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THE CHEMICAL EFFECTS 
 
 OF ALPHA PARTICLES 
 
 AND ELECTRONS 
 
 BY 
 SAMUEL C. LIND, Ph.D. 
 
 PHYSICAL CHEMIST, U. S. BUREAU OF MINES 
 
 
 American Chemical Society 
 Monograph Series 
 
 BOOK DEPARTMENT 
 The CHEMICAL CATALOG COMPANY, Inc. 
 
 ONE MADISON AVENUE, NEW YORK, U. S. A. 
 1921 
 
 LIBRARY 
 iUOVEKSITY OF CALIFORNIA 
 
Copyright, 1921, By 
 
 The CHEMICAL CATALOG COMPANY, Inc. 
 
 All Rights Reserved 
 
 Press of 
 
 J. J, Little & Ives Company 
 
 New York, U. S. A. 
 
GENERAL INTRODUCTION 
 
 American Chemical Society Series of 
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4 GENERAL INTRODUCTION 
 
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GENERAL INTRODUCTION 5 
 
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AUTHOR'S PREFACE 
 
 In the decade preceding the recent European war, the sub- 
 ject of photochemistry first began to receive attention commen- 
 surate with its great importance. The experimental and theo- 
 retical aspects of the subject were presented in the well-known 
 works of Plotnikow, Weigert, Sheppard, Benrath, and others. 
 
 The chemical effects produced by some of the other forms of 
 radiant energy or matter have also been investigated, more or 
 less fully, but the experimental results in this field have not 
 hitherto been brought together in monographic form. The chemi- 
 cal effects of the various kinds of corpuscular radiation may be 
 regarded as constituting one division of the general subject of 
 radio chemistry (as defined in this monograph), of which photo- 
 chemistry proper forms another division. The various effects, 
 such as those of a and p particles, high velocity electrons, posi- 
 tive rays, recoil atoms, etc., have been regarded as being so in- 
 directly related either to photochemistry or to radioactivity, that 
 they have received rather scant treatment in the standard 
 treatises on those two subjects. 
 
 It is the object of this monograph to collect the experimental 
 material and, as far as possible, to present it in such a way as 
 to emphasize the relations between the chemical effects of the 
 material and of the photochemical radiations. The theoretical 
 development has also been carried as far as the available data 
 permit at the present time. In the main, however, the subject 
 is still in the empirical stage and must await further evidence 
 as to the behavior of individual atoms and gaseous ions before 
 final conclusions can be drawn regarding the exact mechanisms 
 of the radiochemical reactions. 
 
 The field of photochemistry has been touched upon, in the 
 present work, only in comparing the nature of the various radio- 
 chemical effects, and also in connection with the Einstein photo- 
 chemical equivalence law, which shows a close analogy with the 
 ionic-chemical equivalence of the corpuscular radiant effects. 
 
 7 
 
8 AUTHOR'S PREFACE 
 
 A fairly full consideration of the experimental tests of the photo- 
 chemical equivalence law appeared to have additional justifica- 
 tion, from the fact that the recent evidence has not yet been 
 treated in the standard texts of photochemistry. 
 
 The subject of radioactivity has been introduced only in so 
 far as was necessary to afford an insight into the principles artd 
 technique involved in the utilization of radioactive substances 
 as sources of radiation in the production of the chemical ef- 
 fects under consideration. For the radioactive data included in 
 this monograph, the writer is indebted to the following texts: 
 Rutherford's "Radioactive Substances and Their Radiations" 
 (1913), Mme. Curie's "Traite de Radioactivite" (1910), Meyer 
 and V. Schweidler's "Radioaktivitat" (1916), Bragg's "Studies in 
 Radioactivity" (1912), and to J. J. Thomson's "Rays of Posi- 
 tive Electricity" (1913). 
 
 The writer is also greatly indebted to the cooperation of the 
 Editors of the Scientific Monographs of the American Chemical 
 Society, who have supervised the publication of the present mono- 
 graph, to Dr. G. L. Wendt of the University of Chicago for 
 his very helpful suggestions and criticisms, and to the Chemical 
 Catalog Company, Inc., which has efficiently carried out the 
 plans of the Editors. 
 
CONTENTS 
 
 PAGE 
 
 Chapter 1. Radiochemistry 17 
 
 1. Definition of Radiochemistry. — 2. Radiant Energy 
 and Matter. — 3. Photo- and Radio-Chemistry. 
 
 Chapter 2. Brief Outline of Radioactivity and Some 
 
 Properties of the Radiations 20 
 
 4. Nature of Radioactivity — Rutherford-Soddy Hy- 
 pothesis. — 5. Radioactive Phenomena. — 6. Kinds of 
 Radiation. — 7. Radioactive Families and their Trans- 
 formation Products. — 8. Radioactive Equilibrium. — 
 9. Kinetic Energy of a Particles. — 10. Range of a 
 Particles. — 11. Ionizing Power of a Particles. — 12. 
 Enumeration of a Particles. — 13. Some Additional 
 Properties of a Particles. — 14. Characteristics of 
 Members of the Radium Family as Sources of Radia- 
 tion. 
 
 Chapter 3. Electrical Effects — Ionization . . 37 
 
 15. Saturation Current as a Measure of Ionization. — 
 
 16. Ionization by Electronic Shock. — 17. Some Prop- 
 erties of p Particles and Electrons. — 18. y Rays and 
 X Rays. 
 
 Chapter 4. Qualitative Radiochemical Effects . . 46 
 19. General Classification. — 20. Qualitative Observa- 
 tions. — 21. Coloration and Decomposition of Radium 
 Salts. — 22. Coloration of Glass and Minerals. — 23. 
 Thermo-luminescence produced by Radiation. — 24. 
 Luminescence and Phosphorescence produced by 
 Radiation. — 25. General Character of the Chemical 
 Effects of the Rays of Radium. 
 
 Chapter 5. Chemically Quantitative Investigations in 
 
 Liquid Systems 59 
 
 26. Decomposition of Water by Radium Salts in 
 Solution. — 27. Formation of Hydrogen Peroxide in 
 Water. — 28. Reactions produced by Penetrating Rays. 
 
 .9 
 
10 CONTENTS 
 
 PAGE 
 
 Chapter 6. Reactions Produced by Radium Emana- 
 tion. (First Experiments) 65 
 
 29. Radium Emanation as a Source of Radiation. — 30. 
 Experiments of Cameron and Ramsay. — 31. Experi- 
 ments of Usher on the Ammonia Equilibrium. 
 
 Chapter 7. Relation between Gaseous Ionization and 
 
 Radiochemical Effects 74 
 
 32. Historical Development of the Ionization Theory 
 of the Chemical Effects of Corpuscular Radiation. — 
 
 33. Production of Ozone by a Particles. — 34. Other 
 Gas Reactions. — 35. Calculation of the Average Path 
 of a Particles. — 36 Results of Various Investigations. 
 37. Reactions in Liquid Systems — Results of Duane 
 
 • and Scheuer on the Decomposition of Water, Ice and 
 Water Vapor. — 38. Experiments of Scheuer on the 
 Formation of Water by a Radiation. — 39. Experi- 
 ments of Wourtzel on the Decomposition of Gases. 
 
 Chapter 8. Kinetics of the Chemical Reactions Pro- 
 duced BY Radium Emanation 94 
 
 40. Classification of the Reactions. — 41. Development 
 of General Kinetic Equation for the Action of Emana- 
 tion when Mixed with Gases in Small Volumes. — 42. 
 Application of Kinetic Equation to Experimental Re- 
 sults. — 43. Influence of the Size of the Reaction Vessel, 
 Law of the Inverse Square of the Diameter of the 
 Sphere. — 44. Use of Kinetic Results to Evaluate M/N. 
 
 Chapter 9. Additional Relationships of the Radio- 
 chemical Effects 107 
 
 45. Influence of Varying the Proportions of Hydrogen 
 and Oxygen. — 46. Action of a Rays on Pure Oxygen 
 or Pure Hydrogen. — 47. Comparison of the Chemical 
 Effects of a and of Penetrating Rays. — 48. General 
 Discussion of Ionic-Chemical Equivalence. — 49. Ex- 
 ceptions to Ionic-Chemical Equivalence, Reactions in 
 which M exceeds N. — 50. Reactions in which N ex- 
 ceeds M. — 51. Energy Utilization of a Rays in 
 Chemical Reactions. — 52. Chemical Reaction Pro- 
 duced by Electrical Discharge in Gases. — 53. Produc- 
 tion of Free Electrical Charges by Chemical Action. 
 
 Chapter 10. Photochemical Equivalence Law . . 132 
 54. Einstein's Application of the Quantum Theory to 
 Photochemical Action. — 55. Experimental Tests of the 
 
CONTENTS 11 
 
 PAGE 
 
 Law of Photochemical Equivalence. — 56. Comparison 
 of Photochemical Equivalence Law and Ionic-Chemical 
 Equivalence. — 57. Mechanism Proposed by Nernst for 
 the Hydrogen-Chlorine Photo-Reaction. — 58. General 
 Radiation Theory of Chemical Action. 
 
 Chapter 11. Positive Rays and Recoil Atoms . . 148 
 59. General Nature of Positive Rays. — 60. Thomson's 
 Method of Positive Ray Analysis. — 61. Isotopes of 
 Neon. — 62. Discovery of Other New Isotopes by Aston. 
 — 63. General Properties of Recoil Atoms. — 64. 
 Chemical Reaction produced by Recoil Atoms. 
 
 Chapter 12. Atomic Disintegration by a Particles . 162 
 65. Scattering and Impacts of a Particles. — 66. Swift 
 Hydrogen Atoms. — 67. Decomposition of Nitrogen and 
 Oxygen. — 68. Experiments of Rutherford with Other 
 Light Atoms. — 69. Artificial Radioactivity. 
 
 Index of Subjects 173 
 
 Index of Authors 178 
 
TABLES 
 
 Subject 
 
 NUMBER PAGB 
 
 I. Uranium-Radium Series 28 
 
 II. Stopping Power and Ionization of a Particle . 33 
 
 III. Decomposition of Water by Emanation (Cam- 
 
 eron and Ramsay) 69 
 
 IV. Formation of Water (Moist) by Emanation 
 
 (Cameron and Ramsay) 71 
 
 V. Formation of Water (Dry) by Emanation (Cam- 
 eron and Ramsay) 72 
 
 VI. Radiometric Method to Determine Range of a 
 
 Particles 78 
 
 VII. Chemical-Ionic Equivalence (M/N) . . 85,86 
 
 VIII. Decomposition of Water, Ice, and Water Vapor 
 
 (Duane and Scheuer) 89 
 
 IX. Decomposition of Gases by Emanation (Wourtzel) 93 
 
 X. Application of Kinetic Equation to Results of 
 
 Cameron and Ramsay . . . . 97,98 
 
 XI. Application of Kinetic Equation to Results of 
 
 Lind . 99 
 
 XII. Effect on the Velocity Constant of Varying the 
 
 Diameter 101 
 
 XIII. Effect on the Velocity Constant of Excess of 
 
 Hydrogen 109 
 
 XIV. Effect on the Velocity Constant of Excess of 
 
 Oxygen 110 
 
 XV. Primary Light Reactions (Bodenstein) . . 134 
 
 XVI. Secondary Light Reactions (Bodenstein) . 137, 138 
 
 13 
 
14 TABLES 
 
 NUMBER CAQB 
 
 XVII. Test of Einstein's Photochemical Equivalence 
 
 Law (Frl. Pusch) 139 
 
 XVIII. List of New Isotopes by Positive Ray Method 
 
 (Aston) 153 
 
 XIX. Chemical Effect of Recoil Atoms — Data and Cal- 
 culations (Lind) 157 
 
 XX. Analysis of Recoil Atom Effect (Lind) . . 160 
 
 Appendix 
 
 A. Rate of Decay of Radium Emanation, e"^' 
 
 (Kolowrat) 170-171 
 
 B. Radioactive Isotopes (Fajans) .... 172 
 
ILLUSTRATIONS 
 
 NUMBER Subject 
 
 OF FIG. PAGE 
 
 1. Ionization Curve of an a Particle .... 30 
 
 2. Curve of Saturation Current and of Ionization by- 
 
 Electronic Shock 38 
 
 3. Apparatus of Cameron and Ramsay for Gas Re- 
 
 actions (Emanation) 67 
 
 3a. Apparatus of Cameron and Ramsay for the Decom- 
 position of Water 67 
 
 4. Apparatus of Camerpn and Ramsay for Various Re- 
 
 actions 68 
 
 5. Diagram for the Calculation of the Average Path 
 
 of a Particles in a Sphere of Diameter less than 
 
 the Range (Lind) 82 
 
 6. Apparatus for the Combination of Hydrogen and 
 
 Oxygen (Emanation) 100 
 
 7. Curves showing the Chemical Effect of Recoil 
 
 Atoms (Lind) 158 
 
THE CHEMICAL EFFECTS OF 
 ALPHA PARTICLES AND ELECTRONS 
 
 Chapter 1. 
 Eadiochemistry. 
 
 1. Definition of Radiochemistry. 
 
 The relationships existing between the various forms of 
 energy and the transformations of the different kinds into one 
 another are of fundamental importance in the physical sciences. 
 The chemist is primarily concerned with those transformations 
 in which chemical energy is one of the forms involved. Thermo- 
 and electro-chemistry represent two of the most highly devel- 
 oped branches of physical chemistry and deal with the relations 
 between chemical energy on the one hand and thermal and elec- 
 trical energies, respectively, on the other. Of no less importance 
 are the relations between chemical and radiant energies, which 
 constitute a subject that should, according to the same system 
 of terminology, be designated as radiochemistry. 
 
 The term radiochemistry has already been used otherwise by 
 some authors to designate the chemistry of the radioactive ele- 
 ments and of their transformations by atomic disintegration. 
 Since this more special usage is relatively new and not thoroughly 
 intrenched, and since the term radiochemistry is the only logical 
 one to conform with such terms as electro-, thermo-, photo- 
 chemistry and radiotherapy, it appears desirable to adopt the 
 use of the term radiochemistry in the broader sense, exactly 
 analogous to and including that of photochemistry, in the sense 
 that all relations between chemical energy and any form of 
 radiant energy or matter should be comprehended by the term 
 radiochemistry. 
 
 17 
 
18 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 2. Radiant Energy and Matter. 
 
 In the strictest sense, perhaps, radiochemistry should deal 
 only with truly radiated energy to the exclusion of the kinetic 
 energy of projected particles of matter such as a particles or of 
 electrons and [3 particles. This would practically narrow the 
 subject to that of photochemistry itself. It is not only a matter 
 of convenience to include also the relations involving material 
 particles, but the relationships and reactions are in many ways 
 so similar, and the analogies of such far-reaching importance, 
 that it forms one of the chief objects of the present work to 
 treat both from the same standpoint, without any particular 
 distinction as to the vehicle of the radiated energy. 
 
 The forms of radiant energy or matter to which attention will 
 be given are: a and p particles, y rays, recoil atoms, positive 
 rays, electrons including the various forms of electrical discharge 
 such as corona, silent and spark discharges, and, to a certain ex- 
 tent, visible and ultraviolet light and X rays. The differentia- 
 tion in terms involved in the usage a or |3 particle and y ray 
 will not be adhered to strictly. For the sake of brevity, free 
 use will be made of the older terms a and p rays. 
 
 3. Photo- and Radio-Chemistry. 
 
 A full appreciation of the vastly important function of light 
 in our terrestrial economy, both past and present, in transform- 
 ing and storing chemical energy will serve to emphasize the im- 
 portance of photochemistry. While it can not be claimed that 
 either the recognition of the relative position of photochemistry 
 or the actual beginning of the science is new, it is only within 
 the decade preceding the recent European war that its develop- 
 ment may be regarded as commensurate with its preeminent im- 
 portance. Compared with the state of development in thermo- 
 or electro-chemistry, photochemistry must be conceded to be in 
 its beginning and not yet past the first stages of empiricism. 
 
 It appears unnecessary to seek far afield, as some authors 
 have done, for the causes of the slow development of photo- 
 chemistry. The earlier development of one of its technical 
 branches, photography, doubtless contributed to the neglect of the 
 mother science, as has been suggested by Luther,^ but other con- 
 
 » B. Luther, Bunsengcsellsch. 1908 ; Zoit. f. Elcktrochcm., U, 445-53. 
 
RADIOCHEMISTRY 19 
 
 tributing factors demand consideration, such as the difficulties 
 presented by the intricate technique of photochemical experimen- 
 tation, the necessity of awaiting progress in the sciences of radi- 
 ology and of atomic structure, and also the early unfortunate 
 overemphasis of the catalytic nature of photochemical phe- 
 nomena. 
 
 As has been stated in the preface several treatises have ap- 
 peared which deal very adequately with the subject of photo- 
 chemistry. It is not the purpose of the present monograph to 
 duplicate this field, but rather to attempt to extend it by pre- 
 senting the experimental results of the investigation of chemical 
 reactions brought about by some other forms of radiant energy, 
 such as electrical and radioactive discharges, with the object of 
 pointing out those analogies an"d differences which appear to 
 exist. 
 
 The general subject of radiochemistry is, like photochemistry, 
 still in the experimental stage and must be approached from the 
 empirical side without any expectation of arriving at once at 
 final principles. It is therefore the object of this work to present 
 the experimental results for the chemical effects of some of the 
 other forms of radiant energy than light in the hope that their 
 examination and comparison with the results of photochemical 
 investigations may contribute to a somewhat more comprehen- 
 sive view of the field of radiochemistry as a whole. Although 
 the branch of radiochemistry to be treated is of recent develop- 
 ment and has been open, on account of the scarcity of some of 
 the necessary radioactive material, only to a limited number of 
 investigators, nevertheless, very definite results have been ob- 
 tained for a few reactions and some principles have been estab- 
 lished that appear to have fairly general applicability. 
 
Chapter 2. 
 
 Brief Outline of Eadioaetivity and Some Properties 
 of the Radiations. 
 
 4. Nature of Radioactivity — Rutherford-Soddy Hypothesis. 
 
 While it lies outside the province of radiochemistry to con- 
 sider the subject of radioactivity in its entirety, it is impos- 
 sible to treat the chemical effects of the radiations accompany- 
 ing and produced by radioactive changes without giving some at- 
 tention to the various radioactive elements and their radiations. 
 
 Historically it is interesting to recall that the discoveries 
 both of X rays by Roentgen and of radioactive radiations by 
 Becquerel were made through the means of their radiochemical 
 actions on the photographic plate. Although other more con- 
 venient methods of investigation were soon developed, the photo- 
 graphic method has continued to play a role of some impor- 
 tance. 
 
 The continuous emission of heat and of radiations was one 
 of the first properties of radioactive substances to be observed, 
 and also proved to be one of the most puzzling since it appeared 
 to contravert the law of the conservation of energy. In looking 
 for a general theory of radioactivity it appeared to Pierre Curie 
 and A. Laborde ^ not impossible that radioactive matter might 
 be merely the receptor of a form of radiant energy coming from 
 extraterrestrial sources and capable of affecting only the ele- 
 ments of heaviest atomic weight. To ascertain if the sun might 
 be the source of the supposed radiant energy, comparison was 
 made of the activity of a radioactive substance measured at noon 
 and again at midnight to find if the interposition of the earth's 
 thickness would diminish the activity. A negative result was 
 obtained. 
 
 Although it was early suggested that radioactivity is purely 
 an atomic phenomenon, it was not until 1903 that Rutherford 
 
 »P. Curie and A. Laborde, Comp. rend., 13G, G73 (1903). 
 
 20 
 
SklEP OtJTLINE OF RADtOActlVlTY ^1 
 
 and Soddy ^ proposed and elaborated a concrete theory of suc- 
 cessive atomic disintegration which explained all the phenomena 
 exhibited by radioactive substances, and left no doubt that the 
 source of radioactive energy and radiation is from within the 
 radioactive atom itself. All subsequent investigations have only 
 strengthened this hypothesis, until now it is supported by a chain 
 of evidence, both experimental and " theoretical, which is unique 
 in its completeness and perhaps without parallel in the physical 
 sciences. 
 
 5. Radioactive Phenomena. 
 
 Radioactive substances exhibit the following striking prop- 
 erties : 
 
 (1) The continuous emission of heat. 
 
 (2) The continuous emission of certain rays and particles. 
 
 (3) The production of luminescent effects in some sub- 
 stances. 
 
 (4) The ionization of the surrounding air (or of other 
 gases). 
 
 (5) The production of chemical reaction in substances 
 subjected to radiation. 
 
 (6) The production in some substances of certain effects 
 such as color, thermoluminescence, etc., which may or 
 may not be due to chemical action. 
 
 The most notable of these phenomena is the emission of 
 electrically charged particles at high velocity from the radio- 
 active atom, due to some internal disturbance of the electrical 
 equilibrium of the atom, the cause and exact nature of which 
 are not yet wholly understood. All of the other phenomena 
 enumerated may be regarded as secondary effects of the radia- 
 tions. 
 
 6. Kinds of Radiation. 
 
 Three distinct kinds of radiation are emitted by the various 
 radioactive substances: a particles, p particles, and y rays. 
 a Particles. The corpuscular nature of a particles was first 
 
 'Rutherford and Boddy, Phil. Mag. (6) 4, 370; 569 (1902), 5, 441; 576 
 (1903). 
 
22 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 suggested by Mme. Curie ^ in 1900 to explain the peculiarities 
 of their absorption or loss of energy in passing through matter. 
 Strutt* suggested their being positively charged, Rutherford^ 
 demonstrated their deflection both by magnetic and by electrical 
 fields. Later Rutherford and his co-workers ® showed that a par- 
 ticles are doubly positively charged helium atoms. They are 
 emitted from the radioactive atom at a very high initial velocity 
 (1/15 to 1/20 that of light), and since they possess mass of 
 atomic dimensions, they represent an enormous concentration of 
 kinetic energy. In fact the a particle is the most powerful agent 
 yet known to science and in all probability will remain so, as it 
 is hardly conceivable that any means will ever be devised of 
 imparting to ponderable matter a velocity exceeding that at 
 which the a particle is dispelled from the atomic nucleus. It is 
 therefore not surprising that we find in the a particle a powerful 
 agent in bringing about ordinary chemical changes in matter 
 with which it comes into contact, but, as Rutherford^ has re- 
 cently shown, at least two kinds of atoms (nitrogen and oxygen) 
 when squarely struck by an a particle are completely altered, 
 producing hydrogen or helium atoms (see Chapter XII). Of the 
 total energy emitted by radioactive substances, by far the larger 
 proportion is carried by the a particles, and it is principally the 
 transformation of this eniergy that results in the production of 
 the thermal, electrical and chemical effects already referred to. 
 
 P Particles. The (3 particles emitted by radioactive matter 
 have been proved by numerous authorities to consist of elec- 
 trons, singly charged atoms of negative electricity, ejected from 
 the nucleus of the radioactive atom at varying velocities, in some 
 cases approaching closely to that of light. 
 
 Y Rays for a long time presented an unsolved problem as to 
 their exact nature and origin. They are emitted only by sub- 
 stances which also emit p particles and evidently are connected 
 with this emission. It is now generally conceded that they con- 
 sist of ether pulses of very short wave length and therefore have 
 the general properties of light and may be most aptly compared 
 
 •Mme. Curie, Comp. rend., 130, 7G (1900). 
 *R. J. Strutt. Phil. Trans. Roy. Soc. A 19G, 507 (1901). 
 •E. B* Rutherford. PhU. Mag. {G) 5, 177 (1903) ; Phys. Zeit., 4, 235 (1903). 
 •Rutherford and Geigcr, Proc. Roy. Soc. A 81, 162 (1908). Phys. Zeit., 
 10, 42 (1909). Rutherford and Royds, Phil. Mag., 17, 281 (1909). 
 'Rutherford, Phil. Mag. (6) 37, 537-587 (1919). 
 
BRIEF OUTLINE OF RADIOACTIVITY 23 
 
 with X rays, except that they greatly exceed in shortness of 
 wave length and penetrating power any X rays that have yet 
 been produced. A fuller discussion of the properties of these 
 three kinds of radiation will be found in subsequent paragraphs. 
 Recoil atoms also constitute a form of radiation that has been 
 shown to produce chemical effects. A recoil atom is the re- 
 mainder of a radioactive atom just after the emission of an a 
 (or P) particle while it is still in rapid motion owing to the "re- 
 coil" action. Ionization and other radiation effects are produced. 
 Further reference to recoil atoms will be found in Chapter XI. 
 
 7. Radioactive Families and Their Transformation Products. 
 
 Of the common elements only two, uranium and thorium, 
 have been found to possess distinct radioactive properties. Each 
 of these two elements is the parent of a series of radioactive ele- 
 ments undergoing atomic decay. There is also a third family 
 having as its parent, actinium, an element of very rare occur- 
 rence, apparently a side-chain offspring of the uranium series. 
 These three families comprise about thirty-five members which 
 differ from each other in chemical, physical and radioactive prop- 
 erties, the latter being characterized by the radiations emitted 
 and by the rate of change of one element into the next lower 
 member in the series. Employing the usual terminology of chemi- 
 cal kinetics, each simple radioactive change has proved to be 
 mono-molecular, and not only corresponds perfectly to the re- 
 quirements of the logarithmic equation of the so-called first order 
 reactions, with respect to time rate of change, but the rate of 
 change persists unaltered no matter to what physical or chemical 
 influences it may be subjected. A simple radioactive trans- 
 formation represents par excellence the first order reaction. 
 The rate of change is usually formulated as: E=Eo.e-^*, in which 
 Eq is the initial quantity of radioactive material undergoing 
 change, and E the quantity remaining unchanged after the lapse 
 of any interval of time t, e is the base of the Naperian logarithmic 
 system, and X is the decay constant, by which is meant the frac- 
 tion of the total which changes in unit of time; l is the recipro- 
 cal of 6 J the ^'average lije^^ of a radioactive element, which is not 
 to be confused with the term "half period" of the element. The 
 half period is the time in which just one-half of the initial quan- 
 
24 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 tity undergoes change; and, as is also the case for all first order 
 reactions, it makes no difference what time or quantity is 
 chosen as initial. The relation between the two is: average life 
 (d) = half period x nat, log 2 (= 1.4428). It may be men- 
 tioned that the usual form of the differential equation for first 
 order reactions, dx/dt = k(A-x) <^) can be readily converted into 
 the form given above for radioactive changes. The average life 
 for a given element is its most fundamental physical constant, 
 and is found to vary for the different elements from a very small 
 fraction of a second up to several billion years. As far as known 
 the reactions are irreversible. 
 
 Uranium and thorium are the two elements possessing the 
 highest known" atomic weights, and the property of radioactivity 
 does not seem to be possessed by elements of atomic weight less 
 than 210, excepting, perhaps, potassium and rubidium, which 
 have been shown ^ to emit p rays. 
 
 According to the Rutherford and Soddy hypothesis one atom 
 of a radioactive substance A changes to form one atom of sub- 
 stance B, and in case of the emission of a particles, one atom of 
 helium is ejected from each atom of A in changing to B. It fol- 
 lows that B must have an atomic weight four units lower than 
 that of A, also that the enumeration of the a particles emitted 
 serves as a measure of the rate and quantity of change, and also 
 that the accumulation of helium gas over, a known period may 
 serve as a measure of the same constants; or, vice versa, if the 
 rate of change be known, the accumulation of helium is a meas- 
 ure of the period of time during which the accumulation has 
 taken place. Reference to the fuller texts on radioactivity ^° 
 will show that all these factors have been abundantly verified ex- 
 perimentally and fit into the network of evidence confirming 
 the Rutherford and Soddy theory of radioactive change. 
 
 8. Radioactive Equilibrium. 
 
 Although the radioactive changes, as already stated, are ir- 
 reversible and hence incapable of attaining a state of equilibrium 
 
 (8) S. L. Bigelow, "Thoorotical and Physical Chemistry," p. S.'S (1912). 
 K. G. Falk, "Chemistry of Enzymo Actions," p. 22 (1921). 
 
 •N. R. Campbell and A. Wood, Proc. Camh. Phil Soc, 14, 15 (1907). 
 
 "Rutherford, "Radioactive Substances and Their Radiations" (1913). Mme. 
 Curie, "Traite de Radioactivity" (1910). Meyer and von Schweidler, "Radlo- 
 aktivitat" (1916). > 
 
BRIEF OUTLINE OF RADIOACTIVITY 25 
 
 in the ordinary way of reversible reactions, yet a state of 
 dynamic equilibrium may be attained between a parent element 
 and one or more of its decomposition products. This occurs 
 through the change of the product, not back into the original, 
 but into new products at the same rate that it is being produced 
 from the parent. Thus the parent element, which is producing 
 its decay product at the same rate that the latter is undergoing 
 further change, has attained a state of dynamic equilibrium in 
 which a constant ratio between the quantities of the two elements 
 involved is maintained. Such radioactive equilibrium may apply 
 to a whole family or to any part of a family, beginning with a 
 parent element of longer life than its products. For example, 
 uranium in nature, after the lapse of geological ages, is found to 
 be in equilibrium with all the members in its family. Radium 
 attains equilibrium with its next succeeding decay products in 
 about one month, while radium emanation reaches equilibrium 
 with its immediate products in four hours. 
 
 From the physical-chemical standpoint these equilibria rep- 
 resent nothing different from what one should expect from a se- 
 ries of successive irreversible mono-molecular reactions. By 
 the superposition of equations of the first order Rutherford ^^ has 
 dealt with the equilibria, which on the whole must be regarded 
 as the most complete series of successive reactions known to 
 physical chemistry. They may appear intricate on account of 
 their number, but otherwise they are wonderfully simple and free 
 from complications such as would arise in the treatment of ordi- 
 nary chemical reactions. 
 
 From the radioactive standpoint the dynamic equilibria are 
 of great importance from the following considerations: When 
 two or more radioactive elements are in equilibrium, the number 
 of atoms of each element being formed and decaying per unit 
 of time is the same. Throughout a whole system of elements in 
 radioactive equilibrium, the number of atoms of each element 
 changing per unit time is identical and is also measured by the 
 number of a particles being emitted per unit of time by any 
 member of the system. This means of course that equilibrium 
 quantities of all elements in the same radioactive family emit 
 the same number of a particles per second. For example, if one 
 gram of radium emits 3.72x10^° a particles per second, that 
 
 " Rutherford, "Radioactive Substances and Their Radiations," Chapter 11. 
 
26 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 quantity of any other member of the uranium family which 
 would be in equilibrium with one gram of radium would also 
 emit the same number of a particles per second. This makes it 
 evident that in chosing units for radioactive elements it is much 
 simpler to deal with the relative equilibrium quantities rather 
 than with absolute masses, particularly since many of the radio- 
 elements can not be obtained in ponderable quantities and are 
 measured only through some radiant property. Such a system 
 of units was devised and adopted at the direction of the Inter- 
 national Congress of Radiology and Electricity, Brussels, 1910. 
 One gram of elemental radium was chosen as the basic unit. 
 Standard preparations of radium were prepared by Mme. Curie 
 in Paris and by Honigschmid in Vienna from which secondary 
 standards ^^ have been furnished to all the principal countries 
 for the standardization of radium by means of its y radiation. 
 That quantity of any other member of the uranium family in 
 equilibrium with one gram of radium has been called the curie, 
 a unit which has come into universal use for radium emanation, 
 and which has been subdivided into milli- and micro-curies, sig- 
 nifying the thousandth and millionth parts, respectively. 
 
 9. Kinetic Energy of a Particles. 
 
 Since all a particles are doubly charged helium atoms it is 
 evident that those from the different radioactive substances can 
 differ from each other only in the initial velocity with which 
 they are emitted; and that furthermore, when one a particle has 
 lost velocity until it has just become equal in velocity to one 
 emitted at a lower value, from that point on the two will have 
 identical properties in the same medium. These statements 
 have been fully proved by W. H. Bragg ^^ who has also shown 
 that all the a particles emitted by the same kind of radioactive 
 substance have the same initial velocity, which means that they 
 are possessed of the same kinetic energy and in the same medium 
 will have the same penetrating power and other properties identi- 
 cal. 
 
 "Meyer and v. Schweidler, "RadioaktivitUt" (191C), p. 210. 
 
 '"W. H. Bragg, "Studies In Radioactivity" (1912); Bragg and Kleeman, 
 PMl. Mag. (6) 10, 318-40; 11, 4GG-84 ; W. H. Bragg, ibid., 11, G17-32 ; 13, 507- 
 16 ; 14, 425. 
 
