CAUTION
Refractive indices of powdered samples
shall be measured by such an indirect
method as mentioned below because it
is impossible to measure them directly.
Sample matters that can be measured in
the following way are transparent
powders such as glass powder,
powdered clear ores (quartz, crystal,
some gem stones), etc.
33
10. Measurement of powdered sample
a)
b)
c)
After measurement finishes, wipe up wet and soiled parts of the instrument with
tissues moistened with alcohol or neutral detergent. Moreover, wipe down the
whole instrument with dry tissue to remove moisture completely from it.
This method requires to use two
different kinds of clear liquids
whose refractive indices (assume
that they are n1 and n2
respectively) are different from
each other. Moreover, it is expected
that n1 and n2 are respectively
higher and lower than the
Refractive Index of the powdered
sample to be measured.
Regarding the chemical
characteristics of the two liquids,
they must well be mixed in each
other without reaction and the
mixture must prevent the powdered
sample from dissolving in it.
After taking a small amount the
powdered sample in a clean test
tube, pour about 1ml of a liquid (n1)
into it. The powered sample mixed
in the liquid is seen whitish.
d) Carefully pour the other liquid (n2)
into the test tube little by little while
mixing it well in the former liquid.
The powdered sample becomes
invisible in a short time because the
refractive indices of the powdered
sample and the mixture correspond
to each other.
As soon as the powdered sample is
invisible, stop pouring the second
liquid and measure the mixture for
the Refractive Index. Therefore the
Refractive Index of the powdered
sample can be known because it is
equivalent to that of the mixture.
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