Using The Refractometer - Optica 2WAJ Manual De Instrucciones

5.0 FUNCTION AND CONSTRUCTION OF THE REFRACTOMETER
The dispersion free prism group consists of a pair of equidispersion Amici prisms, and has the
function to obtain a variable dispersion to offset the dispersion resulting from the refractive
prism in relation to the test substance.
Using the telescopic objective (5), the bright/dark boundary line is imaged on the reticule
(6) and can be observed through the eyepiece (7). The scale plate (11) is illuminated by the
daylight from the condenser (12), which connects the scale plate (11).
At the same time the swingable mirror (3) swivels around the graduation centre. The values
of refractive indices of different positions will be imaged on the screen (6) with the help of the
mirror (10), the reading objective (9) and the paralleling prism (8) (as shown on the bottom
part of fig. 2).

6.0 USING THE REFRACTOMETER

6.1 Preparations
Calibration
Before measuring, it is necessary to calibrate the instrument using the calibration standard (a
glass block with a known refractive index) that comes with the instrument.
Then do the following:
- Open the refracting prism.
- Drop one or two drops of naphthalene bromide on the surface of the glass block.
- Place the specimen on the incident prism.
- Adjust the eyepiece to focus the visual field.
- Adjust the dispersion correction knob until it is possible to distinguish two separate fields, one
light one and one darker.
- Use the refractive index graduation adjustment knob to move the separation line between the
two fields until it is exactly where the two diagonal lines intersect.
- Read the refractive index from the lower scale.
- If the reading is not accurate with the index printed on the standard specimen, adjust the re-
gulation screw at the back of the instrument.
- Warning: The naphthalene bromide must be wiped off as soon as possible after the measu-
rement as it may damage the prism.
If there is any doubt about the determined refractive index during routine testing work, the
above-mentioned methods can be used for correction.
Cleaning
Before measuring and doing the calculation, the rough surface of the incident prism, the po-
lished surfaces of the refracting prism and the standard specimen should be cleaned with a
piece of absorbent cotton dipped with a 1:1 absolute alcohol and ether solution to remove dirt
which can affect image sharpness and measuring accuracy.
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