Fraunhofer's method used to measure the refractive index of
liquids has been modified. The modification includes an electric
circuit containing a sensitive photodiode in order to measure
accurately the deviation angle of a HeNe laser beam. The
refractive index of pure water and four different concentrations
of NaCl solution is measured at temperature range 5-90°. Four
mathematical equations relating the refractive index to the
temperature and concentration are obtained using the least
squares method. The effect of temperature and concentration on
refractive index are explained using Lorentz-Lorenz formula.
K. M. Aly, E. Esmail, "Refractive index of salt water: effect of
temperature," Opt. Mater.,2, 195-199 (1993).