Gibbs Phase Rule for a non-reactive system: F = 2 + C – P where F is the number of degrees of freedom, C is the number of components, and P is the number of phases. Lever rule for two liquid phases (a , b) in equilibrium:

where a is the amount of the a phase, b is the amount of b phase, a and b are distances on the phase diagram, and M is the overall composition of the system.