16
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 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.
Summary of Contents for AD-1653
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