Distribution law was given by Nernst. He found that if a substance is present in different phases (say liquids) in a system at equilibrium then the solute distributes itself between two immiscible solvent in contact with each other in such a way that at constant temperature the raiio of its concentration in the two liquids is constant, whatever the total amount may be. It is known as distribution law.
If C1 and C2 represent the concentration of a solute in the two solvents then C2C1= constant =K where K is distribution or partition coefficient