and a good signal to watch in connection with the care
and operation of his Delco-Light plant and battery. (Further mention
will be made of the pilot ball in connection with the subject of
proper operation.)

It is necessary that the maximum specific gravity of pilot cells be as
near 1.220 as possible. Any great variation higher or lower will
affect the operation of the pilot balls. Therefore, every effort
should be made to adjust the maximum specific gravity of pilot cells
to 1.220 when placed in service.

Batteries equipped with one pilot cell contain a white pilot ball
which will be up when the specific gravity of the electrolyte is
approximately 1.185. This ball will drop DOWN when the specific
gravity falls a little below 1.185.

In other words, the pilot ball will float at a specific gravity of
1:185 or higher, and will sink at a specific gravity lower than 1.185.

Therefore, when the pilot ball is UP, the battery is more than half
charged. When the pilot ball is DOWN, the battery is more than half
discharged.

Batteries equipped with two pilot cells have one cell which contains a
white ball and the other cell a white ball with a blue band.

The plain white ball will be UP when the specific gravity is
approximately 1.175. The blue band ball will be UP when the specific
gravity is approximately 1.205.

When both balls are UP, the battery is charged. When DOWN, the battery
is discharged. The blue band ball will drop soon after the battery
starts on discharge, or, in other words, when the specific gravity
falls below 1.205. The white ball will remain UP until the specific
gravity falls below 1.175.

The Ampere-Hour Meter

The ampere-hour meter, Fig. 304, is an instrument for indicating to
the user the state of charge of the battery at all times and serves
to-stop the plant automatically so equipped, when the battery is
charged. (Further mention will be made of the ampere hour meter on
page 471.)

In order to check the speed of the ampere-hour meter, use the
following rule: On charge, the armature disc should give 16
revolutions in 30 seconds, with a charging rate of 15 amperes; on
discharge, the armature disc should give 20 revolutions in 30 seconds,
with a discharging rate of 15 amperes.

[Fig. 304 Delco-Light Ampere-Hour Meter]

Hydrometers

The standard hydrometer for service men is known as the Type V-2B.

A special type hydrometer showing three colored bands in place of
numbers has