Hydrometer
A hydrometer usually consists of a sealed hollow glass tube with a wider bottom portion for buoyancy, a ballast such as lead or mercury for stability, and a narrow stem with graduations for measuring.
The lower the density of the fluid, the deeper a hydrometer of a given weight sinks; the stem is calibrated to give a numerical reading.
The hydrometer probably dates back to the Greek philosopher Archimedes (3rd century BC) who used its principles to find the density of various liquids.
[3] Hypatia of Alexandria (b. c. 350–370; d. 415 CE), an important female Greek mathematician, is the first person traditionally associated with the hydrometer.
[3] In a letter, Synesius of Cyrene asks Hypatia, his teacher, to make a hydrometer for him: The instrument in question is a cylindrical tube, which has the shape of a flute and is about the same size.
[6] It appeared again in the 1675 work of Robert Boyle (who coined the name "hydrometer"),[3] with types devised by Antoine Baumé (the Baumé scale), William Nicholson, and Jacques Alexandre César Charles in the late 18th century,[7] more or less contemporarily with Benjamin Sikes' discovery of the device by which the alcoholic content of a liquid can be automatically determined.
Where no sugar or other dissolved substances are present, the specific gravity of a solution of ethanol in water can be directly correlated to the concentration of alcohol.
Many have scales marked with volume percents of "potential alcohol", based on a pre-calculated specific gravity.
[12][13] A saccharometer is a type of hydrometer used for determining the amount of sugar in a solution, invented by Thomas Thomson.
[16] The first brewers' saccharometer was constructed by Benjamin Martin (with distillation in mind), and initially used for brewing by James Baverstock Sr in 1770.
[18] It consists of a large weighted glass bulb with a thin stem rising from the top with calibrated markings.
A hydrometer calibrated to read specific gravity relative to water at 60 °F (16 °C) is a standard tool for servicing automobile batteries.
A battery hydrometer with thermometer (thermohydrometer) measures the temperature-compensated specific gravity and electrolyte temperature.
[21] A salinometer is a hydrometer used to measure the salt content of the feed water to a marine steam boiler.
As urine's specific gravity is dictated by its ratio of solutes (wastes) to water, a urinometer makes it possible to quickly assess a patient's overall level of hydration.
