The uniformity of the liquid meniscus as a requirement of exact density détermination, dépends on the purity of the liquid surface and on that of the stem. Exact readings are only achieved by a regularly rising liquid meniscus that does not visibly change, if the hydrometer is moved up and down.
For this reason it is impératif that the carefully cleaned instrument is held above the scale and that it is dipped slowly into the medium to about 5 mm above the intended reading point, otherwise it will be getting heavier than water and will falsify the measurement.
During the procedure of reading it is also impératif that the hydrometer body does not touch the side of the jar.
At once after the density détermination the température of the test liquid is to be taken. If it is different from the reference température indicated on the hydrometer scale a correction will be necessary.
With regard to this correction and others compare DIN 12 791 sheet 1.
Besides, the détermination of the density of minerai oils and related materials is described in detail in DIN 51 757.
The hydrometers „suitable for government testing” are exellent quality.
All the other instruments are offered as more favourable, less-demanding type and may show higher tolérances than the thermometers „suitable for government testing” .
Colour code hydrometers offer more reliable results in measuring because the surface tension and the kind of reading can be jugded at first glance. The following colour codes are the most used ones for DIN hydrometers:
on foot with spout
several sizes 50ml upto 2000ml capacity.
Cardanic Suspension Device
complete with glass cylinder c.450mm long,
inner-diam 40mm upto 54mm
spare glass cylinder.
Spare glass cylinder
interior diam c. 40 mm
Cat. Nr. H 798 774
interior diam c. 54 mm
Cat. Nr. H 798 778
Cardanic suspension device for work with hydrometers