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Also known as refractometry

thumb|Hand-held refractometer A refractometer is a laboratory or field device for the measurement of an index of refraction (refractometry). The index of refraction is calculated from the observed refraction angle using Snell's law. For mixtures, the index of refraction then allows the concentration to be determined using mixing rules such as the Gladstone–Dale relation and Lorentz–Lorenz equation.