Define Miscibility in binary liquid systems?

When two different pure liquids are unable to mix in all proportions, they are said to be partially miscible. When these liquids are placed in contact with one another and allowed to come to thermal, mechanical, and transfer equilibrium, the result is two coexisting liquid mixtures of different compositions. Liquids are never actually completely immiscible. To take an extreme case, liquid mercury, when equilibrated with water, has some H₂O dissolved in it, and some mercury dissolves in the water, although the amounts may be too small to measure. The Gibbs phase rule for a multi component system to be described later shows that a two-component, two-phase system at equilibrium has only two independent intensive variables. Thus at a given temperature and pressure, the mole fraction compositions of both phases are fixed; the compositions depend only on the identity of the substances and the temperature and pressure. A typical binary liquid mixture that spontaneously separates into two phases when the temperature is lowered. The phase separation is usually the result of positive deviations from Raoult's law. Typically, when phase separation occurs, one of the substances is polar and the other non polar.