Battery, Varley's.
A Daniell battery of the Siemens' and Halske's type (see Battery,
Siemens' and Halske's), in which zinc oxide is substituted for the paper
pulp of the other battery. It has been very little used.
Battery, Volta's.
The original acid battery. It has a negative electrode of copper, a
positive electrode of zinc; the excitant is sulphuric acid diluted with
sixteen times its volume of water. It rapidly polarizes, and is very
little used.
Battery, Voltaic or Galvanic.
An apparatus for converting chemical energy directly into electric
energy. This is as broad a definition as can well be given. The general
conception of a battery includes the action of electrolysis, a solution
in the battery acting upon one of two conducting electrodes immersed in
such fluid, which dissolves one of them only, or one more than the
other. The best way to obtain a fundamental idea of a battery is to
start with the simplest. Dilute sulphuric acid dissolves neither pure
zinc nor copper. But it has a far stronger affinity for the first named
metal. If now we immerse in dilute acid two plates, one of pure zinc,
and one of copper, no action will be discernible. But if the plates are
brought in contact with each other a stream of bubbles of hydrogen gas
will escape from the surface of the copper and the zinc will dissolve.
By applying proper tests and deductions it will be found that the copper
and zinc are being constantly charged with opposite electricities, and
that these are constantly recombining. This recombination produces what
is known as an electric current.
To constitute a battery the zinc and copper plates must be connected
outside of the solution. This connection need not be immediate. Any
conductor which touches both plates will bring about the action, and the
current will pass through it.
The easiest way to picture the action of a battery is to accept the
doctrine of contact action. In the battery the molecules of water are
pulled apart. The hydrogen molecules go to the copper, the oxygen
molecules go to the zinc, each one, leaving its contact with the other,
comes off charged with opposite electricity. This charges the plates,
and the continuous supply of charge and its continuous discharge
establishes the current.
The accumulation of hydrogen acts to stop the action by polarization.
Its own affinity for oxygen acts against or in opposition to the
affinity of the zinc for the same element, and so cuts down the action.
A depolarizer of some kind is used in acid batteries for this reason. As
such depolarizer has only to act upon one plate, in most batteries it is
usual to surround such plate only, as far as it is possible, with the
depolarizer. The solution which dissolves the zinc is termed the
excitant or exciting solution.
To this concrete notion of a voltaic battery the different modifications
described here may be referred. Zinc, it will be seen, forms the almost
universally used dissolved plate; carbon or copper forms the most usual
undissolved plate; sulphuric acid in one form or another is the most
usual excitant.
The solution in a voltaic battery is electrolyzed (see Electrolysis).
Hence the solutions must be electrolytes. The sulphuric acid and other
ingredients play a secondary role as imparting to the battery fluids
this characteristic.
It is not necessary to have electrodes of different substances, the same
metal maybe used for both if they are immersed in different solutions
which act differentially upon them, or which act with more energy on one
than on the other. Such are only of theoretical interest.