BRIEF OUTLINE OF RADIOACTIVITY 27 
 
 10. Range of a Particles. 
 
 The distance which an a particle can penetrate in a given 
 medium before its kinetic energy is dissipated is called its range. 
 The range usually refers to a gaseous medium, but the same 
 term is used for penetration in liquids or solids. It is believed 
 that at the end of its range, as observed by the cessation of 
 gaseous ionization, the kinetic energy of an a particle is re- 
 duced practically to zero, though there has been some question 
 on this point. It has been shown by Duane ^* that the a particle 
 loses its ability to produce ionization, luminescence and cliemical 
 action simultaneously. Either ionization or luminescence may 
 be used to determine the range, preferably the former. \ 
 
 The following Table I shows the members of the uranium- 
 radium family in the order of their sequence, indicates the kind 
 of radiation accompanying each transformation and its half pe- 
 riod; and for a particles shows the range in air at 15° ajad 760 
 mms., the initial velocity, and the total number of pairs of ions 
 produced by a single a particle in its whole range. ? 
 
 11. Ionizing Power of a Particles. I 
 
 An a particle projected from an atom with enormous yelocity 
 travels in a straight line penetrating all the atoms encountered 
 in its path. By penetration is meant that the a particle passes 
 through the electrical field due to the electrons surrounding 
 the atomic nucleus of positive charge, as conceived in the Ruther- 
 ford-Bohr ^^ atomic model. According to Rutherford's idea, re- 
 sulting from the study of the deflections of a particles near the 
 end of their paths, an atom consists of a very small positive 
 nucleus with an elemental charge a little less than one-half the 
 atomic weight, surrounded by electrons equal in number to the 
 positive nuclear charge, situated in rings at relatively great dis- 
 tance from the positive nucleus. According to this idea of 
 atomic structure which has now become generally accepted, it 
 is evident that an a particle may pass through a large number 
 of atoms without ever coming close enough to the nucleus to 
 have its course altered, as long as its velocity is great. 
 
 ^MVm. Duane, Comp. rend., 11,6, 958-60 (1908). 
 
 'Mtutherfoid. Nature, 92, 423 (1914); Phil. Mag. (6) 27, 488-98 (1914). 
 N. Bohr, Phil. Mag. (6) 20, 1-25; 47G-502 ; 857-75 (1913). 
 
28 
 
 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 
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 Cr!cr!cnp^fr:piP:^P4p4« 
 
BRIEF OUTLINE OF RADIOACTIVITY 29 
 
 As may be seen in Table I, a single a particle from Ra C 
 produces in its entire path in air 237,000 pairs of ions, which 
 means that it detaches this many electrons from the atoms en- 
 ct)untered. Using his classical oil droplet method, Millikan^^ 
 has recently shown for several of the common gases, including 
 air, that only one electron is detached by an a particle from 
 each molecule, leaving a singly positively charged residual mole- 
 cule or ion. This process of ionizing requires a certain expendi- 
 ture of energy which continues to lower the kinetic energy of 
 the a particle by reducing its velocity until it is no longer able 
 to produce ionization, which marks the end of its range. Unless 
 acted on by an external electrical field the positive and negative 
 ions thus separated would recombine and the net result of the 
 expenditure of energy would be the production of heat (assum- 
 ing that no permanent chemical action has resulted) ; or in- 
 versely, the heat evolution of radioactive substances emitting 
 a particles is a measure of the total energy available for ioniza- 
 tion. From a knowledge of the total number of ions, the energy 
 necessary to produce one pair of ions in air has been calculated 
 to be 5.5x10"^^ ergs.^'^ 
 
 The property of producing ionization not only constitutes 
 the most delicate test for radioactive substances but also forms 
 the basis of their quantitative measurement. Furthermore, as 
 will be shown in Chapter VII, the relation between the ioniza- 
 tion and the chemical effects of the radiation is in many cases 
 of importance. In radiochemistry one is interested not only in 
 the total ionization produced by an a particle but also in the 
 distribution of the ionization along the path of the particle. 
 This subject has been carefully investigated by Bragg, Geiger 
 and others.^^ Fig. 1 represents the ionization curve for a single 
 a particle from Ra C in air, in which the length of path is plotted 
 as abscissae and the number of ions (pairs) as ordinates. 
 
 The form of the curve shows that for the first two or three 
 centimeters of path the ionization remains practically constant 
 at about 2.2x10* pairs of ions per cm. of path traversed. The 
 number then begins to rise and increases quite rapidly toward 
 
 "R. A. Millikac, V. H. Gottschalk, M. J. Kelly, Phys. Rev. (2) 15, 157-77 
 (1920). 
 
 " Rutherford, "Radioactive Substances and Their Radiations," p. 159. 
 
 "W. II. Bragg, "Studies in Radioactivity," Chapters 3 and 4. H. Geiger, 
 Proc. Roy. Soc, 82, 489 (1909). 
 
30. THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 8 
 
 U 
 
 o 
 
 o 
 
 BC 
 
 w 4 
 
 z 
 o 
 
 CO 
 
 2 3 4 5 6 
 
 RANGE IN CENTmETEf?SOF AIR 
 
 Fig. 1. 
 
 the end of the range and then drops almost abruptly to zero. 
 The total number of ions produced in the whole course is evi- 
 dently represented by the area within the curve. Since a par- 
 ticles from any other source are identical except in initial veloc- 
 ity, their ionization curves would be identical after any point at 
 which they attain the same velocity as that represented on the 
 curve for Ra C. For example, the curve for Ra A would be 
 represented by counting backward from the end of the curve 
 4.7S cms., the length of the range of the a rays from Ra A. 
 Similarly if either end of the path of an a particle is incomplete 
 through the interposition of a partial screen, or if the ray is 
 absorbed in another medium before completing its course, the 
 effective ionization may still be obtained by referring only to 
 the effective part of the path. 
 
BRIEF OUTLINE OF RADIOACTIVITY 31 
 
 It has been shown by Geiger ^^ that the ionization curve for 
 an a particle corresponds to a relation between the velocity (v) 
 and the range (R) of the form: v^ = const.xR, and that the 
 ionization, (I) = const.xR^/^, from which it follows that the 
 total ionization of a single a particle (k) = koR^/^, in which 
 ko is a constant with the value 6.76x10*. 
 
 12. Enumeration of a Particles. 
 
 From what has been said in the foregoing paragraphs it is 
 evident that the counting of the number of a particles emitted 
 per unit time by any given radioactive substance is very impor- 
 tant. Since the number being emitted from an active substance 
 like radium is very large (3.72x10^^ per gram per second), it is 
 necessary to reduce both the quantity of substance and the solid 
 angle from which the effective radiation is received. Two meth- 
 ods of detecting and counting the particles have been employed: 
 (1) by observation of the number of scintillations produced on 
 a phosphorescent ZnS screen under low magnification, each 
 spark corresponding to the impact of one particle; (2) by ob- 
 servation of the number of deflections of an electrometer in se- 
 ries with a condenser in which the a particles are received. 
 These two entirely different methods have given concordant re- 
 sults for the value for radium.^° From the statements in § 8 it 
 is clear that any other member of the uranium-radium series 
 which emits a particles will emit this same number per second 
 from the equilibrium quantity. For example, the emission from 
 radium in equilibrium with emanation, Ra A and Ra C will be 
 four times the number per gram of radium; the emission from 
 one curie of emanation in equilibrium with Ra A and Ra G 
 would be three times this same number. While the number, 
 thirty-seven billion helium atoms, ejected per second from one 
 gram of radium, appears very high, it should be remembered 
 that at even this rate of decay, the half period of radium is 1580 
 years, accounted for by the tremendous number of atoms repre- 
 sented in one gram or even one cubic centimeter of a gas, which 
 is of the order of billions of billions. 
 
 "H. Geiger, Proc. Roy. 800., 83A, 505 (1910). 
 *» Rutherford, Phil. Mag. (6) 28, 320-7 (1914). 
 
32 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 13. Some Additional Properties of a Particles. 
 
 The great kinetic energy possessed by an a particle com- 
 pared with that of even the swiftest p particle (roughly 100 
 times as great) is due to the large mass of the former, approxi- 
 mately 7,000 times that of an electron. The a particle collides 
 with a large number of molecules in a short path, thus limiting 
 its total penetrating power in spite of its great momentum. 
 Hence a particles must be classed as non-penetrating radiation. 
 As may be seen in Table I, they have ranges in air at ordinary 
 pressure of 3 to 8 cms., and penetrate other substances in the 
 inverse order of the "stopping power" of the given substance. 
 
 Stopping Power. The term stopping power of a substance, 
 referring to its power to stop a particles, was first introduced by 
 Bragg.2^ Proceeding from the generalization that the a ioniza- 
 tion curves of different gases differ from each other only in a 
 shortening or lengthening of all the ordinates or abscissae by the 
 same ratio, the following very simple procedure was proposed by 
 Bragg. Instead of having to determine the complete curve of 
 ionization for each gas it is only necessary to find the ioniza- 
 tion, I, at one particular point, R, in the path of an a particle. If 
 I' and R' are the corresponding values for air, the ratio of the 
 .total ionization (k) in the two media may then be expressed by 
 •RI/R'I'=k/k'(l) ; and putting k', the total ionization for air 
 equal to 1, the total ionization of any gas is referred to that in 
 air and may be called the total specific ionization. But if it is 
 desired to refer not to the total ionization, but to that produced 
 along a certain length of path, which is evidently equivalent to 
 referring to the relative ionization in a single molecule of each 
 gas, or in any equal number of molecules of each gas, one must 
 use the ratio I/I', which can be shown to be equal to Bragg's 
 ks, in which s is the stopping power, as follows: Putting the 
 reciprocals of the ranges R and R' equal to s and s', the respec- 
 tive stopping powers, and substituting in equation (1) above: 
 I/I'=ks/k's'=ks, by putting k's' for air equal to 1. This value 
 may be called the molecular specific ionization (Bragg's ks) to 
 distinguish it from the total specific ionization (k) . In Table II 
 will be found the values for a number of common gases and 
 other substances taken from Bragg.^^ 
 
 a»W. H. Bragg, "Studies in Radioactivity," Chapters 5 and 6 (1912). 
 ^rbid. p. 65 (1912). 
 
BRIEF OUTLINE OF RADIOACTIVITY 
 
 33 
 
 TABLE II 
 
 Stopping Power and Ionization (by a Rays) of Different Gases 
 According to Bragg 
 
 
 k X 100 
 
 s X 100 
 
 ks X 100 
 
 Air 
 
 100 
 
 100 
 
 100 
 
 H, 
 
 100 
 
 24 
 
 23.3 
 
 N3 
 
 96 
 
 98.9 
 
 94 
 
 0. 
 
 113 
 
 106.4 
 
 109 
 
 CO 
 
 101.5 
 
 98.5 
 
 100 
 
 NO 
 
 .... 
 
 .... 
 
 128 
 
 CO3 
 
 103 
 
 150.5 
 
 152 
 
 N,0 
 
 105 (99) 
 
 146 
 
 153 
 
 NH3 
 
 90 
 
 
 81 
 
 CS2 
 
 137 
 
 218* 
 
 299 
 
 SO2 
 
 103 
 
 
 201 
 
 He 
 
 .... 
 
 2o!i 
 
 21.1 
 
 Ar 
 
 • • . . 
 
 95.1 
 
 124.5 
 
 Br 
 
 
 
 390 
 
 HBr 
 
 129* 
 
 
 
 
 HI 
 
 129 
 
 
 
 
 
 HCl 
 
 129 
 
 . . . 
 
 
 
 CH4 
 
 118 
 
 86 
 
 110* 
 
 CH4O 
 
 122 
 
 , . . , 
 
 174 
 
 C,H3 
 
 126 
 
 112 
 
 140 
 
 C,H, 
 
 122 
 
 135 
 
 165 
 
 C^He 
 
 130 
 
 151.4 
 
 197 
 
 C5H12 
 
 135 
 
 354.4 
 
 485 
 
 C^HeO 
 
 123 
 
 200 
 
 246 
 
 C.H, 
 
 129 
 
 333 
 
 430 
 
 CH3I 
 
 133 
 
 258 
 
 343 
 
 C,H,I 
 
 128 
 
 312 
 
 400 
 
 CHCI3 
 
 129 
 
 316 
 
 408 
 
 CCl, 
 
 132 
 
 400 
 
 528 
 
 CH3Br 
 
 132 
 
 203 
 
 275 
 
 Stopping Power (s) ; Total Ionization (k) ; and Molecular 
 Ionization (ks). 
 
 Bragg's generalization in regard to stopping power does not 
 hold strictly for different substances but approximates closely 
 enough to be of service for all practical purposes in radio- 
 chemistry. 
 
 It will also be of general interest to note that the study of 
 the stopping power of different substances for a particles is not 
 
34 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 confined to gases. By the use of very thin sheets as screens the 
 stopping power of the heaviest metals has been determined and 
 may be translated into terms of air equivalent. Bragg and his 
 co-workers Have found (loc. cit.) that the stopping powers of 
 the various metals are proportional to the square roots of their 
 atomic weights. The same relationship holds approximately 
 even for gases as light as air and hydrogen. Bragg has also 
 found the stopping power to be an atomic property which is 
 additive in the compounds of the elements. The same does not 
 hold, however, for specific ionization, which is by no means 
 additive for compounds. This must mean that the manner in 
 which the atoms are held together has an influence on the ease 
 with which electrons can be detached, and since it is now gen- 
 erally agreed, that the atoms are held together by means of the 
 electrons, this reasoning appears all the more plausible. From 
 Table II it can be observed that as the molecular weight of 
 chemical substances increases, the easier it becomes for a par- 
 ticles to produce ionization in them. 
 
 14. Characteristics of Members of the Radium Family as 
 Sources of Radiation. 
 
 Up to the present only members of the radium series have 
 been used quantitatively in studying radiochemical effects. The 
 members preceding radium in the series are all so weakly active 
 that they do not come into consideration as artificial means of 
 investigating radiochemical effects, but in nature they play a 
 role which will be given special attention in some of the later 
 chapters of this work. This statement as to the effects in nature 
 would apply equally well to the members of the other radio- 
 active families. 
 
 Radium itself has no general applicability except in equilib- 
 rium with its products through Ra C, which necessitates its 
 being maintained in a sealed container on account of the gaseous 
 nature of radium emanation. Owing to the non-penetrating char- 
 acter of a rays, only (3 and y radiation would be obtained 
 through the walls of the container. Radium salts sealed in glass 
 tubes, therefore, constitute the most convenient source of pene- 
 trating rays, having the advantage of constancy of radiation 
 after the first month subsequent to sealing, but the disadvantage 
 
I 
 
 SRlEP OUTLINE OP RADIOACTIVITY 35 
 
 that it is usually difficult to determine what part of the radia- 
 tion is effective in a given absorbing system under working con- 
 ditions. Radium in equilibrium with Ra C has four sets of a 
 particles, one each for Ra, Ra Em, Ra A, and Ra C. (See also 
 § 8.) ^ 
 
 Radium Emanation represents one of the most convenient and 
 most used sources of radiation. It can be handled as a gas, can 
 be measured with ease, and can be introduced into the interior 
 of many systems in very small volume. The volume of 1 curie 
 of emanation (the quantity in equilibrium with 1 gm. of Radium) 
 is only 0.58 mm.^ and furnishes a very concentrated form of ra- 
 diation. It does not, unlike radium salts, appreciably absorb 
 its own radiations. On account of its relatively short life, it has 
 no permanent value and can therefore be subjected to danger 
 of loss, breakage, etc., in ways that would not be feasible with 
 radium salts. Practically its only disadvantage consists in its 
 short life and continually changing activity, but since this change 
 takes place according to a perfectly well established and in- 
 variable law, it can readily be taken into account. Its radiations 
 include those of Ra A, Ra B, and Ra C, with which it attains 
 equilibrium after four hours in a closed vessel. 
 
 Active Deposit. Ra A, Ra B, and Ra C together constitute 
 the so-called active deposit of radium emanation formerly called 
 also "induced activity," because they are deposited as solids on 
 the walls of a containing vessel or on any surrounding objects 
 to which the emanation may diffuse and owing to their activity 
 appear to impart to these objects a temporary radioactivity. 
 Ra A emits only a rays, Ra B only rather non-penetrating |3 and 
 Y rays. On account of the extremely short life of Ra C 
 (10-® sec), both Ra C^ and Ra C will be, in the following 
 pages, referred to collectively as Ra C, which then constitutes 
 not only a source of a rays, but also of the most penetrating 
 P and Y rays in the radium series. The y rays of Ra C furnish 
 the best means of measuring either radium or radium emanation. 
 
 Radium D and E possess no rays of radiochemical impor- 
 tance. Ra F (polonium) is unique in furnishing only a rays 
 and is the most convenient source of this form of radiation free 
 from penetrating rays. It is usually deposited electrolytically 
 on copper, which then, of course, absorbs that half of the a radia- 
 
36 THE CHEMICAL EFPECtS OP ALPHA PARTICLES AlfD EtECfROm 
 
 tion directed toward it. Especially for use in liquid systems, 
 polonium is a very suitable source of a rays. 
 
 As generally applicable to all a particles, it should be men- 
 tioned that Rutherford and Geiger ^^ utilized the a radiation 
 from polonium to determine the probability variations of the 
 emissions of a rays both with respect to time and space and 
 found their distribution fully obeying the laws of chance. 
 
 a» Rutherford and Geiger, Phil. Mag. (6) 20, 698-704 (1910). 
 
Chapter 3. 
 Electrical Effects — Ionization. 
 
 15. Saturation Current as a Measure of Ionization. 
 
 The general principle of the method of the measurement of 
 gaseous ionization deserves at least brief consideration. Let us 
 suppose that the air in a closed chamber provided with electrodes 
 is subjected to a constant radiation that will produce a fixed 
 number of ions in the chamber in unit time. Connect the elec- 
 trode terminals, which must be carefully insulated from the 
 chamber and from the surrounding air, in series with an instru- 
 ment capable of measuring low electrical current, such as a 
 quadrant electrometer. Apply from a high voltage battery suc- 
 cessively increasing voltages and plot a current-voltage curve as 
 in Fig. 2. For low voltages the curve rises linearly, indicating 
 that the current increases in direct proportion to the applied 
 voltage just as would be required by Ohm's law in a conductor 
 of the first class. On applying yet higher voltage the current 
 rises more slowly than the voltage and finally reaches a constant 
 maximum in the part of the curve AB (Fig. 2) which remains 
 horizontal. It can now be inferred that all the available ions are 
 being drawn to the electrodes and are discharged, and that fur- 
 ther increase of voltage within suitable limits produces no in- 
 crease of current. This current is designated as saturation cur- 
 rent, which is evidently a direct measure of the total number of 
 ions being formed per unit time in the chamber. It is also in- 
 ferred that under conditions in which insufficient voltage is ap- 
 plied the ions not attracted to the electrodes recombine with each 
 other by ordinary diffusion. 
 
 The potential that must be applied to produce saturation cur- 
 rent will depend on the strength of the ionization and the gaseous 
 pressure, the lower the pressure the smaller the required volt- 
 age. At atmospheric pressure 2,000-5,000 volts per cm. will suf- 
 fice in most cases. However, if the ionization is very great, such 
 as that produced by a strong a ray source, it becomes impossible 
 
 37 
 
38 THE CHEMICAL EFFECTS O^ ALPHA PARTICLES AND ELECTRONS 
 
 to produce saturation current. The measurement even of mod- 
 erate ionization produced by a rays has been found to present 
 especial difficulties, supposedly due to the high concentration of 
 ions along the path of the particle. One is seldom able to meas- 
 ure directly the ionization of a rays of an intensity suitable for 
 
 the measurement of its chemical action also, and must resort to 
 indirect methods of calculating the ionization which will be 
 treated in Chapter VII.^ * 
 
 * In connection with tlie mcasurcmont of gaseous ionization by moans of 
 saturation current, it sliould be pointed out tbat while the practice among 
 physicists of referring to the total number of pairs of ions is fairly common, 
 the expression ions where pairs of ions is meant is also unfortunately preva- 
 lent. This is particularly confusing to the chemist, who in dealing with electro- 
 lytic ions in connection with the solution tlieories, always means total positive 
 and negative ions, never ions of only one sign. Naturally the physicist in tak- 
 ing current units as the measure of gaseous ionization is prone to neglect the 
 other half of the ionization, thus leading to confusion in cases where the number 
 of ions of both signs is important. 
 
ELECTRICAL EFFECTS— IONIZATION 39 
 
 16. Ionization by Electronic Shock. 
 
 To return to the curve in Fig. 2, if the voltage be increased 
 beyond that necessary for saturation current, the electrons and 
 ions attain still greater velocities, and soon the electrons reach 
 velocities within their free paths, at which their kinetic energy 
 becomes sufficient to ionize the gas molecules with which they 
 come in contact, thus increasing the total number of electrical 
 carriers beyond the number being produced by primary radiation. 
 Owing to the rapid increase in the number of carriers the cur- 
 rent again begins to rise, as indicated by the curve BC, on ac- 
 count of this process which has been called ionization by "shock" 
 or collision. 
 
 As will be later shown (§ 52) this form of ionization prob- 
 ably plays a very important part in the chemical action pro- 
 duced by electrical discharge through gases. Evidently there 
 is no limit to the current resulting from such an increase in 
 voltage until the sparking potential is reached. The current 
 resulting from ionization by shock usually will not represent 
 a condition of saturation. At ordinary gas pressures, only a 
 small fraction of the total number of ions produced by an in- 
 tense discharge reaches the electrodes before recombining, and it 
 is only this small fraction, of course, which carries the current; 
 the other ions may recombine to form the original product, or 
 may combine to form a new chemical product, hence their interest 
 in radiochemistry. 
 
 X ray Tubes may be very aptly employed to illustrate ioni- 
 zation by shock. The old ordinary form of X ray tube depends 
 upon shock ionization for a sufficient number of carriers to con- 
 duct the current, which explains why the gas pressure had to be 
 held within rather narrow limits; if too high, the free path of 
 the electrons was too short to enable them to obtain the neces- 
 sary velocity to produce ionization by shock; if too low, not 
 enough encounters resulted to maintain discharge. The ordi- 
 nary X ray tube has a well known tendency to become "hard" 
 by reduction of the gas pressure, which is also a result of ioniza- 
 tion. It means that some of the positive gas ions attain a ve- 
 locity sufficient to cause them to adhere to the electrode upon 
 reaching it, thus reducing the pressure. Whether the effect is 
 chemical or physical has not been definitely determined. The 
 
40 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 same general type of "clean up" may be illustrated by passing 
 a discharge through radium emanation in a small Geissler tube. 
 After the tube has operated for some time under suitable con- 
 ditions, it will be found that quite a fraction of the gas has 
 been driven into the negative electrode, or into the platinum mir- 
 ror immediately surrounding it, so that it can not be pumped 
 out. The exact location of the emanation can be most conven- 
 iently found by dissecting the tube and examining the various 
 parts for y radiation. 
 
 The Coolidge ^ X ray tube does not depend on ionization by 
 shock, but on the direct production at a highly heated tungsten 
 cathode of enough therm-electrons to carry the current. Conse- 
 quently the gas pressure in a Coolidge tube may be lowered ad 
 libitum, which gives the electrons much longer free paths, result- 
 ing in their arriving at the target with very high velocity, pro- 
 ducing X rays of much shorter wave length and higher pene- 
 trating power. It has not yet been possible to equal y rays in 
 these respects. 
 
 17. Some Properties of p Particles and Electrons. 
 
 P particles are electrons emitted from radioactive substances. 
 They differ very markedly from a particles in many respects. 
 Their much smaller mass prevents their carrying the same order 
 of kinetic energy even when moving at velocities approaching 
 that of light. The initial velocities of the various p particles 
 vary from 0.3 to 0.98 of the velocity of light. Like a particles 
 they produce ionization and phosphorescent and photographic 
 as well as chemical effects. The electrical method presents the 
 best means for their study. The idea that formerly prevailed 
 that each radioactive substance emits only a single simple type 
 of p radiation has had to be abandoned in favor of the view that 
 great variations exist with respect to velocity of emission. 
 Coupled with the fact that their ionizing and penetrating 
 properties are highly dependent upon velocity, a degree of com- 
 plexity and uncertainty is encountered in dealing with p par- 
 ticles which is quite foreign to the exact nature of our knowl- 
 edge regarding a particles. The apparent mass of the electron 
 
 »W. D. Coolldgo, Phys. Rev. (2) 2, 409-30 (1914). 
 
tJLECtRICAL EFFECTS— lONIZAf ion 41 
 
 has also been found to vary with its velocity. Kaufmann^ 
 has made the most exact investigation of this subject. 
 
 The absorption phenomena for p rays are also very different 
 from those for a rays. It has already been pointed out that the 
 cc particle, while non-penetrating to collective matter owing to 
 the large number of collisions made in a short path, is extremely 
 penetrating with reference to the individual atom, traveling in 
 a straight line through an immense number before its energy 
 is expended. For p particles exactly the opposite is true. To 
 matter collectively they are quite penetrating, because owing to 
 their small size and high velocity they "slip between" the mole- 
 cules, making a much smaller number of collisions per unit 
 path, but suffer a much greater deflection or scattering for each 
 collision. Consequently the paths by which p particles traverse 
 matter ate very far from straight lines; they are even frequently 
 deflected through 180° and return in the opposite direction. 
 This ease of deflection corresponds to the well known ease with 
 which they are deflected by electrical and magnetic fields. Be- 
 sides the gradual reduction in velocity experienced by p rays 
 similar to that of a rays, it is also probable that at any part of 
 its course a P ray may collide with a molecule in such a way that 
 it is stopped abruptly. This means that instead of all p rays 
 with a given initial velocity traveling the same distance in an 
 absorbing medium, as do a rays, they are gradually absorbed 
 proportionally to the number remaining to be absorbed at any 
 point in the path, which behavior would be expressed by an 
 exponential law. Owing, however, to the various complications 
 which arise through scattering, unequal velocities and other 
 causes, the direct application of an equation of the form: 
 I=Io(l-e-^^) is possible only in a few special cases, lo being the 
 initial intensity, and I that after the radiation has traversed the 
 thickness d in a medium with an absorption coefficient \i. 
 
 Owing to its smaller mass and kinetic energy, a p particle 
 produces much less ionization than does an a particle, 200 fold 
 less on the average per unit path for p particles expelled from 
 radium. The total number of p particles emitted by radioactive 
 substances is not known with the same degree of accuracy as in 
 the case of a particles, but the evidence points to the conclu- 
 sion that the emission of one p particle per atom decaying is the 
 
 aw. Kaufmann, PJujs. Zeit., 4, 54 (1902). 
 
42 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 rule for elements showing p radiation. A very strong piece of in- 
 direct evidence in favor of this view is the principle discovered 
 and elaborated by Russell,-* Soddy,^ Fajans,^ v. Hevesy/ and 
 others, according to which an element emitting a particles pro- 
 duces an element possessing chemical valence two units less than, 
 and occupying a place in the periodic system two places to the 
 left of, that of the parent element; while an element emitting p 
 radiation produces an element shifted one unit in the opposite 
 direction with respect to valence and position in the periodic 
 system. These relations evidently require a unit relationship be- 
 tween the number of atoms changing and the number of a or p 
 particles primarily emitted. Experimental evidence also indicat- 
 ing a number of p particles of that order was obtained by Mose- 
 ley ® and more recently by Hess and Lawson.^ The total num- 
 ber of ions produced in air by the p rays from one 'gram of 
 radium in equilibrium was found by Moseley and Robinson ^° to 
 be about 9x10^* per second, and by the y rays 13x10^* per sec- 
 ond. Rutherford ^^ estimates for radium in equilibrium that of 
 the total radiated energy, 3.2% is in the form of p rays and 
 4.7% in the form of y rays, the balance being represented by 
 a radiation. 
 
 The swiftest p rays from Ra C will penetrate in air about 
 3 m. but are entirely stopped by 2 mm. of lead. Owing to their 
 great range in air and the sparsity of the ionization along their 
 paths, p rays can not be utilized very effectively to produce 
 radiochemical actions in a gaseous system. Their greater absorp- 
 tion in liquids and solids is more favorable for chemical effects. 
 
 As in the case of a particles, the ionization produced in gases 
 by P and y rays has been shown by Millikan and his co- 
 workers ^^ to consist in the detachment of one electron from each 
 molecule, leaving a singly charged positive ion. 
 
 The subject of the production of ionization by electrons has 
 
 *A. S. Russell, Clicm. News, 107, 49-52 (1913). 
 
 •F. Soddy, "Chemistry of the Kadioelenients," Pt. II, pp. 16-20 (1914). 
 •K. Fajans, Phya. Zeit., 14, 1.31 (1913) ; ibid., IG, 450 (1915). 
 'v. Hevesy, ibid., 14, 49 (1913). 
 
 •H. G. J. Moseley, Proc. Roy. Soc, 87A, 230 (1912). 
 
 •v. F. Hess and R. W. Lawson, Sltb. Vienna Acad. Ila, 125, GG1-G74 
 (1916). 
 
 '«>H. G. J. Moseley and IT. Robinson, Phil. Mag. (G) 2S, 327-37 (1914). 
 "Rutherford, "Radioactive Substances," pp. 579-80 (1913). 
 "R. A. Millilian and II. Fletcher, Phil. Mag. (G) 21, 753 (1911). 
 
ELECTRICAL EFFECTS— IONIZATION 43 
 
 already been considered in its qualitative aspects in § 17. The 
 
 quantitative relations have been most thoroughly investigated by 
 
 Townsend ^^ for ionization produced by electrons of photo-electric 
 
 origin accelerated by various voltages in an electrical field of 
 
 definite dimensions. The general equation of Townsend has the 
 
 Ho (a 6)e(''— '^^'^ 
 
 form: n = ■ ^ {a-p)^ ^^ which Uq is the number of ions 
 
 set free at the cathode, n is the initial number of ions reach- 
 ing the other electrode if a is the average number of new ions 
 produced per cm. by each negative ion, and p by each positive 
 ion, d is the distance between the electrodes, with the potential 
 X and the gas pressure P remaining constant. When X/P is 
 small the ionization produced by positive ions is sensibly zero 
 and the equation takes the simple form : n = UoCa'^. More re- 
 cently Horton ^* has proved the applicability of Townsend's 
 equation to ^/lerm-electrons. Townsend's results show that for 
 a pressure of 1 mm. of air, maximum ionization is attained by 
 increase of voltage when the ionization reaches a value of about 
 20 pairs of ions per 1 cm. of path. 
 
 Recently many investigations have been made to determine 
 the minimum voltage at which radiation and ionization effects 
 begin in different gases, in connection with the application of 
 the quantum theory. Consideration of these results is outside 
 the scope of the present work. 
 
 In general it may be pointed out that up to the present, 
 except for the work of Kirkby (see § 52), the chemical effects 
 of the passage of electricity through gases have not been studied 
 under conditions at which Townsend's equations would be ap- 
 plicable, and the total ionization has, therefore, been unknown. 
 Comparison of the amount of chemical action with other fac- 
 tors such as current, voltage, ultra-violet radiation, etc., has not 
 proved very illuminating. It is to be hoped that future work will 
 throw more light upon the fundamental relations involved, 
 through a study of the chemical effects of the passage of elec- 
 tricity through gases under more suitable experimental condi- 
 tions. 
 
 '3 J. S. Townsend, PMl. Mag. (6) 1, p. 198 (1901) ; iUa., 3, 557 (1902) ; 
 "Theory and Ionization of Gases by Collision" (1910). 
 i*F. Horton, Phil. Mag. (6) 34, 461-78 (1917), 
 
44 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 18. Y Rays and X Rays. 
 
 The announcement by Roentgen in 1895 of the discovery of 
 the so-called X or Roentgen rays marked the beginning of a 
 new era in the progress of science. Almost immediately it led 
 to the discovery by Becquerel of the radioactive radiations, 
 which was followed but little later by the discovery of radium by 
 the Curies, and by the rapid development of the subject of 
 radioactivity by Rutherford and Soddy and a host of others too 
 numerous to mention here. It was early found that both X and 
 
 Y rays possess in common with a and p rays the power of ioniz- 
 ing gases, and of producing photographic and phosphorescent ef- 
 fects. Unlike the two latter, X and y rays are not deviated by 
 electrical nor magnetic fields, do not carry electrical charge, 
 and are possessed of unusual penetrating powers, in which the 
 
 Y rays far exceed the X rays. 
 
