Extended equation of state for non-ideal mixtures near the consolute critical point.

The problem of constructing the equations of state and calculating the thermodynamic parameters of mixtures near the liquid-liquid critical point using the parameters of their components remains an urgent task of the condensed matter physics.To solve it, the new method of choosing the countdown start for calorific values is founded, in which the corresponding states law for liquids is satisfied. An analysis of thermodynamic consistency conditions in the dissolution of solution components allow concluding that a consistent calculations of the mixture parameters for variable values are approximate due to excessive non-additive contributions to them; similar calculations are exact for values which remain constant for components. Using the proposed approach for liquid components of obtained and literature data for mixtures C4H8O2 - H2O, CH4O – C6H14, C6H7N – D2O, the constant combinations of thermodynamic parameters have been found. It allowed using the consistent rules for calculating the calorific parameters of mixture and obtaining the parameters of the theory of critical mixtures.