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CHAPTER 2.
BATTERIES IN GENERAL

There are two ways of "generating" electricity on the car: 1.
Magnetically, 2. Chemically. The first method is that used in a
generator, in which wires are rotated in a "field" in which magnetic
forces act. The second method is that of the battery, and the one in
which we are now interested.

If two unlike metals or conducting substances are placed in a liquid
which causes a greater chemical change in one of the substances than
in the other, an electrical pressure, or "electromotive" force is
caused to exist between the two metals or conducting substances. The
greater the difference in the chemical action on the substances, the
greater will be the electrical pressure, and if the substances are
connected together outside of the liquid by a wire or other conductor
of electricity, an electric current will flow through the path or
"circuit" consisting of the liquid, the two substances which are
immersed in the liquid, and the external wire or conductor.

As the current flows through the combination of the liquid, and the
substances immersed in it, which is called a voltaic "cell," one or
both of the substances undergo chemical changes which continue until
one of the substances is entirely changed. These chemical changes
produce the electrical pressure which causes the current to flow, and
the flow will continue until one or both of the substances are changed
entirely. This change due to the chemical action may result in the
formation of gases, or of solid compounds. If gases are formed they
escape and are lost. If solids are formed, no material is actually
lost.

Assuming that one of the conducting substances, or "electrodes," which
are immersed in the liquid has been acted upon by the liquid, or
"electrolyte," until no further chemical action can take place, our
voltaic cell will no longer be capable of causing a flow of
electricity. If none of the substances resulting from the original
chemical action have been lost as gases, it may be possible to reverse
the entire set of operations which have taken place. That is, suppose
we now send a current through the cell from an outside source of
electricity, in a direction opposite to that in which the current
produced by the chemical action between the electrodes and electrolyte
flowed. If this current now produces chemical actions between
electrodes and electrolyte which are the reverse of those which
occurred originally,