3B Scientific Polarimeter with 4 LEDs (115 V, 50__60 Hz) - Manual (Page 6)

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The analyser contains a second polarising filter with
its polarisation axis at a variable angle to that of the
polariser. The angle is 90° when the rotating scale is
set to 0° (= 360°). In this position, if there is no
optically active substance in the measurement
chamber, the transmitted light intensity will be at a
minimum.
If an optically active substance is then put into the
sample cell, it rotates the plane of polarisation either
clockwise or anti-clockwise, causing an increase in
the transmitted light intensity (brightness). By re-
positioning the analyser, the light intensity can be
brought back to its minimum. The angle that is then
read off below the fixed pointer is the angle through
which the plane of polarisation has been rotated by
the sample.
3. Equipment supplied
1 Polarimeter basic instrument
1 Analyser disc
1 Sample cell
1 Mains adapter
1 US mains adapter (only with U8761161-115)
4. Technical data
Wavelengths: 630 nm (red)
580 nm (yellow)
525 nm (green)
468 nm (blue)
Dimensions: 110
Ч190Ч320 mm 3 approx.
Weight: 1 kg approx.
The polarimeter U8761161-230 is designed for a
mains voltage of 230 V (±10 %), whereas U8761161-
115 is for 115 V (±10 %).
5. Operation
• Lift the analyser disc from the measurement
chamber.
• Take out the cylindrical sample cell and fill it
with the liquid sample. It is important to
carefully wipe the cell dry, ensuring that no
liquid remains on the outside surface.
• Place the sample cell in the measurement
chamber, taking care that no liquid is allowed to
spill and escape into other parts of the
measurement chamber.
• Replace the analyser disc and rotate it so that the
pointer is at the 360° position.
• Connect the mains adapter and supply power to
the instrument.
• Set the LED selector switch to give the desired
wavelength of light.
To measure the angle of rotation of the plane of
polarisation transmitted via the optically active
sample, look at the spot of light through the viewing
hole and rotate the disc so that the brightness is
reduced. Adjust it carefully to find the position where
the brightness is at a minimum and read the pointer.
A substance that rotates the plane of polarisation of
light in the clockwise direction is described as dextro-
rotatory. The optical activity of such substances is
indicated by the sign (+). The difference between the
360° mark and the angle that one reads on the scale
corresponds to the angle by which the plane of
polarisation has been rotated.
Fig.1 Example of a scale reading for a dextro-rotatory
substance (+6°)
A substance that rotates the plane of polarisation of
light in the anti-clockwise direction is described as
laevo-rotatory. The optical activity of such substances
is indicated by the sign (-). For a laevo-rotatory
substance the angle of rotation can be read directly
off the scale.
Fig.2 Example of a scale reading for a laevo-rotatory
substance (-6°)
6. Sample experiments
6.1 Measure the optical activity of a saccharose
solution as a function of the concentration,
the sample thickness, and the colour of the
light
• Prepare a sugar solution (10 g in 100 ml), by
weighing out 10 g of ordinary sugar, dissolving it
in about 60 cm
3 of distilled water, and making
the volume up to 100 cm 3 in the cylindrical
sample cell.