27
9. Measurement of solid sample
Fig. 9-3
Put the sample on the center of the
prism
with
careful
position
of
daylighting and contacting face. Thinly
splay the contact liquid on the entire
spacing of the sample and of the
prism.
When the contact liquid does not
spread, by putting a thin stick tipped
with the contact liquid on a spacing of
the sample and the main prism, splay
it. In addition, error will cause in
measurement if the sample does not
adequately contact with the prism
because of too much contact liquid. In
such case, run off extra contact liquid
by slightly pressing down the top of
the sample. Remove the surplus liquid
which runs off the prism by pressing
such as the edge of tissue paper.
If the contact surface of a sample is
not parallel with the prism surface
owing to dust or other substance
sandwiched between them, it results
in a great error in measurement.
(1)-4 Lighting
Open the secondary prism completely
and
external
light
horizontally
penetrates the sample through the
front side (lighting side) (Fig. 9-3).
Although the natural light generally
serves
as
an
external
light
for
measurement, it is required to use a
monochromatic light source of a
certain wavelength such as a sodium
lamp that radiates D-line (589 nm).
ە
ە
Sodium lamp
Main prism
Sample
Contact
liquid
Eyepiece
Note:
When using D-line lamp for measurement, set the color compensation knob to "30"
of scale value of the color compensation knob NAR-2T.
When the refraction view is not
clear
because
of
intense
illumination of the lamp, shake the
light with white thin paper or tissue
paper by inserting it between the
lamp and test piece.
Note:
Note:
In the case of using LED lamp (approximating to wavelength of D-line) of NAR-2T,
turn the color compensator knob and stop turning when the boundary line becomes
neither reddish nor bluish.
