Improving The Accuracy Of The Result; Density Determination Of Liquids; Fundamentals - Mettler Toledo xs Bedienungsanleitung

4.3

Improving the accuracy of the result

The following tips should help you improve the accuracy of the results in the density determination
of solids.
Temperature
Solids are generally so insensitive to temperature fluctuations that the corresponding density changes
are of no consequence. However, as work is performed with an auxiliary liquid in the density determi-
nation of solids following Archimedes' principle, their temperature must be taken into account as the
temperature has a greater effect with liquids and causes density changes of order of magnitude 0.1 to
1 ‰ per °C. This effect is already apparent in the third decimal place of the result.
To obtain accurate results, we recommend that you always take the temperature of the auxiliary
liquid into account in all density determinations. You can take the appropriate values from a book
of tables. You will find tables for distilled water and ethanol in Section 6.
Surface tension of the auxiliary liquid
Adhesion of the auxiliary liquid to the suspension wires of the holder causes an apparent weight
increase of up to 3 mg.
As the holder is immersed in the auxiliary liquid in both weighings of the solid (in air and in the aux-
iliary liquid) and the balance is tared before every measurement, the influence of the apparent weight
increase can be neglected.
If the greatest possible accuracy is required, use a few drops of the wetting agent (9) supplied.
5

Density determination of liquids

5.1

Fundamentals

The density of a liquid is determined using a sinker of known volume. The sinker is weighed in air
and then in the liquid whose density is to be determined. The density ρ can be determined from the
two weighings as follows:
A-B
α
ρ
Density:
=
V
With an electronic balance it is possible to determine the weight of the displaced liquid P (P = A–B),
and thus the buoyancy, allowing the preceding formula to be simplified to:
Density determination kit for Excellence XP/XS analytical balances
+ ρ
L
9