 The electro-magnetic nature of X rays was recognized quite 
 early and they were classified as ether pulses of short wave 
 length having, naturally, the same velocity as light. Although 
 the general similarity between X and y rays was evident from 
 the first, it was not until much later that it was possible to 
 demonstrate clearly that y rays are also ether pulses having yet 
 greater frequency and correspondingly shorter wave lengths than 
 X rays. 
 
 Not only did the discovery of X and y rays play an important 
 part in the initiation of the new development in physics and 
 chemistry, but their further investigation has proved extremely 
 fruitful in several directions. The discovery by Laue ^^ of the 
 interference principle for X rays and its application by Friedrich, 
 Knipping and Laue ^® to the use of crystals as three dimensional 
 diffraction gratings was shortly followed by the brilliant work 
 of W. L. Bragg ^^ on the use of crystals for the specular reflec- 
 tion of X rays, which resulted in investigations of fundamental 
 importance both with respect to crystal structure and the nature 
 of X rays.^® The classical discovery by Moseley ^^ of the rela- 
 
 " M. Laue, Sitzb. Akad. Wiss. Muenchen, 1912, pp. 2G3-73. 
 
 »«W. Friedrich, P. Knipping, and M. Laue, ibid., 1912, pp. 303-22. 
 
 I'W. L. Bragg, "Nature," 90, 410 (1912) ; Proc. Camb. Phil. Soc, 17, 43- 
 57 (1913). 
 
 ""X Rays and Crystal Structure," W. H. and W. L. Bragg (1915). W. L. 
 Bragg, Phil. Mag. (6) 40, 169-89 (1920). 
 
 »H. G. J. Moseley, Phil. Mag. (G) 26, 1024-34 (1913) ; 27, 703-13 (1914). 
 
ELECTRICAL EFFECTS— IONIZATION 45 
 
 tionship between the X ray spectra of different elements, leading 
 to the establishment of the so-called atomic numbers, has opened 
 the way to substantial progress in the solution of the problem 
 of atomic structure. The work of Barkla,^*' Darwin, Sadler, and 
 later of Siegbahn,^! Duane,^^ Hull,^^ and others on the various 
 types of characteristic radiations from the elements can merely 
 be cited. 
 
 Through some of the work on characteristic radiations just 
 referred to, Rutherford was led to suspect that the y rays may 
 be the characteristic radiation excited by the emission of p rays. 
 The plausibility of this hypothesis has been supported from sev- 
 eral different points of view until no doubt remains of the ex- 
 istence of this relation of the origin of y rays from p radiation. 
 This does not mean, however, that a single p ray sets up a single 
 Y ray pulse. As was seen in the preceding paragraph the total 
 ionization by y rays from radium in equilibrium was found by 
 Moseley and Robinson (loc. cit.) to be of the order 13x10^* pairs 
 per second, about 50% greater than that from the total p radia- 
 tion. 
 
 The most penetrating y rays traverse several centimeters of 
 lead or several hundred meters of air. In the latter part of the 
 path through lead the absorption becomes exponential in char- 
 acter. Owing to their great penetrating powers it is difficult to 
 utilize Y rays efficiently in the study of radiochemical effects. 
 The subject appears to have great importance, however, since 
 it has been found that it is the physiological effects of the y fo^ys 
 which are utilized therapeutically, but whether or not the ef- 
 fect is produced through the intermediation of chemical action re- 
 mains as yet wholly unknown. The utilization of the new power- 
 ful types of X ray tubes, such as the Coolidge tube (§ 17), 
 also offers an attractive future field for the investigation of radio- 
 chemical effects. 
 
 20 C. G. Barkla, Phil. Mag. (6) 22, 396-412; PTiys. Zeit., 15, 160 (1914). 
 
 »Manne Siegbahn, Phys. Zeit., 15, 753-6 (1914) ; Verh. deut. phys. Ges. 18,. 
 150-3 (1916) ; Nature, 96, 676 (1916) ; Yerh. deut. phys. Ges. 18, 278-82 (1916). 
 
 " Wm. Duane and Kang-Fuh Hu, Phys. Rev. (2) 11, 489 (1918) ; Duane 
 and T. Shimizu, iMd., 13, 306 (1919). 
 
 2«A. W. Hull, Am. Joum. Roentgenol. 2, 893 (1915) ; J. Frank. Inst., 181, 
 423. 
 
Chapter 4. 
 Qualitative Radiochemical Effects. 
 
 19. General Classification. 
 
 The observation and investigation of radiochemical effects 
 have embraced a fairly broad field with rather undefined bound- 
 aries. At the one extreme are those effects of radiation which 
 are not definitely known to be chemical in nature, such as phos- 
 phorescence, coloring, and thermoluminescence. Their quantita- 
 tive aspects from the chemical standpoint have hardly been 
 touched upon. At the other extreme will be found a very limited 
 number of definite chemical reactions which have been found to 
 take place under the influence of a radiation, and which have 
 been very thoroughly investigated both with respect to the nature 
 and amount of the chemical action produced, and also with re- 
 spect to the amount of radiation producing it, and the mode of 
 the expenditure of the radiant energy in the system acted on. 
 Between these two extremes will be found all degrees of varia- 
 tion with respect to the qualitative or quantitative character of 
 the 'chemical and radiant factors involved in the reactions 
 studied. 
 
 Radiochemical investigations may be arbitrarily classified as 
 follows: 
 
 (1) Reactions of doubtful chemical nature which have nbt 
 yet been thoroughly explained. 
 
 (2) Reactions undoubtedly chemical in nature but in which 
 the exact chemical composition of some of the products has not 
 been determined. 
 
 (3) Reactions, the chemical products of which have been 
 identified but not quantitatively measured. 
 
 (4) Reactions in which the products have been identified 
 and measured but where the quantity of radiation was not 
 known. 
 
 (5) Reactions in which the products were identified and 
 
 46 
 
QUALITATIVE RADIOCHEMICAL EFFECTS 47 
 
 measured and the total quantity of radiation was known, with- 
 out being able to determine what part of the radiation was 
 effective in the given system. 
 
 (6) Reactions characterized by (5) with the additional 
 knowledge of the effective radiation. 
 
 (7) Reactions characterized by (6) with complete informa- 
 tion as to the kinetics of the reaction from the physical-chemicaj 
 standpoint. 
 
 20. Qualitative Observations. 
 
 The observation of some of the remarkable chemical effects 
 of the rays of radium followed very closely upon its discovery. 
 P. and Mme. Curie ^ in 1899 reported the coloration of glass 
 and of porcelain, as well as the formation of ozone from oxygen 
 (observed by Demarcay). F. Giesel ^ found that coloration of 
 the alkaline halides was produced similar to that by cathode 
 rays, and that water is decomposed into its elements. Becquerel ^ 
 showed that the p and y rays produce many of the reactions 
 that can be brought about by the action of light, such as the 
 change of white to red phosphorus, and the decomposition of 
 hydriodic acid solution and of mercuric chloride. Jorissen and 
 Woudstra * showed that the coagulation of some colloidal solu- 
 tions is caused- by the penetrating radium rays. Jorissen and 
 Ringer ° demonstrated the combination of hydrogen and chlorine 
 gases at ordinary temperature under the influence of the pene- 
 trating rays. 
 
 21. Coloration and Decomposition of Radium Salts. 
 
 Radium salts mixed with barium salts in various proportions 
 undergo spontaneous alterations which are first marked by a 
 change of color from the original pure white to a brownish tint 
 which increases in depth with a rapidity dependent upon the 
 quantity of radium present. This progressive change in color 
 is exhibited very strikingly by Ba(Ra)Br2; if successive frac- 
 
 ip. and M. Curie, Comp. rend. 129, 823 (1899). 
 
 2F. Giesel, Verh. deut. phija. Gea. 2, 9 (1900). 
 
 3 II. Becquerel, Comp. rend. 133, 709-12 (1901). 
 
 * W, P. Jorissen and H. W. Woudstra, Zeit. Chem. u. Industrie d. Kolloide 
 10, 280 (1912). 
 
 "W. P. Jorissen and W. E. Ringer, Ber. 38, 899 (1905) ; 39, 2093 (1906) ; 
 Arch. Ndcrland. Sci. Exact, et Nat. (ii) XII, p. 157 (1907). 
 
48 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 tions with approximately the same radium content are crystal- 
 lized daily, it is possible to judge their relative ages during the 
 first few weeks by the depth of color. Honigschmid ^ has ob- 
 served that radium salts which have not been heated above 
 200° C. take on only a weak yellowish or gray color even after 
 several years, while those which are heated to red glow become 
 almost black in one or two days. Since he found the drying to 
 be complete in either case Hoenigschmid did not attribute the 
 difference to traces of water of crystallization. (Like the corre- 
 sponding barium salts, both RaBra and RaClg crystallize as 
 RaBr2.2H20 and RaCl2.2H20.) Radium chloride undergoes a 
 similar change in color, which does not appear to develop so 
 rapidly as in the case of the bromide. A further proof of the 
 spontaneous chemical change of radium salts is obtained on dis- 
 solving them in water after they have been stored for some time. 
 Solution is invariably accompanied by a more or less copious 
 evolution of gas. On dissolving the chloride in water an odor 
 of CI and CIO2 is often perceptible. The dry salt stored in a 
 desiccator also has the odor of free chlorine and of ozone. The 
 nature of the changes produced in the salt itself has not been 
 thoroughly investigated, but it is probable that the larger part 
 of the gas evolution observed on dissolving is due to the release 
 of some hydrogen (and oxygen) produced by the radiochemical 
 decomposition of remaining traces of water. In containers filled 
 with air part of the salt is also doubtless converted into oxy- 
 halide, oxide, and even some carbonate. 
 
 It has been shown by P. Curie and Debierne ' that a vacuum 
 can not be maintained over the solid salts, and that from a solu- 
 tion of radium salts a continuous evolution of hydrogen and 
 oxygen takes place. Ramsay,® Debierne,® and others found that 
 there is some excess of hydrogen in the gases evolved, which was 
 attributed by Kernbaum ^° to the formation of some HaO, in 
 the solution. It should be pointed out, however, that the rather 
 large excess of hydrogen which accompanies radium emanation 
 in the usual method of collecting it from aqueous solution of 
 radium halides is to be attributed to another cause. The halide 
 
 •O. IlSnigschmId, Sitzb. Akad. Wise. Wien, Ila, 121, 1979 (1912). 
 'P. Curie and A. Debierne, Comp. rend. 132, 770 (1901). 
 "W. Ramsay, J. Chcm. Soc, Lond.. 91i. 931 (1907). 
 »A. Debierne, Comp. rend, 148, 703 (1909). 
 "M. Kernbaum, Lc Radium, C, 225-8 (1909). 
 
QUALITATIVE RADIOCHEMICAL EFFECTS 49 
 
 acid which is also present in the solution is decomposed into 
 hydrogen and free halide. The latter combines with the mer- 
 cury in the collecting system, leaving the corresponding hydro- 
 gen in excess of the oxygen. The rate of the decomposition of 
 water by radium and by radium emanation has been quantita- 
 tively investigated by a number of authorities, whose work will 
 be fully reported in subsequent chapters. 
 
 It may not be amiss to mention here that the decomposition 
 of H2O in any form by the a rays renders the practice of sealing 
 radium salts in small tubes for long periods of time a dangerous 
 one unless certain precautions are observed. Accidents involving 
 serious loss of radium have occurred through the explosion of 
 tubes by the accumulated pressure of hydrogen and oxygen. It 
 appears to be dangerous to heat an old tube or to exert any 
 mechanical stress upon it. It is possible that weakening of the 
 glass container by the continued radiant bombardment en- 
 hances the danger through devitrification of the glass. A far- 
 reaching disintegration of quartz containers by radium rays has 
 been reported.^^ The principal precaution to be observed in 
 sealing radium salts in glass containers is the thorough dehydra- 
 tion of the salt, which should be accomplished by heating for 
 not less than twenty minutes to a temperature not under 250° C. 
 Preferably, the salt should be raised to a red glow in a quartz 
 dish for a shorter time. A good criterion that a temperature has 
 been reached at which complete dehydration takes place rapidly 
 will be furnished by the character of light emitted by the radium 
 salt after heating. The light should show the intensely blue 
 rather than the ordinary pale yellow luminescence of radium 
 salts. The blue luminescence is a result of the effect of tempera- 
 ture and is not directly connected with the degree of dehydra- 
 tion, since the intense blue light persists even under water as 
 long as any salt remains undissolved. Karrer and Kabakjian ^^ 
 have made a study of this blue luminescence and attribute it to 
 the formation of a double salt of radium and barium. This ap- 
 pears difficult to reconcile with Honigschmid's ^^ observation 
 that RaClg of the highest purity, prepared for atomic weight de- 
 
 " Rutherford, "Radioactive Substances" (1913), p. 308. Honigschmid, 
 Sitzb. Akad. Wiss. Wien, Ila, 120, 1G24 (1911) ; St. Meyer and V. F. Hess, 
 ibid, 121, 255 (1912). 
 
 "E. Karrer and D. H. Kabakjian, J. Franklin Inst., 186. 317-40 (1918). 
 
 "Q, Honigsclimid, Sitzb. Akad. Wfss, Wien, Ila, IgO, 16^7-52 (191Q), 
 
60 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 termination, showed the blue color in a very enhanced degree 
 after fusing. The blue light does not remain constant but dies 
 out rapidly in the course of a few days to a small fraction of the 
 original intensity, but still remains more bluish or lavender than 
 the light from salts which have not been highly heated. 
 
 22. Coloration of Glass and Minerals. 
 
 The color produced in glass and many transparent minerals 
 by radium rays and other forms of radiation has been a fre- 
 quent subject of investigation, without the establishment of a 
 final theory of its nature. C. Doelter^* has devoted a monograph 
 to the experimental and descriptive phases of the subject. Many 
 attempts have been made to find a connection between the color 
 produced and the presence of some constituent of the glass or 
 mineral. Most glasses are colored either violet or brown, and it 
 has been stated that soda glasses take the violet and that potash 
 glasses take the brown shades. Others would attribute the violet 
 to manganese, as appears to be true for the coloration by ordi- 
 nary light of glass containing manganese. Bancroft ^^ has pro- 
 posed a physical theory depending on the partial coagulation of 
 coloring material in the colloidal state until a particle of a cer- 
 tain size is produced capable of scattering some wave lengths and 
 transmitting others, which coagulating process, he believes, might 
 be stimulated by radiation. Meyer and Przibram ^® found that 
 the photo-electric effect is increased in glass, and more markedly 
 in fluorspar and kunzite, that had been colored by radiation with 
 radium rays, and therefore favored a physical theory of the eU 
 feet. 
 
 It does not appear possible at present to formulate a satis-* 
 factory theory of the coloring effects, nor to decide whether they 
 are chemical or physical in nature. Very great difficulties are 
 encountered in trying to ascribe the color to any definite com- 
 ponent, though it seems to be rather generally agreed that the 
 presence of impurities, possibly in extremely minute quantity 
 beyond the range of chemical determination, influences the color 
 production. This would be suggested by the erratic differences 
 
 "C. Doclter, "Das Radium iind die Farben" (1910). 
 »W. D. Bancroft, Jour. Phys. Chcm. 22, 601 (1918). 
 
 '•St. Meyer and K. Przibram, Sifzh, Akad. Wiaa. Wicn, Ila, 121, 14^4 
 (J912), 
 
QUALITATIVE RADIOCHEMICAL EFFECTS 51 
 
 found for the same mineral from different localities. Goldstein ^^ 
 estimates that impurities amounting to not more than one part 
 in a million produce color effects under the influence of cathode 
 rays. The confusion that arises in attempting to settle on some 
 certain component or impurity as responsibile for the color may 
 be illustrated by some of the following observations. Meyer and 
 Przibram {loc. cit.) report that they have observed the produc- 
 tion of the violet and of the brown color simultaneously on dif- 
 ferent parts of the same glass vessel, which were subjected to a 
 difference only in the intensity of the radiation ; while, in general, 
 difference in intensity or even the kind of radiation influences 
 only the rate at which color is produced. An outer glass tube 
 enclosing an inner one (of the same glass) containing radium 
 salt, takes on the same color as the inner one, though more slowly, 
 although the outer one receives no a radiation and a different 
 intensity of penetrating radiation from that received by the inner 
 one. Hard glasses high in silica, of the pyrex or Jena type, in- 
 variably take the brown color, but silica vessels, including the 
 transparent variety made from pure fused quartz, take the same 
 violet color as ordinary soft glass. Lead glass is colored brown. 
 In all cases the glass appears finally to become saturated and the 
 color no longer deepens. Thick layers of glass appear to be more 
 intensely colored on account of the depth of layer. Very thick 
 glass, like the walls of a desiccator, becomes almost opaque 
 upon prolonged radiation. The power of luminescing diminishes 
 as the coloring increases. (Mme. Curie, "Radioactivite," II, p. 
 219 [1910].) 
 
 The color produced in glass and minerals by radium rays 
 and by cathode rays can be discharged by heating almost to the 
 softening point of glass. The same color is again restored by 
 renewed radiation, and the cycle may be repeated, apparently in- 
 definitely, without any fatigue effect. 
 
 As a result of an extended investigation of the coloring and 
 thermoluminescence produced in artificial salts and natural min- 
 erals by various forms of radiation JMeyer and Przibram ^^ were 
 led to discard definitely the idea of the influence of impurities, 
 and to favor a return to the theory frequently put forward, of 
 colloidal coloring by metallic particles. Attempts to distinguish 
 discrete particles by means of the ultra-microscope were unsuc- 
 
 "E. Goldstein, Ann. d. Physik, 54, 371 (1895) ; "Nature," 94, 494 (1914). 
 18 S. Meyer and K. Przibram, Hitzh. Akad. Wise. Wien, 123, 653 (1914). 
 
52 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 cessful except in the case already known of the heating of rock 
 salt previously radiated. 
 
 It has been shown by Rutherford ^^ and by Joly ^^ that the 
 depth of the layer of glass or mineral colored by a rays corre- 
 sponds to the range of a particles in the given substance. Joly 
 first pointed out that the so-called "pleochroic halos," small dark 
 spots in certain kinds of mica (biotite, cordierite, and musco- 
 vite) , are due to coloring produced by minute radioactive centers 
 in the mineral. Joly ^^ and Joly and Fletcher ^2 have made an 
 extended study of the subject, showing that the diameters of the 
 concentric rings constituting the halo correspond to the ranges of 
 the different sets of a particles in the uranium-radium series, and 
 that there is a relation between the development of the halo and 
 the geological age of the mineral. 
 
 23. Thermo-luminescence Produced by Radiation. 
 
 It has been found by many observers that salts, glass, min- 
 erals, and other substances after being exposed to radium or to 
 cathode rays become luminous in the dark at temperatures from 
 40° to 200° C. This appears to be due to an effect of the radia- 
 tion which is as yet little understood. The mistake has been 
 rather commonly made of supposing that there is a close con- 
 nection between the discharge of color produced in glass, for in- 
 stance (see preceding paragraph), and the thermoluminiscent 
 effect. However, it has recently been pointed out by Lind ^^ that 
 thermoluminescence can usually be exhausted at about 200° 
 without at all diminishing the color, which is not discharged 
 from ordinary violet colored glass below 400° to 500° C, so that 
 there is evidently no direct connection between the two effects. 
 Meyer and Przibram^* have made an interesting observation 
 which has been confirmed by Lind (lot. cit.) that if glass col- 
 ored brown by radium radiation be heated gently until its 
 thermoluminescence is exhausted, its color is changed to the 
 more common violet tint which then behaves as in glass originally 
 
 "Rutherford, "Radioactive Substances" (1913), p. 307 et acq. 
 
 «> J. Joly, Phil. Mag. (0) 13, 381 (1007). 
 
 »J. Joly, ••Radioactivity and Geology" (1909), pp. 64-9; Phil. Mag. (6) 
 19, 327 (1910). 
 
 "J. Joly and A. L. Fletcher, i6fd., 19, 630 (1910). 
 
 «S. C. Lind, Journ. Phya. Chem. 24, 437 (1920). 
 
 "St. Meyer and K. Przibrara, Sitzb. Akad. Wiss. Wien, Ila, 121, 1414 
 (1912). 
 
QUALITATIVE RADIOCHEMICAL EFFECTS 53 
 
 colored violet, except that no further thermoluminescence is ex- 
 hibited. Upon renewed radiation the color returns to brown. 
 
 Freshly radiated glass will show thermoluminescence to the 
 well rested eye at temperatures quite below the boiling point of 
 water, while glass which has been kept for three or four years 
 after exposure must be raised to the neighborhood of 200° be- 
 fore luminescence sets in (Lind, loc. cit.). 
 
 From the foregoing statements it appears that if the colora- 
 tion and thermoluminescence of glass and minerals are due to 
 chemical causes, at least two different sets of reactions are in- 
 volved which may have little or no connection with each other. 
 The whole subject presents an attractive field for further investi- 
 gation. 
 
 Meyer and Przibram (loc. cit.) examined the thermolumin- 
 escence of a series of artificial borates and silicates of the alkalis, 
 alkaline earths and some other metals. It appeared that the 
 wave length of light emitted by a given group decreased with in- 
 creasing atomic weight of the metal. 
 
 24. Luminescence and Phosphorescence Produced by Radia- 
 tion. 
 
 Certain substances under th^ influence of various kinds of 
 radiation emit light of visible wave lengths at ordinary and even 
 at extremely low temperatures. The use of phosphorescent zinc 
 sulfide screens to count a particles by means of the scintillations 
 produced was referred to in § 12. The phenomenon of scintilla- 
 tion is not only important as a means of counting the a particles, 
 but historically important as the first experimental evidence of 
 the individual existence of atoms, and also as representative of 
 fluorescence in its simplest form. Scintillations can be individu- 
 ally observed and counted only when the number of a particles 
 falling on a given area of screen in unit time is limited. When 
 the number is greatly increased the screen appears to be uni- 
 formly illuminated. In the radium luminous paints, radium salts 
 are intimately mixed with phosphorescent zinc sulfide, which 
 mixture is then applied to a dial or other surface to be illu- 
 minated. These luminous mixtures have come into extensive 
 use oh watch and clock dials, electric push buttons, etc., and 
 during the War were widely used for illuminating dials on aero- 
 
54 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 planes, battleships, or in any place where it was desired to have 
 a feeble light not visible for more than a few yards. 
 
 The nature of the reaction furnishing the light is not thor- 
 oughly understood. Rutherford ^^ has proposed a theory that a 
 phosphorescent substance contains initially a large number of 
 "active centers" or molecular aggregates which are disrupted by 
 a particles with the emission of light. Marsden ^^ examined the 
 effect of intense a radiation on phosphorescent zinc sulfide and 
 found that the intensity of the light emitted falls off rapidly. 
 The number of scintillations remains constant, but the light 
 emitted from each scintillation becomes feebler, owing to the 
 gradual exhaustion of the active centers. Rutherford has calcu- 
 lated that a single a particle destroys all the centers in its path 
 within a radius of about 1.3x10"^ cm. for ZnS, and about 2.5x10"^ 
 cm. for willemite. The decay curves of luminous radium paints 
 such as used by the British Admiralty have been carefully deter- 
 mined by Paterson, Walsh, and Higgins,^^ whose results are not 
 only of great practical but of much theoretical interest. After 
 mixing with a radium salt the luminosity of the paint increases 
 owing to the growth of radium emanation and active deposit; 
 after ten to twenty days this increase is counterbalanced by 
 the decay of the ZnS, so that a maximum is attained. The lumi- 
 nosity then begins to fall, slowly at first and then more rapidly. 
 At the end of six or seven weeks the rate of decrease becomes ex- 
 ponential with the time according to the equation: B/Bo=e-^S 
 in which Bo and B are the luminosities initially and at any time 
 t, and k is the decay constant. Between 40 and 200 days the 
 rate of decay follows this law closely, and then becomes slower. 
 After 500 days a practically constant value is attained of about 
 1/4 the luminosity at maximum. Walsh ^^ has proposed a "re- 
 covery" theory, according to which a state of equilibrium i& 
 reached between the two opposing reactions: 
 
 Decay of active centers ^ Regeneration of active centers. 
 
 Walsh established kinetic equations and showed that they fit 
 such an assumption without any hypothesis as to the nature of 
 the two reactions. 
 
 »E. E. Rutherford, Proc. Roy. 8oc. 83A 5C1 (1910). 
 ME. Marsden, ibid. 83A, 548 (1910). 
 
 " C. C. Patterson, J. W. T. Walsh, and W. F. Higgins, Proc. Phya. Soc, 
 Lond. 29, 215-49 (1917). 
 
 «J. W. T. Walsh, Proo. Roy. 8oc. 93A 550 (1917). 
 
QUALITATIVE RADIOCHEMICAL EFFECTS 55 
 
 Both the luminosity and rate of decay of the luminous com- 
 pounds depend upon the quality of the phosphorescent ZnS and 
 the proportion of radium in the mixture. Evidently it is undesir- 
 able to use for any purpose a more luminous paint than is re- 
 quired, both on account of the initial cost of the radium and the 
 shortened life of the compound through more intense radiation. 
 The upper limit of radium is about one part to four thousand of 
 ZnS. Below this, various grades are used down to one part in 
 one or two hundred thousand. The purity of the radium salt 
 employed should be between 10 and 100%. A very interesting 
 fact pointed out by Patterson, Walsh and Higgins {loc. cit.) 
 is that the rate of decay and luminosity of a paint are three 
 to four times smaller after application to a dial than before. 
 This is evidently due to the partial absorption of the a radia- 
 tion by the binding agent used to make the paint adhere to the 
 dial. It is very fortunate that the great loss in luminosity is 
 compensated by a corresponding lengthening of its life. 
 
 On account of the long life of radium and the consequent 
 waste in applying it to a dial, the use of which is limited to a few 
 years, it has been proposed ^^ that the corresponding member of 
 the thorium series, meso-thorium, should be used, which has a 
 half-period of 6.7 years ^° and would be effective for a period 
 sufficient for all practical purposes. Walsh ^^ has discussed the 
 theory of meso-thorium paints and developed the theoretical de- 
 cay curves. Meso-thorium itself emits no a radiation, which 
 must be generated by the growth of radio-thorium with a half 
 period rate of 1.876 years,^^ which involves the disadvantage of 
 requiring the "ripening" of meso-thorium salts for one or more 
 years before using, but the advantage that, if used before a radia- 
 tion attains a maximum, its growth will in part compensate the 
 deterioration of the ZnS. It has been reported that the use of 
 radio-thorium for luminous paints has become common in the 
 Swiss watch industry. The parent meso-thorium is employed 
 therapeutically through the use of its y radiation, and at suitable 
 intervals, a year or two, the salt is put into solution and radio- 
 thorium precipitated for luminous preparations, the meso-tho- 
 rium being then returned into therapeutic use. It is questionable, 
 
 " R. B. Moore, Bull. Am. Inst. Min. Met. Engs., Aug., 1918. 
 ""L. Meitner, Phys. Zeit. 19, 257-63 (1918). 
 «ij. W. T. Walsh, Proc. Roy. Soc. 93 A, 562-5 (1917). 
 »B. Walter, Phya. Zeit. 18, 584 (1917). 
 
56 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 however, if the use of such a short-lived product as radio-thorium 
 in the luminous paint industry can be recommended. 
 
 The method of preparing phosphorescent zinc sulfide has not 
 been fully described in the literature. Crystalline ZnS (Sidot's 
 blende) , also called hexagonal ZnS, can be prepared in a variety 
 of ways. Its phosphorescent qualities vary greatly and appear 
 to depend on at least two factors, the heat treatment and the 
 presence of small quantities of certain impurities. The methods 
 in commercial use have been carefully guarded and it is not pos- 
 sible to give full details. The heat treatment consists in raising 
 the ZnS mixture for a limited time out of contact with air to 
 a temperature at which incipient crystallization begins. The de- 
 velopment of large, coarse crystals is to be avoided ; on the other 
 hand, the crystalline structure should be distinct after cooling. 
 Fine grinding of the crystals damages their luminescent qualities. 
 The temperature and time of heating will depend to a large ex- 
 tent upon other experimental conditions. 800° to 900° C. at 
 least is necessary for best results though some phosphorescence 
 begins to be developed as low as 600°. 1300° appears to be the 
 upper limit at which favorable results can be obtained. With 
 respect to the impurities necessary there is the widest divergence 
 of views. It has even been claimed that the purest possible ZnS 
 is best. This has been definitely disproved by experiments of 
 C. W. Davis ^^ in the laboratory of the U. S. Bureau of Mines. 
 Starting with a very pure zinc spelter and taking great precau- 
 tions with all the reagents used, it was possible to prepare ZnS 
 of such purity that no heat treatment would develop any phos- 
 phorescent properties towards ordinary light and only a faint 
 luminescence under the action of relatively large quantities of 
 radium emanation. The admixtures which have been mentioned 
 as advantageous are manganese, copper, or bismuth salts, sodium 
 chloride, and salts of the rare earths. Chemical examination of 
 some commercial samples of phosphorescent ZnS has failed to 
 disclose the effective impurities and it is quite possible that the 
 quantities required are not chemically determinable. It also 
 appears that neutral salts are sometimes added to "camouflage" 
 the presence of the effective agents. 
 
 The properties of phosphorescence toward ordinary light and 
 of response to a radiation are not necessarily coincident, and for 
 
 »8 Unpublished results of C. W. Davis. 
 
QUALITATIVE RADIOCHEMICAL EFFECTS 57 
 
 certain purposes it is desirable to obtain a rather non-phosphor- 
 escent preparation for radium paint. 
 
 The nature and proportions of the microchemical admixtures 
 are varied according to the use for which a given luminous ma- 
 terial is intended. Increased intensity seems always to be at- 
 tained at the expense of the duration. 
 
 Many other phosphorescent substances respond to various 
 kinds of radiation. ZnS is the most sensitive to a rays; barium 
 platinocyanide is more sensitive toward |3, y, and X rays. Wil- 
 lemite, natural and artificial, responds to both a and penetrating 
 radiation. Many minerals have been found responsive to cathode 
 rays, though different specimens of the same mineral show great 
 variations. Kunz and Baskerville ^* have described the luminous 
 effects produced in different gems by radium rays. 
 
 There are among the alkaline earth sulfides also a number 
 of compounds or mixtures which are strongly phosphorescent fol- 
 lowing exposure to light, which do not respond to radiation by 
 radium rays. They have been fully treated by Klatt and Len- 
 ard,^^ by Wiedemann and Schmidt,^^ by Waentig,^^ and others. 
 It is beyond the scope of the present work to go into the subject 
 further than to point out that it appears quite well established 
 that the reactions are physico-chemical in nature, that the pres- 
 ence of two or preferably three components is necessary to pro- 
 duce a responsive compound and that in all probability the for- 
 mation of a double compound in crystalline form is necessary. 
 According to modern ideas crystals are molecular aggregates so 
 that there is no conflict with this view and Rutherford's theory 
 of active centers. Waentig treats the subject from the physical- 
 chemical view of solid solution. 
 
 25. General Character of the Chemical Effects of the Rays of 
 Radium. 
 
 Before proceeding in the following chapters to consider in de- 
 tail the quantitative side of the chemical reactions brought about 
 by the radiations from radium and other sources, it will be of 
 
 8*G. Kunz and C. Baskerville, Science 18, 769 (1903). 
 sop. Lenard and V. Klatt, Wied. Ann. 38, 90 (1889), 
 
 38 E. Wiedemann and G. C. Schmidt, ibid. 54, 604 (1895) ; 56, 201 (1895) ; 
 64, 78 (1898). 
 
 «P. Waentig, Zeit. phys. Chem. 51, 435-72 (1905). 
 
58 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 some interest to touch briefly on some of their general character- 
 istics and to compare them with photochemical reactions. The 
 wide variety of chemical actions brought about, particularly by 
 the a rays, is surprising, and one must be struck by the univer- 
 sality of the phenomenon of chemical change by corpuscular ra- 
 diation. This is in marked contrast with photochemical action, 
 where the specific nature of the reaction and of the system being 
 acted on depends entirely upon the wave-length of the light, and 
 its capability of being absorbed by the given system. The highly 
 specific and selective nature of photochemical reactions is their 
 chief characteristic; whereas, we find that a and p rays, in their 
 passage through molecules, are almost universally capable of 
 changing them chemically; their action does not depend upon 
 any reciprocal relation with the atom or molecule affected, sim- 
 ilar to a resonance effect. Owing to the tremendous kinetic 
 energy of the a particles they always ionize and frequently pro- 
 duce chemi(!al changes in the substances through which they 
 pass. Several different views have been expressed regarding the 
 mechanism of the reactions, which may be classified in general 
 terms as: catalytic, mechanical and electrical. Discussion of 
 the theories will be deferred until after the experimental data 
 have been presented, but it may not be amiss to state by way of 
 anticipation that the evidence supporting an electrical or ioniza- 
 tion theory of the chemical effects appears to have much in 
 its favor and will be given full consideration in Chapters 7 to 9. 
 
