The advantage of using a ternary plot for depicting chemical compositions is that three variables can be conveniently plotted in a two-dimensional graph. Ternary plots can also be used to create phase diagrams by outlining the composition regions on the plot where different phases exist.

Why do we use ternary phase diagrams?

Ternary phase diagrams are used to represent all possible mixtures of three solvents [1]; they are described in Chapter 3. ... The two systems belonging to the same tie-line separate into two phases that have exactly the same composition.

What is the point on the ternary phase diagram where the compositions of the two phases in equilibrium become identical?

The liquid and vapor portions of the binodal curve meet at the plait point, a critical point at which the liquid and vapor phases are identical. Thus, the plait-point mixture has a critical temperature and pressure equal to the conditions for which the diagram is plotted.