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

Density determination kit for Excellence XP/XS precision balances
10
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 determination 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 auxiliary
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 (12) 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: =
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:
+ ρ
L
V