Chapter 5. 
 
 Chemically Quantitative Investigations in Liquid 
 
 Systems. 
 
 26. Decomposition of Water by Radium Salts in Solution. 
 
 The first observations of the decomposition of water by ra- 
 dium in solution were qualitative, as has already been men- 
 tioned. As soon as a standard for the measurement of radium 
 was made possible through the researches of Mme. Curie, it ap- 
 peared, to be very simple to measure the amounts of hydrogen 
 and oxygen liberated from solution per unit of radium in unit of 
 time. The wide variations in the values reported, by different 
 authorities were sufficient, however, to convince one that the sub- 
 ject was more complicated than was at first anticipated. 
 
 Although the decomposition is produced mainly by the a rays, 
 which would be entirely absorbed by very thin layers of water, 
 and which, so far as those from radium alone are concerned, 
 would expend all their energy within the liquid system, additional 
 factors must be considered. In the first place, it was not at once 
 recognized that the decomposition is really due to a radiation. 
 It should be mentioned here and reiterated as later occasions 
 arise, that the first attempts to explain the chemical effects of 
 radium, somewhat naturally but unfortunately, took the uncer- 
 tain paths of catalysis, which was perhaps regarded as peculiarly 
 suited to explain the effects of the radioactive changes, them- 
 selves so puzzling to chemists in the beginning. It was not until 
 1910 that Usher ^ stated that the reactions are due to a rays and 
 can in no sense be regarded as catalytic. This means simply 
 that more definite laws have been established — which may later 
 be accomplished for other classes of reactions now classed as 
 catalytic. (See also § 58.) 
 
 The second factor which produced confusion and which goes 
 hand in hand with the failure to recognize that the decompo- 
 sition is due to a rays, w^as the false idea that the seat of reaction 
 
 ' F, L, Usher, Journ. Chcm. Hoc. Lond. 97j , 389-405 (1910), 
 
60 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 is confined to the radium in solution; whereas, in reality, radium 
 emanation distributes itself, as would any slightly soluble gas, 
 between the liquid and gas phases in a proportion dependent 
 upon the temperature. The a radiation from the gas phase is 
 much less effective than that in the water, since part of the ra- 
 diation is absorbed by the walls of the container. In some early 
 experiments a small amount of water was used to hold the ra- 
 dium salt in solution in a relatively large vessel, thus greatly 
 reducing the efficiency of absorption of the radiation by the 
 water to be acted on. Taking into account the partition of the 
 emanation and its active products, it is evident that not only the 
 relative volumes of gas and liquid phases, but also the tempera- 
 ture, the surface of the liquid phase, and the absolute dimensions 
 and the shape of the containing vessel would influence the amount 
 of water decomposed by a given quantity of radium in solution. 
 Neglect of these factors accounts for the wide variations in dif- 
 ferent observations. Maximum decomposition can be attained 
 only in the absence of any gas phase, which is difficult to realize 
 on account of the evolution of hydrogen and oxygen. These 
 conditions have perhaps never been fulfilled experimentally for 
 a radium solution, but an indirect calculation will give the maxi- 
 mum sought. Duane and Scheuer ^ found for radium emanation 
 in equilibrium with Ra A, B, and C: 2.9 cm.^ (per hour per 1 
 curie) of electrolytic gas. Assuming that the decomposition pro- 
 duced by the a particles of radium is proportional to the ioniza- 
 tion or to the energy absorbed (see Table I, page 28), one cal- 
 culates for the maximum decomposition of water by a radium 
 solution in equilibrium with Ra A, B, and C: 3.6 cm.^ of hydro- 
 gen and equivalent oxygen per hour per gram of radium. Fuller 
 consideration of the results of Duane and Scheuer and of Usher 
 on the decomposition of water by radium emanation will be re- 
 served for the following chapter. 
 
 27. Formation of Hydrogen Peroxide in Water. 
 
 It has been observed by Runge and Bodliinder,^ Ramsay,* 
 Kernbaum,^ and Duane and Scheuer ^ that the mixture of hydro- 
 
 »W. Duane and O. Schouer. Lc Radium 10, 42 (1913). 
 
 «C. Runge and G. BodlUnder, Ber. 35, 3G05 (1902). 
 
 *W. Ramsay, Jour. Chcm. Soc. Lorul. Olj, 931 (1907). 
 
 "M. Kornbauni. Comp. rend. 14S, 70.'» ; Lc Radium i\, 22r> (1909). 
 
 «W. Duane pnd O. Scheuer, Le Radium 10, 33-40 (1910), 
 
CHEMICALLY QUANTITATIVE INVESTIGATIONS 61 
 
 gen and oxygen obtained by the decomposition of water by ra- 
 dium radiation contains an excess of hydrogen. The excess is 
 greater in the early stages of the reaction and has been found 
 to amount to an excess of 36% above theoretical in one case.® 
 Kembaum ^ showed that hydrogen peroxide is formed in the wa- 
 ter in an amount equivalent to the deficiency of oxygen in the 
 gaseous mixture. As the quantity of hydrogen peroxide accumu- 
 lates in the solution a point is reached where its rate of decom- 
 position just balances the new formation, under which condition 
 of dynamic equilibrium the gases evolved would have normal 
 composition. This explains the gradual diminution in the ob- 
 served excess of hydrogen. It is also conceivable that under a 
 slightly changed condition, such as rise of temperature, decom- 
 position of peroxide might for a time exceed its formation which 
 would result in an excess of oxygen. The decomposition of H^Og 
 is partly spontaneous and partly produced by the radiations (see 
 following section). Kernbaum {loc. cit.) reports that the action 
 of the penetrating rays results exclusively in the formation of 
 H2O2, the gas evolved being pure hydrogen. Kernbaum found 
 that the energy utilized in the formation of HgOg is about 1/10000 
 of the total, and Mme. Curie ^ estimates that the available energy 
 from the penetrating radiation is about 1/100 of the total, and 
 that therefore the energy utilization of penetrating radiation is 
 about 1%. Kailan ^ on a similar basis estimates from his results 
 about 1.25%. 
 
 28. Reactions Produced by Penetrating Rays. 
 
 A method of very general use in the examination of the chemi- 
 cal effects of the rays of radium, particularly in liquid systems, 
 consists in exposing the system to the penetrating rays from a 
 closed preparation of radium, usually sealed in glass. This 
 method has the advantage of great simplicity of manipulation, 
 and of constancy of the source of radiation for any desired 
 length of time. The disadvantages consist in having to use rela- 
 tively large quantities of radium since only the penetrating rays 
 are available, and in having to be content with only a rough esti- 
 
 'M. Kernbaum, Lc Radium 7, 242 (1910). 
 
 "Mme. Curie, "Trait6 de Radioactivity" (1910), Vol. II, p. 251. 
 
 •A. Kailan, SitzJi. Akad. Wisa. Wien Ha, 120, 1227 (1911). 
 
62 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 mation of the proportion of the radiation that is effectively- 
 absorbed. 
 
 Experiments of Kalian. A very extensive series of experi- 
 ments has been carried out with large quantities of radium in 
 the Institut f. Radiumforschung in Vienna by Anton Kailan, who 
 has investigated a large number of inorganic and organic reaction 
 of very varied character. 
 
 The decomposition of HgOg ^^ was investigated at 13-15° and 
 at 25° in paraffined and in bare glass vessels, and was found to 
 take place approximately according to a first order equation. 
 The temperature coefficient is low, 1.2 per 10° C, which is a 
 property common to most radio- and photo-chemical reactions. 
 The velocity of decomposition was found to increase with the 
 strength of the radium preparations, though not quite propor- 
 tionately to it. 
 
 Using a preparation containing 239 mgs. of radium element, 
 Kailan ^2* was able to confirm Kernbaum's discovery (see pre- 
 ceding section) of the production of HgOg in water. 
 
 Kailan also studied the decomposition of the alkaline (Na 
 and K) iodides,^^ and later of the alkaline earth iodides,^^ in 
 aqueous solution, as well as the effect of the penetrating radia- 
 tion on several other inorganic compounds.^-* The decomposition 
 was greater for KI than for Nal, and greater for both salts in 
 acid than in neutral solution. The rate of decomposition rises 
 very rapidly with the addition of the first quantities of acid 
 (5x10-^ molar doubles the rate), but afterwards the increase is 
 slow for further increase of acid. The decomposition of the 
 iodides also increases with the salt concentration, but far below 
 direct proportionality. 
 
 A somewhat puzzling result obtained by Kailan in connection 
 with the decomposition of KI is that the rate in neutral solu- 
 tion has a negative temperature coefficient. An explanation may 
 be sought in the well-known fact that radiochemical reactions 
 usually have either no temperature coefficient or very small ones, 
 which would account for no additional decomposition with in- 
 crease of temperature. The actual observed diminution in rate 
 would then be explained by the ordinary influence of tempera- 
 
 «>A. Kailan, Sitzh. Akad. Wiss. Wien Ila, 120, 1213-28 (1911). 
 "A. Kailan, ihid., 120, 1373-1400 (1911). 
 "A. Kailan, Ibid., 122, 787-810 (1913). 
 i-^Jbid., 121, 1353-84 (1912). 
 
CHEMICALLY QUANTITATIVE INVESTIGATIONS 63 
 
 ture on the reverse reaction between the liberated iodine and 
 alkali. When one attempts, however, to apply the same rea- 
 soning to decomposition of KI in acid solution, which, according 
 to Creighton and McKenzie,^^ also has a negative temperature 
 coefficient, the explanation becomes more difficult. Kailan fa- 
 vors the view that decomposition of KI is due to the direct de- 
 composition of electrolytically undissoeiated salt molecules. It 
 appears much more likely that the radiation first acts on water 
 to produce an activated (nascent) form of oxygen which reacts 
 with KI in a secondary reaction. 
 
 Penetrating rays were found by Kailan to reduce ferric sulfate 
 in aqueous solution, similar to the action found by Ross^* for 
 ultraviolet light. The decomposition of KBr solution was found 
 to be 20-100 times less than that of KI under the same condi- 
 tions. Decomposition of CaClg could not be detected. The de- 
 composition of the iodides of the alkaline earths and of mag- 
 nesium disclosed the same general relations as did the alkaline 
 iodides. No relation between rate of decomposition and molec- 
 ular weight could be established. 
 
 Comparing the effects of the penetrating rays with those of 
 ultraviolet light, Kailan found that a quartz mercury lamp at 
 8 cms. distance gave the same amount of reaction in periods of 
 time 200-800 times shorter than did preparations of radium con- 
 taining 80-200 mgs. of element placed directly in the liquid. 
 
 Kailan ^^ also investigated the effect of penetrating rays on a 
 number of organic compounds and reactions. The inversion of 
 cane sugar was observed and referred to the secondary action of 
 a primary acid formation, which was confirmed by the much 
 smaller effect produced in grape sugar. Ester formation from 
 alcohol and acid is not notably affected by penetrating radia- 
 tion. The decomposition of esters takes place to some extent, 
 but appears to be more of the nature of a shattering of the 
 molecules than of an ordinary saponification. The conversion 
 of nitrobenzaldehyde into acid was produced at a rate of 10-20 
 thousand times as slowly as by a mercury arc lamp at 8 cms. 
 Chinon and oxalic, malonic and tartaric acids showed no posi- 
 
 " H. J. M. Creighton and A. S. McKenzie, Amer. Chem. Journ., 39, 474-93 
 (1908). 
 
 "W. H. Ross, J. Am. Chem. 8oc. 28, 786 (1907). 
 
 "A. Kailan, Sitzh. AJcad. Wiaa. Wien Ila, 121, 1385; 2127 (1912) ; 122, 881 
 (1913) ; 12S, 583; 1427 (1914). 
 
64 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 tive effects. The electrical conductivity of fumaric acid is raised 
 and that of maleic acid lowered by penetrating rays, with the 
 difference that the magnitude of the effect is about equal for the 
 two acids with radium rays, but much greater for maleic acid in 
 ultraviolet light. This seems to justify the conclusion that the 
 photo-equilibrium between the two stereo-isomers would differ 
 from that reached under the influence of p and y rays. 
 
 Kailan ^^ *has also examined the effect of penetrating radia- 
 tion on chloroform and carbon tetrachloride and compared the 
 effect on the former with that produced by ultraviolet light. 
 The radiation from 80 mgs. of element was allowed to act in the 
 absence of light for about three years. In both cases the chief 
 reaction is through the interaction with oxygen of the air; in the 
 case of chloroform resulting in the formation of hexachlorethane, 
 in the case of carbon tetrachloride in the formation of chlorine, 
 and likewise of hydrogen chloride from the reaction of phosgene, 
 primarily formed, with the water present in the compounds. The 
 total decomposition of 30-45 cm.^ of CCl^ in three years amounted 
 to % to %%, while about twice this quantity of CHCI3 was 
 changed to the extent of % ^ %% in the same time, showing 
 that the absolute quantity of change was of the same order in 
 both cases. Similar effects were produced by ultraviolet light 
 in about 1 /300th of the time required for penetrating rays. 
 
 The effect of penetrating radiation on toluene, both in the 
 presence and absence of water, has been determined by Kailan,^^ 
 using 80 mgs. of Ra element for a period of two years. The 
 products of reaction in the presence of air were benzaldehyde, 
 benzoic acid, and probably formic acid. In the case of dry 
 toluene, less than l^% was changed in two years. Effects of 
 the same kind and magnitude could be obtained by 22 hours' 
 radiation with a quartz mercury lamp at 8 cms. The effect of the 
 penetrating rays from 110 mgs. of element in two years on 50 
 cm.^ each of toluene and water produced about three times as 
 much acid as in the case of dry toluene. About 70% of the 
 acid was benzoic, and about 30% formic. Radiation for 22 hours 
 with ultraviolet light produced a little less acid than the two 
 years of penetrating radiation. The products consisted of 44% 
 benzoic, 36% formic, and 20% oxalic acid. 
 
 "A. Kalian, Sitzh. Akad. Wiss. Wien Ila, 126, 741 (1917). 
 "A. Kalian, ibid., Ila, 128, 831-52 (1919). 
 
Chapter 6. 
 
 Reactions Produced by Radium Emanation. 
 (First Experiments.) 
 
 29. Radium Emanation as a Source of Radiation. 
 
 In most respects radium emanation has advantages over any 
 of the other forms of radioactive matter as a source of radiation 
 in the study of the production of chemical reaction. These ad- 
 vantages have already been considered in some detail in § 14. 
 
 The heat evolution from one gram of radium in equilibrium 
 with Ra C has been determined by Meyer and Hess ^ to be 132 
 small gram calories per hour. The evolved heat is generated by 
 the absorption of the various radiations in the matter through 
 which they pass. Rutherford - has calculated the following dis- 
 tribution: a particles (including recoil atoms), from Ra, 25.1 
 cal.; from Emanation, 28.6; from Ra A, 30.5; from Ra C, 39.4; 
 total 123.6; p rays from Ra C, 4-^; y rays from Ra C, 6.5; grand 
 total for radium in equilibrium 134.4- This agrees well with the 
 result of Meyer and Hess obtained under conditions where only 
 15% of the Y radiation was absorbed. 
 
 For radium emanation in equilibrium with active deposit, the 
 total from a rays and recoil atoms would be 109.3, or, including 
 |3 rays, would be 113.6 cal. These heat emissions can be used in 
 calculating the energy efficiency for any given chemical reac- 
 tion in which the absorption is complete within the system. In 
 cases of incomplete absorption in the chemical system more 
 roundabout methods of calculating the efficiency must be re- 
 sorted to. 
 
 The total ionization per second produced by radium emana- 
 tion when mixed with air in cylinders of different sizes may 
 be approximately estimated by means of the empirical formula 
 of Duane and Laborde,^ which may be written in the form: 
 
 iSt. Meyer and V. F. Bfess, SitzJ). Akad. Wiss. Wicn Ila, 121. 603 (1912). 
 
 * Rutherford, "Radioactive Substances," p. 581 (1913). 
 
 * VVm. Duane and A. Labordo, Lc Radium 7, 1G2-4 (1910) ; Duanc, Comp. 
 rend. 140, 581; 786 (1905). 
 
 65 
 
66 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 X = I (max.)/13.5(l-0.572.S/V), in which X is the quantity of 
 emanation produced per second by 1 gram of radium, I (max.) 
 is the saturation current in electrostatic units after 3 hours 
 when emanation is in equilibrium with its decay products, S is 
 the inner surface of the chamber in cm.^, and V the volume in 
 cm.^. The conversion factor from gram-seconds to curies of 
 radium emanation is: 1 curie = 4.795xl0^gm.secs. The formula 
 of Duane and Laborde is purely empirical and does not apply 
 accurately, as has been shown by Leaming, Schlundt and Under- 
 wood * to chambers of volumes or shapes very different from 
 those employed by Duane and Laborde. The ionization pro- 
 duced in gases other than air can also be approximately esti- 
 mated by applying a correction for the specific ionization of the 
 given gas (Table II). 
 
 30. Experiments of Cameron and Ramsay. 
 
 In 1907 and 1908 Cameron and Ramsay ^ carried out an ex- 
 tended series of experiments on the chemical action of radium 
 emanation on water and on a number of gases at ordinary tem- 
 perature. Reactions were chosen that would proceed with a 
 change in pressure at constant volume, by means of which the 
 well-known manometric method of determining velocity of re- 
 action could be applied. Since the quantity of chemical action 
 produced, even by relatively large quantities of emanation, is 
 small, it was necessary to confine the reacting substances in 
 volumes so small (1 to 4 cm.^) that the pressure changes could 
 be readily measured. Although the employment of such small 
 volumes appears disadvantageous from the standpoint of the full 
 utilization of the a rays, the practice is not only justified by the 
 accuracy of the measurement of the pressure changes, but also 
 presents an additional simplification if one wishes to calculate 
 the ionization produced in the gases (see Chapter 8). 
 
 The apparatus used by Cameron and Ramsay is shown in 
 Figs. 3 and 3a. The introduction of emanation into the reaction 
 chamber K is effected by means of the Ramsay gas pipette A.^ 
 
 *T. II. Learning, II. Schlundt, and J. E. Underwood, Tr. Amer. Electro- 
 chem. Soc. 30, 305 (1910). 
 
 "A. T. Cameron and Wm. Ramsay, Journ. Chem. Soc. Lond. 91i, 931; 
 91ii, 1200 ; 1593 ; 92„ 900 ; 992. 
 
 •Wm. Ramsay, Proc. Roy. Soc. 70A, 113 (1905) ; Trans. 91, 939 (1907). 
 
REACTIONS PRODUCED BY RADIUM EMANATION 
 
 67 
 
 Fig. 3. 
 
68 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 The emanation together with -the hydrogen and oxygen resulting 
 from the decomposition of the original radium salt solution were 
 collected in vessel C, where the hydrogen and oxygen were re- 
 moved by means of the spark gap D. After exhausting all the 
 apparatus above the stopcock B through F, the emanation and 
 
 A 
 
 Of 
 
 c 
 
 i 
 
 ^ 
 
 Fia. 4. — Various Reaction Vessels op Cameron and Ramsay. 
 A. Decomposition of HCl, P, Hg cup ; B. combination of Hg and Og (dry) ; 0. com- 
 bination of H2 and O2 (moist) ; D. decomposition of water. 
 
 residual gases were allowed to pass through the P2O5 drying 
 bulb G into K. Any gas or gaseous mixture to be investigated 
 was introduced into the reaction chamber in the same way, be- 
 fore the introduction of emanation. 
 
REACTIONS PRODUCED BY RADIUM EMANATION 
 
 69 
 
 TABLE III 
 
 Results of Cameron and Ramsay on the Decomposition of Water 
 
 by Emanation 
 
 Reaction: (2H2O) = 2H2 + O^. Water Vol. = 2.302 c.c. 
 Gas Vol. = 3.789 c.c. Ra Em. z= 31 milli-curies 
 
 Days 
 
 Pr. in mm. 
 
 Vol. in c.c. 
 
 Voo-Vt 
 
 \oO-.Vo 
 
 % 
 Ra Em left 
 
 0.0 
 
 39.9 
 
 0.200 
 
 0.390 
 
 100.0 
 
 100.0 
 
 0.25 
 
 42.5 
 
 0.212 
 
 0.378 
 
 96.9 
 
 95.6 
 
 0.81 
 
 49.7 
 
 0.248 
 
 0.342 
 
 87.7 
 
 86.4 
 
 0.92 
 
 52.6 
 
 0.262 
 
 0.328 
 
 84.1 
 
 84.8 
 
 1.89 
 
 62.8 
 
 0.310 
 
 0.280 
 
 71.8 
 
 71.4 
 
 2.80 
 
 71.8 
 
 0.358 
 
 0.232 
 
 59.5 
 
 60.5 
 
 3.81 
 
 80.5 
 
 0.401 
 
 0.189 
 
 48.5 
 
 50.6 
 
 4.81 
 
 86.4 
 
 0.431 
 
 0.159 
 
 40.8 
 
 42.2 
 
 5.81 
 
 90.4 
 
 0.451 
 
 0.139 
 
 35.6 
 
 35.2 
 
 6.81 
 
 90.7 
 
 0.484 
 
 0.106 
 
 27.2 
 
 29.5 
 
 10.07 
 
 107.9 
 
 0.538 
 (0.590) 
 
 0.052 
 
 13.3 
 0.0 
 
 16.4 
 
 The experimental arrangement for the measurement of the 
 decomposition of water is shown in Fig. 3a. The water was in- 
 troduced immediately over the mercury. In order to measure 
 several different reactions with the same manometer, the arrange- 
 ment shown in Fig. 4 was employed, in which the special uses 
 of the various reaction vessels are indicated. Vessel D (Fig. 
 4) was the form finally adopted for the decomposition of water. 
 
 In Table III will be found the data of Cameron and Ramsay's 
 Expt. 3 {loc. cit., p. 973) for the decomposition of water in 
 the apparatus shown in Fig. 4. 
 
 Voo, Vt and Vo are the final, intermediate, and initial vol- 
 umes respectively. The fraction 100 ^ ^ is the percentage of 
 
 V 00-Vo 
 
 uncompleted reaction at any time t. The last column shows the 
 percentage of emanation remaining at the corresponding times. 
 The last two columns are in approximate agreement, from which 
 Cameron and Ramsay deduced the general law that the rate of 
 reaction is always proportional to the quantity of emanation pres- 
 ent. It follows that half of the reaction must be completed in 
 
70 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 the half period of emanation, which is 3.85 days. Cameron and 
 Ramsay found the average value of the time required to half 
 complete the reaction in seven different experiments, two for the 
 decomposition of water and five for the combination of hydro- 
 gen and oxygen, to be 3.86 days. The law that the rate of re- 
 action is proportional to the quantity of emanation and dimin- 
 ishes at the same rate with its decay can be accepted for a liquid 
 system, as in the decomposition of water, but in a gaseous sys- 
 tem in which the pressure changes, it no longer holds except in 
 special cases, as will be shown in Chapter 8. The conclusion of 
 Cameron and Ramsay that "each atom of emanation as it dis- 
 integrates produces the same amount of chemical action" is also 
 subject to some modifications. The disintegration is effective 
 in producing chemical action only through the accompanying 
 emission of an a particle. The amount of reaction brought about 
 by each particle will depend upon the length of its path in the 
 gas phase, which will evidently vary for different particles from 
 zero up to the longest path possible in a given vessel, or in large^ 
 vessels would be limited by the range of a particles in the gas. 
 
 In Table IV will be found the data from Cameron and Ram- 
 say's Expt. 4 {loc. cit., p. 974) for the combination of hydrogen 
 and oxygen in the moist gases. 
 
 By comparison of the last two columns it will be observed 
 that the rate of chemical action shows a decided tendency 
 to exceed the rate of decay of emanation. This means that the 
 utilization of the a rays becomes less complete as the reaction 
 proceeds, owing to the reduction in pressure and consequent 
 diminution in the number of molecules encountered by each 
 particle. Later (see Table XI), cases will be given where larger 
 quantities of emanation are used so that the gas pressure changes 
 through much wider limits, and the discrepancy becomes much 
 more pronounced, showing that Cameron and Ramsay's law is 
 a special case, applying in gases, only when the pressure change 
 is slight. This can be illustrated further by comparison of the 
 last two columns in Table V, in which the amount of emanation 
 used is smaller than in Table IV, consequently the relative pres- 
 sure change is less and the agreement between per cent of reaction 
 and of emanation decayed is almost as good as in the case for de- 
 composition of water (Table III). 
 
 In the experiments just reported with moist gas, the plain 
 
REACTIONS PRODUCED BY RADIUM EMANATION 
 
 71 
 
 TABLE IV 
 
 Results of Cameron and Ramsay on the Formation of Water by 
 Emanation (Moist) 
 
 Volume of Tube 2.186 c.c. Ra Em. 46.5 milli-curies. 
 Reaction 2H2 + 02= (2H2O) 
 
 Days 
 
 Pr. in mm. 
 
 Vol. in c.c. 
 
 Vt-Voo 
 
 Vo-Voo 
 
 Ra Em left 
 
 0.0 
 
 523.5 
 
 1.505 
 
 0.668 
 
 100.0 
 
 100.0 
 
 1.02 
 
 487.0 
 
 1.401 
 
 0.564 
 
 84.4 
 
 83.2 
 
 2.07 
 
 442.0 
 
 1.271 
 
 0.434 
 
 65.0 
 
 68.9 
 
 3.07 
 
 405.6 
 
 1.167 
 
 0.330 
 
 49.4 
 
 57.6 
 
 4.13 
 
 384.5 
 
 1.106 
 
 0.269 
 
 40.3 
 
 47.6 
 
 4.99 
 
 369.5 
 
 1.063 
 
 0.226 
 
 33.8 
 
 40.7 
 
 6.11 
 
 352.2 
 
 1.013 
 
 0.176 
 
 26.3 
 
 32.3 
 
 7.07 
 
 343.5 
 
 0.988 
 
 0.151 
 
 22.6 
 
 28.0 
 
 9.11 
 
 321.4 
 
 0.924 
 
 0.087 
 
 13.0 
 
 19.4 
 
 10.16 
 
 319.3 
 
 0.919 
 
 0.082 
 
 12.3 
 
 16.1 
 
 11.04 
 
 316.6 
 
 0.911 
 
 0.074 
 
 11.1 
 
 13.7 
 
 12.10 
 
 312.3 
 
 0.898 
 
 0.061 
 
 9.1 
 
 11.4 
 
 97.0 
 
 291.0 
 
 0.837 
 
 0.0 
 
 0.0 
 
 0.0 
 
 form of tube (Fig. 3a, p. 67) was used. In Table V are the 
 results of Cameron and Ramsay for dry hydrogen and oxygen, 
 using the form B, Fig. 4, in which, part of the tube was filled 
 with P2O5. No difference was observed by Cameron and Ram- 
 say in the action of emanation on dry or on moist hydrogen and 
 oxygen. This has also been confirmed by Lind.'' 
 
 Cameron and Ramsay {loc. cit.) also measured by the same 
 method the effect of radium emanation in decomposing 
 CO2, CO, NH3, and HCl gases and in synthesizing NHg from its 
 elements. The data for some of these reactions will be pre- 
 sented in Table X, § 42, in a somewhat different connection. 
 
 Before passing to other experiments it should be mentioned 
 that Cameron and Ramsay regarded their work as preliminary in 
 nature and it has since been shown ^ that the quantities of ema- 
 nation reported by them were probably higher than the quanti- 
 
 TS. C. Lind, Journ. Amcr. Chem. Soc. 1,1, 540 (1919). 
 8S. C. Lind, ihid. 41, p. 534 and pp. 549-50 (1919). 
 
72 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 TABLE V 
 
 Results of Cameron and Ramsay on the Formation of Water by 
 Emanation (Dry) 
 
 Reaction: 2H2 + 02= (2H2O) 
 
 Expt. 6 iloc. cit, p. 977). Vol. of Tube 4.996 c.c. 
 
 Ra Em. 22.0 milli-curies. 
 
 Days 
 
 Pr. in mm. 
 
 Vol. in c.c. 
 
 Vt-Voo 
 
 '<'1- 
 
 % 
 Ra Em left 
 
 0.0 
 
 577.6 
 
 3.798 
 
 0.555 
 
 100.0 
 
 100.0 
 
 1.07 
 
 564.1 
 
 3.709 
 
 0.466 
 
 84.0 
 
 82.6 
 
 1.96 
 
 552.4 
 
 3.631 
 
 0.388 
 
 69.9 
 
 70.3 
 
 2.84 
 
 546.9 
 
 3.595 
 
 0.352 
 
 63.4 
 
 60.0 
 
 3.80 
 
 535.6 
 
 3.522 
 
 0.279 
 
 50.3 
 
 50.5 
 
 4.80 
 
 530.2 
 
 3.485 
 
 0.242 
 
 43.6 
 
 42.2 
 
 6.80 
 
 521.5 
 
 3.428 
 
 0.185 
 
 33.3 
 
 29.5 
 
 9.88 
 
 505.6 
 
 3.324 
 
 0.081 
 
 14.6 
 
 16.9 
 
 11.91 
 
 502.8 
 
 3.305 
 
 0.062 
 
 11.2 
 
 11.8 
 
 13.90 
 
 496.4 
 
 3.264 
 
 0.021 
 
 3.8 
 
 8.3 
 
 21.89 
 
 493.3 
 
 3.243 
 
 0.0 
 
 0.0 
 
 1.9 
 
 ties actually present (§ 44). Nevertheless their pioneer work is 
 of great interest on account of its scope and methods, and repre- 
 sents the first serious attempt to deal experimentally with this 
 very interesting subject. 
 
 31. Experiments of Usher on the Ammonia Equilibrium. 
 
 In 1910 Usher,'^ working in the laboratory of Ramsay, made 
 an exhaustive study of the decomposition and formation of 
 ammonia by radium emanation. He definitely stated, what 
 Cameron and Ramsay had already considered as possible, that 
 the a particles are the real agents of the reaction, and made 
 the very important advance in recognizing clearly that increase 
 of volume will increase the amount of chemical action produced 
 by a given quantity of emanation through the lengthening of the 
 effective paths of the a rays. Usher calculated that the average 
 number of molecules decomposed by each a particle in a large 
 
 »F. L. Ushor, Journ. Chcm. Soc. Lond. 97,, 389-405 (1910). 
 
REACTIONS PRODUCED BY RADIUM EMANATION 73 
 
 volume (2 liters) was 134,000, which he estimated to be 90% of 
 the maximum, were all the a particles wholly effective. Through 
 considerations involving ionization Lind ^^ used Usher's data in 
 calculating the maximum number of NH3 molecules that would 
 be decomposed by a single a particle to be 274,000. From more 
 recent experiments of Wourtzel ^^ it appears that the number at 
 ordinary temperature must be at least 388,000. The higher effi- 
 ciency found by Wourtzel for the decomposition of NH3 by ema- 
 nation appears to raise some doubt as to the quantity of emana- 
 tion reported by Usher, similar to the discrepancies attaching 
 to the data of Cameron and Ramsay (§ § 30 and 44). 
 
 With respect to the reverse reaction, the formation of NH3 
 from its elements. Usher found a reduction in pressure, as had 
 Cameron and Ramsay, but on analyzing the gaseous products, 
 failed to find any certain quantity of NH3, and concluded that 
 the reduction of pressure was due to some other cause, possibly 
 to the removal of hydrogen by being driven into the glass walls 
 by the a particles. According to Usher, therefore, the equilibrium 
 2NH3 ^ No + 3H2, in the presence of radium emanation at ordi- 
 nary temperature, fies practically wholly on the side of decompo- 
 sition of NH3. 
 
 'OS. C. Lind, Joum. Phys. Chem. IG, 603 (1912). 
 "E. E. Wourtzel, Le Radium 11, 342 (1919). 
 
Chapter 7. 
 
 Eelation Between Gaseous Ionization and Radio- 
 chemical Effects. 
 
