If we take two plates of different kinds of metal, platinum (or copper)
and zinc for example, and immerse them in pure water, having wires
attached to them above, then if the wire of each is brought into
contact in another vessel of water, a galvanic circle will be formed,
the water will be slowly decomposed, its oxygen will be fixed on the
zinc wire, and at the same time a current of electricity will be
transmitted through the liquid to the platina or copper wire, on the
end of which the other element of water, namely, the hydrogen, will
make its appearance in the form of minute gas bubbles. The electrical
current passes back again into the zinc at the points of its contact
with the platina, and thus a continued current is kept up, and hence
it is called a galvanic circle. The moment the circuit is broken by
separating the wires the current ceases, but is again renewed by
making them touch either in or out of the water. If a small quantity
of sulphuric acid be added to the water, the phenomenon will be more
apparent. The end of the wire attached to the piece of platinum or
copper is called the positive pole of the battery, and that of the wire
attached to the zinc the negative pole.
The current of electricity here generated will be extremely feeble;
but this can be easily increased by multiplying the glasses and the
number of the pieces of metal. If we take six such glasses instead of
one, partially fill them with dilute sulphuric acid, and put a piece
of zinc and copper into each, connecting them by means of copper wire
from glass to glass through the whole series, a stronger current of
electricity will be the result. The experimenter must be careful not to
let the wire and zinc touch each other at the bottom of the tumblers,
and must also remember that the copper of glass 1 is connected with the
zinc of glass 2, and so on.