Universal amplitude combinations in critical mixtures of triethylamine and water from refractive index, density, turbidity, and specific heat experiments

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Abstract
We report new data on refractive index (n), density (ρ), and turbidity (τ) in a mixture of triethylamine and water at critical concentration. These data have been obtained simultaneously for the same sample in order to make the comparison of amplitudes the most reliable. The high sensitivity (a few ppm) of the refractive index and density measurements enables the leading critical amplitude to be obtained accurately in both cases. The ratio of these amplitudes is in good agreement with the ratio (dn/dρ) far from Tc or that deduced from a suitably corrected Lorentz–Lorenz formula. This justifies the use of refractive index measurements to determine thermodynamic divergences. From the turbidity measurements, values for the correlation length and osmotic compressibility amplitudes can be obtained, allowing the universal amplitude combinations R+ξ =0.29±0.02 and R+c =0.056±0.01 to be determined. Both values are in agreement with the 2‐scale factor universality based theories. Negative corrections to scaling are found for the susceptibility.