General Cytochemical Methods: Volume 2

In the field of mineralogy, methods of measuring the refractive indices of homogeneous crystals by examining them microscopically when immersed in liquids of similar refractive index, have been employed for over 100 years. Crystals, or other homogeneous transparent objects, are examined in a succession of mounting media, usually oils, of different refractive indices; and when two such fluids are miscible, a continuous range of media of intermediate refractive index can be made and used.