PREFACE
sion of the first, with applications to certain important problems of chemical constitution.
The great importance of the results obtained by Hittorf was not generally recognized at the time of their publication, but only after F. Kolrausch had pointed out their bearing on his investigations on the electrical conductivity of solutions. The elegance of method and accuracy with which these investigations have been, and are still being carried out, place them pre-eminent among investigations of this class. Immediately after sufficient conductivity data had been obtained, Kohlrausch recognized the bearing of Hittorf's investigations upon his results, and was led to the formulation of the law of the independent migration of ions. The paper in which this law was first presented to the Göttingen Academy in 1876 is translated in full. It was not until 1879 that the researches, of which this was the most important conclusion, appeared in complete form in Wiedemann's Annalen.
With the establishment of the laws of Faraday, Hittorf, and Kohlrausch the way was prepared for the dissociation theory of Arrhenius, which was announced in 1886, as soon as the theory of solutions had been formulated by Van't Hoff.
Massachusetts Institute of Technology.
