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Refractometer:
Refractometers are precision optical instruments designed to measure the concentration or mixture ratio of water soluble. Easy to use, just place a few drops of liquid on the prism glass and hold up to the light. And ATC refractometers automatically compensate temperature changes so the user can just drop a few drops of a liquid and read. The Hand Held Refractometers provide with a direct reading of the Scales, and have been professionally designed for testing of concentration of many kinds of solution.
Theory of Refraction:
If you place a pencil in a cup of water, the tip will appear bent. If you then put concentrated sugar water in a cup and try the same experiment, the tip of the pencil should appear even more bent. This is an example of the phenomenon of light refraction. Refractometers are measuring instruments in which this phenomenon of light refraction is put to a practical use. Refractometers are based on the principle that as the density of a substance increases (e.g. when sugar is dissolved in water) , its refractive index rises proportionately.
Principles of Refractometer:
1. Refractometers utilise a prism which possesses a much a greater refractive index than the sample solution to be measured. Measurements are made possible using the refractive phenomena which arise at the interface of the prism and the sample solution.
2. In the case of a weak sample solution, the difference between the refractive index of the solution and that of the prism is great, therefore the angle of refraction is large (see A on the diagram below).
3. In the case of a strong sample solution, the difference between the refractive index of the prism is smaller and therefore the angle of refraction is smaller (see B on the diagram below).
Calibration Procedure:
Step 1.
Flip open the daylight plate on top of the refractometer. Place 2-3 drops of the specimen on the main prism. Close the daylight plate so the sample spreads across the entire surface of the prism without air bubbles or dry spots.
Step 2.
Hold the refractometer (daylight plate) in the direction of a light source and look into the eyepiece. You will see a circular field with graduations down the center (you may have to focus the eyepiece to clearly see the graduations). The upper portion of the field should be blue, while the lower portion should be white.
Step 3.
Take the reading where the boundary line of the blue and white intersect at the graduated scale. The scale will provide a direct reading (nD). USE THE SCALE ON THE FAR RIGHT FOR SPECIFIC GRAVITY. Clean the prism carefully using a damp soft cloth. DO NOT immerse refractometer in water. Please read the Operation Manual carefully before using the Refractometer.
