Refractive Index and Chemical Constitution | Refractivity
Refractive index of a liquid changes not only with the wavelength of light but also with the temperature. It can not, therefore, provide a satisfactory comparison of refractive powers of different liquids relative to their constitution. To eliminate the effect of temperature, Lorenz and Lorentz (1880) showed purely from theoretical considerations that-
where n is the refractive index, d the density and R is a constant which they defined as the Specific refraction or Refractivity. In order to compare the refractive powers of different liquids the specific refractions are multiplied by their respective molecular weights, the resulting products being termed the Molecular refraction or Molecular refractivity.