In order to measure the value, the Abbe refractometer adopts the "half bright and half dark" method, that is, let the Monochromatic radiation shoot from medium A to medium B from all angles of 0-90 degree . At this time, the whole area within the critical angle of medium B has light passing through, so it is bright; The entire area outside the critical angle is dark as there is no light passing through, and the boundary between the light and dark areas is very clear. If observed with an eyepiece above medium B, a semi bright and semi dark image with very clear boundaries can be seen.
Rotate the prism until a boundary or colored light band is observed inside the mirror; If a colored light band appears, adjust the dispersion to make the light dark boundary clear, and then rotate the right angle prism to make the boundary happen to pass through the intersection of the "ten" character. Record the reading and temperature, and repeat the measurement twice to compare the average refractive index of pure water with the standard value of pure water (=1.33299) to obtain the calibration value of the refractometer. Then, use the same method to measure the refractive index of the liquid sample to be tested. The calibration value is generally very small, and if the value is too large, the entire instrument must be recalibrated. When using a refractometer, the following points should be noted:
(1) Abbe's range ranges from 1.3000 to 1.7000, with a precision of ± 0.0001; When measuring, attention should be paid to whether the temperature of the insulation sleeve is correct. If you want to measure accurately to ± 0.0001, the temperature should be controlled within the range of ± 0.1 degree .
(2) The instrument should not be exposed to sunlight during use or storage, and should be covered with black cloth when not in use.
(3) The prism of the refractometer must be carefully protected from scratches on the mirror surface. When adding liquid, the end of the dropper must not touch the prism.
(4) Wash the mirror surface before each drop of sample; After use, the mirror surface should also be washed with acetone or 95 percent ethanol, and the prism should be closed after drying.
