ading before adding any
water, since accurate results can also be obtained in this way.

[Fig. 36 Hydrometer reading showing cell charged, half-charged,
and discharged]

Having taken a reading, the bulb is squeezed so as to return the
electrolyte to the cell.

Care should be taken not to spill the electrolyte from the hydrometer
syringe when testing the gravity. Such moisture on top of the cells
tends to cause a short circuit between the terminals and to discharge
the battery.

In making tests with the hydrometer, the electrolyte should always be
returned to the same cell from which it was drawn.

Failure to do this will finally result in an increased proportion of
acid in one cell and a deficiency of acid in others.

The specific gravity of all cells of a battery should rise and fall
together, as the cells are usually connected in series so that the
same current passes through each cell both on charge and discharge.

If one cell of a battery shows a specific gravity which is decidedly
lower than that of the other cells in series with it, and if this
difference gradually increases, the cell showing the lower gravity has
internal trouble. This probably consists of a short circuit, and the
battery should be opened for inspection. If the electrolyte in this
cell falls faster than that of the other cells, a leaky jar is
indicated. The various cells should have specific gravities within
fifteen points of each other, such as 1.260 and 1.275.

If the entire battery shows a specific gravity below 1.200, it is not
receiving enough charge to replace the energy used in starting the
engine and supplying current to the lights, or else there is trouble
in the battery. Use starter and lights sparingly until the specific
gravity comes up to 1.280-1.300. If the specific gravity is less than
1.150 remove the battery from the car and charge it on the charging
bench, as explained later. The troubles which cause low gravity are
given on pages 321 and 322.

It is often difficult to determine what charging current should be
delivered by the generator. Some generators operate at a constant
voltage slightly higher than that of the fully charged battery, and
the charging current will change, being higher for a discharged
battery than for one that is almost or fully charged. Other generators
deliver a constant current which is the same regardless of the
battery's condition.

In the constant voltage type of generator, the chargin