Hydrometers determine the density of liquids or the concentration of dissolved matter.
Density is frequently indicated in g/cm3 (g/ml) or in °Baumé. Concentration is indicated in percentage by volume (Vol.%) or in percentage by mass (Weight%). Permissible deviations are within ± 2 graduation marks.
Pour the sample into a transparent cylinder (see fig. 1) and adjust its temperature to the indicated reference temperature of the hydrometer. Immediately before measuring, mix well with a glass rod to reduce differing sample densities and temperatures.
A clean hydrometer should only be touched above the scale. Liquid should not adhere more than 5 mm above the reading point. The meniscus should remain even and not change its shape or height when the stem moves up and down. Hydrometer should first be cleaned carefully in Mucasol®.
Once the hydrometer has reached its equilibrium, (floating freely without touching the walls of the cylinder) the density is read "from below" for transparent samples. Non-transparent samples
are read "from above". Check the temperature of
the sample immediately after the reading.
Maximum hydrometer measuring temperature should not exceed 70 °C.