Abbe′ Refractometer

\-_▐rē-_▐frak-^▐tä-mə-tər\ nCommon form of refractometer used for determining the refractive index of oils and other liquids, or of grease-like products which are capable of liquefaction at moderate temperatures. Good accuracy is attainable in the range of 1.3–1.7, readings being given to the fourth decimal place. The prisms, which constitute the most important part of the instrument, and hence the liquid held between their faces, are capable of being maintained accurately at the temperature of the determination. With the use of special liquids to form an optical seal to the prisms and a special technique of viewing, it is also used for determining the refractive index of solids such as plastics cast in sheets with polished surfaces and edges. The refractometer measures the real part of the refractive index and thus helps to answer three different types of questions. First, and most simply, it is useful in the empirical identification of pure substances, it can act as a criterion of...