y the
electrolyte with a chemical action that is greater for one substance
than the other. In the storage cell used on the automobile today for
starting and lighting, the electrodes are lead and peroxide of lead,
and the electrolyte is a mixture of sulphuric acid and water. The
peroxide of lead electrode is the one upon which the electrolyte has
the greater chemical effect, and it is called the positive or "+"
electrode, because when the battery is sending a. current through an
external circuit, the current flows from this electrode through the
external circuit, and back to the lead electrode, which is called the
negative, or electrode.

When starting and lighting systems were adopted in 1912, storage
batteries had been used for many years in electric power stations.
These were, however, large and heavy, and many difficult problems of
design had to be solved in order to produce a battery capable of
performing the work of cranking the engine, and yet be portable,
light, and small enough to occupy only a very limited space on the
automobile. As a result of these conditions governing the design, the
starting and lighting battery of today is in reality "the giant that
lives in a box." The Electric Storage Battery Company estimates that
one of its types of batteries, which measures only 12-5/8 inches long,
7-3/8 wide, and 9-1/8 high, and weighs only 63-1/2 pounds, can deliver
enough energy to raise itself to a height of 6 miles straight up in
the air. It must be able to do its work quickly at all times, and in
all sorts of weather, with temperatures ranging from below 0 deg. to 100 deg.
Fahrenheit, or even higher.

The starting and lighting battery has therefore been designed to
withstand severe operating conditions. Looking at such a battery on a
car we see a small wooden box in which are placed three or more
"cells," see Fig. 1. Each "cell" has a hard, black rubber top through
which two posts of lead project. Bars of lead connect the posts of one
cell to those of the next. To one of the posts of each end cell is
connected a cable which leads into the car, and through which the
current leaves or enters the battery. At the center of each cell is a
removable rubber plug covering an opening through which communication
is established with the inside of the cell for the purpose of pouring
in water, removing some of the electrolyte to determine the condition
of the battery, or to allow gases formed within the cell to escape.
L