Metria RST111, User Manual, Page: 6 / 12

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5.1.2 before performing the measurement and making the calibration of the indication each time, the dull
surface, the polished surfaces of the reflecting prism and standard sample should be cleaned with absorbent
cotton soaked in a mixed solution of absolute alcohol and diethy1 ether (1:1), so as to remove other foreign
substance which will affect the sharpness of image and the accuracy of measurement.
5.2 Measurement
5.2.1 Measurement of transparent or translucent liquid
Add the liquid to be measured on the surface of the refracting prism with a clean dropper, cover the light-
entering prism and lock it with the hand wheel (10). The field of view should be full of the uniform liquid, without
air bubble. Open the hood (3), close the reflecting mirror (1) and adjust the visibility of the eyepiece, making
the image of the graticule clear. At that moment, turn the hand wheel (15) and find the position of the separatrix
in the field of view of the eyepiece, then turn the hand wheel (6) to make the separatrix out of any colour.
Readjust the hand wheel (15) to bring the separatrix in the center of the graticule, then turn appropriately the
condensing lens (12), now the indication displayed in the lower part of the field of view of the eyepiece should
be the refractive index of the liquid to be measured.
5.2.2 Measurement of transparent solid
If the sample to be measured is a kind of solid substance, the solid sample must a smooth polished surface.
When performing the measurement, open the light-entering prism, put one or two drops of a transparent liquid
(e.g. naphthalene bromide), the refractive index of which is higher than that of the sample to be measured, onto
the polished surface of the sample to be measured onto the working surface of the refracting prism an let them
have a good contact. Now find the separatrix in the field of view of the eyepiece; the operating methods of
sighting and reading are the same as above.
5.2.3 Measurement of translucent solid
Stick the polished surface of the translucent solid to be measured on the refracting prism, open the reflecting
mirror (1) and adjust the angle to use the reflecting light beam for measuring. The operating procedures are the
same as above.
5.2.4 Measurement of the mass fraction (Brix) of sugar solution
The operation is the same as the measurement of refractive index; the indication displayed on the upper part of
the field of view is the reading of the mass fraction of sugar solution.
5.2.5 Measurement of average dispersión
Basically the operation procedures are the same as the measurement of refractive index; however, when turn
the dispersion adjustment hand wheel (6) in two different directions, it should be lasted until the color of the
separatrix in the field of view fades away. Record each scale value Z indicated on the scale ring (7) of the
dispersion value and take the average value, then record the value of refractive index nD. Based on the given
nD, the corresponding values of A and B can be found in the same row of the dispersion table of the Abbe
Refractometer (in case nDfalls between two numerical values in the table, the desired value can be found by
interpolation. Finally, the corresponding value of
σ
can beread off from the table according to the given value
of Z. When Z ＞ 30,
σ
is a positive value; when Z ＞ 30, negative value. Substitute the given values of A, B
and σ into the dispersion formula nF – nC = A + B σ , then the average value of dispersion can be got (an
example is given in page 13).
5.2.6 When it is necessary to measure refractive indexed at different temperature, put the thermometer into the
thermometer holder (13), connect the water tube of the thermostat, adjust the temperature of the thermostat to
the required temperature for measuring and open the recirculating water, after the temperature becomes
steady for ten minutes, then perform the measurement
.