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IntroductionMost salts may be classified among the "capillary-inactive substances" which give solutions having a surface tension slightly greater than that of pure water and which are negatively adsorbed in the surface layer within the range of concentration hitherto investigated. Measurements by many early investigators have shown that the surface tension-concentration curves are approximately linear and that the slope and curvature are less influenced by the individuality and valence type of the salt than the corresponding curves for most other properties of solutions of electrolytes.The f i s t careful work on dilute solutions (less than 0.2 N ) appeqrs to have been done under the

After Kohlrausch had developed his method of measuring the electrical conductance of solutions by means of an alternating current bridge, he undertook with the aid of Holborn and Diesselhorst1 the determination of the specific conductance of seven standard reference solutions in absolute units in order that the results might be available to himself and to other experimenters for the calibration of conductance cells. For this purpose they used two cells whose cross sectional areas, a, and length, l, were determined mechanically. The cell constant, l/a, could then be computed in absolute units (cm.""1) from the measured dimensions.The cell constants of a considerable number of other cells with sealed-in electrodes of the usual type were determined electrically by comparison with the primary cells by measurements of resistance when filled with a common solution. These cells, whose cell constants were thus determined indirectly, were then used for the determination of the specific conductance of the seven standard reference solutions at approximately 0, 9, 18, 27 and 36°. The specific conductance of each of these solutions for every degree between 0 and 36°was obtained by interpolation. No actual measurements were made at either 20 or at 25°. The water-bath used to fix the temperature of the cells was not provided with an automatic thermostatic control. The majority of the data on conductance in the literature are based on the values ascribed to these standard reference solutions by Kohlrausch, especially the 1 N and 0.1 N potassium chloride solutions.In the original paper by Kohlrausch, Holborn and Diesselhorst it is stated that the normal potassium chloride solution was prepared by dissolving 74.555 g. of potassium chloride weighed in air and making up to 1 liter at 18°. The 0.1, 0.02, and 0.01 normal solutions were prepared by dilution by volume. The book "Das Leitvermógen der Elektrolyte" by Kohlrausch and Holborn,2 which was published in the same year as the paper referred to, contains alternative directions for the preparation of these solutions by weight. This book has probably been used by other experimenters more than the original paper because it is more generally available.Kraus and Parker3a have pointed out that the alternative instructions for preparing the 0.1, 0.02 and 0.01 normal solutions given by Kohlrausch and (X) F.

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Duplicate cells with nearly pure acetic acid as the solvent could be reproduced to within 0.1 mv. and were constant in electromotive force for several months at least.A cell containing two solid phases in equilibrium with the saturated solution was prepared.The heat of formation of the compound Pb(C2H302)2O.5H20 was determined.