General relations between boiling points and liquid phase mole fraction in a binary system, t=f（x） was derived by the aid of the relative volatility equations which was proposed by Lu²⁾, Clark³⁾ and Prahl⁴⁾.
Predictions of correct boiling points by those relations depend not only upon the accuracy of the Lu-, Clark-and Prahl equation, but also upon the Hirati equation^5） which represents the effect of heat of mixing.