 32. Historical Development of the Ionization Theory of the 
 Chemical Effects of Corpuscular Radiation. 
 
 In the foregoing chapters the chemical effects of the radia- 
 tions, particularly of the a rays, of radium have been considered, 
 first in their qualitative and then in their quantitative relation- 
 ships. The quantitative character of the investigations has ex- 
 tended to the measurement of the chemical change produced, and 
 included a certain knowledge of the quantity of radioactive ma- 
 terial causing the change. As has already been pointed out, 
 this knowledge, though important and quite as far-reaching as 
 that possessed in some other branches of radiochemistry, fur- 
 nishes little information as to the true relation between quantity 
 of radiation and chemical change, since the actual quantity of 
 the former utilized in bringing about the latter was known only 
 very approximately, on account of losses of radiation to the 
 walls of the vessel and other losses difficult to take into account. 
 These difficulties are no greater than are met in dealing with 
 other forms of radiation, and under experimental conditions prop- 
 erly controlled, the difficulties are much less with a radiation 
 from radium emanation than with other forms of radiant energy. 
 
 Very definite laws have been established (Chapter 2) for the 
 absorption of a rays in gases by means of a study of the ioniza- 
 tion produced. As will be shown in the present chapter, it has 
 proved very instructive to relate statistically the ionization in a 
 given system to the chemical action. It is perhaps a matter 
 of surprise that such comparisons were not made earlier than 
 was the case. It will not be without interest to point out some 
 of the reasons historically. Of course, no such comparisons were 
 possible before the development of the standards and methods of 
 measurement of the radioactive substances involved. And in 
 
 74 
 
IONIZATION AND RADIOCHEMICAL EFFECTS 75 
 
 the case of radium emanation, its collection and purification are 
 prerequisites. A knowledge of the ionization in air and in other 
 gases and of the distribution of that ionization along the path 
 of the radiant particles was also essential. The chief draw- 
 back lay in the fact that the ionization was determined for gas- 
 eous systems, whereas the chemical actions were first carried out 
 quantitatively in liquid systems, and a comparison appeared too 
 indirect to have value. Furthermore, the gas reactions which 
 were studied quantitatively were not carried out under condi- 
 tions from which the ionization could be readily estimated. 
 
 In 1907 Bragg ^ first calculated from data of Ramsay and 
 Soddy 2 that the number of molecules of water decomposed was 
 almost exactly equal to the number of ions that would have been 
 produced in air by the emanation employed. Apparently Bragg 
 was not impressed by the equality he found and referred to it as 
 a "curious parallelism in numbers." Mme. Curie ^ stated in 1910 
 with respect to the decomposition of water by a particles that, 
 "the production of electrolytic gas by radium in solution is of 
 the same order of magnitude as that which one would obtain 
 if the number of molecules of water decomposed by the a rays 
 emitted, were equal to the number of ions which these same 
 rays would produce in air." 
 
 In 1910 Le Blanc calculated from Bergwitz's^^ data on the 
 decomposition of water by polonium, that the saturation current 
 in air measured by Bergwitz for the a radiation, corresponded 
 very closely to the current that would be required by Faraday's 
 law to decompose the same amount of water electrolytically as 
 was decomposed by the a radiation of polonium. While Le Blanc's 
 calculation suffers from the disadvantage of comparing air ioni- 
 zation with water decomposition, yet the recognition of the ap- 
 plicability of Faraday's law to this class of reactions, which Le 
 Blanc very aptly classifies under "electrolysis without elec- 
 trodes," is of great importance, and it is unfortunate that it 
 was not given greater prominence than scant mention in his 
 Elektrochemie (5th Ed., p. 317). Later Le Blanc* published 
 
 »W. H. Bragg, Phil. Mag. (6) 13, 333 (1907). 
 
 «W. Ramsay and F. Soddy, Proc. Roy. Soc, 72, 204 (1903). 
 
 "Mme. Curie, "Traits de Radioactivity," Vol. II, pp. 247-8 (1910). 
 
 3a K. Bergwitz, Phys. Zeit. II, 273-5 (1910). 
 
 *M. Le Blanc, Zeit. Phys. Chem. 85, 511 (1913). 
 
76 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 in full his calculations from Bergwitz's data on which his state- 
 ment was founded. 
 
 33. Production of Ozone by a Particles. 
 
 In 1911 the writer^ undertook in the Institut fUr Radium- 
 forschung in Vienna, by measuring the quantity of ozone formed 
 by the action of a rays of radium emanation on gaseous oxygen, 
 to compare the chemical action with the ionization. Instead of 
 adopting the method of Cameron and Ramsay of mixing emana- 
 tion directly with the gas, purified emanation was introduced into 
 an extremely thin-walled small glass sphere about 1 mm. in diam- 
 eter. The wall thickness was of the order 0.005 mm. which would 
 be equivalent to about 1 cm. of air in the absorption of a rays, 
 leaving the a rays from Ra C a free path outside the bulb of 
 about 6 cms. By placing a bulb of this kind at the center of 
 a glass sphere of about 12 cms. diameter filled with oxygen, the 
 free path of the a rays is fully utilized without their reaching 
 the wall. The ozone formed was absorbed in neutral KI solution 
 and measured chemically. 
 
 The construction of such thin a ray bulbs can not be under- 
 taken by the ordinary glass-blower and will therefore be de- 
 scribed in some detail. The first glass vessels thin enough to 
 transmit a rays were used by Rutherford and Royds ^ in their 
 work on the nature of the a particle. They were thin-walled 
 capillary tubes, but since no details of their construction were 
 given, the method of making the thin bulbs was worked out 
 more or less independently by Duane and Lind in the laboratory 
 of Mme, Curie. Thin-walled soft glass tubing of 8-10 mm. di- 
 ameter is first drawn down in the free blast flame to a diameter 
 of about 1 mm. over a length of 6-8 inches. One end is then 
 sealed and the other attached to an ordinary foot-bellows or 
 other source of pressure. Further manipulation is carried on in 
 a simple furnace consisting of a six inch length of hard glass or 
 quartz tubing of about % inch internal diameter open at both 
 ends. The middle portion of the tube furnace is heated either 
 with a blast lamp, or in the case of quartz with a flame contain- 
 ing some oxygen, and should be provided with an asbestos hous- 
 
 »S. C. Lind, Sitzb. Akad. Wisa. Wien Ila, 120, 1709 (1911) ; Monatah. 32, 
 295. Amer. Chem. Journ., 47, 397-415 (1912) ; Lc Radium 9, 104-G (1912). 
 •E. E. Rutherford and T. Royds, Phil. Mag. (6) 17. 2S1 (1909). 
 
i 
 
 IONIZATION AND RADIOCHEMICAL EFFECTS 77 
 
 ing to retain the heat. The glass tube to be worked is then 
 inserted entirely through the furnace and held by the two project- 
 ing ends. The lower temperature of the furnace, as compared 
 with a free flame, is compensated by the higher pressure used in 
 working the glass. Under a suitable pressure the soft tubing 
 is further drawn out until it tapers to a very fine tip which is 
 broken off at the thinnest point capable of being worked. The 
 tip is sealed off without the collection of excess glass by just 
 touching the edge of a very small flame. The tip is then intro- 
 duced into the hottest zone of the furnace and while blowing 
 strongly into the tube, the expansion of a small bulb on the end 
 can be observed from the open end of the furnace. The bulb 
 must be withdrawn just at the right moment to prevent its 
 blowing out. With some practice, bulbs with walls equivalent 
 to 1 cm. of air for a ray absorption can be constructed which 
 will withstand atmospheric pressure in either direction. The 
 bulb may then be sealed to any glass apparatus by means of 
 the original stem, which should be provided with an in-sealed 
 platinum wire to conduct away the unipolar charge if it is de- 
 sired to enclose a large quantity of emanation entirely in glass 
 over mercury. 
 
 The emanation confined in such a bulb can be determined 
 after four hours by its y radiation iu the usual way.'^ A radio- 
 metric method was devised" by Lind {loc. cit.) for determining 
 the maximum range of the a particles from Ra C outside the bulb. 
 It consists in placing the bulb at several known distances above 
 a large ZnS screen in an absolutely dark room and measuring the 
 diameters of the circles of light produced on the screen at differ- 
 ent distances. In all cases the range sought is the distance from 
 the bulb to the outer edge of the light circle, which is the hypoth- 
 enuse of a right triangle of which the vertical distance from 
 the screen and the radius of the light circle are the other two 
 
 diam ^ 
 sides. From the relation: Range^ — — j-^ + dist.^, the range 
 
 can be calculated independently at several different distances, 
 and should agree in all cases. The accompanying Table VI 
 gives the results of a series of such measurements on a tube of 
 about 0.005 mm. wall thickness. 
 
 '^Rutherford, "Radioactive Substances," Appendix A, p. 657 (1913). Ma- 
 kower and Geiger, "Practical Measurements in Radioactivity," p. 106 (1912). 
 S. C. Lind, Joum. Indus. Eng. Chem., 12, 472 (1920). 
 
78 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 TABLE VI 
 
 Radiometric Measurement of the Free Range of a Particles from 
 Ra C Outside a Thin-walled a Ray Bulb 
 
 Dist. from Screen 
 
 Diameter 
 of Light Circle 
 
 Max. Range 
 
 cms. 
 
 cms. 
 
 
 cms. 
 
 5.8 
 
 2.5 
 
 
 5.9 
 
 5.4 
 
 5.0 
 
 
 5.9 
 
 5.0 
 
 6.4 
 
 
 5.9 
 
 4.5 
 
 7.3 
 
 
 5.8 
 
 4.1 
 
 8.5 
 
 
 5.9 
 
 3.3 
 
 10.0 
 
 
 6.0 
 
 
 
 Average 
 
 5.90 dz 0.03 cm. 
 
 Before undertaking measurements depending on such feeble 
 luminosity the eye should be rested for thirty minutes in the 
 dark. Readings should be made with a feeble ruby light. The 
 diameter of the light circle is most conveniently determined by 
 using steel calipers with sharp points which can be used to 
 scratch the surface of the ZnS, producing a momentary spark 
 which serves to locate the boundaries of the light circle. 
 
 The object of obtaining the air range of a rays outside the 
 bulb is to enable the calculation of the ionization produced in 
 the oxygen. The quantities of emanation employed in the ozoni- 
 zation, 25 to 60 millicuries, produce an ionization far too intense 
 to be measured by the saturation current method (§ 15). By 
 referring to the range of a rays from emanation and Ra A 
 (Table I) and to the ionization produced by them and by Ra C 
 along their paths (Fig. 1), and correcting for the specific ioniza- 
 tion of oxygen compared with air (Table II) , the total ionization 
 can be calculated. One additional correction, however, is neces- 
 sary, since the a particles pass through the thin glass wall at 
 all possible angles, one must correct for the obliquity of inci- 
 dence. This was done by a graphical method. 
 
 The total number of a particles emitted by a certain initial 
 quantity of emanation through a given time interval may be 
 calculated in two slightly different ways, both mathematically 
 
IONIZATION AND RADIOCHEMICAL EFFECTS 79 
 
 identical in principle. The average effective emanation E over 
 a time interval t is: E= ^ ° ^^' in which Et may be found at 
 
 any time t by consulting the Kolowrat Table (Appendix, Table 
 A), and I is the decay constant for radium emanation equal to 
 0.0075 hr-i or 0.1800 day^ The average value E in terms of 
 curies then need only be multiplied by the total number of sec- 
 onds and by the number of a particles emitted per second, origi- 
 nally measured as 3.4x10^^ in terms of the Rutherford radium 
 standard, which becomes in terms of the International standard 
 3.57x10^^, or for all three sets, including emanation and Ra A 
 and C 10.71x10^° a particles per second. Hess and Lawson ® have 
 recently determined a higher value 3.72x10^°, which has been 
 adopted for all calculations in the present work. 
 
 The more direct method of calculating the total number 
 emitted is to take into account the quantity of emanation de- 
 caying in the given time interval by reference to the Kolowrat 
 table, and multiplying the quantity by the total number of par- 
 ticles emitted by 1 curie of emanation in its complete disintegra- 
 tion, 1.78x10^® for a single set of a particles, according to Hess 
 and Lawson. For three sets (emanation in equilibrium) : Total 
 a = 5.34xlO^«.Eo(l-e-^t). 
 
 The purification of the emanation used was by a chemical 
 method developed in the Curie laboratory consisting in the re- 
 moval of hydrogen and oxygen by means of copper and copper 
 oxide heated externally in the glass tube leading from the radium 
 solution to the small bulb. In the same way organic gases com- 
 ing from stopcock grease were oxidized by passing over hot 
 KgCrgO^ (or better PbCr207), the products of the two combus- 
 tions being absorbed by P2O5 and fused KOH (or soda lime). 
 Final purification was made by freezing the emanation in a side 
 tube immersed in liquid air while pumping off the residual gases. 
 The emanation is finally confined by mercury in the small a ray 
 bulb so as just to fill it. From radiation considerations it is 
 essential that the mercury shall stand at all times just at the 
 neck of the thin bulb. In using the same apparatus for the 
 combination of hydrogen and chlorine (see p. 119) H. S. Taylor® 
 has added a very ingenious regulator to insure this condition. 
 
 "V. F. Hess and R. W. Lawson, Sitzl). Akad. Wiss. Wien Ila, 127, 405-57 
 »II. S. Taylor, Joum. Amer. Chem. Soc. 37, 24-38 (1915). 
 
80 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 The quantities of ozone found in the different experiments 
 were not concordant, but it was very apparent that the order 
 of magnitude of the total number of ions and of ozone molecules 
 is the same. The experiment in which the maximum quantity of 
 ozone was determined was one in which the average emanation 
 was 58.5 milli-curies acting over 5.0x10* sees, in which time 
 8.4x10^^ a particles were emitted producing 2.6x10^^ pairs of ions, 
 and 1.4x10^® molecules of O3. Using the more recent data of 
 Hess and Lawson for the number of a particles emitted, the ioni- 
 zation becomes 2.8x10^®, and the ratio of the number of pairs of 
 ions (N) to the number of ozone molecules (M) is exactly 2.0, 
 which would be required according to Faraday's law for the for- 
 mation of ozone electrolytically. The justification for giving 
 most weight to the experiment in which the maximum quantity 
 of ozone was found lies in the fact that the lower values were 
 probably due to losses before chemical measurement, perhaps 
 through traces of mercury in the ozonizing chamber. This ex- 
 periment in the ozonization of oxygen constituted the first direct 
 comparison of ionization and chemical effect where both were 
 referred to the same gaseous system. A strong confirmation of 
 the result is furnished by the work of Kriiger,^® who studied the 
 formation of ozone by electronic discharge (Lenard rays) and 
 obtained results similar to those for a rays, drawing the conclu- 
 sion, however, that one pair of ions is involved in the formation 
 of each ozone molecule. 
 
 The formation of ozone outside a thin a ray bulb containing 
 even a few millicuries of emanation is continuously perceptible 
 by its odor. The same is true in the immediate neighborhood of 
 a strong radium preparation or any other source of intense a ra- 
 diation. From the results reported in the foregoing parts of this 
 paragraph, it appears fairly certain that ozonization by a radia- 
 tion and by electronic discharge is an electrical process inti- 
 mately connected with ionization of oxygen. Present data are 
 hardly sufficient to establish the exact mechanism of the reaction, 
 although a number of attempts have been made in this direc- 
 tion. It is not necessary that the electrical quantities involved 
 should be the same as in electrolysis, since the work of J. J. 
 
 'OF. KrUger, Php9. Zeit., 13, 1040-3 (1912) ; Normt FeatachHft, pp. 240-51 
 (J012). 
 
IONIZATION AND RADIOCHEMICAL EFFECTS 81 
 
 Thomson ^^ has shown that the varieties of gaseous oxygen ions 
 is much greater than those known in solution. It would be some- 
 what simpler to propose a theory on the basis of one molecule 
 of ozone per each pair of ions, than for two pairs, and as Milli- 
 kan, Gottschalk and Kelly ^^ have shown, the ionization of some 
 common gases, including oxygen, by a rays results in the removal 
 of but one electron from a molecule. The writer ^^ proposed a 
 very general theory based upon the formation of cluster ions 
 around a charged atom or molecule, which upon being electrically 
 neutralized would break down to the highest stable polymer, in 
 the case of oxygen, ozone. Recent work of Loeb ^* and of Wel- 
 lisch ^^ has cast doubt upon the existence of such cluster ions.^^ 
 Various possible mechanisms for the formation of ozone have 
 been formulated by Strong ^^ and by Rideal and Kunz.^^ The 
 present experimental evidence hardly appears sufficiently exact 
 to decide in favor of any particular theory. Wendt and Lan- 
 dauer ^® have discussed fully the possibilities in connection with 
 the formation of triatomic hydrogen. 
 
 34. Other Gas Reactions. 
 
 The apparently close relation between gaseous ionization and 
 ozone formation rendered it very desirable to see if a similar rela- 
 tion holds for other gas reactions produced by a radiation. The 
 extensive data of Cameron and Ramsay were available for the 
 comparison provided a method could be devised of calculating 
 the effective ionization in the vessels used. Since the volumes 
 used were very small the a particles in all cases completely trav- 
 ersed the gas space, and in most cases the paths would be lim- 
 ited to the first one or two centimeters from the point of origin, 
 in which the ionization remains constant along the path, which 
 presented an additional simplification. The problem seemed to 
 
 "J. J. Thomson, "Rays of Positive Electricity" (1913). Phil. Mag. (6) 
 21, 239 (1911). 
 
 12 R. A. Millikan, V. H. Gottschalk and M. J. Kelly, Phys. Rev. (2) 15, 
 157 (1920). 
 
 " S. C. Lind, Amer. Chem. Joum., 47, 414 (1912). 
 
 '*L. B. Loeb, Phys. Rev. (2) 8, 633 (1916). 
 
 "E. M. Wellisch, J. Franklin Inst. 184, 775 (1917). 
 
 '*G. L. Wendt and R. S. Landauer, Joum. Amer. Chcm. Soc. Ji2, 944 
 (1920). 
 
 "W, W, Strong, Amer. Chcm. Joum. 50, 100-31 (1913). 
 
 "E. K. Rideal and J. Kunz, Joum. Phys. Chcm., 24, 379-93 (1920). 
 
82 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 be then to find a solution for the average path proceeding in a 
 straight line from any point within a given volume or any point 
 on the inner surface in any direction until again encountering 
 the wall. For any volumes except spherical ones the mathe- 
 matical problem is one of great difficulty as will be seen in the 
 following section. 
 
 35. Calculation of the Average Path of a Particles. 
 
 In 1912 the solution of this problem was undertaken by 
 Lind ^® for the sphere. It was established that the average path 
 is a constant fraction of the radius for a sphere of any size. 
 The numerical value of the fraction was found by applying the 
 general formula, at first to ten, and later to one hundred spheres 
 dividing the spherical volume into 100 equal parts. A. C. Lunn ^^ 
 has pointed out that an error was made in using the plane in- 
 stead of the solid angle (§) Fig. 5. The expression according to 
 
 Fig. 5. 
 
 Lunn for a sphere is the following. If p be the average path 
 for all a particles originating at any point P within the sphere 
 and traveling to the wall in a straight line PA at any solid angle 
 ■0 with the line PCB through the center of the sphere, where b is 
 any given distance from the center, and ^i is the ratio b/r, 
 
 y^'T , 
 
 [bcos •» + r V 1 — bVr^ sin 2 <»] sin ^ d d. 
 o 
 
 »S. C. Lind, Journ. Phys. CJiem., 16, 5G7 (1912). 
 
 ="<» Private communication from Prof. A. C. Lunn, Ryerson Physical Labora- 
 tory, University of Chicago. 
 
IONIZATION AND RADIOCHEMICAL EFFECTS 83 
 
 p = l/2f [bx + rV (1 — bVr^) (1 — x^)] 
 
 dx. 
 
 r r 1 — n^ 1 + ^^ 
 Finally for given b: mean p = — -< l-\ log V 
 
 For b r= 1, p = 0.5r. Lunn's integral for the whole spherical 
 volumes gives: p = 0.75r. Taking into account that in small 
 spheres the induced activity is deposited on the wall and there- 
 fore the a particles for Ra A and C originate from the wall, half 
 of them being immediately lost in the wall, while the radium 
 emanation is distributed as gas throughout the volume, the aver- 
 age path of all three sets of a particles from emanation in equilib- 
 rium will be: p = 1/3 (0.75 + 2 x 0.5) . r = 0.5833 r. 
 
 For volumes other than spherical the problem becomes mathe- 
 matically far more difficult. From the use of graphical methods 
 the writer concluded that the average path in cylinders in which 
 the length does not exceed the diameter by more than a few fold 
 of the diameter would be approximately the same fraction of 
 the radius of the sphere of equal volume as if the volume were 
 spherical.2^ In all future work it will be advisable to use 
 spherical vessels in order to simplify the calculation of the ioni- 
 zation. Some work has already been carried out in spheres by 
 the writer which is reported in Chapters 8 and 9. The whole 
 question of the calculation of ionization in vessels of different 
 shapes and sizes is one worthy of further research. The work of 
 Flamm and Mache ^^ on the quantitative measurement of emana- 
 tion in plate condensers with guard-ring has a bearing upon the 
 subject, but is not directly applicable to radiochemical experi- 
 ments. The empirical formula of Duane and Laborde was 
 given in § 29, but is not applicable to small volumes. 
 
 36. Results of Various Investigations. 
 
 By use of the method of calculating ionization by means 
 of the average path of the a particles the experiments of Cam- 
 
 "■ Prof. Lunn is extending his calculations to otlier geometrical forms than 
 the sphere and is convinced that the average path in cylinders of length ten 
 times the diameter will be sufficiently different from that in the sphere of the 
 same volume to be easily tested experimentally. Prof. L. D. Roberts of the 
 Colorado School of Mines has begun an experimental test. 
 
 22 L. Flamm and H. Mache, Sitsh. Akad. Wiss. Wien Ila, 121, 227 (1912) ; 
 122, 535; 1539 (1913). 
 
84 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 eron and Ramsay and of others become available for at least 
 an approximate comparison of the electrical and chemical ef- 
 fects. Other methods more or less indirect have been devised for 
 attaining the same end. Duane and Scheuer ^^ employed large 
 quantities of emanation in thin-walled capillaries. After meas- 
 urement of the chemical effects the tubes were held until the 
 emanation had died to such a low value that saturation current 
 measurements could be applied even to the a radiation. Cor- 
 rection had to be made for the growth of polonium during this 
 period and also for the ionization due to penetrating radiation. 
 Scheuer 2* for large bulbs used the empirical formula of Duane 
 and Laborde^^ and corrected for the specific ionization of the 
 gases employed. Wourtzel ^^ employed still another method, 
 extrapolating from smaller volumes up to those at which absorp- 
 tion and ionization reach a maximum, in order to use the value 
 for total ionization of the whole a particle in the given gas. 
 
 At the end of this paragraph will be found Table VII, in 
 which all the experimental data available for the comparison of 
 chemical effect and ionization have been collected. The appli- 
 cation of the "average path" method to the results of Cameron 
 and Ramsay is not strictly accurate on account of the departure 
 of the volumes from the spherical, but it is unlikely that the 
 errors thus introduced are so great as the uncertainty attaching 
 to the quantities of radium emanation reported in the earlier 
 experiments. Many of the experiments summarized in this table 
 will be given detailed consideration in subsequent paragraphs 
 (see accompanying cross-references) . The data from work prior 
 to 1911, although unreliable in some respects, have been included 
 either for the sake of comparison with the later work, or be- 
 cause they represent for some reactions the only results avail- 
 able. Repetition of the earlier work should be undertaken 
 where it has not already been done. 
 
 A general discussion of the ^/n values will be found in 
 §§ 48-50. 
 
 2> Wni. Duane and O. Scheuer, Le Radium 10, 33-46 (1913). 
 "O. Scheuer, Conip. rend. 159, 423-6 (1914). 
 " Wm. Dunne and A. Lnbordo, Lc Uadliim 7, 162-4 (1910). 
 "E. E. Wourtzel, ibid. 11, 289-98; 332-47 (1919). 
 
IONIZATION AND RADIOCHEMICAL EFFECtS 
 
 it 
 
 TABLE VII " 
 
 /. Gaseous Systems 
 
 Statistical Comparison of Ionization and Chemical Action by a Particles 
 
 N = Total Pairs of Ions. 
 
 Reaction Data of 
 
 + 02=(2H20) (Moist) C.&R. 
 
 (Dry) 
 (130° C.) 
 (Dry or moist) S.^^ 
 
 II <l L 31 
 
 W>2 
 
 M = Total Number of Molecules. 
 
 Chem. Action 
 Designation 
 ofM. 
 M 
 
 ,S) = H^ + (S) 
 
 ;o, = 2C0 + O2 
 
 u 
 
 I; " 
 ICl = H, + CI2 
 , + 3H2 = 2NH3 
 
 ■T 
 
 H2 + Br^ = 2HBr 
 
 3O2 := 2O3 
 
 2C0 = CO2 + (C) 
 
 N,0 = N, + 
 or =: (N + NO) 
 
 2H,0 = 2H, + 0, 
 
 JL + CI2 = (2HC1) 
 It 
 
 ■H,0) = 2H, + 
 
 W.32 
 
 M 
 
 M 
 
 H3O 
 
 « 
 
 U 
 It 
 
 tl 
 
 CO2 
 
 mall 
 
 NH, 
 
 M/N 
 
 0.65 to 0.81 
 
 0.52 to 0.93 
 1.59 
 3.7 
 4.0 
 2.65 
 
 0.38 
 
 % Energy 
 Utilized 
 
 4.9 
 
 34.5 
 6.7 
 
 2.6 
 
 Very small quantity of decomposition. 
 C.&R.2« M 
 
 W.32 
 
 U.33 
 
 W.32 
 
 L.3* 
 
 L.35 
 
 C. & R.2« 
 
 W.32 
 
 C. & R.28 
 
 D. & S.3« 
 B.&T.^^ 
 
 J. & R.3« 
 
 M 
 
 HCl 
 
 M 
 
 0.25 
 
 0.40 
 0.80 at 18° 
 2.55 " 315° 
 
 0.76 
 
 0.25 
 
 1.2 
 
 1.8 
 0.6 
 
 (N, + H,) 
 Very little ammonia formed (chem. anal.) 
 
 M 
 
 JIBr 
 
 M 
 
 0. 
 
 M 
 
 M 
 
 CO 
 NO 
 
 M 
 
 0.54 
 
 0.50 
 
 1.86 
 1.74 at 18° 
 2.16 " -78° 
 2.32 " 220° 
 
 0.5 
 
 2.0 
 
 3.9 
 4.0 
 
 H2O Very little action. 
 
 M 
 
 (H, + CU 
 
 //. Liquid Systems 
 D.30 Mh^o 
 
 C. & R.2« 
 
 •JJ 40 tt 
 
 4000. 
 100-1000 
 
 (0.16) 
 
 0.36 
 0.41 
 
 (1.0) 
 
S6 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 TABLE Yll— Continued 
 Reaction 
 
 2HBr = H2 + Br2 
 
 KI (in acid soln.) = (I + K^) 
 
 Ice (2H2O) = 2H2 + O2 
 
 (-I^J-) rr: Jv -|- i L/. ygiy little decomposition observed for penetrating rays 
 
 (Pblg) = Pb + Ij 
 
 Dafa 0/ 
 D. & S.3« 
 
 C/iem. Action 
 
 Designation 
 
 ofM 
 
 ^H,0 
 
 0.86 to 1.05 
 
 % Enersfy 
 Utilized 
 
 6.4 
 
 L.»* 
 
 ^HBr 
 
 2.6 
 
 2.2 
 
 f< 
 
 Mki 
 
 0.76 
 
 
 ///. Solid Systems 
 
 
 
 D.&S.«« 
 
 Mh,0 
 
 0.05 
 
 0.3 
 
 (PbCl^) = Pb + CI2 " " « " « u „ „ 
 
 (it Dorgj ^=: xD -j- ijT2 No decomposition observed for penetrating rays. 
 
 » Table VII Is corrected and extended from table of Lind, Joum. Phys. Ghent. 16, p. 589 (1912) 
 
 "A. T. Cameron and Wm. Ramsay, Joum. Chem. 80c. Lond. 93, 965 (1908). See §§29 and 30. 
 
 »0. Scheuer, Comp. rend., 159, 423 (1914). See § 38. 
 
 »»Wm. Duane and A. Laborde, Le Radium 7, 162 (1910). See § 29. 
 
 "S. C. Llnd, Journ. Amer. Chem. Soc. 41, 531 1919). See §§ 42, 44. 
 
 »»E. E. Wourtzel, Le Radium 11, 289; 332 (1919). See § 39. 
 
 "F. L. Usher, Joum. Chem. 80c. Lond. 97i 389 (1910). See § 31. 
 
 «*S. C. Llnd, Le Radium 8, 289 (1911). 
 
 "S. C. Llnd, Sitzh. Akad. Wisa. Wien Ila, 120, 1709 (1911) ; Amer. Chem.Joum., 47, 397 (1912). 
 See also % 33. 
 
 "Wm. Duane and O. Scheuer, Le Radium 10, 33 (1913). See § 37. 
 
 " (M. Bodenstein) and H. S. Taylor, Journ. Amer. Chem. Soc. 37, 24 (1915) ; 38, 280 (1910). Id 
 » Bodenstein, Zeit, EleJctrochem.22, 53-61 (1916). See also § 55. 
 
 "Jorlssen and Ringer, Ber. 39, 2093 (1906). Compare Lind, J. Phys. Chem. 16, 610. 
 
 "A. Debierne, Comp. rend. 148, 703 (1909). 
 
 *»F. L. Usher, Jahrh. d. Radioakt. u. Elektr. 8, 323 (1911). See § 47. 
 
 «S. C. Lind. Joum. Phys. Chem. 16, 608 (1912). 
 
IONIZATION AND RADIOCHEMICAL EFFECTS 87 
 
 37. Reactions in Liquid Systems — Results of Duane and 
 Scheuer on the Decomposition of Water, Ice and 
 Water Vapor. 
 
 As may be seen from Table VII, the M/N ratio appears to 
 be of the same order in the few liquid reactions that have been 
 investigated as in the majority of gas reactions. From the chemi- 
 cal point of view this may be regarded as a matter of some sur- 
 prise, but so far as the ionization is concerned, it has been found 
 that variation of pressure of a gas results only in shortening the 
 range of the a particle without affecting the total ionization 
 produced. There is no apparent reason why this should not 
 continue to be true on passing to very high pressures and over 
 into the liquid state. The general assumption has therefore 
 been made in the calculations involved in Table VII that the 
 total ionization by the complete absorption of a radiation is the 
 same as would be produced if the total absorption of the a par- 
 ticle occurred in the same substance in the gaseous state. Owing 
 to the lack of suitable experimental methods of determining the 
 ionization produced in liquids by radiation, it has not been pos- 
 sible to put this conclusion to the test, but if the generality of 
 the equivalence between chemical effects and ionization be con- 
 ceded, then the evidence of Table VII for liquids constitutes a 
 confirmation of the ionization relations assumed, at least within 
 very approximate limits. 
 
 The work of Duane and Scheuer (loc. cit.) carried out in the 
 laboratory of Mme. Curie on the decomposition of water in its 
 three states of aggregation is one of the most careful and com- 
 plete researches in the field of radiochemistry. The experi- 
 mental method for the liquid and solid states consisted in col- 
 lecting purified emanation in a thin capillary glass tube (§33) 
 in which it was allowed to act upon a layer of water or ice 
 sufiicient to absorb the <x radiation completely. The quantity 
 of hydrogen and oxygen liberated was measured in a eudiometer 
 tube and the excess of hydrogen was determined after sparking 
 the mixture. By comparing the rate of reaction with the decay 
 curve for emanation it was found that the two coincide perfectly 
 if the volume of gas liberated is corrected for the oxygen retained 
 as H2O2, which was measured chemically and found to corre- 
 spond to the excess of hydrogen. The conclusion was drawn that 
 
88 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 water is decomposed in a primary reaction and that H2O2 is 
 formed by the secondary action of nascent oxygen on water. A 
 very interesting confirmation of this view was obtained in the 
 examination of the gases liberated by the action of a rays on ice 
 at —183° C, which were found to consist wholly of electrolytic 
 gas, indicating that ice at this temperature is not acted on by 
 nascent oxygen to form HgOg. 
 
 The comparison of the electrical and chemical effects was 
 made by allowing the emanation to decay to a value where the 
 saturation current method could be applied directly. The origi- 
 nal quantity of emanation was calculated from the decay law. 
 The number of gas molecules formed from water is 1.06 times 
 the total number of pairs of ions that would be formed in air 
 in the total absorption of the a radiation. Or expressed a little 
 differently, the a rays capable of producing an ionization cur- 
 rent of one ampere in air will decompose water giving 0.1594 
 cm.^Hg and 0.0797 cm.^Og, values of the same order as 0.125 
 cm.^Hg and 0.0615 cm.^Oa which would be liberated per ampere- 
 second in electrolysis. In Table VII the M/N value calculated 
 from the results of Duane and Scheuer is for ionization in HgO 
 instead of in air, taking the value for the total specific ioniza- 
 tion of H2O as 0.82 that of air. 
 
