Design of the device
S
tructurally
polarimeter consists of the following cores: cases 47, heads of the
analyzer with a linear polarizer 48, the basis in gathering 49, a
cover 50.
It is possible to switch on sodium lamp with the help of toggle-switch 42. Cuvet branch is closed by a cover 45.
The head of the analyzer with a polarizer (a Fig. 4.) is a measuring part of polarimeter and consists of following assembly units: the polarizing device 33, a head of the analyzer 24, an observant tube 28, eye-flap 30. The head of the analyzer and the polarizing device are fixed on the ends of the case cuvet branch 21. The polarizing device consists from protective glass 20, a chromatic phase plate 19, a linear polarizer 18, condenser 17 and an optical filter 16. Linear polarizer and a chromatic phase plate is fixed in frames.
The head of the analyzer 24 consists of the plug 22, a linear polarizer 23, the case 27, a flange 32. Limb 26 is fixed on a cylindrical cogwheel. On limb the scale with points is put. The observant tube consists of an objective 25, stop and an ocular. 29 observant tube is established by rotation of the plug on the sharp image of a line of division of vision fields. In eye-flap 30 there are two magnifiers 35 through which readout are removed from a scale of limb and counting out devices are rigidly fixed. A ditch consists of a tube with plugs, integumentary glasses, linings, plugs and nuts. On a glass tube there is a camber necessary for gathering bubble of air. On a tube ditches its actual length between end faces is put.
Principle of action
In polarimeter the principle of equalizing of brightnesses of the field of vision divided into parts is applied. Division of a field of vision into parts is carried out by introduction in optical system of polarimeter a chromatic phase plate. Brightnesses water comparison equalize near to full blackout of a field of vision. Planes of polarization of a polarizer and analyzer at equality of the minimal brightnesses of fields of comparison make a corner 86,50.
Position of limb and a field of vision at nstallation of the analyzer on equal brightness of a fields of comparison in sensitive position at entered a ditch, filled by the distilled water (zero position).
Light from a lamp, having passed through condenser and a polarizer, one part of a bunch passes through a chromatic phase plate, protective glass, to a ditch and the analyzer, and other part of a bunch only through protective glass, to a ditch and the analyzer.
Position of limb and a field of vision after input the ditches, filled by a solution, and secondary installation of an ocular on sharpness of the image of a line of section of fields of comparison.
Equalizing of brightnesses of fields of comparison make a method of rotation of the analyzer. If between the analyzer and a polarizer to enter сuvet with optical active solution equality of brightnesses of fields of comparison is broken. It can be restored by turn of the analyzer on a corner equal to a corner of turn of a plane of polarization by a solution.
Position of limb and a field of vision at installation of the analyzer on equal brightness of a fields of comparison in sensitive position with cuvet, filled by a solution.
On a corner of rotation of a plane of polarization definition of concentration optically active substances is possible. For the majority optically active substances specific rotation little depends upon concentration and a corner of rotation is proportional to concentration.
(1)
Where - a corner of rotation of a plane of polarization in degrees
- specific
rotation measured оптически
active substance for length of a wave of 589 nanometers and at
temperature 20° С
L - length of cuvet in dm
C - concentration in g/sm3
Knowing a corner of rotation of a plane of polarization in degrees, it is possible to define concentration of substance in g/sm3
(2)
At measurement on polarimeter a corner of rotation of a plane of polarization dextrorotatory optically active solutions readout on a scale of the first counting out devices and limb will be from 0 up to 350.
At measurement of a corner of rotation of a plane of polarization levorotary optically active solutions readout on a scale of the first counting out devices and limb will be from 360 up to 3250, the size of a corner of rotation is defined: readout on a scale of the first counting out devices and limb a minus 3600.
If necessary it is possible to spend measurements of corners of rotation of a plane of polarization more ±350. The error of measurement in this case can be certain experimentally, by definition by result of measurement of specific rotation of substance and its comparison with reference data.
.
DEFINITION OF THE CORNER OF ROTATION OF THE PLANE OF POLARIZATION BY THE OPTICALLY ACTIVE SOLUTION
1. Definition of zero reading is made with cuvet, filled distilled water.
2. To establish an eyepiece on an eye on the sharp image of a line of section of fields of comparison by rotation of the plug of an observant tube.
3. After that, rotating the handle 31 (see fig. 11) to turn the analyzer and to achieve equality of brightnesses of fields of comparison. If in field of vision coloration is observed, it is necessary to wring out cover glass of cuvet.
4. Installation on uniform brightness of a field of comparison to repeat five times with removal of readout on a scale of limb and counting out devices and calculation of average values. The received value is zero reading.
5. Investigated solutions should be transparent, not have the weighed particles.
6. For definition of a corner of rotation of a plane of polarization to a ditch with an investigated solution to put in cuvet branch of polarimeter and to close a cover. Then to establish ocular of an observant tube on an eye on the sharp image of a line of section of fields of comparison.
7. Smooth and slow turn of the analyzer to establish equality of brightnesses of fields of comparison and to remove readout as follows:
-define, on how many degrees the scale of limb in relation to a scale of the first counting out devices is turned,
- Then on strokes of the first and the second counting out devices, conterminous with strokes of a scale of limb to count shares of degree.
9. To number of the degrees taken on a scale of limb first of the counting out device to add average arithmetic readout on a scale of the first and the second counting out devices.
10. To make five experiences and to take an average arithmetic of them.
11. From the received average arithmetic readout to subtract zero reading.
Example 1. At definition of zero position with cuvet, the filled distilled water, has been received result 0,060 , and after input the ditches, filled by an investigated solution, is received readout 3,560 . The difference between final and initial installations is equal readout to a corner of rotation of a plane of polarization of an investigated solution: 3,560- 0,060= 3,500.
Example 2. After input the ditches, filled investigated by a solution with the left rotation, have been received result 357,140. In this case zero reading should be accepted equal to 360,060. The difference between final and zero reading is equal to a corner of rotation of a plane of polarization of an investigated solution: 357,140 - 360,060 = - 2,920