Hofmeister (8) first observed that certain ions assumed a definite order in their effect upon the osmotic pressure of protein solutions and upon physiological reactions. Pauli (18) and Hofmeister (8) arranged the anion series in descending order, as follows: Sulfate, chloride, nitrate, bromide, iodide, sulfocyanate Spiro (23) showed that acids and alkalies had a more pronounced influence than water upon the distension of gelatin and other colloids, and arranged the acids in descending order. More recent work (24) dealing with the effect of neutral salts upon the swelling, osmotic pressure, and viscosity of colloidal proteins has produced comprehensive cation and anion series, some of the anions being arranged in descending order as follows:Sulfate, tartrate, citrate, chloride, bromide, nitrate, iodide, sulfocyanate Anions of the neutral salts have power according to the lyotropic series to lower the freezing point and to change the viscosity and surface tension of water. Urban (24) investigated the action of electrolytes upon the specific heat of water at temperatures ranging from 10°to 40°C. He demonstrated both a cation and an anion series in which the anions were active generally in the same order as in the Hofmeister series.The author undertook the measurement of the partial molal volumes of eight potassium salts of the Hofmeister series, hoping that the rate of change in volume with concentration might produce a well-defined series. The salts selected were the chloride, bromide, iodide, nitrate, sulfocyanate, sulfate, tartrate, and citrate. Direct volume measurements were made on solutions of ten different concentrations (0.005 to 0.5 molal) at eleven different temperature intervals ranging from 5°to 30°C.
