MAGNETOCHEMISIRY by PIERCE W. SELWOOD. PREFACE: People who write books in wartime should have compelling reasons for doing so. This book was started before the full impact of the war effort reached the shores of Lake Michigan. It was finished in the hope that it might contribute, however infinitesimally, to the labors of that army of scientists who seek through natures secrets to parry the blows of an ingenious and pitiless enemy. Magnetochemistry began with Michael Faraday more than one hundred years ago. It enjoyed a vigorous growth under the guidance of Pierre Curie and A. Pascal at the end of the 19th and beginning of the 20th centuries, but it did not reach its prime until Gilbert N. Lewis pointed out the relationship between atomic magnetic moment and chem ical valence. The past few years have seen magnetic susceptibility take its place along with dielectric constant, electron diffraction, x-ray diffrac tion, and molecular and atomic spectra, as one of the most powerful tools at the disposal of the chemist. In order to keep the book within reasonable bounds, it has been neces sary to define magnetochemistry rather severely. The following defini tion has been adopted Magnetochemistry is the application of magnetic susceptibilities and of closely related quantities to the solution of chemical problems. No more than mention will be found of several important branches of magnetism, particularly of magnetooptical phenomena, of the gyromagnetic effect, and of adiabatic demagnetization. The field of atomic magnetism has been slighted, so far as the theoretical side is con cerned, and little has been said of technologically important magnetic properties of the ferrous alloys. But these are topics which have received more than adequate treatment elsewhere. On the other hand, I have tried to omit no major branch of magneto chemistry, so defined. It is especially hoped that no important applica tion of magnetism to structural chemistry has been overlooked. The literature up to about 1934 has been covered in the excellent works of Van Vleck, Stoner, Klemm, and others. I have, therefore, omitted extensive reference to original publications before that date. But from 1934 to the end of 1942 over one thousand papers on magnetochemistry have appeared. A few very recent papers may have been overlooked be of the difficulty in obtaining some periodicals during the war, but in some miraculous fashion the editor of Chemical Abstracts continues to receive abstracts of journals published in occupied and enemy countries. Reference has only occasionally been made to papers reporting mag netic susceptibility measurements for their own sake, and no effort has been made to include tables of susceptibilities. Such data will be found in the International Critical Tables and in the forthcoming Annual Tables of Physical Constants and Numerical Data to be published under the auspices of the National Research Council. I gratefully acknowledge the granting of permission by the American Chemical Society, the American Physical Society, the American Institute of Physics, the American Society for Metals, the American Institute of Mining and Metallurgical Engineers, the Williams and Wilkins Company, and the Editors of the Journal of Physical Chemistry and the Journal of Chemical Education for permission to reproduce diagrams from their respective publications. I am also indebted to the Fisher Scientific Com pany, and to Mr. S. E. Q. Ashley and the General Electric Company for information and diagrams. To Professor J. H. Van Vleck I am grateful for permission to reproduce diagrams from his works...