5
4-4. Influence Of Wire
In solid density measurement, the surface of the liquid rises when a solid sample is placed on the density pan,
which is immersed in the liquid, At this time, the buoyancy corresponding to the weight of the raised liquid is
exerted on the wire (diameter of 1 mm) connecting the upper and lower pans. If the surface of the liquid rises 1
mm, the buoyancy exerted on the wire is about 0.8 g/cm
3
. To minimize the error due to the buoyancy, select a
sample with a smaller volume or correct the value by calculation.
In liquid density measurement, a force (buoyancy ) is exerted on the wire (diameter of 0.2 mm) suspending the
float, when immersed in the liquid. Immersing the wire by 10 mm exerts a buoyancy of about 0.3 mg on the wire.
However, this buoyancy influence can be ignored. When obtaining the liquid density, the difference between the
weight of the float in air and in water is divided by the volume of the float, as described in "
3-5. Density of a
Liquid
". This calculation reduces the error due to buoyancy such that it is negligible.
4-5. Surface
Tension
In solid density measurement, a force (surface tension) of about 5 mg is exerted on the pan between the wire
(diameter of 1 mm) of the density pan and the liquid surface.
The surface tension can be reduced by about 1 mg by adding a surfactant (for example, a wetting agent used for
developing photographs). Adding 0.1 mL (density: 1.2 g/cm
3
) of a surfactant to 200 mL of water will increase the
density of water by about 0.0001 g/cm
3
.
In liquid density measurement, a force (surface tension) of about 1 mg is exerted on the wire (diameter of 0.2
mm) suspending the float. However, this surface tension influence can be ignored. When obtaining the liquid
density, the difference between the weight of the float in air and in water is divided by the volume of the float, as
described in "
6. Measuring The Density Of A Liquid
". This calculation reduces the error due to surface
tension such that it is negligible.
4-6. Bubbles
The buoyancy of a bubble of 1 mm in diameter is about 0.5 mg. Bubble generation depends on the shape and
material of the sample, so take care when making measurements.
In solid density measurement, a surfactant may be added to reduce the influence of bubbles.
