Gives two test procedures which determine refractive index of plastics. Procedure A (refractometric) measures refractive index of moulded parts, cast or extruded film or sheet by using a refractometer. Covers isotropic transparent, coloured, opaque and translucent materials, as well as anisotropic materials. The procedure is reommended when great accuracy is needed. Does not cover powdered or granulated materials. Procedure B (immersion) determines the refractive index of granulated or powdered trans- parent materials using a microscope (making use of the Becke line phenomenon. Generally, monochromatic light should be used to avoid dispersion effects. Accuracy is the same as that of procedure A. It covers isotropic translucent, coloured material, but not materials which are anisotropic or opaque.