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Early 20th-century engraving of a gravity cell. Note
the distinctive crowfoot shape of the zinc anode.
The Daniell cell (var. sp. Daniel cell), also
called the gravity cell or crowfoot cell was
invented in
1836
by
John Frederic Daniell, who was a British
chemist and
meteorologist. The Daniell cell was a great improvement over
and is somewhat safer than the
voltaic cell used in the early days of
battery development. The Daniel cell's theoretical
voltage is 1.1 volts and the
chemical reaction is:
- Zn(s) + Cu2+(aq) → Zn2+(aq) +
Cu(s)
The Daniell cell proper consists of a central
zinc anode
dipping into a porous earthenware pot containing
zinc sulphate solution. The porous pot is, in turn, immersed
in a solution of
copper sulphate contained in a
copper can, which acts as the cell's
cathode. The use of a porous barrier prevents the copper
ions in the copper sulphate solution from reaching the zinc
anode and undergoing reduction. This would bring the battery to
equilibrium without it driving a current. In otherwords, it
would make the battery dead.
In the 1860s, a Frenchman named Callaud invented a variant of
the Daniell cell which dispensed with the porous barrier.
Instead, a layer of zinc sulphate sat on top of a layer of
copper sulphate, the two kept separate by their differing
densities. The zinc anode was suspended in the top layer whilst
the copper cathode sat in the bottom layer. A layer of oil was
often added on top to prevent evaporation. This variant was
known as the gravity cell, and sometimes the crowfoot cell due
to the distinctive shape of the electrodes. This arrangement was
less costly for large multicell batteries but could not be moved
and was vulnerable to loss of integrity if too much
electric current was drawn, which would cause the layers to
mix.
External links
Categories:
Electric batteries |
Electrochemistry |
Chemistry stubs
