Determination of the temperature and concentration dependence of the refractive index of a liquid mixture     W. B. Li, P. N. Segrè, R. W. Gammon, and J. V. Sengers     Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742     M. Lamvik     Division of Thermodynamics, Norwegian Institute of Technology, N-7034 Trondheim, Norway (Received 2 May 1994; accepted 25 May 1994) We have developed a sensitive interferometric technique for measuring the temperature derivative of the refractive index of liquids with an accuracy of 0.5% as illustrated by measurements with mixtures of liquid n-hexane andtoluene. In addition the concentration dependence of the refractive index of these mixtures has been measured with refractometry. The experimentally observed temperature dependence of the refractive index appears to be consistent with a modification of the Lorentz-Lorenz relation proposed by Looyenga.      J. Chem. Phys. 101, 5058 (1994)