No. 4. 1.290 specific gravity sulphuric acid, 1.5 per cent sodium
sulphate.

No. 5. 1.300 specific gravity sulphuric acid.

If such "dope" electrolytes are added to a discharged battery, the
subsequent charging of the battery will add more acid to the
electrolyte, the specific gravity of which will then rise much higher
than it should, and the plates and separators are soon ruined.

Do not put faith in any "magic" solution which is supposed to work
wonders. There is only one way to charge a battery, and that is to
send a current through it, and there is only one electrolyte to use,
and that is the standard mixture of distilled water and chemically
pure sulphuric acid.

7. The specific gravity of the electrolyte should be measured every
two weeks and a permanent record of the readings made for future
reference.

The specific gravity of the electrolyte is the ratio of its weight to
the weight of an equal volume of water. Acid is heavier than water,
and hence the heavier the electrolyte, the more acid it, contains, and
the more nearly it is fully charged. In automobile batteries, a
specific gravity of 1.300-1.280 indicates a fully charged battery.
Generally, a gravity of 1.280 is taken to indicate a fully, charged
cell, and in this book this will be done. Complete readings are as
follows:

1.300-1.280--Fully charged.

1.280-1.200--More than half charged.

1.200-1.150--Less than half charged.

1.150 and less--Completely discharged.

[Fig. 33 and Fig. 34: battery hydrometers]

For determining the specific gravity, a hydrometer is used. This
consists of a small sealed glass tube with an air bulb and a quantity
of shot at one end, and a graduated scale on the upper end. This scale
is marked from 1.100 to 1.300, with various intermediate markings as
shown in Fig. 33. If this hydrometer is placed in a liquid, it will
sink to a certain depth. In so doing, it will displace a certain
volume of the electrolyte, and when it comes to rest, the volume
displaced will just be equal to the weight of the hydrometer. It will
therefore sink farther in a light liquid than in a heavy one, since it
will require a greater volume of the light liquid to equal the weight
of the hydrometer. The top mark on the hydrometer scale is therefore
1.100 and the bottom one 1.300. Some hydrometers are not marked with
figures that indicate the specific gravity, but are marked with the
words "Charged," "Half Charged," "Discharged," or "Full,"