r furnished with the battery.
The hydrometer is a sealed glass tube, with a graduated scale somewhat
resembling a thermometer. The height at which it floats in any given
solution depends on the density of the solution. It should indicate
approximately 1.15 for a storage battery electrolyte before charging.
It should not be over 1.15--or 1,150 if your hydrometer reads in
thousandths.

Only pure water should be used. Distilled water is the best, but fresh
clean rain water is permissible. Never under any circumstances use
hydrant water, as it contains impurities which will injure the
battery, probably put it out of commission before its first charge.

_Pour the acid into the water._ Never under any circumstances pour the
water into the acid, else an explosion may occur from the heat
developed. Mix the electrolyte in a stone crock, or glass container,
stirring with a glass rod, and testing from time to time with a
hydrometer. Let it stand until cool and then pour it into the battery
jars, filling them to 1/2 inch above the top of the plates.

Then begin charging. The first charge will probably take a longer time
than subsequent charges. If the installation is of the automatic type,
all that is necessary is to start the engine. If it is not of the
automatic type, proceed as follows:

First be sure all connections are right. Then start the engine and
bring the dynamo up to its rated speed. Adjust the voltage to the
pressure specified. Then throw the switch connecting generator to
battery. Watch the ammeter. It should register in amperes, one-eighth
of the ampere-hour capacity of the battery, as already explained. If
it registers too high, reduce the voltage of the generator slightly,
by means of the field rheostat connected to the generator. This will
also reduce the amperes flowing. If too low, raise the voltage until
the amperes register correctly. Continue the charging operation until
the cells begin to give off gas freely; or until the specific gravity
of the electrolyte, measured by the hydrometer, stands at 1.24. Your
battery is now fully charged. Throw the switch over to the service
line, and your accumulator is ready to furnish light if you turn on
your lamps.

Occasionally add distilled water to the cells, to make up for
evaporation. It is seldom necessary to add acid, as this does not
evaporate. If the battery is kept fully charged, it will not freeze
even when the thermometer is well below zero.

A storage