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Polarimeter
- Maximum Length of tubes which this model can take is 220mm; smaller
tubes of course can be used. The tubes supplied have a bubble trap.
- Polaroid Sheets used for polarizing the incident light.
- Glass circular scale finely marked in angular degrees and also in ISS degrees. The range on ISS Scale is from—30 o + 130 o .
- Permanent focus: Once the dividing line is focused for the eye. The
focus is not disturbed by inserting tubes containing solutions,
regardless of the nature of solution or of the length of the tube.
- Permanent good definition even with difficult liquids.
- Rotating half shadow Effect.
- Provision for attaching lamp to the instrument thus keeping alignment correct at all times.
Polarimeter is a reliable
instrument for accurate measurement of Optical Rotations, for study of
Polarization effects and for quick and easy discrimination between
right-handed sugars such as Dextrose and left handed sugar such as
levulose. The instruments find use in industries as well as in Colleges
and Universities.
The Polarimeter essentially consists of a pair of polarizes arrange in
a straight line, one of which (analyzer) can be rotated with respect to
the other (Polaris) and the rotation measured on a divided circle. The
analyzer is rotated till it is ‘crossed' with the Polaris. In this
position the planes of he polarization of the polarizer and the
analyzer, are mutually perpendicular, so that there is no transmission
of light across the pair. Now if a tube containing an optically active
solution is introduced between the polarizer and the analyzer, the
light transmission is partially or wholly (if the optical rotation of
the liquid equals90 o ) resorted. The analyzer is rotation again to
obtain the “no transmission” position. This rotation equals, the
optical rotation of the liquid.
Since it is
difficult to recognize the actual “no transmission” position, one is
able to obtain a ”range” only for no transmission. The definition of
this range is quite subjective. To overcome this difficulty, in modern
polarimeter, an extra device is used. This device is a “half-wave
plate”, covering half of the circular field of view. This plate
introduces a certain path difference between light waves in the two
halves of the field of view. Thus when the analyzer is rotated the
intensity in one half of the field of view is extinguished slightly
before the other half. At this point it is easy to continue rotation of
the analyzer to obtain a uniform illumination of the field of view.
This position can be determined quite accurately and is used as the
desired position. The optically active substance (solution) is now
introduced between the polarize and the analyzer and the uniform, field
of view position is determined again to obtain the optical rotation of
the liquid.
The
circular scales are finely marked on a 10cm diameter circle both in
angular measure and in International Sugar Scale. The smallest division
on angular scale is 1 o ISS. The Sugar Scale is calibrated between—30 o
(for Laboratory substances) and +130 o ISS. A divided of 0.05o(3
minutes) on the angular scale and 0.1 o ISS. The Scale is properly
illuminated to facilitate reading.
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