"Half Full,"
"Empty," in place of the figures.

The tube must be held in a vertical position, Fig. 35, and the stem of
the hydrometer must be vertical. The reading will be the number on the
stem at the surface of the electrolyte in the tube, Fig. 36. Thus if
the hydrometer sinks in the electrolyte until the electrolyte comes up
to the 1.150 mark on the stem, the specific gravity is 1.150.

[Fig. 35 Using hydrometer for reading specific gravity]

For convenience in automobile work, the hydrometer is enclosed in a
large tube of glass or other transparent, acid proof material, having
a short length of rubber tubing at its lower end, and a large rubber
bulb at the upper end. The combination is called a hydrometer-syringe,
or simply hydrometer. See Figure 34. In measuring the specific gravity
of the electrolyte, the vent cap is removed, the bulb is squeezed (so
as to expel the air from it), and the rubber tubing inserted in the
hole from which the cap was removed. The pressure on the bulb is now
released, and electrolyte is drawn up into the glass tube. The rubber
tubing on the hydrometer should not be withdrawn from the cell. When a
sufficient amount of electrolyte has entered the tube, the hydrometer
will float. In taking a reading, there should be no pressure on the
bulb, and the hydrometer should be floating freely and not touching
the walls of the tube. The tube must not be so full of electrolyte
that the upper end of the hydrometer strikes any part of the bulb.

The tube must be held in a vertical position, Fig. 35, and the stem of
the hydrometer must be vertical. The reading will be the number on the
stem at the surface of the electrolyte in the tube, Fig. 36. Thus if
the hydrometer sinks in the electrolyte until the electrolyte comes up
to the 1.150 mark on the stem, the specific gravity is 1.150.

If the battery is located in such a position that it is impossible to
hold the hydrometer straight up, the rubber tube may be Pinched shut
with the fingers, after a sufficient quantity of electrolyte has been
drawn from the cell and the hydrometer then removed and held in a
vertical position.

Specific gravity readings should never be taken soon after distilled
water has been added to the battery. The water and electrolyte do not
mix immediately, and such readings will give misleading results. The
battery should be charged several hours before the readings are taken.
It is a good plan to take a specific gravity re