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Solid State Density

Working Group 1.13

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Determination of density and volume of solid samples with high precision

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Research/Development

Cooperation in the project for the re-determination of the Avogadro constant

Density comparison by the pressure-of-flotation method

The pressure-of-flotation method allows investigations of very small density differences to take place by comparing measurements of two silicon samples (e. g. 1 kg silicon-28 spheres). To this end, both samples are immersed in a liquid mixture that has nearly the same density as silicon. The pressure in the liquid is adjusted in such a way that one of the two samples floats freely without rising or sinking. Currently, an apparatus for density comparisons that uses the pressure-of-flotation method is being set up; the desired relative standard uncertainty of the density comparison measurement using this apparatus is 0.01 ppm for silicon-28 spheres. To achieve this uncertainty, both a high resolution of the pressure changes and a temperature stability in the µK range are crucial.

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Services

  • Measurement of the density and volume of solid samples, e. g. solid density standards, air density artifacts and weights from 1 g to 1 kg
  • Calibration of hydrometers

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Information

Automatic hydrostatic weighing apparatus

The automatic hydrostatic weighing apparatus is used to determine the volume of solid samples with a mass of up to about 1030 g and a volume of up to 440 cm3. The measurements are performed at 20 °C. The apparatus has been included in the international CMC tables.
The following expanded measurement uncertainties (coverage factor k = 2) are accepted worldwide:
(0.15 + 0.0015 cm-3 · V) mm3 for the volume V ranging from 50 cm3  to 440 cm3.

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Mass comparison apparatus

In this apparatus, the masses of solid samples with a mass of up to about 1000 g can be compared in order to determine the density of samples.
Mass comparisons can be performed with a measurement uncertainty of 0.10 mg (for a coverage factor k = 2).
Absolute mass determinations with a lower uncertainty (i.e. traceable to the SI mass unit, the kilogram) are performed by Working Group 1.81, “Realization of Mass.”

 

 

 

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Calibration of hydrometers

Hydrometers for measuring densities in the range between 500 kg/m3 and 2000 kg/m3 can be calibrated with expanded uncertainties as low as 0.02 kg/m3 (coverage factor k = 2) using the Cuckow method. This is relevant for the following types of hydrometers: Alcoholometers, hydrometers for aqueous sucrose solutions, for wort, for sulpho spirit, for petroleum and for liquefied petroleum gas. The scale unit may be kg/m3, g/cm3, % mas, or % vol. The reference temperature should be in the range from 15 °C to 25 °C. The scale reading may be "in the liquid's level" or "at the upper rim of the meniscus."

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Hydrostatic determination of the density of solid samples

 

The density of solid samples with masses of up to about 1000 g can be determined in the temperature range from 5 °C to 80 °C by means of hydrostatic weighing.

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