Optical rotatory dispersion of crystals of sodium chlorate and sodium bromate

The rotatory dispersion of crystals of NaClO3 and NaBrO3 has been measured in the visible and ultraviolet region of the spectrum. Apart from a small infrared contribution, the rotatory dispersion of both crystals can be expressed as a difference of two terms. For NaClO3 the positive term has a greater strength than the negative one, whereas for NaBrO3 the reverse is the case. Thus corresponding configurations of the two crystals have opposite signs of optical rotation. The important point is brought out that calculations of optical activity in terms of atomic refractivities but neglecting rotatory dispersion, such as those carried out recently for these two crystals, arc necessarily inconclusive.