Orientational order parameter, S and effective geometry, alpha(g) are calculated from the refractive index in three nematic room temperature liquid crystal mixtures, blOO3, blOO6, and blO38. The method due to Kuczynski etal. used to determine S from birefringence. The effective geometry parameter is alpha(g) = n(o)/n(e). (n(o) and n(e) are the ordinary and extraordinary refractive indices of the liquid crystal material.) The behavior of alpha(g) as a function of temperature and order parameter has also been reported. The S value calculated from alpha(g) is identically equal to the value obtained from Kuczynski etal method, i.e., from birefringence, delta n. Finally, dn(e)/dT and dn(o)/dT are obtained and the crossover temperatures, T-CO the characteristic temperature, which is in fact the temperature of minimum in the ordinary index of refraction in three mixtures for different wavelengths are calculated from dn(o)/dT.