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The determination of hydrogen and hydroxyl ions has gone through the hands of skillful architects of science—men with vision and imagination seeking the truth in the explanation of the hitherto obscure phenomena and behavior of living and chemical processes. About six decades ago there came a vision to a group of chemists like Arrhenius, Nernst, Van't Hoff, and Ostwald who advanced our knowledge and theories of osmotic pressure and electrolytic dissociation. It is from these men the term ion and the electrical nature of matter and reactions received their place in the equilibrium equations of physical-chemical reactions. Before proceeding further, the author wishes to apologize for the inadequacy, on account of limited time and space, of this review of the important historical concepts associated with the development of hydrogen ion determination. Very frequently it is stated that the specific data which are important but purely historical should be left to the historian. Be that as it may, the author's recommendation would be in the form of a suggestion that such a review would save much time and money for future workers in the field of hydrogen ion determination. This review should be carried out and correlated by a carefully selected group of pure and applied scientists. Arrhenius proposed the theory that acids, bases, and salts in the presence of water are broken down into parts which are called ions. Solutions of these substances gave a greater osmotic pressure than would be expected from the concentrations employed. The lowering of the freezing point of water was too great. In dilute molecular solutions of compounds such as H2SO4, BaCl2, etc., the molecular lowering was nearly three times the normal. These facts accord perfectly with the results of the measurements of osmotic pressure, and furnish strong evidence in favor of the theory of electrolytic dissociation—an ion lowering the freezing point to the same extent as a molecule. The theory was tested by determining the values of the coefficient i which had been introduced by Van't Hoff into the general gas equation in order that it might be applied to the osmotic pressure of solutions. The coefficient i was determined by the well-known freezing point method, and, by a comparison of these values, the theory of electrolytic dissociation at once came into prominence.
Myers, C. N.
Retired, Yonkers, N. Y.