a method of determining the indexes of refraction of small grains of solids (down to 0.001–0.002 mm) under a microscope. In the immersion method the grains being studied are immersed in drops of various liquids with known indexes of refraction n that are applied to a slide. After the samples are observed through the microscope, the liquid whose n is closest to that of the given substance is selected. The accuracy of the immersion method is on the order of 0.001; it is significant that the form and character of the surface of the grain being studied are nearly inconsequential in the immersion method.
An immersion set consisting of 98 liquids with n ranging from 1.408 to 1.780 is used in the immersion method. There are also sets of high-refraction liquids (n up to 2.15) and transparent alloys, such as sulfur and selenium (n up to 2.6–2.7). The accuracy of measurement in alloys is approximately one order lower than in liquids.
The immersion method is used in chemical analysis (so-called immersion analysis) to establish the purity of compounds and to determine the ratio of components in mixtures of substances. It is widely used in the study of minerals and rock, and also in some branches of chemical engineering.
REFERENCESTatarskii, V. B. Kristallooptika i immersionnyi metod issledovaniia mineralov. Moscow, 1965.
Ioffe, B. V. Refraktometricheskie metody khimii. Leningrad, 1960.
V. B. TATARSKII