The refractive index of fluid argon was measured by usingthe method of angle of minimum deviation for λNa = 5893Å. Themeasurements were carried out along the coexistence curve and along fourteen single phase isotherms from 150.7° to 163°K at pressures from40 to 90 atmospheres.
The Lorentz-Lorenz relation was used to relate the refractiveindex data to the densities and subsequently to find the isothermalcompressibilities along the singla phase isotherms. Following the lawof rectilinear diameter and the simple power laws for criticalexponents, the values of the critical temperature and exponents forargon were found to be Tc = 150.725° ± 0.010°K, β = 0.3574 ± 0.0027,and γ = 1.170 ± 0.013. Also values of nc = 1.08611 andPc = 47.983 atm were determined. These values agree well withothers reported for argon. Comparison of the values of β and γwith those predicted by the classical theory and the three-dimensionallattice gas model suggests that the latter gives a better descriptionof the critical behavior of fluid argon.
Analysis of the reduced chemical potential differences, computedfrom the refractive index data along the singla phase isotherms,has been made by using the scaled equation of state first proposed byWidom. Reasonable values Tc and γ were obtained when thevalue of β determined above was used.