 The action of a rays on ice and on water vapor is much less 
 efficient than on liquid water, not more than 5% as much re- 
 action being found in maxima. In the case of water vapor the 
 emanation was mixed directly with the vapor at three atmos- 
 pheres pressure at 170° C; the excess of hydrogen amounted 
 to about 50%. Duane and Scheuer express the opinion that the 
 low efficiency of the action of a rays on water vapor is due to 
 recombination of the products. 
 
 In Table VIII will be found the results of Expt. Ill from 
 Duane and Scheuer {loc. cit.). Two additional columns have 
 been added to show the course of the reaction compared with 
 the decay of emanation. It will be noticed that the reaction 
 runs slightly behind the decay of emanation, but if correction 
 be made for the deficiency of oxygen according to the excess 
 of hydrogen, the agreement is within a few tenths per cent in 
 nearly all cases. The most probable value for the decompo- 
 sition of water by emanation is 390 cm.^ of electrolytic gas per 
 curie. 
 
IONIZATION AND RADIOCHEMICAL EFFECTS 
 
 TABLE VIII 
 
 89 
 
 Decomposition of Water by Emanation according to Duane and 
 
 Scheuer 
 
 Initial Emanation 191.5 milli-curies. 
 
 Days, 
 
 Hrs. 
 
 
 
 16 
 
 1 
 
 16 
 
 3 
 
 16 
 
 4 
 
 16 
 
 5 
 
 16 
 
 6 
 
 16 
 
 7 
 
 16 
 
 8 
 
 16 
 
 10 
 
 16 
 
 17 
 
 16 
 
 22 
 
 20 
 
 32 
 
 16 
 
 48 
 
 20 
 
 Hz + Ooinc.c. 
 
 0.1730 
 0.4061 
 0.7903 
 0.9314 
 1.0574 
 1.1501 
 1.2372 
 1.3149 
 1.4385 
 1.6224 
 1.6690 
 1.7071 
 1.7099 
 
 % Excess Hr 
 by Vol 
 
 16.1 
 8.55 
 
 6.90 
 
 4.96 
 
 2.77 
 1.74 
 0.48 
 
 fo Reaction 
 Completed 
 
 10.1 
 23.9 
 46.2 
 54.4 
 61.8 
 67.2 
 72.3 
 76.9 
 84.0 
 94.9 
 97.5 
 99.7 
 100.0 
 
 % 
 
 Emanation 
 
 Decayed 
 
 11.3 
 25.9 
 48.4 
 56.8 
 63.9 
 69.9 
 74.8 
 79.0 
 85.3 
 95.8 
 97.9 
 99.7 
 100.0 
 
 It may be pointed out that the. use of thin- walled a ray 
 bulbs excludes the participation of recoil atoms in the reaction, 
 since they do not penetrate the wall. (See § 64.) 
 
 Duane and Scheuer saw in the equivalence between the ioni- 
 zation produced by a particles and the decomposition of water 
 "a coincidence having a profound significance in the theory of 
 electrolysis and the decomposition of matter by the a rays of 
 radium." 
 
 38. Experiments of Scheuer on the Formation of Water by a 
 Radiation. 
 
 The very careful work in the Curie Laboratory on the 
 chemical effects of radium radiation was extended by Scheuer *^ 
 to the formation of water from its elements. In order to utilize 
 the a rays as fully as possible Scheuer employed rather large 
 glass spheres in which emanation was mixed with electrolytic 
 
 *2 0. Scheuer, Comp. rend. 159, 423-6 (1914). 
 
90 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 mixture of hydrogen and oxygen under increased pressure. After 
 the lapse of several days to a month the quantity of reaction 
 was determined by analyzing the gases. In all cases Scheuer 
 reported the formation of some HgOg, which in one case repre- 
 sented 16% of the combined hydrogen. Two experiments were 
 made using a ray bulbs at the center of the gaseous mixture. 
 The ionization was calculated by means of the Duane and La- 
 borde formula (see § 29), but since this is directly applicable 
 only to air, some correction for specific ionization of electrolytic 
 gas must have been made. The M/N values for four different 
 experiments are very concordant between 5.40 and 5.61 with 
 an average of 5.51, where M refers to the total number of 
 2H2 + O2 molecules combining, which is equivalent to 3.7 mole- 
 cules of water formed (disregarding H2O2 and treating the entire 
 reaction as water formation). This value, though much higher 
 than the older ones of Cameron and Ramsay (see Table VII), 
 agrees fairly well with the more- recent one of Lind (loc. cit.) 
 3.9 (or 4.0 using Lunn's value of average path and Hess and 
 Lawson's value for number of a particles and making a slightly 
 different assumption as to the position of Ra A in the reaction 
 bulb). 
 
 In the two experiments where Scheuer used a ray bulbs at 
 the center of his mixture he still employed the formula of Duane 
 and Laborde to calculate ionization, although it is inapplicable, 
 as he realized. By confining all the emanation at a point source 
 in the center, the full radius of the sphere is utilized, instead of 
 the average path, which is equal 0.5833 x radius (see § 35) . By 
 
 multiplying Scheuer's values for ^^^'' + ^^^ ■ (8.08 and 8.88) by 
 
 this value, one obtains 4.7 and 5.1 in fair agreement with his 
 other values reported above. Scheuer also carried out one ex- 
 periment with oxygen mixed with emanation but found very little 
 ozone under his experimental conditions. For further considera- 
 tion of Scheuer's results in another connection see § 43. 
 
 Scheuer*^ also investigated the reduction of CO by H2 in 
 the presence of radium emanation, which reaction had already 
 h'een studied under somewhat different conditions by Stoklasa, 
 Sebor and Zdobnicky,^* who found formaldehyde to be one of 
 
 *>0. Scheuer, Comp. rend. 158, 1887-9 (1914). 
 
 «* J. Stoklasa, J. Sebor and V. Zdobnicky, ibid., 15G, G4G-8 (1913). 
 
IONIZATION AND RADIOCHEMICAL EFFECTS 91 
 
 the products of reaction. This was confirmed by Scheuer, who 
 reported, however, that the final product is mainly CH^. 
 
 Equilibrium between Hydrogen and Oxygen mixed with 
 Emanation. Although this subject was not treated by Scheuer, 
 it is very appropriate to consider it in connection with his re- 
 sults ori the formation of water and those of Duane and Scheuer 
 (loc. cit.) on its decomposition. Since Duane and Scheuer 
 showed that the decomposition of water vapor is very slight, we 
 should expect that the homogeneous gaseous equilibrium would 
 lie quite far on the side of combination. No direct experiments 
 have been made on the subject. In the case of the heterogeneous 
 equilibrium between hydrogen and oxygen and such small quan- 
 tities of water as could result from the combination of electro- 
 lytic gas in small volume at pressures not excessive, the solu- 
 bility of emanation in the water phase may be neglected, and 
 we should expect equilibrium near 68% of combination (on the 
 basis of M/N for formation = 4, and for decomposition M/N = 
 1), provided that the condensed water is so distributed that it is 
 exposed to the total radiation (equal distribution over the entire 
 surface), and taking the average path as 0.58 x radius. It has 
 been shown by Lind,*^ however, that the combination proceeds 
 under the experimental conditions just mentioned to within 
 nearly 1% of complete combination. This was attributed to 
 local condensation of the water so that it receives only a small 
 part of the radiation it would receive if evenly condensed over 
 the entire surface. The heterogeneous equilibrium in the pres- 
 ence of larger quantities of water would depend upon a great 
 number of factors which make it difficult to calculate. The case 
 has not been experimentally investigated. The case of the gen- 
 eration of high pressure in a sealed radium salt (§ 21), owing to 
 the decomposition of residual water of crystallization, is interest- 
 ing, because theoretically the equilibrium requires low instead of 
 high pressure. It has been suggested by Lind {loc. cit.) that 
 the gas is hydrogen alone, and that all the oxygen combines with 
 the radium (or barium) salt. 
 
 "S. C. Lind, Trans, Amer. Electrochem. Soc, 34, 214 (1918). 
 
92 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 39. Experiments of Wourtzel on the Decomposition of Gases. 
 
 The radiochemical researches of the Curie Laboratory were 
 continued by Wourtzel *® whose experimental method consisted 
 in mixing purified emanation with the gas to be decomposed in 
 spherical glass balloons of about 4 cm. diameter, enclosed over 
 mercury but separated from it by a long capillary connection. The 
 quantity of emanation employed was measured by the y ray 
 method. The ionization was calculated for complete absorption 
 by an empirical formula K = Koo (1 — C/Rp) , in which K is the 
 quantity of reaction produced by 1 curie of emanation at any 
 pressure p, Koo is the amount of reaction at infinite pressure 
 where the ionization and chemical action reach a maximum owing 
 to complete absorption of the a radiation, R the radius and C 
 a constant. The specific ionization for each gas was calculated 
 from the results of Bragg,*^ Kleeman ^^ and Taylor.'*^ The amount 
 of chemical action was determined by freezing the undecomposed 
 gas and emanation in liquid air and measuring the decomposition 
 products manometrically, and in some cases also chemically. 
 
 The decomposition of HgS, NH3, NgO, and CO2 was studied. 
 The results are summarized in Table IX. 
 
 The effect of temperature on the reactions observed by 
 Wourtzel is of great interest. The negative coefficient for HgS, 
 the positive one for NH.^, the minimum for NgO at 18° have as 
 yet remained unexplained. With respect to the M/N values re- 
 ported by Wourtzel at temperatures other than ordinary, N re- 
 fers to ionization at ordinary temperature, since no data were 
 available at other temperatures. The failure of a rays to de- 
 compose CO2 is further considered in § 50. 
 
 More recently Wourtzel ^^ has elaborated a theory of chemi- 
 cal action by collision with the a particle, as distinguished from 
 the ionization theory (see §§ 48-50). He employs his data on 
 the decomposition of HgS, NH3, NgO, and those of Scheuer (loc. 
 cit.) for the combination of electrolytic gas to compare with the 
 calculated number of encounters per second per curie of emana- 
 
 "E. E. Wourtzel, Le Radium, 11, 289-298; 332-347 (1919). Journ. Ruas. 
 Phya. Chem. Soc. Proc. 47, 210, 493 f) (1915). Comp. rend. 157, 929 (1913). 
 «W. II. Bragg, Phil. Mag. (6) 13, 333 (1907). 
 "R. D. Kleeman, Proc. Roy. Soc, 79, 220 (1907). 
 "T. S. Taylor, Phil. Mag. (6) 21, 571 (1911). 
 •®E. Wourtzel, Journ. de Phys. et le Radium (G) 1, 77-9G (1920 ». 
 
IONIZATION AND RADIOCHEMICAL EFFECTS 
 
 93 
 
 TABLE IX 
 
 Decomposition of Gases by Emanation at Different Tempera- 
 tures According to Wourtzel 
 
 Gas 
 
 Temp. 
 
 Decomposedby 
 
 1 Curie Em. 
 
 c. c. 
 
 M/N 
 
 % Energy 
 Utilized 
 
 H,S 
 
 18° 
 
 1011 
 
 2.65 
 
 6.7 
 
 
 95° 
 
 902 
 
 2.17 
 
 ... 
 
 
 220° 
 
 707 
 
 1.85 
 
 ... 
 
 
 — 190° 
 
 Solid HgS : Decomposition of same order 
 
 
 
 as gas at 18°. 
 
 
 
 NH3 
 
 18° 
 
 282 
 
 0.80 
 
 1.2 
 
 
 108° 
 
 556 
 
 1.58 
 
 
 
 220° 
 
 824 
 
 2.33 
 
 ... 
 
 
 315° 
 
 900 
 
 2.55 
 
 ... 
 
 N,0 
 
 — 78° 
 
 823 
 
 2.16 
 
 
 
 18° 
 
 737 
 
 1.74 
 
 (4.6) 
 
 
 220° 
 
 884 
 
 2.32 
 
 ... 
 
 CO2 
 
 18° 
 
 Very little decoi 
 
 mposition observed. 
 
 tion. The agreement with the measurements of chemical action 
 is satisfactory, especially at higher temperatures. Wourtzel 
 suggests that at the lower temperatures, where the number of 
 encounters exceeds the number of molecules reacting, some .of 
 the encounters are not effective. In the case of N2O, where at 
 all temperatures the quantity of chemical action exceeds the 
 number of encounters, Wourtzel assumes secondary action. This 
 is the same assumption as proposed to explain excessive reaction 
 by ionization, and it hardly appears possible with present data 
 to decide between the two theories on statistical grounds. It 
 also appears questionable if Wourtzel's assumption in calculat- 
 ing the number of encounters made by a particles that the di- 
 mensions of the particle are identical with those of the helium 
 atom can be justified. 
 
Chapter 8. 
 
 Kinetics of the Chemical Reactions Produced by 
 Radium Emanation. 
 
 40. Classification of the Reactions. 
 
 In dealing with the kinetics of chemical reactions produced 
 by radium emanation, two general factors must be considered: 
 (1) change in the agent producing the reaction, namely, the ra- 
 dium emanation; (2) change in the system being acted on. The 
 decay of emanation has been generally recognized as one of the 
 controlling factors of the rate of reaction and has been taken 
 into account by all authorities since Cameron and Ramsay first 
 called attention to it. Besides the decay of emanation another 
 factor controlling its effectiveness in producing chemical reaction 
 is its distribution in the system being acted on. In a gaseous 
 system, emanation is distributed as a gas and its effectiveness is 
 limited only by the effective paths of the a particles in the gas 
 phase, which subject has been treated in § 35. In a liquid sys- 
 tem complete absorption of the a radiation occurs, provided the 
 emanation is entirely confined within the liquid. If a gas phase 
 exists, the distribution of the emanation between the two phases 
 must be known as well as all the other factors involved in de- 
 termining the proportion of radiation from the gas phase that 
 will be effective on the liquid. In general, the reaction in the gas 
 phase itself will be negligible compared with that in the liquid. 
 In a liquid system the conditions of absorption of the radiation 
 remain unchanged at maximum, unless a gas phase should be 
 produced by the reaction. The inconveniences attending such a 
 possibility can be avoided by the use of the a ray capillary 
 as was done by Duane and Scheuer (§ 37). 
 
 In gaseous reactions a number .of cases are to be considered. 
 The simplest case is that of an elementary gas acted on in such 
 a way that its volume and concentration remain constant while 
 the product of reaction is continually removed from the field of 
 
 94 
 
KINETICS OF THE CHEMICAL REACTIONS 95 
 
 action. If its concentration (pressure) diminishes or increases 
 at constant volume, then this change must be taken account 
 of in regard to its influence upon the effectiveness of a ray absorp- 
 tion. Such a case would be represented by the ozonization of 
 oxygen mixed with emanation at constant volume, where the 
 ozone formed was being continuously absorbed by mercury. In a 
 mixture of gases, a simple case is presented by electrolytic hydro- 
 gen and oxygen; the product water is condensed and nothing 
 changes in the gas phase except the pressure. More -complicated 
 cases arise when the products of reaction remain in the gas phase, 
 as in NH3 decomposition. Not only does the question of reverse 
 reaction then present itself, but also that of an indirect effect 
 of the products in rendering the radiation effective for the pri- 
 mary reaction. Furthermore, in the case of mixtures one may 
 inquire whether only one component is activated or more, and 
 what the effect of a foreign gas will be in the mixture. These 
 and other similar questions are natural ones from the kinetic 
 standpoint.. But before they can be attacked it is necessary to 
 develop a general kinetic equation for the influence of emanation 
 on gas systems as a function of the pressure, which is in turn 
 itself a function of the rate of reaction, dependent upon the 
 quantity of emanation, its rate of decay, the size of the vessel 
 and other factors. 
 
 41. Development of General Kinetic Equation for the Action 
 of Emanation When Mixed with Gases in Small Vol- 
 umes. 
 
 The following equations were developed by Lind ^ from the 
 standpoint of ionization, but the final general form, equation 
 (3), is equally valid for the influence of emanation without any 
 reference to ionization. 
 
 If N be the number of pairs of ions formed in a time in- 
 terval t, 
 
 dN/dt = 3 X 3.72.10i«.Et.2.4.10^p.i.P/760. (1) 
 
 in which 3 x 3.72.10^° is the number of a particles emitted per sec- 
 ond by 1 curie of emanation in equilibrium with Ra A and C, 
 Et is the emanation in curies at any time, 2.4.10* is the number 
 of pairs of ions formed per cm. by each a particle along the 
 
 'S. C. Lind, Journ. Phya. Chem., 16, 571; 591-4 (1912). 
 
96 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 first two or three cms. of the path in air at atmospheric pres- 
 sure, p is the average path in cms. as defined in § 35, i is the 
 specific ionization for any gas compared with that of air un- 
 der the same conditions, P/760 is the pressure reduced to stand- 
 ard conditions. Equation (1) may be condensed to the form: 
 dN/dt = kEfP = kEoe-^^P, in which k is the ionization constant 
 including all the constant terms of (1). 
 
 The relation between chemical action and ionization may be 
 expressed as: 
 
 — dC/dt =: const. dN/dt, 
 
 in which dC is the change in concentration of the substance 
 undergoing reaction. 
 
 In the case where the rate of chemical action is measured 
 manometrically by the decrease in pressure, 
 
 — dP/dt=:ndN/dt, (2) 
 
 where P = Po — jaN, if P = Po for N = 0. Combining equations 
 (1) and (2): 
 
 ~ l/[i.dP/dt = kEoe-^* P, and dP/P + kfxEoe-^Mt = 
 
 log P/Po = k^A.Eo(e-^* — 1) (3) 
 
 P = P^e(»'AtA)Eo(e-^t _ 1) ^^j 
 
 Substituting to introduce N: 
 
 N= (l/^l)Po [1 — e^/^AEo(e-^t-l) ] (5) 
 
 For reactions being measured manometrically by the pressure 
 change, equation (3) can be conveniently employed as a kinetic 
 equation in the form: 
 
 kn/X =z velocity const. = ^ ^^ ° 
 
 42. Application of Kinetic Equation to Experimental Results. 
 
 The kinetic equation developed in § 41 will be strictly appli- 
 cable only in cases where all the constants included under k actu- 
 ally remain constant during the course of the experiment. This 
 will be true for the specific ionization only when the products 
 of reaction are removed from the field of action. As already 
 pointed out this condition is satisfied by the electrolytic mixture 
 of hydrogen and oxygen at ordinary temperature through the 
 
KINETICS OF THE CHEMICAL REACTIONS 
 
 97 
 
 condensation of water. For this reason the kinetic equation 
 was appHed by Lind (loc. cit.) to the results of Cameron and 
 Ramsay for this reaction, as shown in Table X. It was also ap- 
 plied to some of the other reactions studied by them and by 
 Usher. In the decomposition of CO and of NHg the partial pres- 
 sures of the CO and NH3 are used instead of the total pressures, 
 including the decomposition products. The satisfactory constant 
 in the case of CO indicates the correctness of such a procedure, 
 and the absence of any influence of the CO2 formed upon the rate 
 of reaction, confirms Wourtzel's (§ 39) result that CO2 is little 
 acted on by emanation. On the other hand the results for the de- 
 composition of NH3 are in accord with the equation only for the 
 first part of the reaction ; during the latter part, where the prod- 
 ucts have accumulated, the apparent rate falls off owing to some 
 
 TABLE X 
 
 Application of Equation (3) § 41 to the Results of Cameron and 
 Ramsay and of Usher 
 
 2H2 + 02 
 
 = (2H2O) (moist). 
 
 2C0 
 
 = C02+(C). 
 
 Vol 
 
 . = 2.186 c. 
 
 c. 
 
 Vol. (calcd.) =z 2.567 c. c. 
 
 Eo = 
 
 = 0.0465 curie. 
 
 Eo 
 
 =: 0.025 curie. 
 
 t (days) 
 
 P (mm.) 
 
 kyi/l 
 
 t (days) 
 
 PofCO 
 
 (mm.) 
 
 kii/l 
 
 0.0 
 
 523.5 
 
 
 0.0 
 
 297.0 
 
 
 1.02 
 
 487.0 
 
 (9.3) 
 
 0.81 
 
 282.0 
 
 17.2 
 
 2.07 
 
 442.0 
 
 (11.7) 
 
 1.89 
 
 263.0 
 
 17.9 
 
 3.07 
 
 405.6 
 
 12.9 
 
 2.8 
 
 251.0 
 
 17.8 
 
 4.13 
 
 384.5 
 
 12.7 
 
 3.8 
 
 245.0 
 
 16.1 
 
 4.99 
 
 369.5 
 
 12.8 
 
 4.8 
 
 233.0 
 
 17.3 
 
 6.11 
 
 352.2 
 
 12.8 
 
 5.8 
 
 225.0 
 
 17.5 
 
 7.07 
 
 343.5 
 
 12.6 
 
 6.8 
 
 221.6 
 
 17.0 
 
 9.11 
 
 321.4 
 
 13.0 
 
 10.1 
 
 218.0 
 
 15.2 
 
 10.16 
 
 319.3 
 
 12.7 
 
 14.8 
 
 206.2 
 
 16.0 
 
 11.04 
 
 316.6 
 
 12.5 
 
 19.9 
 
 208.4 
 
 (14.9) 
 
 12.10 
 
 312.3 
 
 12.5 
 
 23.8 
 
 201.4 
 
 15.1 
 
 97.0 
 
 291.0 
 Mean 
 
 12.6 
 
 26.8 
 
 200.2 
 Mean 
 
 16.2 
 
 
 .. 12.71 
 
 .. 16.5 
 
THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 TABLE X— {Continued) 
 
 2NH3 = 
 
 N2 + 3H2 (Usher). 
 
 N2 + 3H2 = (2NH 
 
 3 ? ), 
 
 Vol 
 
 . = 2.406 c. 
 
 c. 
 
 Vol. = 2.30 c. ( 
 
 ■» 
 
 Eo: 
 
 = 0.145 curie. 
 
 Eo = 0.1195 curie. 
 
 t (days) 
 
 i;(2) (ccj 
 
 k\i/\ 
 
 t (days) 
 
 P (total) 
 
 k\i/l 
 
 0.0 
 
 0.909 
 
 
 0.0 
 
 745.6 
 
 
 0.07 
 
 0.895 
 
 8.3 
 
 0.79 
 
 720.8 
 
 (2.15) 
 
 0.76 
 
 0.781 
 
 8.2 
 
 1.76 
 
 714.1 
 
 (1.34) 
 
 1.08 
 
 0.735 
 
 8.3 
 
 2.77 
 
 707.6 
 
 (1.13) 
 
 1.75 
 
 0.664 
 
 8.0 
 
 3.77 
 
 701.6 
 
 1.04 
 
 2.08 
 
 0.630 
 
 8.1 
 
 4.85 
 
 694.3 
 
 1.03 
 
 2.78 
 
 0.581 
 
 7.9 
 
 5.77 
 
 690.1 
 
 1.01 
 
 3.75 
 
 0.527 
 
 7.7 
 
 6.76 
 
 686.6 
 
 0.98 
 
 4.75 
 
 0.493 
 
 7.4 
 
 7.76 
 
 683.1 
 
 0.98 
 
 6.75 
 
 0.441 
 
 7.1 
 
 9.76 
 
 677.1 
 
 0.97 
 
 7.75 
 
 0.431 
 
 6.8 
 
 11.0 
 
 675.0 
 
 0.97 
 
 8.75 
 
 0.421 
 
 6.7 
 
 12.8 
 
 672.4 
 
 0.96 
 
 13.77 
 
 0.399 
 
 6.2 
 
 14.8 
 
 671.9 
 
 0.98 
 
 32.0 
 
 0.385 
 
 5.9 
 
 17.9 
 
 669.1 
 
 0.94 
 
 
 Mean .... 
 
 
 
 
 Mean 
 
 . 0.99 
 
 (-) The use of vol. Instead of pr. in equation (3) is readily understood. 
 
 kind of reverse action, such as seen under the reaction: No + 3H2. 
 Usher found little or no NH3 formed, but the manometric effect 
 would be in the same direction as that of a reverse action, even 
 if it is only a mechanical loss of Hg. 
 
 A complete kinetic study of the reaction 2H2 + O2 was more 
 recently undertaken by Lind {loc. cit.) with the following ob- 
 jects: to study the applicability of equation (3) over wider va- 
 riations of pressure, to enable the exact evaluation of M/N, to 
 determine the influence of the size of the spherical vessel, and to 
 establish the effect of varying the proportions of hydrogen and 
 oxygen. 
 
 The apparatus used by Lind was •a simplified form of that 
 of Cameron and Ramsay and is shown in Fig. 6. The emanation 
 was measured by the y ray method after introduction into the 
 emanation chamber. By comparison of the columns for per 
 cent reaction (completed) and per cent emanation (decayed) it 
 
KINETICS OF THE CHEMICAL REACTIONS 
 
 99 
 
 
 CO 
 
 
 
 a 
 
 
 ^ 
 
 
 
 o 
 
 
 <i3 
 
 
 
 00 
 
 
 CO 
 
 
 
 
 
 CO 
 
 
 
 II ^ 
 
 
 
 
 
 . '^ 
 
 
 O 
 
 
 ^ 
 
 B'^ 
 
 
 o 
 
 
 <i:> 
 -< 
 
 a 
 ^ 
 
 C3 ^ 
 
 CO T-1 
 
 
 
 
 i 
 
 a ° 
 Z il 
 
 
 
 
 ^ 
 
 
 II 
 
 
 
 ?3w 
 
 
 CI 
 
 o 
 
 
 
 
 
 + 
 
 
 
 11 
 
 
 
 
 
 
 
 w 
 
 
 
 o 
 
 
 (M 
 
 
 
 > 
 
 
 5J 
 
 
 
 
 »— 1 
 
 X 
 
 so 
 
 CO 
 
 •2 
 
 
 
 w 
 
 Q 
 
 ^ 
 
 
 
 
 
 1 
 
 
 
 H 
 
 CO 
 
 so 
 
 ^ 
 
 
 = 1.925 cm. 
 
 es. 
 
 
 03 
 
 
 
 
 ft^ 
 
 
 ^ 
 
 B 3 
 
 
 O 
 
 
 
 03 O 
 
 
 so 
 
 
 
 
 
 ^ 
 
 
 =§• 
 
 QS 
 
 
 
 
 , 
 
 tH 
 
 
 so 
 
 
 PN-^ 
 
 « 
 
 
 Q 
 
 
 
 QO o 
 
 
 & 
 
 
 
 KW 
 
 
 t^ 
 
 
 
 CO 
 
 
 -^ 
 
 
 
 II 
 
 
 so 
 
 
 
 > 
 
 
 « 
 
 
 
 
 
 O 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 a. 
 
 
 
 
 
 a. 
 
 
 
 
 
 -^ 
 
 
 
 
 Const, 
 
 •t^cooiOT-Ht^cocoeoi:^ 
 •cococdcocococdcococo 
 
 CO 
 
 
 P t>; -«iH <M. ^. p ^, ^, lO (N (N 
 
 c5 (>i i>^ t>^ rH i>I (m' c5 05 o o 
 
 T-HrHC^COCO-^iOiOt^CT) 
 
 g 
 
 o 
 
 s 
 
 
 COCOt^QOcOt^OSCOCO 
 
 OCOt^rHTthrH^i-HTtHOO 
 
 ot^c^toddcococdt^d 
 
 THCNCO-^iOiOCOl^QOO 
 
 T-t 
 
 a: 
 
 r^oqt^osocoos^Tt^coco 
 t-^QOcoo6r^i6t^dd<M'co 
 
 ^rHOt^OTjHCOT-IOOCOCO 
 
 
 1 
 
 COOOiOCX)lr^(Mt>iOO 
 i-HtOiO(NOCOOii-i(NiO 
 
 ^o6rHQ6(HQ6i-3dc»o6(N 
 
 i-H ,-1 1-1 CM tH rH (M 
 
 00 
 
 Si 
 
 OOT-iT-iC^C^cOCOiOt>(N 
 
 rH 
 
 11 
 
 ;ODoqQqrHcop(Ncopio 
 
 ?5 
 
 .1 
 
 CDCOtJHtJHCOCOCOCOCOiO 
 p lO (M, p rH(N rH 00 »0 p CO 
 dcOcdcdi-HOTtHTHrHCOt^ 
 
 i-i<MCOCO'^OCOI> 
 
 i 
 
 ^1 
 
 _CX)OOrJHiOcDiCiO'^CO 
 Oi-iOC0C0'^CDC0O(NO 
 
 Oi-iodcooTj^i^'^TtHdco 
 
 T-lT-(Tt<iOCOCOI>.00O5O5 
 
 
 poqooooc^c^ost^-cDT^ 
 cdt>^o6QddiOi-iTHai(N'd 
 
 TtH CO CO (N (M !-< ^ 1-1 
 
 1 
 
 poqiqi>;COOCD(MiOOO 
 
 dTjHQodi>c5i>^ddc>co 
 
 1 
 
 OOOiHiH(M(MCOTiHCOOO 
 
 
100 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 will be seen that the former runs far ahead of the. latter, espe- 
 cially in the 2 cm. sphere where the reduction in pressure is 
 greater. This shows that the agreement found by Cameron and 
 Ramsay (§ 30) is the special case in which the relative pressure 
 change is slight. In cases of large variation the pressure must 
 be taken into account as has been done in equation (3). Com- 
 plete justification of the treatment is seen in the agreement of 
 the k^i/X values over the whole range of the reaction. 
 
 Fig. 6. 
 
 43. Influence of the Size of the Reaction Vessel, Law of the 
 Inverse Square of the Diameter of the Sphere. 
 
 By determining the velocity constant of the interaction of 
 electrolytic hydrogen and oxygen in several different spherical 
 vessels of diameters from 1 to 5% cms., Lind (loc. cit.) estab- 
 lished a general relation, applicable up to a certain size. From 
 the standpoint of the average path of the a particles in limited 
 spherical volumes (§ 35), the nature of the relation can be pre- 
 dicted. Increase of diameter of the sphere lengthens the average 
 path by the same ratio and therefore increases the quantity of 
 chemical action in direct proportion to the increase of the diam- 
 
KIKETICS OF THE CHEMICAL REACTIONS 
 
 101 
 
 eter. The pressure effect, however, of a given amount of chemi- 
 cal action will be inversely proportional to the volume and, 
 therefore, to the cube of the diameter. Combination of these 
 two oppositely directed influences predicts that the pressure 
 change will be inversely proportional to the square of the diam- 
 eter of the spherical reaction vessel, and therefore velocity con- 
 stants expressed in terms of pressure (as in Equation (3) ) will 
 diminish as the square of the diameter of the spherical reaction 
 vessel increases. By comparing the velocity constants k\i/k for 
 the 2 cm, and 5 cm. spheres in Table XI, it will be seen that 
 a large decrease in the case of the latter was observed. In the 
 following Table XII are summarized the results of Lind for 
 spheres of several different diameters obtained by the same 
 method. 
 
 TABLE XII 
 
 Effect on the Velocity Constant of the Reaction 2H2 + 02 = 
 (2H2O) of Varying the Diameter of the Reaction Sphere 
 
 Approx. 
 
 Diam. of 
 
 Sphere (cms.) 
 
 True Diam. 
 D (cms.) 
 
 Vol. of 
 
 Sphere 
 
 cm.^ 
 
 (found) 
 
 k\i/X X D^ 
 
 1 
 2 
 3 
 
 4 
 5 
 
 51/2 
 
 0.9647 
 
 1.925 
 
 2.924 
 
 3.963 
 
 4.893 
 
 5.613 
 
 0.4701 
 3.738 
 
 13.272 
 
 32.58 
 
 61.32 
 
 92.60 
 
 (89.6) « 
 23.04 
 
 9.92 
 
 5.30 
 
 3.52 
 
 2.68 
 
 Mean 
 
 83.4 
 85.3 
 
 84.8 
 83.2 
 84.3 
 84.1 
 
 84.1 
 
 ' Extrapolated value. See Chapter 11 on Recoil Atoms. 
 
