hydrometer
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A hydrometer calibrated with specific gravities
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An instrument to measure the density of
a liquid. In essence it consists of a closed
glass tube calibrated along its stem and blown into a bulb, which is weighted
at the end. The hydrometer floats upright in the liquid to be tested: the
denser the liquid, the more the instrument is buoyed up (in accordance with
Archimedes' principle). The
scale is read at the level of the liquid's surface. Though the instrument
measures density directly, it is usual to calibrate the stem in terms of
specific gravity, the ratio of
the density of the liquid to the density of water at that temperature. Other
scales are used for specific purposes.
Related category
• INSTRUMENTATION
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