Liquid Handling

HydrometersTemperature and DensityHydrometersMeasuring ProceduresHydrometers determine the density of liquids or the concentrationof dissolved matter.Density is frequently indicated in g/cm 3 (g/ml) or in °Baumé.Concentration is indicated in percentage by volume (Vol.%) or inpercentage by mass (Weight%). Permissible deviations are within± 2 graduation marks.12'from below'/'from above'Temperature correction1. Measuring instrumentCertain applications may requirea correction to accountfor the thermal expansion ofthe hydrometer glass, if themeasuring temperature deviatesfrom the reference temperatureof the hydrometer.This factor corrects the resultfor the corresponding measuringtemperature.K t = (1-γ (t - t 0 )) ρK t For the density aftercorrectionγ Volume expansion coefficientof the hydrometerglass (25 ± 2) 10 -6 K -1t Measuring temperature °Ct 0 Reference temperature °Cρ Density reading g/mlMeasuring procedurePour the sample into a transparentcylinder (see fig. 1) andadjust its temperature to theindicated reference temperatureof the hydrometer. Immediatelybefore measuring, mixwell with a glass rod to reducediffering sample densities andtemperatures.A clean hydrometer shouldonly be touched above thescale. Liquid should not adheremore than 5 mm abovethe reading point.The meniscus should remaineven and not change its shapeor height when the stemmoves up and down.Hydrometer should first becleaned carefully in Mucasol ®(see page 312).Once the hydrometer hasreached its equilibrium, (floatingfreely without touchingthe walls of the cylinder) thedensity is read "from below"for transparent samples,non-transparent samples areread "from above". (see fig. 2).Check the temperature of thesample immediately after thereading. Maximum hydrometermeasuring temperature shouldnot exceed 70 °C.Note!2. SampleConversion tables for measureddensities to differenttemperature can be found inmany chemical references.These tables can provideexpansion coefficients anddensities for different sampletemperatures and concentrations.All scales are shown in originalsize.For hydrometers no certificatesare provided.224info@brand.de