Describe the method, which can be used to separate two compounds with different solubilities in a solvent S.

Explanation

Two compounds having different solubilities in a solvent S can be separated from each other by fractional crystallisation. The process involves a serie of repeated srystallisation. The mixture of the two compounds in the solvent S is heated so as to make it saturated. When the hot solution is allowed to cool, the less soluble substance crystallises out first while the more soluble substance remains in the solution. The crystals of the first compound are separated from the mother liquior and the mother liquor is again concentrated and allowed to cool when the crystals of the second compound are obtained.