A new approach to determining bubble point or dew point of a binary mixture has been proposed. From an equilibrium still operating steadily at a constant pressure

a portion of the equilibrium binary solution (its composition x1(0) to be evaluated) is replaced by an equal amount of solution having a known composition x1(1). If the equilibrium temperature before and after the replacement remains unchanged

i. e. T(0) - T(1)=0

then x(0)=x1(1) and the bubble point[T(1)

x1(1)] is thus obtained. On the contrary

an inequality of T(0) and T(1) indicates x1(0)≠x1(1). In the latter case

pure component 1 or 2 is added in successive small increments to adjust the temperature in the still to the neighborhood of T(0)

and then the replacement is repeated by a new solution of composition x1(2). The foregoing procedure is repeated until | T(n-1)-T(n)| or | x1(n-1)-x1(n)| comes up to the desired precision and the final point[T(n)

x1(n)] is the bubble point of the system. In a similar way

the dew point could be obtained by replacement of the equilibuium vapor in the still.