at the top and the neutral in the center, and the negative
at the bottom.

If the polarity of the charging line wires is not known, it may be
determined by a voltmeter, in the same way as the batter-, polarity is
determined. If this is done, care should be taken to use a meter
having a range sufficient to measure the line voltage. If no such
voltmeter is available, a simple test is to fill a tumbler with weak
electrolyte or salt water and insert two wires attached to the line.
The ends of these wires should, of course, be bare for an inch or
more. Hold these wires about an inch apart, with the line alive.
Numerous fine bubbles of gas will collect around the negative wire.

With the polarities of all the batteries known, arrange them so that
all the positive terminals are at the right. Then connect them to the
individual switches (see Figure 43), or connect them together with
jumpers (see Figure 44), being sure to connect the negative of one
battery to the positive of the next. Connect the positive charging
line wire to the positive terminal of the first battery, and the
negative line wire to the negative terminal of the last battery. See
page 105.

With all connections made, and before starting to charge, go over all
the batteries again very carefully. You cannot be too careful in
checking the connections, for if one or more batteries are connected
reversed, they will be charged in the wrong direction, and will most
likely be severely damaged.

As a final check on the connections of the batteries on the line,
measure the total voltage of these batteries and see if the reading is
equal to two times the total number of cells on the line.

Now inspect the electrolyte in each cell. If it is low, add distilled
water to bring the electrolyte one-half inch above the plates. Do not
wait until a battery is charged before adding water. Do it now. Do not
add so much water that the electrolyte comes above the lower end of
the vent tube. This will cause flooding.

Charging, Rate. If you connect batteries of various sizes together on
one circuit, charge at the rate which is normal for the smallest
battery. If the rate used is the normal one for the larger batteries,
the smaller batteries will be overheated and "boiled" to death, or
they may gas so violently as to blow a considerable portion of the
active material from the plates.

It is quite possible to charge 6 and 12 volt batteries in series. The
important point is not to