Measurements of heat capacities and turbidities for binary mixtures {water + 2,6-dimethylpyridine} and {water, or heavy water + 2,6-dimethylpiperidine} in the critical regions

• The isobaric heat capacities and turbidities were measured.
• Critical exponents and critical amplitudes were determined.
• Universal critical amplitude ratios were tested.
• Complete scaling theory was examined in significantly asymmetric systems.

The isobaric heat capacities per unit volume in both one-phase and two-phase regions and the turbidities in the one-phase region for the significantly asymmetric binary mixtures of {water + 2,6-dimethylpyridine} and {water, or heavy water + 2,6-dimethylpiperidine} were carefully measured, from which the corresponding critical exponents were obtained and found to be consistent with the 3D-Ising values. The values of the system-dependent critical amplitudes for the heat capacity, the correlation length and the osmotic compressibility were deduced, which together with the values of the critical amplitudes related to the coexistence curves reported previously were used to test some universal critical amplitude ratios. Moreover, the importance of the heat capacity related term in the formalism of the complete scaling theory was confirmed. It was also found that the complete scaling formalism possibly becomes somewhat inapplicable for the significantly asymmetric systems.