Correction temperature for density hydrometers
If the hydrometer reading is taken at a temperature other than the standard temperature for the hydrometer, the reading will be in error due to the change in volume of the hydrometer between the two temperatures. Appropriate corrections making allowance for this temperature effect are given in the table.
Corrections for temperature applicable to density hydrometers standardized at 20°C (68°F) or
These corrections when applied to the hydrometer reading at t°C give the density of the liquid in kg/m³ or
g/ml at t°C.
Surface tension of the hydrometers
Reading of a hydrometer depends on the surface tension of the liquid in which it is used.This table gives an indication of possible errors, in the form of corrections which may be applied on account of difference between the surface tension of the liquid and the surface tension for which the hydrometer is graduated.
NOTE - For hydrometers of different dimensions permitted under this specification the surface tension allowances may vary from the above amounts by up to approximately ± 10%.
Exemple of surface tension
Due to the extreme variability of the surface tension of acetic acid solutions, such solutions have not been included in the table.