KERN & SOHN EMB 500-1BE - Manual (Page 34)

EMB-V-BA-e-1422 34
9.2.3 Liquids
Solids are generally not sensitive to temperature changes, so that the corresponding
density changes are not relevant. However, since you work with an aid liquid by the
density determination of solids, according to the "Archimedean Principle", its
temperature is taken into account. The temperature change effects liquids greater
and causes changes in the density in order of 0.1 to 1 ‰ per °C. Hereby, the third
digit after the decimal point is affected.
9.2.4 Surface
The suspension bracket of the sample dish penetrates the surface of the fluid. This
state undergoes continuous change. If the sample or the sinker is relatively small, the
surface tension will impair repeatability. The addition of a small amount of detergent
makes the surface tension negligible and
increases repeatability.
9.2.5 Sinker for density determination of liquids.
To save test fluids by the density determination of liquids, a small glass beaker and
an appropriate sinker is to be used. Hereto, it should be noted that a larger sinker
achieves greater accuracy.
Determine the buoyancy and volume of the sinker as accurately as possible. For the
determination of fluid density these results are applied to the common denominator
as well as the numerator of the formula.
9.3 General information
9.3.1 Density / Relative Density
Relative density follows from the weight of a specimen divided by the weight of water
(at 4° Celsius) of the same volume. For this reason relative density does not have a
unit. Density equals mass divided by volume.
The application of the relative density instead of the density of a fluid in a formula
produces an incorrect result. In the case of fluids only their density is
physically meaningful.
9.3.2 Drift of Balance Display
The drifting of a balance does not influence the final result of the density
determination although the shown weight of weighing in air is affected. Accurate
values are merely required if the density of fluids is determined by means of a sinker.
When changing the ambient temperature or location, an adjustment of the balance is
necessary. Hereto, remove the density kit and carry out an adjustment with the
standard weighing plate (See chapter 6.6).