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

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 210260 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 210260 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 0.2 mm diameter.
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 immersed.
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.
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).
Density determination kit for Excellence XP/XS precision balances
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