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IS0
O RG A N IZATl O N FO R STA N D AR D I Z AT I O N
I N T ERN AT1 O N A L
IS0 RECOMMENDATION
R 489
PLASTICS
DETERMINATION OF THE REFRACTIVE INDEX
OF TRANSPARENT PLASTICS
1st EDITION
July 1966
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The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 489, Plastics - Determination of the Refractive Index of
Transparent Plastics, was drawn up by Technical Committee ISO/TC 61, Plastics, the Secre-
tariat of which is held by the American Standards Association, Inc. (ASA).
Work on this question by the Technical Committee began in 1959 and led, in 1962, to
the adoption of a Draft IS0 Recommendation.
'v
In June 1963, this Draft IS0 Recommendation (No. 582) was circulated to all the IS0
Member Bodies for enquiry. It was approved, subject to a few modifications of an editorial
nature, by the following Member Bodies :
Argentina Hungary Romania
Australia India Spain
Austria Italy Sweden
Japan Switzerland
Belgium
Netherlands United Kingdom
Chile
Czechoslovakia New Zealand U.S.A.
Finland Poland U.S.S.R.
France Portugal Yugoslavia
Germany Republic of South Africa
No Member Body opposed the approval of the Draft.
W
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council
which decided, in July 1966, to accept it as an IS0 RECOMMENDATION.
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lSO/R 489 - 1966 (E)
IS0 Recommendation R 489 July 1966
PLASTICS
DETERMINATION OF THE REFRACTIVE INDEX
OF TRANSPARENT PLASTICS
1. SCOPE
1.1 This IS0 Recommendation describes two methods of test for determining the refractive
index of transparent plastics :
Method A. Refractometric method for measuring the refractive index of transparent cast,
moulded or sheet materials by means of a refractometer. The method is recommended
when great accuracy is required. It cannot be used for powdered or granulated transparent
materials.
Method B. Immersion method (Becke line phenomenon) for determining the refractive index
of powdered or granulated transparent materials by means of a microscope and making
use of the Becke line phenomenon. Monochromatic light should, in general, be used
to avoid dispersion effects. The accuracy of this method is about the same as that of
method A.
1.2 Refractive index is a fundamental property which can be used for the control of purity and
composition, for the identification of materials and for the design of optical parts.
The change of refractive index with temperature may give an indication of transition points
of materials.
2. APPARATUS AND CHEMICALS
2.1 Method A
(a) Abbe refractorneter or any other refractometer that can be shown to give the same
results.
(b) Source of white light.
(c) Contacting liquid (see Note 1).
2.2 Method B
(a) Microscope having a magnifying power of at least 200 diameters, an 8 mm objective
of good quality, and a centring substage condenser capable of being stopped down
to a very narrow axial beam.
(b) Immersion liquids with different refractive indices (see Note 2).
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ISO/R 489 - 1966 (E)
3. PREPARATION OF TEST SPECIMENS
3.1 Method A
The test specimens cut from the sample should be of such a size as will fit on the face
of the fixed half of the refractometer prisms.
:
The following dimensions are convenient
6 mm wide
12 mm long
3 mm thick
For maximum accuracy the surface of the test specimen in contact with the prism should
be quite flat and well polished. Satisfactory contact between the test specimen and the
prism is indicated by the dividing line between the light and dark halves of the eyepiece
field appearing sharp and straight. A second surface with a fair polish is prepared perpen-
dicular to the first and on one end of the test specimen.
These two polished surfaces should intersect along a sharp line without a bevelled or
rounded edge.
For anisotropic materials, see Note 3.
3.2 Method B
The sample consists of particles of the material to be examined, e. g., powder, granules,
chips, etc. The particles should have linear dimensions sufficiently small and be so distrib-
uted as to permit simultaneous observation of approximately equal areas of the sample and
surrounding in the field.
The thickness of the particles should be significantly less than the working distance of the
microscope objective.
4. PROCEDURE
4.1 Method A
The procedure for the Abbe refractometer is described here. For other refractometers the
procedure may be modified, if necessary.
The determination is carried out at 20 f 0.5 OC.
A small drop of the contacting liquid is placed on the polished surface of the test specimen
firm contact with the surface of the prism with the polished edge
which is then placed in
of the specimen towards the source of light. The index arm of the refractometer is then
adjusted until half of the eyepiece field is dark. The compensator (Amici prisms) drum is
then
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