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-7-
Influence of Wire
When a solid sample is placed on the density pan, which is immersed in a liquid, for a
density measurement, the liquid surface position rises. At this time, the wire (
φ
1 mm)
connecting the upper and lower pans is subject to the buoyancy whose magnitude is
equal to the weight of the raised liquid. 1-mm raise of the liquid surface exerts a
buoyancy of about 0.8 mg to the wire. To minimize a measurement error caused by
the buoyancy, adjust the sample size so that it will not raise the liquid surface so
much, or perform a mathematical correction.
When measuring the density of a liquid, the float-suspending wire (
φ
2 mm) immersed
in the liquid affects the measurement. Immersing the wire by 10 mm exerts a
buoyancy of about 0.3 mg to the wire. However, this buoyancy can be ignored
because it is divided by the volume of the float when the density of the liquid is
obtained.
Surface
Tension
When the density of a solid is measured, a force of about 5 mg (surface tension) is
applied to the pan, between the wire (1 mm in diameter) of the pan and the surface of
the liquid.
The surface tension can be reduced to about 1 mg by adding a surface-active agent
(for example, a water droplet preventive solution as used for developing photographs).
Adding 0.1 ml (1.2 g/ cm
3
density) of a surface-active agent to 200 ml of water will
increase the density of the water by about 0.0001 g/cm
3
.
When the density of a liquid is measured, a force of about 1mg is exerted by the wire
of 0.2 mm in diameter. However, this force can be ignored because it is divided by the
volume of the float.
Bubbles
The buoyancy of a bubble of 1 mm in diameter is about 0.5 mg. Stickiness of bubbles
depends on the shape and material of a sample. Make measurements considering the
characteristic of bubbles.
When the density of a solid is measured, a surface-active agent may be added to
reduce the influence of surface tension and bubbles.
Содержание GX-13
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