A new method of high accuracy for the calibration of reference standard hydrometers

Abstract

Abstract In this method, standard hydrometers are weighed first in air and then when immersed to the level of the graduation mark in question in xylene of determined density. The density of a liquid which would cause the hydrometer to float with this mark in the plane of the level surface of the liquid is calculated, essentially by linear extrapolation, from these weights and the associated densities of air and xylene. Further weighings with different degrees of immersion enable calibrations to be made at a number of points on the hydrometer scale in quick succession, the working liquid remaining nominally unchanged in density and temperature throughout. By comparison, the basic method of working, employing a freely floating hydrometer, calls for a liquid of different density for each point to be calibrated. Calibrations are made exactly at graduation marks. The rate of working of the present method is at least four times higher than that of the basic method and an intercomparison of calibrations effected by the two methods shows that there is no detectable loss of accuracy. An open scale hydrometer, which can be read to 0·00000I g./ml., is described for observing the density of the xylene. A nomogram is described for computing the surface tension factors of hydrometers in terms of their weight.

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