Three hydrometers, 1700-1730.
© Science Museum / Science & Society Picture Library
Hydrometers have been used for testing the specific gravity of many liquids. The example in the jar is a gilt hydrometer from around 1700. The two ivory hydrometers are weighted with lead shot and date from about 1700-1730. These hydrometers were made at a time when they were just coming into regular use for testing the strength of alcoholic spirits. As duties were increased, hydrometers were improved to give more accurate readings, but not until the end of the 18th century was alcoholometry put on a sound basis.