Technical analysis of the principle and use of polarimeter

　　The light emitted from the light source passes through the condenser, color filter and polarizer to become plane polarized light, and a three-part field of view is generated at the half-wave plate. The three situations shown in Figure 2 can be observed through the analyzer and the objective and eyepiece group. When the analyzer is rotated, the brightness of the three parts in the field of view is consistent only at zero degrees (the polarimeter is adjusted before leaving the factory). When the test tube containing the solution to be tested is placed, the plane polarized light is rotated by an angle due to the optical rotation of the solution, and the zero-degree field of view changes (as shown in Figure 2 a or c). Rotating the analyzer by a certain angle can reappear a field of view with consistent brightness. This angle is the optical rotation of the solution, and its value can be read from the dial through a magnifying glass.

　　After measuring the optical rotation of the solution, the specific rotation of the substance can be calculated. According to the size of the specific rotation, the purity and content of the substance can be determined.

　　For ease of operation, the optical system of the polarimeter is installed on the base at an angle of 20°. The light source is a 20-watt sodium lamp (wavelength λ=5893A°). The current limiter of the sodium lamp is installed at the bottom of the base, and no external current limiter is required. The polarizers of the polarimeter are all polyvinyl alcohol artificial polarizers. The three-dimensional field of view is a Laurent quartz plate device (half-wave plate). The shadow angle of the three-dimensional field of view can be adjusted by rotating the polarizer (the polarimeter is adjusted to about 3° when it leaves the factory). The polarimeter uses double vernier readings to eliminate the eccentricity of the dial. The dial is divided into 360 grids, each grid is 1°, and the vernier is divided into 20 grids, which is equivalent to 19 grids on the dial. The vernier can read directly to 0.05° (as shown in Figure 4). The dial and the analyzer are integrated and can be rotated in coarse and fine directions by the hand wheel (1). Two 4x magnifying glasses are installed in front of the vernier window for reading.

　　2. How to use the polarimeter

　　(1) Connect the polarimeter to a 220V AC power supply. Turn on the power switch. After about 5 minutes, the sodium lamp will emit light normally and the instrument can start working.

　　(2) Check whether the zero position of the polarimeter is accurate, that is, when the polarimeter is not placed in a test tube or a test tube filled with distilled water is placed in it, observe whether the brightness of the field of view is consistent at zero degrees. If it is inconsistent, it means there is a zero position error, and the deviation value should be subtracted or added to the measurement reading. Or loosen the four screws on the back of the dial cover and slightly turn the dial cover to correct it (only about 0.5° error can be corrected, and serious errors should be sent to the manufacturer for repair).

　　(3) Select a test tube of appropriate length, fill it with the test liquid, install the rubber ring, and screw on the nut until it stops leaking. The nut should not be screwed too tight, otherwise the protective glass will cause stress and affect the accuracy of the reading. Then wipe off the residual solution at both ends of the test tube to avoid affecting the clarity of observation and the accuracy of measurement. Spot welding machine

　　(4) Determine the optical rotation reading: Rotate the degree disk and analyzer to find a position with uniform brightness in the field of view, and then read the reading from the degree disk. A positive reading indicates a right-handed substance, and a negative reading indicates a left-handed substance.

　　(5) The result can be obtained by the double vernier reading method according to the following formula:

　　Where: A and B are the readings of the two vernier windows. If A=B, and the equation is satisfied when the dial is turned to any position, it means that the polarimeter has no eccentricity error (usually the polarimeter has been calibrated before leaving the factory), and the pair reading method is not necessary.

　　(6) Optical rotation is also related to temperature. For most substances, when measured with λ=5893A° (sodium light), the optical rotation decreases by about 0.3% when the temperature rises by 1°C. For more demanding measurements, it is best to carry out the measurement at 20°C±2°C.

　　3. Maintenance of polarimeter

　　(1) The polarimeter should be placed in a well-ventilated, dry place with appropriate temperature to avoid moisture and mold.

　　(2) The continuous use time of the polarimeter should not exceed 4 hours. If it is used for a long time, it should be turned off for 10 to 15 minutes to wait for the sodium lamp to cool down before continuing to use it, or use an electric fan to blow it to reduce the heat of the lamp tube to avoid a decrease in brightness and shortening of life.

　　(3) After using the test tube, pour out the solution immediately, wash it with distilled water, wipe it dry and store it away. All lenses should not be wiped directly by hand, but should be wiped with a soft flannel.

　　(4) When the polarimeter is not in use, the plastic cover should be put on. When packing, it should be placed in the box in a fixed position and pressed tightly.