Hydrometer

hydrometer. (hay-dra’-muh-d:er)
A glass instrument for measuring the specific gravity of liquids as compared to that of water, consisting of a graduated stem resting on a weighted float. Most hydrometers are calibrated for use at 60 °F (15.6 °C), and tables or charts are provided listing corrections for variations to that temperature. The accuracy of a hydrometer is tested in water at 60 ° F (15.6 °C), where it should read zero. See also: hydrometer jar.