User manual

PBS-A03/A04-BA-e-1213 9
ρ =
V
A-B
L
ρ
+
Determining density of liquids
The density of a fluid is determined with the help of a sinker providing a known volume [ V
]. The sinker is weighed in air [ A ] as well as in the test fluid [ B ].
According to the Archimedes’ Principle a body immersed in a fluid experiences a force of
buoyancy. [ G ]. This force equals the weight force of the fluid displaced by the volume of
the body.
The volume [ V ] of the immersed body equals the volume of the displaced fluid.
G = buoyancy of sinker
Buoyancy of sinker =
Weight of the sinker in air [ A ] - weight sinker in test liquid [ B ]
From this follows:
ρ = Density of test liquid
A = weight of sinker in air
B = weight of sinker in sample fluid
V = volume of sinker*
ρ
L
= Air density (0.0012 g/cm³)
* If the volume of the sinker is unknown, this can be determined e.g. in water and be
calculated as follows, see chap. 5.1.
V = volume of sinker
A = weight of sinker in air
B = weight of sinker in water
ρ
W
= density of water
3.1 Influencing magnitudes and error sources
 Air pressure
 temperature
 Volume deviance of the sinker (± 0,005 cm
3
)
 Surface tension of the liquid
 Air bubbles
 Immersion depth of the sample dish of sinker
 Porosity of the solid