prepared by mixing a
solution of chloride of ammonium with "agar-agar," or Ceylon moss.
This type permits the use of larger plates, and adapts the battery for
lighting small electric lamps. Skrivanoff has modified the De la Rue
cell by substituting a solution of caustic potash for the ammonium
chloride, and his battery has been used for "star" lights, that is to say,
the tiny electric lamps of the ballet. The Schanschieff battery,
consisting of zinc and carbon plates in a solution of basic sulphate of
mercury, is suitable for reading, mining, and other portable lamps.
The Latimer Clark "standard" cell is used by electricians in testing, as a
constant electromotive force. It consists of a pure zinc plate separated

from a pool of mercury by a paste of mercurous proto-sulphate and
saturated solution of sulphate of zinc. Platinum wires connect with the
zinc and mercury and form the poles of the battery, and the mouth of
the glass cell is