PREFACE
In the present volume are collected those papers on electrochemistry which contain the original statement of the fundamental laws and experiments on which the modern theory of electrolytic conduction is based. Of these, Faraday's law of definite electrochemical action and electrochemical equivalents, first stated in 1834, naturally takes precedence. This law is universally recognized as one of the few rigidly exact laws of nature, and lies at the basis of all electrochemical theory and practice. Of the extended series of experiments in electrochemistry, contained in the fifth and seventh series of Faraday's Experimental Researches, all of which touch more or less on the law in question, only those sections which have a direct bearing on the establishment of the law are here presented. Faraday's brief paper on the "Relation by Measure of Common and Voltaic Electricity" has been added as an introduction, as it was in this article that he was first led to a statement of the probable existence of the law to which he afterwards devoted so much attention.
Second only to Faraday's law, the classical researches of Hittorf on the concentration changes produced at the electrodes during electrolysis, have proved of fundamental significance in the explanation of electrolytic phenomena. The explanation given by Hittorf in 1853 of this phenomenon is still that generally accepted by physicists at the present time. Of Hittorf's five papers bearing on this subject, all of which are easily accessible in German in Ostwald's Klassiker der Exakten Wissenschaften, the first only has been here translated. This, however, is complete in itself, and contains not only a statement of Hittorf's theory, but also a comprehensive and remarkably careful experimental investigation of the phenomenon of transference. The later papers are mainly an exten-
