Chapter I: 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

Radio-activity a permanent property--Induced
activity--Discovery of Uranium X--Conclusions drawn--Search
for new radio-active bodies--Methods of investigation--Nature
of the radiations--Life-periods--Equilibrium series 17

CHAPTER IV

NATURE OF THE ALPHA PARTICLE

Disintegrating of the elements--Identification of the
rays--The alpha rays--Alpha rays consist of solid
particles--Electrical charge--Helium formed from alpha
particles--Discovery of Helium--Characteristics of
Helium--Table of constants 25

CHAPTER V

THE STRUCTURE OF THE ATOM

Properties of Radium--Energy evolved by radium--Necessity for
a disintegration theory--Disintegration theory--Constitution
of the atom--Rutherford's atom--Scattering of alpha
particles--Stopping power of substances 32

CHAPTER VI

RADIO-ACTIVITY AND CHEMICAL THEORY

Influence upon chemical theory--The periodic system--Basis
of the periodic system--Influence of positive
nucleus--Determination of the atomic number--Use of X-ray
spectra--Changes caused by ray-emission--Atomic weight
losses--Lead the end product--Changes of position
in the periodic system--Changes from loss of beta
particles--Isotopes--Radio-activity in nature--Radio-active
products in the earth's crust--Presence in air and soil
waters--Cosmical radio-activity 41

INDEX 53

A BRIEF ACCOUNT OF RADIO-ACTIVITY