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CELLS AND BATTERIES 55

acid into the water. A copper wire is fastened with a screw
or by soldering to the top of each of the strips, and care
must be exercised to keep the wires apart.

As has been said, the zinc and copper must never be al-
lowed to touch each other in the solution, but must be kept
at opposite sides of the jar.

The sulphuric acid solution attacks the zinc, causing it
slowly to waste away and disappear. This action is called
oxidation, and in reality is a very slow process of burn-
ing. The consumption of the zinc furnishes the electric
energy, which in the case of this cell will be found to be
sufficient to ring a hell or buzzer, or run a very small toy
motor.

As soon as the plates are immersed in the acid solution,
bubbles will begin to rise from the zinc. These bubbles
contain a gas called hydrogen and they indicate that a
chemical action is taking place. The zinc is being dissolved
and the hydrogen gas is being set free from the acid. It will
be noticed that no bubbles arise from the copper plate and
that there is little if any chemical action there. In other
words, it seems that the chemical action at one plate is
stronger than that at the other.

A cell might be likened to a furnace in which the zinc is
the fuel which is burned to furnish the energy. We know
that if the zinc is burned or oxidized in the open air it will
give out energy in the form of heat. When it is burned or
oxidized slowly in acid in the presence of another metal it
gives out its energy in the form of electricity. The acid

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