Study of a Binary Critical Mixture of 2,6‐Dimethyl Pyridine/Water: Measurements of Static and Dynamic Light Scattering and Specific Heat Near the Lower Critical Point

Static and dynamic light scattering experiments are reported for the system 2,6‐dimethyl pyridine/water to determine the critical amplitude ζo of local concentration fluctuations and the critical amplitude Ωo of the characteristic frequency ΩD to scale ultrasound absorption data. It is found: ζo = (2.7 ± 0.2) · 10−8 cm and Ωo/π = 2.9 GHz. Measurements of the temperature dependence of specific heat capacity at constant pressure lead to a critical amplitude A = (0.183 ± 0.002) J g−1 K−1. The two scale factor universality is tested by combining the values of ζ0 and A as well as the values of ζ0 and τ*0 and B* (B*: critical amplitude of the coexistence curve, τ*0 critical amplitude of turbidity). The two ratios of the critical amplitudes calculated from the experimental data are higher by about 15% than the highest theoretical predicted value.