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4.3. Temperature of Liquid
The density of the liquid that is used for measuring the density of a solid varies with the liquid
temperature. Therefore, the decimal places beyond the first decimal place of the measured value
contain errors.
Obtain the density of a liquid according to the temperature from Table 1 for distilled water or from
other reference documents for other liquids.
When measurement accuracy to the third decimal place or beyond is necessary, use a thermometer
with a tolerance of ±0.2°C or less.
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
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
about 0.0001 g/cm
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 "3.5. 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.
3
) of a surfactant to 200 mL of water will increase the density of water by
.
7
3
.
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