General method for measuring refractive index of chemical reagents

Refractive index and average dispersion are one of the important optical constants of a substance, and can be used to understand the optical properties, purity, concentration, and dispersion of a substance. The instrument can measure the percentage of sugar content in the sucrose solution (0~95%, corresponding to a refractive index of 1.333~1.531). Therefore, the instrument is widely used in the petroleum industry, the oil industry, the pharmaceutical industry, the paint industry, the food industry, the daily chemical industry, the sugar industry, and the geological survey. It is indispensable for schools and research institutes. One of the commonly used devices.

1 Scope

Abbe refractometer is a general method for determining the refractive index of liquid organic reagents. It is suitable for the determination of liquid organic reagents with light color, transparency and refractive index ranging from 1.3000 to 1.7000.

2. Principle of the method

Refractive index, the ratio of the speed of light in air to the speed of light in the object under the condition of sodium line D, 20 ° C or the ratio of the sine of the angle of incidence and the sine of the angle of refraction when the white air passes through the object .

When light enters a prism with a refractive index N from a substance to be measured having a refractive index n, the incident angle is i, and the angle of refraction is r, then:
Sin i / Sin r = N / n...........(1)
In the refractometer, the incident angle I = 90°, the generation (1) is:
1 / Sin r = N / n
n = N · Sin r...................(2)
When the refractive index N of the prism is a known value, the refractive index n of the test substance can be obtained by measuring the refraction angle r.

3. Instrument

Abbe refractometer DR-A1

The circulating constant temperature water bath 60-C4 can provide the temperature to the prism (10 to 60 ± 0.2) °C

4. Determination

(1) Preparing for work;

(1) The reading must be calibrated with a standard sample before starting the measurement. Add 1~2 drops of bromine to the polished surface of the refractive prism, and then paste the polished surface of the standard sample. When the reading field of view indicates the value on the standard sample, observe whether the boundary between the light and dark in the telescope is in the middle of the crosshair.

(2) After the calibration is completed, it is not allowed to move the part at will during the subsequent measurement. If there is any doubt about the measured refractive index indication in daily work, it can be tested with the standard sample as described above, whether there is an initial error and corrected.

(3) The matte side of the light-increasing prism, the polished surface of the refractive prism and the polished surface of the standard sample must be used before each measurement work and during the calibration of the indication, using a mixture of absolute alcohol and YIMI (1:4). Lightly wipe off with non-fat cotton to avoid leaving other substances, affecting image clarity and measurement accuracy

(2) Determination method:

(1) Connect the constant temperature water bath to the prism, adjust the temperature of the constant temperature water bath, and keep the prism temperature at (20.0±0.1) °C.

(2) The surface of the prism needs to be cleaned before the measurement, and it can be washed with ethanol, YIMI or a mixture of ethanol and YIMI, and then the solvent is dried by the medical cotton.

(3) Drip a sample of about 20 °C to the surface of the prism with a dropper, immediately close the prism and tighten it tightly, so that the sample is uniform, no bubbles and full of field of view, until the prism thermometer reads back to 20.0 ± 0.1) ° C

(4) Adjust the mirror to make the field of view bright, rotate the reading handwheel to make the light and dark boundary in the field of view, and rotate the dispersive prism (polarizer) handwheel to make the color disappear completely at the boundary, then rotate the reading handwheel to make The light and dark boundary is at the center of the crosshair. Observe the scale value indicated on the right side of the field of view of the reading mirror, which is the measured refractive index value.

(5) Read the refractive index value and estimate it to the fourth decimal place.

(6) Determination of transparent translucent liquid:

The liquid to be tested is applied to the surface of the refractive prism with a clean dropper, and the light-receiving prism is covered, and the hand wheel (10) is locked, and the liquid layer is required to be uniform, full of field of view, and no air bubbles. Open the visor (3), close the mirror (1), adjust the eyesight of the eyepiece, and make the crosshair image clear. At this time, rotate the handwheel (15) and find the position of the light and dark boundary line in the field of view of the eyepiece, then rotate The hand wheel (6) makes the dividing line without any color, fine-tunes the hand wheel (15), so that the dividing line is at the center of the cross line, and then rotates the concentrating mirror (12) appropriately. At this time, the value displayed below the eyepiece field of view is the liquid to be measured. Refractive index.

(7) Measuring the concentration of sugar in sucrose:

The operation is the same as when measuring the refractive index of the liquid. The reading can be read directly from the upper half of the field of view, which is the percentage of the sugar content of the sucrose solution.