b. The hydrometer has a glass cylinder containing a glass float. A rubber
inlet tip is fitted to the bottom of the cylinder and a rubber bulb at the top. A
scale on the neck of the float has numbers ranging from 1.100 to 1.300. The scales
may also be marked off in zones that are identified as full charge, half charge,
and discharged, or good, fair, poor, and dead. The level of the hydrometer float
in a liquid indicates the specific gravity of the liquid.
c. To test the gravity of a battery cell squeeze the hydrometer bulb and
insert the inlet tip into the electrolyte of a battery cell (fig 21). Hold the
hydrometer in a vertical position and release the bulb to draw in Just enough
electrolyte so the float moves freely. To avoid wrong readings, the float should
not touch the sides or the top and bottom end of the cylinder. Hold the hydrometer
so the surface of the liquid is level with your eyes, then read the mark on the
scale at this level. Always put the electrolyte back into the cell to prevent
weakening the mixture. Test all cells in the battery in the same manner.
d. The hydrometer should be kept clean by flushing it out once in a while
with soapy water so the parts will not stick together. Inspect the hydrometer
often for cracks. The float is hollow and if it develops a leak the hydrometer
will no longer give the right readings.
OS 010, 3-P25