11
Example of recording sheet
Value A : | Weight of float in air
-
Weight of float in liquid | (g)
9.9704 g
Temperature of liquid (°C)
25 °C
Volume of float (g/cm
3
)
10.01 cm
3
Density of air (g/cm
3
)
0.001 g/cm
3
Weight of float
-
Weight of float
in air
in liquid
ρ
=
+
Density of air (g/cm
3
)
Volume of float
0.997 g/cm
3
(Calculated)
7. Frequently Asked Questions
Questions Answers
I’d like to measure the density of a resin pellet
or sheet, which floats in water. Is it possible?
Use a liquid that has a lower density than water and does not
dissolve the sample, such as methanol (density 0.798) or kerosene
(density 0.80). The density of the liquid used is measured using the
float provided with the kit.
Can a sample containing bubbles be
measured?
The density of a sample with bubbles can be measured as it is. But
as time passes, the bubbles disappear and the apparent density
may change. A sample that floats in water due to the low density
can not be measured.
The measurement repeatability may be
affected by the water’s surface tension. What
can I do about this?
A few drops of a surfactant (for example, a mild detergent for
washing dishes) added to the water reduce the influence of surface
tension. A few drops of a surfactant will affect the liquid density only
a very small amount. When methanol is used in place of water, the
influence of surface tension is small, even without a surfactant.
When tap water is used, bubbles are gradually
generated on the sample surface and a
measurement error occurs. What can I do
about this?
Tap water contains dissolved gases such as oxygen and carbon
dioxide. When tap water is used, the released dissolved gases
generate bubbles. It is recommended that pure water or distilled
water, which contains few dissolved gases, be used.
When I try to measure a highly water- repellent
material such as rubber, bubbles stick to the
sample. What can I do about this?
Before measurement, soak the sample in the water with an
appropriate amount of surfactant added. Doing this increases the
sample surface hydrophilicity and makes it more difficult for bubbles
to stick to the sample surface.
Up to what size of sample can be measured?
In consideration of the density pan size, the maximum sample size
that can be measured is:
Diameter
φ
25 mm,
Height 30 mm,
Mass 100 g
Can I measure the density of a liquid with a
high viscosity?
A liquid with a viscosity up to 500 mPa·s can be measured. If the
viscosity exceeds this value, the float takes excessive time to sink
and a measurement error occurs. Measuring adhesive is not
recommended because the adhesive sample may be difficult to
remove from the float.
Does using a semi-micro balance improve
accuracy?
The effects of surface tension cause errors in the measurement
value of around 0.2 to 1.0 mg. In measurement using the 0.1 mg
range, the magnitude of error and the level of balance accuracy are
almost the same. In measurement using the 0.01 mg range, the
magnitude of error greatly exceeds the level of balance accuracy,
so using a semi-micro balance is not recommended.
