UNITED STATES DEPARTMENT OF COMMERCE Sinclair Weeks, Secretary • A. V. Astin, Director Electrochemical Constants Proceedings of the NBS Semicentennial Symposium on Electrochemical Constants Held at the NBS on September 19 21. 1951 For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price $2 (buckram) East Engin. Pur Bernan 1-4-54 Foreword A knowledge of standards of electromotive force, resistance, and current are of importance in all fields of electrochemistry. A knowledge of other electrochemical constants, including equivalent conductances, transference numbers, ionization constants, activity coefficients, electrode potentials, and the parameters of electrode. kinetics, polarography and electrophoresis, is of importance in studies of electrochemical equilibria and mechanisms. Research in electrochemistry was one of the first functions of the National Bureau of Standards. Maintenance of standards of electromotive force and determinations of standards of resistance and current were authorized as legal functions of the National Bureau of Standards by an Act of Congress in 1901. At that time, the values of the ampere and faraday were determined with silver coulometers. The standard of electromotive force, the unit of which is the volt, is maintained by a group of standard cells in the Bureau's Electrochemistry Section. This standard is compared periodically with the international standard maintained at the Bureau International des Poids et Mesures, Sèvres, France. The papers in this volume present some of the latest results, both experimental and theoretical, in the field of fundamental electrochemistry from many leading establishments in the United States and abroad. They were initially presented at the Symposium on Electrochemical Constants, the seventh of a series of twelve symposia held by the National Bureau of Standards during its Semicentennial in 1951. The cooperation of the Office of Naval Research in making possible the symposia series is gratefully acknowledged. The Symposium on Electrochemical Constants was planned and conducted by the Bureau's Electrochemistry Section, Electricity Divisionin particular by Dr. Walter J. Hamer, chairman of the symposium, who arranged the program and prepared this volume. A. V. ASTIN, Director, National Bureau of Standards. Foreword.. Contents 1. Problem of inclusions in the silver of the silver coulometer, by Arthur F. 2. Determination of the faraday constant by the electrolytic oxidation of oxalate ions, by D. Norman Craig and James I. Hoffman. 3. The faraday and the omegatron, by H. Sommer and J. A. Hipple_ 4. Extended Onsager equation as applied to dilute aqueous electrolyte solutions, by Edward G. Baker and Charles A. Kraus_ 5. High field conductance of some paraffin chain electrolytes, by S. Gusman 6. A study of iodide-iodine solutions with the electromotive-force centrifuge, by Ď. A. MacInnes and Margaret Oakley Dayhoff. 7. Moving boundary measurements in methanol and water solution with indicator concentrations below the critical Kohlrausch value, by 8. Moving boundary separation of salt mixtures, by L. G. Longsworth 9. Diffusion coefficients of electrolytes in dilute aqueous solutions, by 10. Septa in standard cells, by Marion Eppley and George D. Vincent_ 11. Aging of standard cells, by F. X. Lamb... 12. Standard cells and the unit of electromotive force, by Walter J. 1. Problem of Inclusions in the Silver of the Silver Coulometer By Arthur F. Scott1 Introduction The question of the purity of coulometer silver was a very active field of research during the first 15 years of this century and then, for various reasons, it ceased to attract attention. The suspicion that the silver deposit is not pure arose originally from some early studies of the silver coulometer; it was strengthened considerably by the fact that the value of the faraday determined by the iodine coulometer is about 18 parts per 105 greater than the value found with the silver coulometer. This difference is more than can reasonably be attributed to obvious experimental errors. The determination of amount and nature of foreign material in silver crystals deposited in the coulometer was first seriously considered by Lord Rayleigh and Mrs. Sidgwick [1] in 1884, and in the following thirty years it engaged the attention of investigators in many countries. It is the purpose of this review to describe briefly the efforts which have been made to estimate the amount of inclusions in deposits laid down in the silver coulometer and to attempt to evaluate the experimental results. Experimental Methods for Estimating Amounts of Included Material in Silver Deposits Attempts to estimate the amount of inclusions in coulometer silver have been by three different methods: A, determination of the loss in weight of the deposit upon heating; B, direct analysis of volatile material expelled from the deposit; and C, direct analysis of the deposited silver for its silver content. Estimate of Inclusions by Loss in Weight Upon Heating This method first employed by Rayleigh and Sidgwick [1] involves drying the silver deposit at around 160° C and measuring its loss in weight when heated to red heat (500° to 600° C). Usually, heating has been performed with the deposit still in the platinum cathode dish. It is assumed that heating to red heat will cause expulsion of all volatile material. Doubtless because of its simplicity, this method has been a favorite one, and seven determinations are on record in the literature. A postscript to the results of these determinations was presented by Vinal and Bovard [2] in 1916. When the deposit in a platinum 1 Chemistry Department, Reed College, Portland, Oreg. 2 Figures in brackets indicate literature references on page 9. |