In addition to providing the compositions of the liquid and vapor phases, T-x-y (and H-x-y) diagrams allow us to determine the relative amounts of vapor V and liquid L that compose the total sample at equilibrium. If a binary mixture with total mole fraction z separates into two phases in equilibrium, then the "lever rule" states that the ratio of the difference between the vapor and total composition (the length of AB in the diagram) to the difference between the total and liquid compositions (length AC in the diagram) is equal to the ratio of L to V: AB / AC = L.V, Use a material balance to derive this rule.