Ohaus Density Determination Kit Manual - Manual (Page 9)

Density Determination Kit EN-6
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 great
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 3mg.
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.
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:
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 = Density of liquid
A = Weight of sinker in air
B = Weight of sinker in the liquid
V = Volume of sinker
ρ
L
= Air density (0.0012 g/cm
3
)
α = Balance correction factor (0.99985), takes air
buoyancy of the adjustment weight into account
P = Weight of displaced liquid (P = A - B)