A hydrometer is calibrated on a defined range of surface tensions (= measurable tensile force that normally acts across the unit length of a liquid surface like a thin film and which causes a convex build-up. The size respectively the weight of this convex meniscus sensibly effects the depth of immersion of the hydrometer and, thus, on the visibility. Surface tension being primarily a material property of the test liquid. That is why an hydrometer should be choosen which is as closely as possible to the surface tension of that test liquid. Surfacetensions of most liquids can be taken from corresponding tables or else can be determined by means of special instruments.

By missing of a client’s wish KUEBLER allocates the surface tension as follows:

If the range of the hydrometer’s measuring capacity is not falling into one of the above density intervals then a surface tension has to be determined primarily orientating on the average density result of the individual hydrometer. With any and all KUEBLER hydrometers designed for the measurement of one specific liquid (in those cases, the designation of that test liquid – for example:

<ethanol-water-mix> or <grape must> - is imprinted on one of the indicator scales of the hydrometer), there is absolutely no need for any further considerations relating to the surface tension as any and all aspects have to be observed in the design and construction of the hydrometer. Whenever there is a significant gap between the surface tension of the test liquid and the range of surface tensions that has been used to calibrate the hydrometer being employed the convex build-up will be bigger/smaller than specified and in consequence of this the hydrometer will sink deeper / less deep then corrections have to carried out to gain high accurate measurements.