Thus, in the simple cell under consideration the sulphuric acid, by
dissociation, splits up into hydrogen ions bearing positive charges,
and SO_{4} ions bearing negative charges. The solution as a whole is
neutral in potential, having an equal number of equal and opposite
charges.

[Illustration: Fig. 60. Simple Voltaic Cell]

It is known that when a metal is being dissolved by an acid, each atom
of the metal which is torn off by the solution leaves the metal as a
positively charged ion. The carrying away of positive charges from a
hitherto neutral body leaves that body with a negative charge. Hence
the zinc, or _consumed_ plate, becomes negatively charged.

In the chemical attack of the sulphuric acid on the zinc, the positive
hydrogen ions are liberated, due to the affinity of the negative
SO_{4} ions for the positive zinc ions, this resulting in the
formation of zinc sulphate in the solution. Now the solution itself
becomes positively charged, due to the positive charges leaving the
zinc plate with the zinc ions, and the free positively charged
hydrogen ions liberated in the solution as just described are repelled
to the copper plate, carrying their positive charges thereto. Hence
the copper plate, or the _unconsumed_ plate, becomes positively
charged and also coated with hydrogen bubbles.

The plates or electrodes of a voltaic cell need not consist of zinc
and copper, nor need the fluid, called the _electrolyte_, be of
sulphuric acid; any two dissimilar elements immersed in an electrolyte
that attacks one of them more readily than the other will form a
voltaic cell. In every such cell it will be found that one of the