Optical rotation of solid solutions of sodium chlorate and sodium bromate

The optical rotary dispersion (ORD) data for a mixed crystal of sodium chlorate and sodium bromate have been analysed. It is found that the ORD exhibited by these solid solutions cannot be explained using Vegard's law of additivity. Based on the model proposed by Wasastjerna, a special form of additivity of polarisability is assumed in which the asymmetric distribution of the anions around the cation is considered. A formula has been proposed for the additivity of optical rotation in solid solutions and this is found to fit the data for optical rotation in mixed crystals of NaClO₃-NaBrO₃ of different compositions.