Produced by The Online Distributed Proofreading Team at http://www.pgdp.net (This file was produced from images generously made available by The Internet Archive/American Libraries.) A BRIEF ACCOUNT OF RADIO-ACTIVITY BY FRANCIS P. VENABLE, PH.D., D.SC., LL.D. PROFESSOR OF CHEMISTRY, UNIVERSITY OF NORTH CAROLINA AUTHOR OF "A SHORT HISTORY OF CHEMISTRY," "PERIODIC LAW," ETC. D. C. HEATH & CO., PUBLISHERS BOSTON NEW YORK CHICAGO COPYRIGHT, 1917, BY D. C. HEATH & CO. IA7 PREFACE I have gathered the material for this little book because I have found it a necessary filling out of the course for my class in general chemistry. Such a course dealing with the composition and structure of matter is left unfinished and in the air, as it were, unless the marvellous facts and deductions from the study of radio-activity are presented and discussed. The usual page or two given in the present text-books are too condensed in their treatment to afford any intelligent grasp of the subject, so I have put in book form the lectures which I have hitherto felt forced to give. Perhaps the book may prove useful also to busy men in other branches of science who wish to know something of radio-activity and have scant leisure in which to read the larger treatises. It is needless to say that there is nothing original in the book unless it be in part the grouping of facts and order of their treatment. I have made free use of the writings of Rutherford, Soddy, and J. J. Thomson, and would here express my debt to them--just a part of that indebtedness which we all feel to these masters. I wish also to acknowledge my obligations to Professor Bertram B. Boltwood for his helpful suggestions in connection with this work. CONTENTS CHAPTER I DISCOVERY OF RADIO-ACTIVITY PAGE The beginning--Radio-active bodies--An atomic property--Discovery of new radio-active bodies--Discovery of Polonium--Discovery of Radium--Other radio-active bodies found 1 CHAPTER II PROPERTIES OF THE RADIATIONS Ionization of Gases--Experimental confirmation--Application of electric field--Size and nature of ions--Photographing the track of the ray--Action of radiations on photographic plates--Discharge of electrified bodies--Scintillations on phosphorescent bodies--Penetrating power--Magnetic deflection--Three types of rays--Alpha rays--Beta rays--Gamma rays--Measurement of radiations--Identifications of the rays 7 CHAPTER III CHANGES IN RADIO-ACTIVE BODIES