Improving The Accuracy Of The Result; Supplementary Information; Influencing Factors - Mettler Toledo xs Bedienungsanleitung

Density determination kit for Excellence XP/XS analytical balances
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5.3

Improving the accuracy of the result

The following tips will help you improve the accuracy of the results in the density determination of
liquids.
Volume tolerance of the sinker
The optional sinker 00210260 recommended for the density determination of liquids corresponds to
the requirements of the German Weights and Measures Regulation (EO 13–4, paragraph 9.21). The
volume of the sinker 00210260 including the upper half of the suspension wire is so adjusted that the
maximum error in the density determination of water at a temperature of 20 °C is ±0.0005 g/cm
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Supplementary information

This section offers information on the influencing factors which can have an adverse effect on the
accuracy of the experimental results. In addition, you will find density tables for distilled water and
ethanol in this section.
6.1

Influencing factors

In addition to temperature, air buoyancy and surface tension of the liquid, the following factors can
affect the experimental results:
– Immersion depth of the holder or the sinker
– Air bubbles
– Porosity of the solid body
Immersion depth of the holder or sinker
The sinker for the density determination of liquids is suspended from a platinum wire of 0. mm di-
ameter. In water the wire experiences a buoyancy of approx. 0.3 mg per 10 mm immersion depth.
Example: If the liquid is 10 mm above the suspension eye of the sinker, approx. 40 mm wire are im-
mersed. This results in a buoyancy of 1.2 mg at densities around 1. Owing to division of the buoyancy by
10 cm (= volume of the sinker), the error in the result is negligibly small and need not be corrected.
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The immersible part of the holders for the density determination of solids comprises 2 wires each
of diameter 0.7 mm. With a liquid density of 1, this results in a buoyancy of approx. 0.4 mg per
millimeter immersion depth.
In the weighing of the solid in air, the immersion depth of the holder remains the same. The buoyancy
force on the holder is thus constant and can therefore be neglected. However, it is important to ensure
that the liquid level is not changed between weighings (the change in the liquid level by immersion
of the solid is usually insignificant).
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