Transcriber’s Notes Text printed in italics has been transcribed _between underscores_, bold face text ~between tildes~. Small capitals have been replaced with ALL CAPITALS. _{text} and ^{text} represent subscript and superscript texts respectively. More Transcriber’s Notes may be found at the end of this text. THE RARE EARTHS THE RARE EARTHS THEIR OCCURRENCE, CHEMISTRY, AND TECHNOLOGY BY S. I. LEVY B.A. (CANTAB.), B.SC. (LOND.), A.I.C. LATE HUTCHINSON RESEARCH STUDENT OF ST. JOHN’S COLLEGE CAMBRIDGE WITH ILLUSTRATIONS LONDON EDWARD ARNOLD 1915 [All rights reserved] PREFACE During the thirty years which have elapsed since Dr. Auer’s application of the rare earths to the production of artificial light, the incandescent mantle industry has developed to an extent which gives it a prominent place among those chemical industries which may be considered essential to modern civilisation. This technical development has in turn assisted and stimulated the scientific examination of the elements of this group, with the result that ordered and accurate knowledge is beginning to replace the confused and uncertain data which had been collected by earlier workers in the field. These advances have served to emphasise the scientific interest and importance of the rare earth group, and the difficulty of bringing it into relation with the other elements. The relatively scant attention devoted to the study of this province of inorganic chemistry by teachers and students in England is probably due no less to the difficulty in classification, and the uncertainty with regard to the homogeneity and individuality of the various members of the family--an uncertainty by no means entirely removed even now--than to the fact that the very extensive literature on the subject is somewhat confused and difficult of access, especially to those unfamiliar with the French and German languages. The present work is intended to give a general but fairly comprehensive account of the rare earth group. In accordance with general usage, the elements zirconium and thorium have been included, though these are now recognised as falling outside the limits of the rare earth group proper. The inclusion of titanium, which chemically is so far removed from the cerium and yttrium elements, has been considered desirable, not only on account of its general occurrence in the rare earth minerals, and its position in Group IVB with zirconium, cerium, and thorium, but also on account of its increasing chemical and technical interest, and its use in the ordinary quantitative laboratory operations.