 The results of Table XII appear to establish the nature of 
 the law governing the influence of the size of the containing 
 sphere on the velocity of the interaction of electrolytic gas as 
 brought about by radium emanation intermixed with it. The 
 fact that it is in agreement with the predictions of the principle 
 of average path of the a particles supports the validity of the 
 principle and its application in calculating ionization. On pass- 
 ing to volumes other than spherical, it has not been possible, as 
 
'102 THE CHEMICAL EFEECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 stated in § 35, to give a mathematical treatment of the average 
 path. One experiment was made with a cylinder 1.8 cm. in di- 
 ,ameter and 4 cms. long of volume 6.787 c. c, equal to the volume 
 of a sphere 2.375 cms. in diameter. Using 0.01219 curie of 
 jemanation, a value of k^i/X was obtained of 14.8, which multi- 
 plied by (2.375)2 gives 83.1, a value agreeing within the limits 
 of experimental error with those of the spheres in Table XII. 
 Results for more elongated cylinders are to be desired. The use 
 of such a small quantity of emanation gave a pressure reduction 
 of only 578.1 to 480.5 mm. in 30 days. Comparison of the rate 
 of reaction and the rate of decay of emanation showed agree- 
 ment within about 1%, thus confirming the experimental realiza- 
 tion of Cameron and Ramsay's special case (§ 30). 
 
 It may be of interest to inquire how great the diameter of the 
 reaction sphere may become before the validity of the relation 
 k[x/X = 84.1/D2 is impaired. Evidently it holds for the largest 
 bulbs used in Table XII (5% cms. diam.). By applying Equa- 
 tion (3) to the results of Scheuer for the same reaction (§38) a 
 single, value of kpi/X may be found for still larger spheres. In 
 his experiment with a sphere of 7.18 cms. diameter the pressure 
 diminished from 1580 mm. to 1433.8 mm. in 26 days with 0.0613 
 curie of eijnanation, which gives a value of k\i/X of 1.601. The 
 value calculated according to k[i/X =z 84.1/D2 is 1.633, showing 
 that for ai sphere of 7 cms. containing 2 atmospheres of elec- 
 trolytic gais, the amount of reaction found is only 2% below the 
 theoretical value for the completely utilized average path. On 
 going up to Scheuer's sphere of 8.94 cms. diameter and a gas 
 pressure of 1680 mm., k[i/X (exptl.) is only 0.987 against 1.054 
 (theory). And in a sphere of 6 cms. diameter at the high pres- 
 sure 11,445 mm., k\i/X (exptl.) is only 0.3278 against 2.278 (the- 
 ory). The difference is due to the number of a particles which 
 can not complete their paths at this pressure before being com- 
 pletely absorbed. The limit of the applicability of the formula 
 for average path appears to be about 7 cms. for a pressure of 
 1580 mm. of 2H2 + O^, which would correspond to a diameter of 
 10 cms. at 1 atmosphere, corresponding to an average path in 
 air of about 3.5 cms. One should expect that the general law of 
 chemical action proportional to ionization by a particles would 
 hold only over the first two or three cms. of path, where ioniza- 
 
KINETICS OF THE CHEMICAL REACTIONS 103 
 
 tion remains constant. This would doubtless be true for a single 
 type of a particle, for example, from Ra C alone, but comparison 
 with Bragg's ionization curves combined for all the a particles * 
 shows that ionization per length of path for emanation in equilib- 
 rium would remain almost constant up to about 4 cms. from the 
 source in air. 
 
 The interaction of hydrogen and oxygen mixed with radium 
 emanation can come to an end through the approximate ex- 
 haustion either of the emanation or of the gaseous mixture being 
 acted on ; the latter takes place in small bulbs with high emana- 
 tion, the former in large bulbs. The actual pressure (P) at any 
 time t (or after decay of all emanation) may be calculated for 
 any given case from the equation: 
 
 (log P/Po) /(Eo(e-^*— 1) ) r=84.1/D2 
 
 Contrary to the opinion expressed by some authorities, the 
 ratio of quantity of emanation to quantity of reacting gas is not 
 important from the kinetic standpoint. The ratio of emanation 
 to reacting gases may rise continuously, as is the case in small 
 volumes where the gases react at a faster percentage rate than 
 the emanation decays, may pass through a maximum as in 3 cm. 
 spheres with about 100 millicuries of emanation, or may fall 
 continuously, as in larger spheres, without affecting the velocity 
 constant. This shows that, while the ratio of emanation to gas 
 influences greatly the actual velocity of reaction, it does not 
 change the value of k\i/l, thus proving that the general kinetic 
 equation proposed holds, regardless of the relative concentra- 
 tions, except as provided for in the equation. 
 
 It may also be mentioned that the kinetic equation will hold 
 in volumes even greater than those at which the average path 
 formula no longer applies, but with very large volumes the pres- 
 sure changes produced by attainable quantities of emanation 
 would become too small for accurate measurement. There is 
 also no reason to suppose that the same formula: velocity con- 
 stant = const./D^ should not hold for other reactions than 
 2H2 + ^^2, with different values, however, for the constants in- 
 volved. 
 
 *W. H. Bragg, "Studies in Radioactivity" (1912), p. 21; Phil. Mag. (6) 
 10, 323 (1905). 
 
104 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 44. Use of Kinetic Results to Evaluate M/N. 
 
 The study of the reaction between hydrogen and oxygen pro- 
 vides through the general formula for spheres (preceding §) 
 and the value of the average path of the a particle in spheres, a 
 method of evaluating M/N which has great validity, since it de- 
 pends not on any one experiment but on the results of a whole 
 concordant series for which a general law has been demonstrated. 
 It has just been shown that k^i/X = 84.1/D-. Therefore for a 
 sphere with D = 1, kfx/X = 84,1, and it is only necessary to evalu- 
 ate k and solve for \i. X is the decay constant for radium emana- 
 tion = 2.085 X 10"^ sec.~^. \i is an efficiency factor for the chemical 
 effect of ions and may be expressed as ^ = (M/N).(760/V.2.75x 
 10^®) . K = ionization coefficient = number of a particles per 
 second for 1 curie of emanation in equilibrium with Ra A and C 
 (3 X 3.72 X 10^*^) X number of ions per a particle per 1 cm. of 
 path (2.4 X 10*) X specific ionization of the gas mixture (for 
 2H2 + IO2) 1/3 (2x0.24 + 1.09) =0.523) x average path for 
 sphere of 1 cm. diam. (0.2967 cm.) x 1/760 (to refer to 1 mm. 
 of pressure) . Therefore, k = 4.16 x lO^M/760. 
 
 Substituting in kfi/X = 84.1 and solving for M/N: 
 
 M/N = 6.0, or M^ ^/N = 2/3 M/N = 4.0. (See also end 
 
 of this §.) 
 That is, for each pair of ions produced by emanation in the 
 gaseous mixture 2H2 + O2, about 4 molecules of water are 
 formed. This is calculated on the basis that all the reduction in 
 pressure represents the formation of water. If H2O2 is formed 
 it must have but temporary existence, since in one experiment 
 of Lind ^ an intitial pressure of 982.9 mm. of electrolytic gas was 
 reduced in 12 days by 0.1868 curie of emanation at a volume of 
 3.375 c. c. to only 11.5 mm. The M/N value 4-0 is in fair 
 agreetaent with that of Scheuer 3.7 (also see Kirkby, p. 125) , but 
 much higher than the older values of Cameron and Ramsay which 
 were less than 1.0. The kinetic evidence of §§ 42 and 43 indi- 
 cates that Cameron and Ramsay's low results are to be attributed 
 to an incorrect report of the quantities of emanation used in 
 their experiments, which were not the result of direct measure- 
 ment in loco but of a calculation from the amount of radium in 
 
 »S. C. Lind, Tranfi. Amer. Electrochcm. Soc. 34, 214 (1918). 
 
KINETICS OF THE CHEMICAL REACTIONS 105 
 
 the original solution. If the evolution or collection from the 
 solution was inefficient, the quantities of emanation reaching the 
 reaction chamber may well have been several fold lower than 
 estimated. For example, the value of k\i/k found in § 42 for 
 one of Cameron and Ramsay's experiments was 12.71, but, from 
 the general formula for a vessel of that volume, should have 
 been 3243. 
 
 In calculating the M/N value for the formation of water by 
 the average path method, one assumption was made which re- 
 quires some discussion. The average path was calculated as- 
 suming that all a particles of Ra A and C originate on the wall 
 of the containing sphere, which involves the assumption that 
 Ra A after being generated from emanation in the gas phase has 
 time to diffuse to the wall before emitting its a radiation. No 
 data having a very direct bearing on this subject appear to exist. 
 A. Debierne ^ has made the most complete examination of the 
 rate of diffusion of active deposit by using parallel plates at 
 different distances apart exposed to emanation. His results 
 show that the practical limits of diffusion are much smaller than 
 the theoretical calculated from atomic weights, and indicate a 
 particle 140 times as heavy as the atom of the decay products. 
 Some direct experiments were undertaken by Lind {loc. cit.) by 
 allowing the emanation to reach equilibrium in electrolytic gas 
 in glass spheres of the same sizes as those used for the velocity 
 of combination. By suddenly driving the gases before mercury 
 into a new vessel, the initial y radiation in the latter would dis- 
 close the quantity of Ra C transferred and consequently the pro- 
 portion left on the wall of the reaction chamber. In a sphere of 
 2 cm. diameter filled with electrolytic gas at atmospheric pres- 
 sure the percentage of Ra C transferred was 6.7%; or 93.3% was 
 deposited on the original wall. From a 6 cm. sphere 11.6% 
 passed into the new vessel; or 88.4% remained on the wall of the 
 original. This result, not to be expected from Debierne's data, 
 is probably due to heat convection. At any rate it is evident 
 that under the experimental conditions a large part of the Ra C 
 reaches the wall of even a 6 cm. sphere. This would not be 
 necessarily true for Ra A in the same spheres owing to its much 
 shorter life, but the velocity constants in Table XII do -not in- 
 
 8 A. Debierne, Le Radium G, 97-108 (1909). 
 
106 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 i 
 
 dicate any difference between large and small spheres for effec- 
 tiveness of the emanation (plus decay products). Whatever 
 assumption is made, therefore, as to position of decay products 
 for one size must be made for all. The one made was that 
 both Ra A and C completely diffuse to the wall before decaying. 
 If one assumes instead that Ra A remains largely in the gas phase 
 while Ra C diffuses to the wall, the value of the average path _ 
 
 is changed from 0.5833 to 0.6667 times the radius, and the M/N ^ 
 
 value would be lowered to 3.50. From considerations to be 
 pointed out in § 48 a value slightly less than 4 has greater prob- 
 ability than one above 4. This discussion is deferred to § 48 
 where all the evidence for and against an ionic theory of the a 
 ray effects is summarized. 
 
Chapter 9. 
 
 Additional Relationships of the Eadiochemical 
 
 Efeects. 
 
 45. Influence of Varying the Proportions of Hydrogen and 
 Oxygen. 
 
 In studying the interaction of hydrogen and oxygen under 
 the influence of radium emanation mixed with the gases, the ef- 
 fect of varying the relative proportions of the two components 
 was investigated by Lind.^ The effect of an excess of either gas 
 on the rate of reaction can be predicted on the assumption that 
 the change in rate will be in proportion to the ability of the mix- 
 ture to absorb the energy of the a particle, which is in proportion 
 to the ionization. The specific (molecular) ionization compared 
 with air is according to Bragg (§ 13) 1.09 for oxygen and 0.24 
 for hydrogen. Consequently an initial excess of oxygen should 
 increase the reaction velocity relative to that of the normal elec- 
 trolytic mixture, while excess of hydrogen should produce the 
 opposite effect. The velocity constant calculated from the gen- 
 eral kinetic equation should be initially higher than the normal 
 value in the case of excess of oxygen, and should continue to 
 rise as the mixture becomes relatively richer in oxygen with the 
 progress of the reaction. With initial excess of hydrogen ex- 
 actly the opposite should be true; the velocity constant should 
 be initially abnormally low and show a further fall as the mix- 
 ture enriches relatively in hydrogen. 
 
 Both cases were experimentally investigated and the predic- 
 tions just made were found to be fully confirmed, as will be seen 
 from Table XIII. Since the specific ionization now becomes va- 
 riable, the general kinetic equation is not strictly applicable. 
 The development of a new equation taking into account the 
 changing specific ionization or "stopping power" is so compli- 
 cated that the simpler procedure has been adopted of using the 
 
 ^ S. C. Lind, Journ. Amcr. Chein. Soc. 41, 542 (1919). 
 
 107 
 
108 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 equation to show that the change in its velocity constant is pro- 
 portional to the change in specific ionization. Since the velocity 
 constant (k^/X) now becomes a variable, it should be calculated 
 over short intervals to avoid undue masking of its variability. 
 To accomplish this the value of k\i/X is calculated, not from the 
 beginning through the entire time interval in each case, but 
 from each measurement to the next, a procedure quite commonly 
 employed in chemical kinetics.^ 
 
 The equation may be written in this form: 
 
 m- 
 
 ^^ (6) 
 
 Eo (e-^^i — e-^*2) 
 
 Table XIII gives the data for the initial mixture 4H2 to 
 IO2. In column 5 the application of equation (6) shows that 
 (kfx/X)' is not constant but falls approximately as required by 
 the change in specific ionization (compare column 6) . Column 6 
 is calculated from the normal value (kji/X = 84.1/D2) _ iqq^ 
 for a sphere of the size used, and from the change in specific 
 ionization calculated by applying the simple law of mixtures to 
 the values for pure hydrogen and oxygen. 
 
 A consideration of the results shown in Table XIII will throw 
 light upon an important question, namely, whether it is only one 
 component of the reaction, or both, which are activated by the 
 a radiation ; or, in terms of ionization, are both the hydrogen and 
 oxygen ions capable of taking part in the chemical reaction pro- 
 duced at ordinary temperature? Since the rate of reaction 
 appears to be proportional to the specific ionization of the 
 mixture, this question is already answered in favor of the suppo- 
 sition that both ions are" active. But a still more definite answer 
 is obtained by calculating (kfx/X)' for partial pressures of the 
 components. In the last column of Table XIII are values of 
 (k[i/'k) ' calculated from the partial pressure of oxygen, and it is 
 seen that the values rise, whereas the reaction is really slowing 
 up from the rate shown by a normal mixture, which must be 
 interpreted as meaning that the partial pressure of oxygen 
 alone does not control the rate of reaction. The calculation from 
 partial pressures of hydrogen would in this case not differ suf- 
 
 « J. W. Mellor, "Chemical Statics and Dynamics" (1904), pp. 31, 3G, 37. 
 
THE RADIOCHEMICAL EFFECTS 
 
 109 
 
 TABLE XIII 
 
 Effect of the Excess of H^ on the Velocity Constant of the Re- 
 action 2H2 + 0, = (2H2O) 
 
 Init. Mixt. 4H,:10,. Vol. = 11.64 c. c. Diam. = 2.812 cm. 
 Eo = 0.1169 curie. 
 
 Days 
 
 Hrs. 
 
 
 
 0.0 
 
 
 
 19.25 
 
 1 
 
 3.25 
 
 1 
 
 23.00 
 
 2 
 
 23.67 
 
 4 
 
 19.33 
 
 6 
 
 3.75 
 
 7 
 
 19.67 
 
 8 
 
 23.75 
 
 11 
 
 19.33 
 
 13 
 
 22.33 
 
 15 
 
 22.50 
 
 Total Pr. 
 
 Partial 
 
 (k[i/l/ 
 
 (k\i/iy 
 
 mm. Hg. 
 
 Pr.O, 
 
 (found) 
 
 (calcd.) 
 
 682.8 
 
 136.6 
 
 
 
 605.9 
 
 110.9 
 
 7.92 
 
 7.93 
 
 580.3 
 
 102.4 
 
 7.30 
 
 7.50 
 
 528.2 
 
 85.0 
 
 7.17 
 
 7.38 
 
 480.6 
 
 69.2 
 
 6.80 
 
 7.17 
 
 425.2 
 
 50.7 
 
 6.42 
 
 6.89 
 
 397.9 
 
 41.6 
 
 6.24 
 
 6.62 
 
 375.8 
 
 34.2 
 
 5.74 
 
 6.46 
 
 363.9 
 
 30.2 
 
 5.89 
 
 6.30 
 
 346.7 
 
 24.5 
 
 5.24 
 
 6.10 
 
 338.4 
 
 21.8 
 
 5.50 
 
 5.97 
 
 332.9 
 
 19.9 
 
 5.65 
 
 5.90 
 
 (h\i/iy 
 
 for Par. 
 Pr.O, 
 
 13.20 
 13.50 
 14.20 
 14.90 
 16.30 
 18.61 
 19.50 
 22.71 
 22.75 
 27.91 
 30.24 
 
 ficiently from that by the total pressures to make a decision, but 
 may be undertaken for mixtures with initial excess of oxygen. 
 
 In Table XIV will be found data for mixtures with excess of 
 oxygen. 
 
 In Table XIV the comparison with the theoretical values 
 calculated from ionization is not made, since the change in spe- 
 cific ionization is not so great as in the case with the mixture 
 4H2:1 O2 (Table XIII), but it can be seen that the constants 
 show a tendency to rise in all cases and begin abnormally high 
 when compared with the normal value for electrolytic mixture, 
 as required by theory. 
 
 From the data for the 2 to 1 and 4 to 1 mixtures in Table 
 XIV it will be observed that when the hydrogen is exhausted, 
 the pressure reduction does not stop entirely, but the velocity of 
 reaction falls at once to one of an entirely lower order as indi- 
 cated by the velocity constants in the last column. This is 
 caused by some reaction that oxygen alone undergoes when acted 
 
110 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 > 
 
 XI 
 
 
 m 
 
 ^ 
 
 t?S 
 
 II 
 
 §11 
 
 O 
 + 
 
 8> 
 
 •a 
 
 SO 
 
 SO 
 
 § 
 
 «to 
 
 CO 
 
 o 
 
 O 
 
 03 
 
 
 W ^ 
 
 E:- II 
 
 IIS-^ 
 I 111 
 
 (punof) 
 
 rJ^ T^ CO CO iq 00 (N CO (M_ 
 
 L6i6cDcd»o(NOc5o 
 
 '6jj 'mm 
 
 ^. l>C<l^l>«|>0000 
 2 05 t^ CO i-H 
 
 •iSjf 'mm 
 'J'dmoj, 
 
 cocqio^, (M_t>oqcqT-jco 
 di-HcoaJi>^TtHi-Ho6T}^co 
 
 CO(:OiO>OrtH"^TH"^ThiTti 
 
 'SdH 
 
 COOO(MO(Nt^COOOQ 
 
 dcDi-H,-H(Ncdcsii-Hiocsi 
 
 SfiVQ 
 
 OOOOrHi-lrHTt^CqOO 
 
 O TtH 
 (M 00 
 
 gl II 
 
 Oi <M ^ 
 
 CO<N»S 
 
 bCo 
 
 6> 
 
 § 111 
 
 (punof) 
 Ax/M) 
 
 COCOOo5COC3^'^'^> 
 i-H p 00 p "r^ P T-H rtj lO 
 
 c^icocO'r^iococodd 
 
 tH rH 1— I T-H rH T-H 
 
 •5/f "mm 
 
 iqc^. i-jcsiot^pppp 
 TjHcocdco(Ncodc$c>d 
 
 00 i-l 05C0 C<1 T-H 
 
 'dfj -mm 
 •J^dV^^ojj 
 
 iOCDOiOiO(NCOi-Hpp 
 
 cocdi-Hir^dt^cociidoi 
 
 iOTtl(M(MT-H05^'^'>*''^ 
 iOTt^TlHCOCO(M(NC<l(N<N 
 
 'SdH 
 
 SfiVQ 
 
 _iOOOiOoOOOiO»Ot^OO 
 
 Ocddcdc>c5coc6di>l 
 
 1-H C^ rH (M T-H C^ rH 
 
 OOOi-H'-itNC^C^iOOO 
 
 S « a 
 
 d " 
 
 ^^ T— I /.^N 
 
 ^^11^ 
 
 o 
 
 m GO 
 
 o Co 
 
 g II 
 
 o s " a 
 
 (punof) 
 
 •pT^pp(NCOCO'^T-H 
 
 •c<i(>icdcoTjH'?jH'^c5aJ 
 
 •t-Ht-HtHi-Ht-Ht-Hi-HC^ 
 
 'djj 'mm 
 
 c^coQOrjHoqoooqppp 
 
 uocd<NidTjHpg5id(Nc5 
 
 »OO5l>-T-H00"^C^rH 
 (N i-H rH i-H 
 
 •ddimojj 
 
 TjHOOOI>;OOpCOi-Hpp 
 
 oc^cod-^'coc^oot- 
 
 S?^OOoSot^»OCO(N 
 iO'^COCO<M<M'— '^'-''~' 
 
 •s^i/ 
 
 lOiOt^OOOQCJ 
 Opt^t^T-HOppP"^. 
 
 ddcocot>^ddddo 
 
 T-H(M(Ml-H(M(NC^r-H 
 
 sfivQ 
 
 OOOi-HC^COTtHiOCDt- 
 
THE RADIOCHEMICAL EFFECTS 111 
 
 on by a rays, which is more fully discussed in the following 
 section. 
 
 46. Action of a Rays on Pure Oxygen or Pure Hydrogen. 
 
 The limits of changing the proportions of hydrogen and 
 oxygen, discussed in the foregoing section, are pure oxygen or 
 pure hydrogen. According to the results of Lind (§ 33), under 
 different experimental conditions, ozone is formed by the action 
 of a rays on pure oxygen. In the presence of mercury a sec- 
 ondary reaction with the ozone formed might be expected, which 
 is clearly indicated by the results near the end of the reactions 
 in Table XIV. Scheuer [loc. cit.) found that emanation mixed 
 with oxygen led to very little pressure reduction, but it was not 
 stated whether the reaction took place in the presence of mer- 
 cury. Direct experiments by Lind with the same form of appa- 
 ratus as used for electrolytic gases (Fig. 6, p. 100) showed that 
 a decided diminution in pressure does take place, but that the 
 velocity of reaction is dependent upon the extent of the surface 
 of mercury that is exposed. When the surface is only that 
 exposed by the mercury ordinarily in the stem of the reaction 
 bulb, the reaction is relatively slow; but, if the mercury is 
 allowed to rise in the bulb and spread out, the rate of reaction 
 increases many fold. This probably means that primary ozoni- 
 zation takes place in all cases, but that de-ozonization also takes 
 place unless the opportunity for ready combination with mercury 
 is presented. The surface of the mercury becomes black, loses 
 its coherence, clings to the glass and is finally covered with a 
 black powder, probably mercurous oxide. The repetition of this 
 experiment under more definite conditions offers the possibility 
 of an independent method of measuring ozone formation by a 
 rays. 
 
 In the case of pure hydrogen mixed with emanation a similar 
 but smaller diminution in pressure was observed by Lind [loc. 
 cit.), accompanied by a darkening of the mercury and a loss of 
 its coherence, though no powder became visible on the surface as 
 in the case with oxygen. The diminution of pressure ceased after 
 a time and could not be made to proceed further by increasing 
 the mercury surface. To explain reduction of pressure in hydro- 
 gen exposed to a radiation, several possibilities present them- 
 
112 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 selves. Usher ^ found in trying f o cause hydrogen and nitrogen 
 to unite under the action of emanation that the reduction in 
 pressure was mainly due to some other action of the a particles, 
 presumably a purely physical one. On the other hand Duane 
 and Wendt* have discovered the existence of an active 
 modification of hydrogen produced by radium emanation, which 
 reacts chemically with sulfur at ordinary temperature to form 
 HgS which can be detected by passing over paper impregnated 
 with a solution of lead acetate. Langmuir ^ has reported 
 the discovery of a very active atomic form of hydrogen, and 
 recently Wendt and Landauer ^ have described the activa- 
 tion of hydrogen by a rays and by the corona discharge, and 
 present evidence of its triatomic nature. Though not so active 
 as monatomic hydrogen, the triatomic form has been shown by 
 Wendt and Landauer to react at ordinary temperature with 
 sulfur, arsenic, phosphorus, mercury, nitrogen, and both neutral 
 and acid KMn04. It is unstable and reverts to the ordinary 
 form in about one minute. It can be distinguished from the 
 monatomic form by the ease with which it passes through glass 
 wool. 
 
 47. Comparison of the Chemical Effects of a and of Pene- 
 trating Rays. 
 
 Since the chemical reactions produced by a rays have been 
 shown to be at least approximately proportional to the ioniza- 
 tion in most cases, it is logical to inquire whether the same is 
 true for the chemical effects of the penetrating rays. At any 
 rate the question should be carefully investigated experimentally. 
 There is quite a divergence of opinion on the subject. Besides 
 the experimental difficulties, which are serious, some of the early 
 attempts to explain p ray effects were directed toward a consid- 
 eration of the primary charge carried by the p particles them- 
 selves, which are of course very insignificant in comparison with 
 the large number of electrons liberated and positive ions produced 
 by the passage of (3 particles through matter. 
 
 »F. L. Usher, Joum. Chem. Soc. Lond., 97^, 389 (1910). 
 
 *Wm. Duane and G. L. Wendt, Phya. Rev. (2) 10, 116-128 (1917). 
 
 »I. Langmuir, Joum. Amcr. Chcm. Soc. 34, 1310-25; 36, 1706 (1914) ; 37, 
 417 (1915). 
 
 •G. L. Wendt and R. S. Landauer, Joum. Amer. Chem. Soc. 42, 930-46 
 (1920). 
 
THE RADIOCHEMICAL EFFECTS 113 
 
 The chemical effects of p and y rays are so minute for nearly 
 all gas reactions that a direct comparison of ionization and 
 chemical action has not been possible in a strictly quantitative 
 sense. Of course, by increasing the absolute quantity of the 
 radioactive source this difficulty could in part be obviated, 
 although this is hardly possible for y radiation, the relative ioni- 
 zation produced by which is of the order of 1/10000 of that of 
 the corresponding a radiation. But a still more serious difficulty 
 is encountered in the low absorption coefficients of p, and par- 
 ticularly of Y rays, which precludes the possibility of anything 
 approaching complete utilization of the radiation in a gaseous 
 system of reasonable dimensions. For this reason the investiga- 
 tion of the chemical effects of penetrating rays has been mainly 
 confined to liquid systems (§ 28), and then under such conditions 
 that a very small proportion of the y radiation is absorbed. 
 
 The most careful comparison of a and p-y ray effects has 
 been made by Usher.^ Using emanation in a glass capillary 
 tube of 0.17 mm. thickness, 0.208 cm.^ of electrolytic gas was 
 produced by the action of the penetrating radiation from 0.067 
 mm.^ of emanation in one month while the combined action of 
 the a and penetrating radiation from 0.025 mm.^ of emanation 
 till completely disintegrated gave a total of 5.840 cm.^ of electro- 
 lytic gas (including B.^ from some H2O2 formation). Reduced 
 to the same quantities of emanation, the joint effect of the rays 
 is seen to be about 75 times as great as that of the penetrating 
 rays alone, or the effect of the latter is about 1.3% of the com- 
 bined effect. This is about what one should expect from the 
 relative ionizations or kinetic energies. This appears to be 
 strong evidence in favor of the same relationship between ioni- 
 zation and chemical action as that which has been shown to 
 exist for a rays. 
 
 It should be mentioned, however, that a different interpre- 
 tation was put upon his results by Usher from that just proposed. 
 By taking into account all the soft p rays which were not able 
 to penetrate the thin glass wall, and by assuming that each one 
 of them would have had the same power of decomposing water 
 as those had which did penetrate the wall. Usher estimated that, 
 where emanation is dissolved directly in water, and hence all 
 
 ^F. L. Usher, Jahrl). d. RadioaU u, Elcktr. 8, 323-34 (191X). 
 
114 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 non-penetrating rays are absorbed, the proportion of decomposi- 
 tion by the a rays is not more than twice that produced by the p 
 rays. Apparently Usher was led to this view through the assump- 
 tion of chemical effect proportional to the primary charges of 
 the p particles themselves, according to which all p particles 
 would produce the same chemical effect, regardless of their 
 velocity, kinetic energy, or penetrating power. This is not only 
 contrary to the idea of equivalence of ionization and chemical 
 action, since the charge carried by the p rays would fall many 
 thousand fold short of accounting for the chemical effects in a 
 sense consistent with Faraday's Law; but, in the case of the very 
 soft p rays, the law of the conservation of energy would be con- 
 traverted, since they do not possess enough kinetic energy to 
 account for the amount of water decomposition assumed by 
 Usher. In other words, the chemical activity of a or ^ rays must 
 be attributed to their kinetic energy and ionizing power, not to 
 their own charges, which in comparison with the secondary 
 charges produced are wholly insignificant, as would be shown 
 by the fact that a single a particle from Ra C, having two posi- 
 tive elemental charges, produces in its total path in air about 
 237,000 pairs of positive and negative charges, and even more 
 than this in some other gases. The total ionization for water 
 by 1 a particle has not been directly measured, but is probably 
 of the order 195,000 pairs of ions. 
 
 In § 36, Table VII, the results of Usher for the decomposition 
 of water by emanation are seen to be considerably lower than 
 those of Duane and Scheuer, using the a ray capillary method. 
 Debierne® has measured the decomposition of water by the 
 penetrating rays from a radium salt, and found that 0.115 cm.^ 
 of electrolytic gas are formed per day per gram of radium. This 
 rate of decomposition is somewhat lower than that found by 
 Usher per curie of emanation, as would be expected, owing to 
 the greater absorption of radiation in Debierne's apparatus by 
 the double glass wall and by the salt itself. 
 
 48. General Discussion of Ionic-Chemical Equivalence. 
 
 All the experimental evidence bearing on this subject has been 
 presented in the foregoing sections except that pertaining to 
 
 8 A. Debierne, Comp. rend, 148, 703-5 (1909). 
 
THE RADIOCHEMICAL EFFECTS 115 
 
 recoil atoms which will be treated in Chapter XI. A general 
 summary of the results is not without interest, although it may 
 be impossible to reach a final conclusion acceptable to all author- 
 ities, from the data at present available. 
 
 It has been shown that in nearly all the reactions brought 
 about by a rays that have been investigated there is an approxi- 
 mate statistical agreement between the number of ions generated 
 and the number of molecules acted on. This appears to be true 
 to the same degree of approximation both in gaseous and liquid 
 systems. The results have been brought together for compari- 
 son in Table VII, § 36. It will be seen that the M/N ratio varies 
 in different reactions from about 0.5 to about 4.0. An agreement 
 within these limits for such a variety of reactions proceeding 
 both with and opposed to the chemical free energy in both liquid 
 and gaseous systems, when the disagreement might have been 
 many million fold in either direction, appears to have funda- 
 mental significance and to warrant the application of a modified 
 form of Faraday's Law to these reactions.^ 
 
 Besides the direct evidence from a particles, it was shown in 
 § 45 that when the proportions of hydrogen and oxygen are 
 varied, the reaction to form water changes its rate in a ratio 
 that can be predicted from the change in specific ionization of 
 the mixture. Passing to other forms of radiant energy which 
 produce ionization accompanied by chemical action, it was shown 
 in § 47 that the same equivalence holds in the decomposition of 
 water by p radiation. In § 33 the results of Krueger for the 
 ozonization of oxygen by Lenard rays (high velocity electrons) 
 were cited to show that the same relation exists; finally, in 
 Chapter XI it will be shown that the recoil atoms from a radi- 
 ation cause the combination of Hg and O2 in the same propor- 
 tion to the ionization as found for a particles. Such evidence 
 has been sufficient to convince many authorities that ionization 
 is directly involved in the production of chemical reaction. Qn 
 the other hand the results of Scheuer on the formation of water 
 (§ 38) and those of Wourtzel (§ 39) on the decomposition of HgS 
 and of N2O, which show M/N values exceeding unity by two to 
 four fold, have convinced Debierne, Scheuer, and Wourtzel that 
 
 »S. C. Lind, Trans. Amor. Elcctrochem. 8oc. 21, 177-84 (1911); Journ. 
 Phys. CJiem., 16, 564-G13 ; Le Radium, 9, 426-31; Zeit. phys. Chem., 84, 
 759-61 (1913). 
 
116 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 the ions are not the intermediate products causing the chemi- 
 cal action. Debierne ^° has proposed a theory of thermal decom- 
 position along the path of the a ray but extending outside the 
 limits of ionization and therefore statistically exceeding the ioni- 
 zation. Wourtzel {loc. cit.) finds in the negative temperature 
 coefficients, which he obtained for the decomposition of HgS 
 and of NgO, grounds for rejecting the thermal theory of Debierne 
 and has substituted a theory of collision. 
 
