The Lorentz–Lorenz relationship in the phase diagram of triethylamine and water. Application to the coexistence curve

The refractive index (n) of the partially miscible mixture of triethylamine and water has been measured at various temperatures (T) and concentrations. The data have been fitted to an analytic function. By using existing density data, the validity of the Lorentz–Lorenz formula has been tested. The same discrepancies that are usually observed in liquids have been found (−0.4% on n, and −13% on dn/dT). No supplementary deviation has been detected in the vicinity of the critical point. These data have been used to obtain a precise determination of the coexistence curve.