scope:

Specifies two methods of test for determining the refractive index of transparent plastics, namely Method A: Refractometric method for measuring the refractive index of transparent cast, moulded or sheet materials by means of a refractometer. The method is recommended when great accuracy is required. It is not applicable to powdered or granulated materials. Method B: Immersion method (Becke line phenomenon) for determining the refractive index of powered or granulated transparent materials by means of a microscope and making use of the Becke line phenomenon. Monochromatic light should, in general, be used to avoid dispersion effects. the accuracy of this method is about the same as that of method A. It is applicable to isotropic translucent, coloured or opaque materials as well as anisotropic materials.