National comparison of hydrometer calibrations

A national comparison of hydrometer calibrations was performed by the verif ication offices in Berlin, Ilmenau, Munchen and Wertheim and by the Physika lisch-Technische bundesanstalt (PTB) which acted as reference laboratory. F our hydrometers for density and concentration with a high resolution and in tended for use in different liquids were calibrated at three scale lines ea ch. Correction values for two hydrometers were given for different referenc e temperatures (15 degrees C and 20 degrees C) and for reading both in the liquid plane and at the upper level of the liquid meniscus. Two verificatio n offices and the PTB used the Cuckow method. The other laboratories compar ed the hydrometers in appropriate liquids with standard hydrometers. The 10 7 correction values determined by the verification offices agree with the P TB's reference values within the stated uncertainties The constancy of hydr ometers is demonstrated by the correction values of one hydrometer over a p eriod of 26 years.