分配電位差に関するネルンストの慧眼とその射程

抄録

The article W. Nernst published in 1892, entitled “Über die Löslichkeit von Mischkrystallen,” (On the solubility of mixed crystals), Z. phys. Chem., 9, 137-142 (1892), deserves to be cited as the original paper reporting the so-called Nernst equation for the ion-partitioning between the two immiscible electrolyte solutions. However, Nernst did not present the equation for the distribution potential across the interface emerged after equilibrium partitioning of all the ions present in the system, though claimed to be derivable with ease. The absence of a clear distinction between the systems having different degrees of freedom, i.e., a two phase system consisting of two immiscible electrolyte solutions and that of an aqueous electrolyte solution saturated with two sparingly soluble solid salts, precludes the derivation of an appropriate expression for the distribution potential. The equation of the distribution potential that appropriately describes the latter case has been derived. The practical range capability of his idea is thus next to zero, while Roozeboom's article published in 1891 has a much longer range capability to date, when the mixtures of two hydrophobic ionic liquids have been of contemporary significance and interest.