Hydrometer

An instrument used for measuring the specific gravity of a liquid.

A hydrometer consists of a glass volume with a weight at the bottom and a graduated scale on the stem.

The hydrometer is gently lowered into a volume of liquid and allowed to settle. The reading is taken at the top surface of the liquid.

This liquid is denser than the liquid in the next image.

In batteries hydrometers are used to indicate the state of charge by the specific gravity of the electrolyte.

See also: Specific Gravity.