Phase Rule Consideration:

Let us consider the situation when a solute is in contact with two immiscible solvents. If we apply Gibbs Phase Rule to this system,

P + V = C + 2

where P is the number of phases, V is the variance or degrees of freedom and C is the number of components.

Here, we are dealing with two phases, i.e. two immiscible solvents and one solute distributed between them. Therefore, variance will be unity. This will amount to the fact that the concentration of the solute in one phase will fix the concentration of the solute in another phase. There will be a definite relationship between the solute concentrations in each of the two solvent phases. This ultimately forms the basis of the distribution law.