INDUSTRIAL A N D ENGINEERING CHEMISTRY
622
Vol. 17. No. 6
A Graphic Comparison of Potential Scales and Electrode Potentials' By Louis J. Bircher VANDERBILT UNIVBRSITY,
HIS GRAPH has for its purpose the visualization of the relationships existing between typical electrode potentials and their values measured with reference to certain standard or convenient reference electrodes. While the advocates of the metric system are attempting to establish a uniformity of systems of measures, weights, temperatures, etc., there is creeping into existence an accumulation of electrode potential values based on three recognized scales or measured with reference to any several reference electrodes
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1 Received
February 12, 1925.
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which have been proposed because of convenience or stability. This condition is further complicated because of lack of uniformity in the sign given these potential values in the common reference or textbooks. If there are workers who are interested primarily in the industrial applications of electrochemistry, or students of this subject who have not ' completely familiarized themselves with these relations, it is possible that these may find this a convenient device for "keeping straight." It would be difficult to prepare a chart that would show all the electrodes met with in electrochemistry, but it is thought that a sufficient number of the typical junctions are given for a chemist with his knowledge of the electromotive series to be able to place other junctions not herein given.
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The vertical lines represent the three commonly used potential scales and two other convenient scales in proper relation. The horizontal lines represent the single potentials of typical half cells and if they are used as standard reference electrodes they are represented by full lines. The numbers represent the potential values of these half cells on the three standard scales. All potential values are for 25" C. Electrodes found lower in the graph are positive t o those found higher up. Potential v a l u e s for metal-solution junctions in which the metaf ion is less concentrated than those given in the chart would appear higher in the chart by an amount given by the Nernst relation. Nonmetal electrodes in more dilute solutions would appear lower in the chart. The potential values given in this chart have been selected from those presented in the more recent literature dealing with this subject.
