comparisonof static and flowing junctions 1285 2. Static junctions of the type 0.1 M HCl/satd. KC1 or 0.01 M HC1/ satd. KC1 must be made very definitely in order to be reproducible or constant, and when so made are constant for days to ±0.04 mv. average deviation, and reproducible to less than 0.1 mv.3. The junction between 0.1 and 0.01 M hydrochloric acid is constant and reproducible within the limits of dependability of the silver chloride electrodes used, or within 0.02 mv.4. The potential of the cell system Hg-HgCl-satd. KC1/0.01 M HC1/0.10 M HCl/satd. KCl-HgCl-Hg commonly called the boundary potential between 0.01 and 0.10 M hydrochloric acid has been determined to be 38.04 ± 0.04 mv. average deviation.

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Static liquid junctions have caused endless difficulties since measurements of single electrode and concentration cell potentials were first attempted.2 To get results at all reproducible, investigators have adopted numerous arbitrary methods for overcoming these difficulties, but none are accepted as satisfactory. Such procedures, of course, have rendered the data empirical.3 An extensive study of the most promising devices was made by Lamb and Larson.4 They concluded that results with static junctions, made in various ways, are unsatisfactory, and, therefore, proceeded to develop the flowing junction.There are many instances, however, where it is not possible or convenient to use flowing junctions and yet it is highly important that constant and reproducible values be obtained; for instance, in the comparison of the standard hydrogen with a calomel or any other electrode, liquid junction potential is included in the measurement and becomes a part of the value given to the calomel or other electrode. All such values are as uncertain as the boundary potential, and whenever the calomel electrode is used as a standard the assumption must be made that the solution potential, which is a part of its value, always remains the same.When a saturated calomel electrode or a bridge of saturated potassium chloride is used, the common assumption is that no boundary potential exists under these conditions. It is well known, however, that neither of these assumptions is justified. The present work is an attempt to construct static boundaries of this nature in such a manner as to give potentials more constant and reproducible than have previously been done. The 1 The material in this article is from a portion of the thesis submitted to the Graduate School of the University of Michigan by Kenneth Van Lente in partial fulfilment of the requirements for the degree of Doctor of Philosophy.2 The present authors do not include a bibliography because several are now in print; see, for instance, Guggenheim, This Journal, 52, 1315 (1930).3 These remarks do not apply to junctions which consist of two different concentrations of the same electrolyte. Such boundaries, according to both theory and practice, give but little trouble.

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