 As already stated, the writer is of the opinion that the statis- 
 tical agreement between ionization and chemical action, although 
 inexact, points strongly to the intermediation of ions in bringing 
 about the chemical reactions. The departures from the direct 
 requirements of electrical and chemical equivalence are not too 
 great to be brought into accord by making possible assumptions 
 in regard to the mechanisms of reaction, which assumptions are 
 quite within reason, although it is impossible with present data 
 either to prove or disprove them absolutely. At any rate the 
 departures of M/N from unity are quite small when compared 
 with the real exceptions to be taken up in the following section. 
 It might also be mentioned that whether ionization is primarily 
 involved in the chemical reactions brought about by radiation, 
 or whether it is a secondary accompaniment, it is at the present 
 time the most convenient index of reference and can readily be 
 made a means of comparing chemical action with any factors 
 involved in the absorption of the energy of radiation. 
 
 Before going on to a consideration of the large exceptions 
 from the general rule of equivalence of ionization to chemical 
 action, the case of the combination of electrolytic hydrogen and 
 oxygen under the influence of a rays will be used as an example 
 to illustrate the possibility of proposing a mechanism of reaction 
 that will explain the value Mjj q/N = 4, without violating the 
 general principle of equivalence. 
 
 Millikan, Gottschalk and Kelly (loc. cit.) have shown that 
 the ionization of a number of ordinary gases by a particles con- 
 sists exclusively in the removal of a single electron from each 
 molecule affected, thus leaving an equal number of singly posi- 
 tively charged gaseous ions, which in the case under consideration 
 would be H2 or Oj. Of course there will be a certain tend- 
 ency for immediate recombination of the electrons with the 
 
 "A. Debierne, Ann. de Physique (9) 2, 97-127 (1914). 
 
THE RADIOCHEMICAL EFFECTS 117 
 
 oppositely charged ions but our general knowledge of the recom- 
 bination of gaseous ions ^^ informs us that its rate is not exceed- 
 ingly great, and on account of the large excess of electrically 
 neutral H2 and O2 molecules in the gaseous mixture, there will 
 be ample opportunity for the free electrons to attach themselves 
 to these molecules, forming negative ions H2 or O2. The chemi- 
 cal activity of ions may be admitted on general grounds, and 
 it is therefore fair to assume that all four kinds of ions can form 
 H2O2 by combining with the hydrogen or oxygen present. If it 
 is then assumed that each molecule of H2O2 retains its positive 
 or negative charge until it is reduced by electrically neutral 
 hydrogen to form two molecules of water from each molecule 
 of H2O2, we should thus have as a net result from each original 
 pair of ions two molecules of charged H2O2, each of which would 
 produce by combination with Hg two molecules of H2O, making 
 four molecules of HgO for each original pair of ions. It has 
 already been shown that Scheuer found 3.7, and that the results 
 of Lind give a value either slightly less (3.5) or exactly four, 
 depending upon what assumption is made as to the position 
 of Ra A in the reaction vessel at the time of its decay. A 
 value somewhat below 4 could be explained by cross reactions 
 between charged molecules; for example, it could be assumed 
 that the H2O2, actually found as a product of the reaction by 
 Scheuer, had resulted from its stabilization by becoming electri- 
 cally neutralized, preventing its reduction by hydrogen. The 
 mechanism just proposed at least shows that the ratio M/N = 4 
 is still within the limits of possible ionic explanation without 
 resorting to other theories. If it be assumed with Bodenstein 
 (§ 55) that a free electron can attach itself to activate a molecule, 
 is again detached at the moment of reaction, and continues to 
 act thus through a large number of cycles until consumed by 
 some reaction in which it is not again liberated, there is almost 
 no limit to the multiple activity of a single electron. 
 
 49. Exceptions to Ionic-Chemical Equivalence — Reactions in 
 Which M Exceeds N. 
 
 By consulting the column of M/N values given in Table VII, 
 § 36, in which M is the number of molecules involved in a given 
 
 ".T. S. Townsend, Phil. Trans. Roy. Soc. 193A, 157 (1899). R. K. Mc- 
 Clung, Phil. Mag. (6) 3, 283 (1902) ; P. Langevin, Tliesis Paris (1902), p. 151. 
 
118 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 chemical reaction and N is the number of ions produced by the 
 radiation, it will be observed that the cases in which M exceeds 
 N fall into two general classes, those in which the M/N ratio 
 lies between 1 and 4, and those in which it attains values of an 
 entirely different order amounting to several thousand. With 
 respect to those values falling in the former class it has been 
 suggested in the foregoing paragraph that they do not constitute 
 real exceptions, but that by making certain assumptions as to 
 the mechanism ofXhe reactions, an agreement between ionization 
 and chemical action in a sense concordant with Faraday's Law 
 may still be attained. In the case of the reaction brought about 
 between hydrogen and oxygen by a rays, such a mechanism was 
 proposed and discussed in detail in § 48. On account of our 
 incomplete knowledge of the entire behavior of gaseous ions, 
 and also on account of an insufficiency of exact experimental 
 data, it does not appear possible at present to reach a final deci- 
 sion as to the exact relation between gaseous ionization and 
 chemical action, nor would it be profitable to discuss theoretical 
 possibilities as to exact mechanisms for other reactions. The 
 number of possible variables exceeds greatly the number of 
 equations now available for the solution of the problem. 
 
 Of the second class of reactions, in which M exceeds N by a 
 large quantity, there is at the present time only one example, 
 namely, the interaction between hydrogen and chlorine gases. 
 This particular reaction has also been of great photochemical in- 
 terest for more than a generation. The classical experiments of 
 Bunsen and Roscoe ^^ followed the work of Draper ^^ in calling 
 attention to the importance of this most prominent example of 
 photochemical action, and further investigation of the various 
 phases of the reaction has continued to the present time. It has 
 been repeatedly shown that the activity of the hydrogen-chlorine 
 mixture with respect to light varies with the purity of the mix- 
 ture. The influence of the impurities exhibits itself in retarding 
 the rate of the photochemical action and of lengthening the dura*- 
 tion of the so-called "induction period" during which the rate of 
 
 " R. Bunsen and H. E. Roscoe, Ostumld'a Klasaiker Noa. Si and S8 (Leip- 
 zig, 1892). Grig. Refs. Pogg. Ann. 100, 43-88; 481-510; 101. 235-63 (1857); 
 ibid., 108, 193-273 (1859). 
 
 « Draper, PhU. Mag. (3) 23, 401 (1843). 
 
THE RADIOCHEMICAL EFFECTS 119 
 
 reaction increases to a maximum. Chapman and MacMahon^* 
 have made exhaustive investigations of the inhibition of the 
 photochemical interaction of hydrogen and chlorine. They have 
 determined that oxygen is one of the most effective inhibitors 
 and that the rate of reaction is inversely proportional to the 
 quantity of oxygen present for oxygen contents from 0.08-1.0% 
 by volume. They later showed that ozone is a very effective 
 inhibitor. These discoveries have a very important bearing on 
 the theory advanced to explain the excessive action of a rays on 
 the Hg — CI2 mixture. 
 
 As has already been stated (p. 85) the results of Jorissen 
 and Ringer on the combination of Hg + CI2 under the influence 
 of penetrating rays enabled Lind to estimate that the M/N ratio 
 exceeded unity by 100 to 1000 fold. This exceptional ratio led 
 Bodenstein and Taylor {loc. cit.) to determine the effect of a 
 rays on the same reaction. It was found that the reactivity of 
 the mixture varied with its purity, as in the case of the photo- 
 reaction, and that in a mixture of maximum sensitiveness at 
 least 4000 molecules of Hg and Clg combine for one pair of ions 
 formed. As will be shown in the following chapter, Bodenstein 
 calculated that the rate of the photochemical interaction of H2 
 and CI2 exceeds the predictions of Einstein's photochemical 
 equivalence law by a factor of about 10®. Bodenstein was led 
 to propose an electronic theory for photochemical action accord- 
 ing to which an electron primarily liberated by any form of 
 radiation can successively activate a large number of chlorine 
 molecules, which then react with hydrogen, again liberating the 
 electron at the time of reaction. This process would continue 
 indefinitely from even a small number of initial free electrons 
 except for the fact that finally the electron activates a foreign 
 molecule (Chapman's inhibitors) and is not again liberated by 
 the reaction. Bodenstein assumed oxygen to be the inhibitor in 
 this case and that the ozone formed again decomposes to give 
 oxygen. This fits with a number of other observations, namely, 
 the inhibitive effect of oxygen and of ozone actually observed by 
 Chapman and MacMahon, and with the observation of Lind 
 that ozone formation is statistically equivalent to the ionization, 
 from which it follows that the free electrons are consumed in the 
 reaction. It also explains why the reaction does not proceed after 
 
 "D. L. Chapman and P. S. MacMahon, Joum. Chem. Soc. Lond. 95j, 959-04 ; 
 95ii, 1717-20 (1909) ; 97^, 845-51 (1910). 
 
120 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 cessation of the radiation. As will be seen later, Bodenstein had 
 to abandon the theory as applied to photochemical action of 
 chlorine gas on account of the lack of ionization which he had 
 assumed; but in the case of the action as produced by a parti- 
 cles where we have actual ionization, his theory remains appli- 
 cable, in principle at least, to explain the abnormally high value 
 of the M/N ratio. As alternative theories we shall have that of 
 Nernst for the photochemical interaction Hg + Clg and the later 
 one of Bodenstein, both of which will be presented in the follow- 
 ing chapter. The fact that the Hg + Bvr, mixture at ordinary 
 temperature is not photo-sensitive and that its M/N value for a 
 radiation is normal is of much interest. 
 
 50. Exceptions to Ionic-Chemical Equivalence. Reactions in 
 Which N Exceeds M. 
 
 A study of the M/N ratios for various reactions in Table VII, 
 § 36, shows that the cases in which the ratio drops below unity 
 may be divided into those where the departure from unity is 
 not below 0.5, and those where considerably lower values are 
 attained. The case of slight departures needs no further dis- 
 cussion; the agreement may be regarded as satisfactory from 
 the data at present available. The small deviations might be 
 explained either on ionic grounds or by the assumption of some 
 recombination to form the original product, thus reducing the 
 reaction efficiency. 
 
 The cases in which the M/N ratio drops to much lower values 
 seem to divide themselves into two classes, those where difference 
 in state of aggregation is the controlling factor, and those in 
 which the inherent properties of the reaction itself produce the 
 low rate. 
 
 In the case of the decomposition of water it is very evident 
 that the state of aggregation plays a large role. It has been 
 shown in § 37 from the results of Duane and Scheuer that, while 
 water in the liquid state is readily decomposed by a radiation 
 in almost exactly the quantity required by ionic-chemical 
 equivalence (or by electrolysis), the decomposition of ice un- 
 der the same conditions is only about 5% of that of water. 
 While for water vapor for the same amount of a radiation 
 absorbed, the decomposition showed variable values somewhat 
 
THE RADIOCHEMICAL EFFECTS 121 
 
 lower yet than those for ice. On the other hand Wourtzel (§ 39) 
 found that the decomposition of solid HgS at —190° was of the 
 same order as found for the gas at 18°. This does not necessarily 
 mean that the decomposition of gaseous and solid HgS at the 
 same temperature would be equal, since Wourtzel found the rate 
 of decomposition of the gas at higher temperatures to have a 
 marked negative temperature coefficient, which, if continued to 
 lower temperatures, might mean that the decomposition of the 
 gas at —190° would be (were it possible to determine it at this 
 temperature) much higher than at 18°. It is difficult to find a 
 plausible explanation for the results for water vapor and ice. In 
 the case of water vapor one would be inclined to attribute the low 
 value to recombination owing to the greater mobility of the sys- 
 tem, but one is confronted with the case of ice, where mobility 
 must be at a minimum, and yet the decomposition is much lower 
 than that of water. The explanation might be entirely through 
 temperature effect. This would require a maximum at ordinary 
 temperature for the rate of decomposition of water. While 
 Wourtzel has observed a minimum for NgO at ordinary tem- 
 perature, no maxima have yet been found. Since the tempera- 
 ture coefficients themselves remain unexplained, speculation in 
 this direction is not illuminating. 
 
 To return to a consideration of gases, Wourtzel found in the 
 case of CO, but slight decomposition, which he attributed to the 
 greater stability of this compound, in other words, to the excessive 
 amount of energy necessary to bring about its decomposition. 
 Such a view is not in accord with the ionization theory of the 
 reactions, since we know that CO2 is readily ionized by a par- 
 ticles and that the amount of energy expended in producing its 
 ionization is greatly in excess of that necessary for its chemical 
 decomposition. As will be seen in the following section, there 
 does appear to be some tendency for reactions proceeding in the 
 direction of the chemical free energy to utilize a greater propor- 
 tion of the kinetic energy of a radiation than do those taking 
 place opposed to the free energy. But among those of the latter 
 class there is no distinct tendency for the reaction to be controlled 
 by this factor, and it is very certain that the failure of the 
 decomposition of CO2 gas by a rays is not due to lack of the 
 necessary kinetic energy or of ability of CO2 to absorb it, as evi- 
 denced by the ionization. 
 
122 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 The question of the chemical action of a rays on solids has 
 not been very thoroughly examined experimentally. As pointed 
 out in §§ 28 and 36, the decomposition of some of the halides of 
 the alkalis and alkaline earths has been investigated with pene- 
 trating radiation and found to be very small, in some cases 
 almost zero. It is very fortunate that all solid substances are 
 not attacked and chemically changed by radium radiations, as 
 it would be impossible to carry out manometric measurements 
 in glass or other vessels or to determine the true volume of 
 radium emanation, if gases like oxygen, for example, were being 
 continually liberated from the glass wall. There is no evidence 
 of such being the case. Radium emanation may be retained in 
 glass without the production of measurable quantities of pres- 
 sure. It is very desirable to extend the investigation of the 
 chemical effects of a rays to other solid substances both crys- 
 talline and colloidal. 
 
 It is interesting to point out that no great deviations have yet 
 been observed of the M/N value for reactions of any substances 
 in the liquid state, that the deviations in the solid state are all 
 in the direction of low values of M/N, while in the gaseous state 
 we have examples of large deviations from unity in both 
 directions. 
 
 51. Energy Utilization of a Rays in Chemical Reactions. 
 
 In the last column of Table VII, § 36, are estimates of the 
 percentage of the total energy of the a rays absorbed in a given 
 system which is utilized by the resulting chemical action. The 
 values have direct significance only in the cases where the reac- 
 tion produced is opposed to the chemical free energy and there- 
 fore requires the expenditure of external energy. Values are 
 also given, however, for the reactions proceeding with the chemi- 
 cal energy, in order to show that with the one large exception 
 of the hydrogen-chlorine reaction, and to a much less degree 
 that of hydrogen-oxygen combination, the order of the values is 
 not very different from those of reactions opposed to the chemical 
 free energy. This indicates that the chemical free energy does 
 not, at ordinary temperature, play an important part in reactions 
 produced by a particles. In other words, it appears necessary 
 to do work on the molecules to render them chemically active, 
 
I 
 
 THE RADIOCHEMICAL EFFECTS 123 
 
 and from the low energy utilization, it is evident that the work 
 of the primary action involves energy quantities very much in 
 excess of the net chemical energy, and that the amount of energy 
 necessary to do this work is of the same order, whether the reac- 
 tion is proceeding with or opposed to the chemical energy. If 
 ionization is the intermediate step involved, this is just what 
 would be expected. Since the energy necessary to form a pair 
 of ions (5.5.10"^^ ergs) is large compared with the chemical 
 energy of reaction referred to a single molecule, the energy trans- 
 formation will be small. For example, if the M/N value is unity 
 for a reaction of which Q = 100 Cals., q or the heat of reaction 
 referred to a single molecule would be 6.10~^^ ergs, and the energy 
 utilization would be about 10%. 
 
 For most of the reactions where expense of energy is actually 
 required the utilization factor is about 2% or less. Warburg ^^ 
 has pointed out that a low order of energy transformation is one 
 of the chief characteristics of photochemical action. Warburg 
 explains this by the assumption of a primary reaction consisting 
 in splitting the molecules into atoms, a process that would require 
 much more energy than that involved in the finally resulting 
 chemical reaction, were it wholly molecular in mechanism. It 
 does not appear at all impossible that free atoms are the inter- 
 mediate products in photochemical reactions, while free ions and 
 electrons may be the intermediate products or agents in reactions 
 produced under ionizing conditions. 
 
 It might be mentioned that the values for energy transforma- 
 tion given in the last column of Table VII vary considerably in 
 reliability. The later values for water formation, and for decom- 
 position of water, ammonia, hydrogen sulfide, and nitrogen pro- 
 toxide may be accepted with assurance. The data involved in 
 most of the other cases are older and perhaps should be verified 
 before they can be accepted with the same degree of certainty. 
 
 52. Chemical Action Produced by Electrical Discharge in 
 Gases. 
 
 The subject of the chemical effects of electrical discharge 
 through gases is too large to be considered in its entirety within 
 the limits of the present work. Attention will be confined to 
 
 "l*:. Warburg, Sitzb. Aka(l. Wi^s. Berlin, pp. 746-64 (X9XX), 
 
124 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 those phases of the subject which are more closely related to 
 radiochemistry and to the ionic theory of gas reactions. 
 
 As soon as it had been shown that ozone formation from oxy- 
 gen is proportional to, and probably statistically equal to, the 
 ionization (§33) both in the cases of a radiation and certain 
 kinds of electronic discharge, the application of the same princi- 
 ple to the broader field of ozone formation by silent, spark, and 
 other forms of electrical discharge, followed naturally. Theories 
 were independently proposed by Kabakjian,^^ by Lind,^^ and by 
 Kriiger ^^ which were practically identical. The generalization 
 was made that probably in all cases ozone formation in gaseous 
 oxygen is the result of the primary ionization of oxygen by some 
 form of electronic discharge. The quantity of ionization involved 
 in the ozone formation is not directly related to the flow of cur- 
 rent, but is the far greater number of ions produced in the gas 
 by electronic shock (§ 16), which never reach the electrodes and 
 therefore take no part in the electrical conduction, since the 
 intensity of ionization far exceeds the limiting conditions for 
 attaining saturation current. This predicts that the quantity of 
 ozone formed should not be related to the current flowing, as 
 required by direct application of Faraday's Law, but should be 
 a much greater quantity. The experiments of Warburg ^^ on 
 ozone formation by silent discharge confirm this fully. Under 
 some conditions Warburg found that about one thousand fold 
 as much ozone is formed as would correspond to the current, or 
 that instead of the theoretical 96,500 coulombs required per 
 chemical equivalent, less than 100 coulombs suffice for the pro- 
 duction of one gram-equivalent of ozone. Hitherto it has not 
 been possible to confirm the theory that the total ozone forma- 
 tion would be accounted for by the ionization by electronic 
 shock, because we have no means of measuring the total ioniza- 
 tion produced. Conversely the conditions under which ioniza- 
 tion by shock have been measured ^" are not suitable for the 
 formation and measurement of ozone. 
 
 Recently the subject of ozone formation in corona discharge 
 
 »D. H. Kabakjian, Phys. Rev., 31, 122-35 (1910). 
 »»S. C. Lind, Trans. Amcr. Electrochem. Soc, 21, 181-3 (1912) 
 "F. Krugor, Phya. Zcit., 13, 1040-3 (1912). 
 
 "B. Warburg, Sitzh. Akad. Wi88. Berlin, p. 1011 (1903); ibid., p. 1228 
 (1904). Ann. d. Physik 20, 734-42 (190G) ; ibid., 20. 751 ct aeq. (190G). 
 " See tbe dlsgusslop of Townse«d"s work in Chapter 4. 
 
I 
 
 THE RADIOCHEMICAL EFFECTS 125 
 
 has been investigated by Anderegg ^^ and by Rideal and Kunz.^^ 
 Anderegg expresses the opinion that oxygen atoms are probably 
 present in all cases of ozone formation, but defers judgment as 
 to whether ozone is formed from oxygen ions. Rideal and Kunz 
 have paid especial attention to the distribution of ozone in the 
 direct current corona of positive or negative sign. Their meas- 
 urements of the quantity of ozone were made by two independent 
 methods, chemical and photometrical. While the quantities of 
 ozone formed in the positive and in the negative corona are 
 approximately the same, the distribution differs in a marked man- 
 ner in the two cases. The various ways in which ozone can be 
 formed in the light of the radiation hypothesis (see following 
 chapter) were also reviewed by Rideal and Kunz, and the con- 
 clusion drawn that molecules of one kind can be activated by 
 radiation to different extents. 
 
 The combination of electrolytic hydrogen and oxygen under 
 the influence of electrical discharge has been investigated by 
 Kirkby.^^ The experimental conditions were regulated sq as to 
 "parallel those employed by Townsend (§§ 16 and 18) in his 
 studies of ionization by collision. Very low gas pressures (a 
 few mms, of Hg) were used. The distance between the electrodes 
 was varied from about 0.25 to nearly 2 cms. Kirkby found that 
 the rate of combination is proportional to the current passing, 
 and that about 4 molecules of HgO are formed per pair of ions. 
 It is very interesting to observe that this number is the same as 
 that obtained by Lind (and practically the same as that of 
 Scheuer) (loc. cit. § 48) for the same reaction under the influence 
 of a particles. Kirkby concluded that hydrogen molecules react 
 with uncharged oxygen atoms, which are dissociated by collision 
 with electrons under certain conditions. Only one half of the 
 collisions of electrons with the necessary velocity actually results 
 in the dissociation of the oxygen molecule. For the action 
 within the positive column Kirkby proposed a general formula: 
 Njj Q = 7.9p.e-*2-^p/Y, in which p is the pressure in mms. and 
 Y is volts.cm-\ The applicability of the formula is independent 
 of the apparatus. 
 
 a^F. O. Anderegg, Journ. Amer. CTiem. Soc. 39, 2581-95 (1917). 
 22 E. K. Rideal and J. Kunz, Journ. Phys. Chem. 24, 379-93 (1920). 
 =3 p. J. Kirkby, Phil. Mag. (6) 7, 223-32 (1904); 9, 171-85 (1905); 13, 
 289-312 (1907) ; Proc. Roy. Sqc. 85A, 151-74 (1911), 
 
126 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 Among other gas reactions produced by electrical discharge 
 may be mentioned the very careful investigation by Davies ^* 
 in LeBlanc's laboratory at Leipzig of the decomposition and 
 formation of ammonia in a Siemens tube. Davies investigated 
 the reaction and equilibrium from the standpoint of the applica- 
 tion of the mass action law. He found that the course of the 
 reaction may be expressed by a first order equation, that the 
 rate of decomposition is approximately proportional to the cur- 
 rent strength, and that the rate of decomposition has a very small 
 temperature coefficient, the rate at 100° being double that at 
 ordinary temperature. Excess of hydrogen was found to lower 
 the rate of decomposition, while excess of nitrogen increased it. 
 Equilibrium attainable from both directions was almost inde- 
 pendent of the current strength and corresponded to ammonia 
 formation to the extent of 6% of the maximum possible. With 
 excess of either component the equilibrium changes in favor of 
 further ammonia decomposition. The law of mass action is not 
 applicable to the equilibrium. The rate of ammonia formation 
 decreases slightly in excess of nitrogen and increases slightly in 
 excess of hydrogen; this result is in accord with those for influ- 
 ence of excess on the decomposition, but are not those that would 
 be expected by analogy with influence of excess of components 
 in water formation by a rays (§ 45), where the excess of lighter 
 gas diminished the rate while excess of the heavier increased it. 
 Falckenberg ^^ and Pohl 2« have studied the decomposition of 
 ammonia in a Siemens tube rather from the physical and elec- 
 trical standpoint and find Faraday's law inapplicable to the rela- 
 tion between current flowing and quantity of ammonia decom- 
 posed. From what has been said previously in regard to ozone 
 formation it is evident that one should not expect any direct 
 relation between the two. To make the statement more general 
 it is quite as unreasonable to expect equivalence between the 
 current flowing and the chemical effect in the case of electrical 
 discharge through gases, as it would be to expect equivalence 
 between the total primary charge of a rays and their chemical 
 effects. In both cases equivalence must be sought in the far 
 greater number of ions produced by collision. 
 
 »*J. H. Davies, Zeit. phys. Chem. 64, 657-85 (1908). M. LeBlanc, Verh. 
 Sachs. Qea. W<««., Leipzig, 60, 3S-63 (1014). 
 3» Falckenberg, Thesis, Berlin (1006). 
 "XI. Pohl, Ann. d. Physik (4) 21, 879 (1906), 
 
THE RADIOCHEMICAL EFFECTS 127 
 
 Further consideration of the experimental data on the chemi- 
 cal effects of the passage of electrical discharge through gases is 
 not within the scope of this work.^^ In its most general aspects 
 the subject may be regarded as having great scientific and per- 
 haps important commercial possibilities which are well worthy of 
 further research. For example, the possibility of an electro- 
 chemical process in which only 100 coulombs are required for 
 the production of one chemical equivalent ought to prove attrac- 
 tive to the electrochemical engineer, provided the energy rela- 
 tions should not prove to be too unfavorable. 
 
 Besides the reactions produced by electrical discharge in gases 
 at ordinary pressure there is a class of reactions observed at low 
 pressures which may or may not be of chemical nature. The 
 ''clean up" of gases in spectrum tubes has been observed for 
 many gases, but is especially puzzling for the gases of the inert 
 series where we can not assume ordinary chemical reactions to 
 take place. Although a mechanical or electrical explanation, 
 such as that discussed for the hardening of X ray tubes (§§ 16 
 and 18) might be proposed, Collie ^^ has recently observed the 
 clean up of pure xenon in a manner very puzzling to explain. 
 Xenon differs from the other inert gases in that heating does not 
 again liberate it from the electrode or "splashed" mirror sur- 
 rounding the electrode. Using platinum, aluminum and copper 
 electrodes. Collie cleaned up more than 2 c. c. of xenon, of which 
 he was unable to recover more than a few per cent even by chemi- 
 cally dissolving the electrodes, the mirror and the glass spectrum 
 tube itself. Collie was almost forced to conclude that xenon 
 had entered into some form of chemical combination from which 
 it was not liberated as gas by the radical treatment employed. 
 Radium emanation has been found by several authorities ^^ to be 
 cleaned up in a spectrum tube in a similar way. Since radium 
 emanation can always be detected by its y radiation it would be 
 very interesting to repeat the experiments of Collie employing 
 emanation instead of xenon to ascertain if any light would be 
 thrown upon the nature of the "clean up." 
 
 The Research Staff of the General Electric Company of Lon- 
 
 27 References to the literature will be found in the paper of Davies (loc. 
 cit.). 
 
 '"J. N. Collie, Proc. Roy. Soc. 97A, 349-54 (1920). 
 
 2« Rutherford, "Radioactive Substances" (1913), p. 482. 
 
128 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 don recently presented ^° the results of an investigation of the 
 disappearance of gas in the electric discharge, from which it 
 appears that the phenomenon is closely connected with the 
 appearance of a glow in the discharge tube, which is believed to 
 result from a reversible chemical action. 
 
 53. Production of Free Electrical Charges by Chemical 
 Action. 
 
 Related to the question of the production of chemical action 
 by ionization is the converse one as to the liberation of charges 
 by chemical reaction. Various opinions have been expressed as 
 to the reality of this phenomenon. There can be no question 
 but that chemical action is often accompanied by the liberation 
 of electrical charges, but whether or not this is ever true in a 
 homogeneous gaseous system where there is no possibility of the 
 accompanying influence of high temperature or of some physical 
 process, requires careful consideration. 
 
 By introducing a gold leaf electroscope directly into a mix- 
 ture of hydrogen and chlorine gases and causing them to react 
 under the stimulation of light, J. J. Thomson ^^ showed most 
 conclusively that no free charges are produced either in the 
 "induction period" or during vigorous reaction. X rays pro- 
 jected intq the same system caused the gold leaf to discharge, 
 proving its sensitiveness, but failed to increase the rate of com- 
 bination of hydrogen and chlorine as observed by the Bunsen 
 and Roscoe actinometer. It might be mentioned parenthetically 
 that this does not prove that X rays do not cause hydrogen and 
 chlorine to react (proportionately to the ionization), since the 
 sensitiveness of the gold leaf discharge to detect ions and that 
 of the Bunsen and Roscoe actinometer to detect the disappear- 
 ance of molecules by diminution in volume are of a wholly dif- 
 ferent order. Klimmell ^^ later thought he had found evidence 
 contrary to that of Thomson, but Thomson's result was con- 
 firmed by a very careful investigation by LeBlanc and Vollmer,^^ 
 
 'ophil Mag. (6) 40, 585-611 (1920). (Conducted by N. R. Campbell and 
 J. W. II. Ryde.) 
 
 »» J. J. Thomson, Proc. Camb. Phil. Soc, 11, 90 (1901) ; "Conduction of 
 Elect. Through l/ases," 2nd Edit., p. 229. 
 
 «»G. Kunimcll, Zeit. Klcktrochem. 17. 409 (1911). 
 
 "M. LeBlanc and M. Vollmer, ibid., 20, 494-7 (1914). 
 
 1 
 
THE RADIOCHEMICAL EFFECTS 129 
 
 who also demonstrated for the first time a chemical effect of 
 X rays in a gas reaction (H2 + CI2). 
 
 On the other hand Haber and Just^* have demonstrated in 
 an extended series of experiments that the action of certain gases, 
 including water vapor, the halides and phosgene, on alloys or 
 amalgams of the alkali metals results in charging the metal 
 positive owing to the liberation of electrons from its surface. 
 Haber and Just demonstrated that temperature has an influence; 
 iodine vapor at —79° C. had no effect, while at +3° there was 
 an effect which became strong at +13°. They showed that the 
 combined effect of light and chemical action emits more electrons 
 than the sum of the separate emissions. Other metals than the 
 alkalis show an effect if the temperature be raised. Aluminium 
 begins to show an effect at 180°, which becomes rapid at 240°. 
 The unipolarity of the effect begins to disappear at higher tem- 
 peratures. Amalgams of Cs, K, and Li gave negative ions 
 instead of electrons. The quantities of electricity emitted were 
 far below Faraday equivalence; for example, the formation of 
 one gram-molecule of KCl was associated with an emission cor- 
 responding to 65 coulombs instead of 96,500. 
 
 In a study of the oxidation of metallic Na, K and alkaline 
 earths, Reboul ^^ showed that the electrical effects accompany- 
 ing these reactions are weak and difficult to detect when the 
 reaction is unaccompanied by some purely physical phenomenon 
 such as emission of light, high temperature, etc. Nevertheless 
 he does not think we are justified in discarding the idea that 
 ionization may accompany all chemical action. Bloch ^^ has 
 repeated some of the earlier gas experiments of Reboul ^^ and 
 concludes that for the reaction NH3 + HCl, ionization is doubt- 
 ful; that none is produced by the reactions: 2NO2 + 0; SO2 + O 
 (contact method) ; H2 + S; S + O2; and decomposition of AsHg. 
 Only the case 2P + 50 gave ionization. Pinkus ^^ employ^ an 
 electroscopic method for two reactions : for 2N0 + O2 he found no 
 ionization ; for the reaction NO + Clg no ionization was found for 
 
 8*F. Haber and G. Just, Ann. d. Phys. (4) 30, 411-15 (1909) ; Zeit. Elektro- 
 chem., 10, 275-9 (1910) ; 17, 592 (1911) ; 20, 483-5 (1914) ; Ann. d. Phys. (4) 
 36, 308-40 (1911). 
 
 s'G. Reboul, Le Eadium, 8, 370-81 (1911). 
 
 38 L. Bloch, Comp. rend. 149, 278-9 (1909) ; Ann. de phys. ct chim., 22, 370- 
 417; 441-495 (1911). 
 
 "G. Reboul, Comp. rend. 149, 110-3 (1909). 
 
 "8 A. Pinkus, Journ. de CJiim. Phys. 16, 201-27 (1918). 
 
130 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 equivalent quantities nor for small excesses of either gas, but 
 for large excess of NO some ionization appeared to occur. 
 Broglie and Brizard ^^ concluded, after an exhaustive study of 
 the evidence, that chemical action produces ionization only 
 when accompanied by a physical reaction such as passage of a 
 gas through liquid, breaking a crystalline surface, luminescence, 
 etc. They state that there is no ionization in the case of reactions 
 of the following classes: (1) Between gases in the cold; (2) double 
 decomposition in liquids; (3) dry decomposition of amorphous 
 substances at slightly elevated temperature; (4) rupture of an 
 inactive surface by bubbling. While there is ionization in the 
 following cases: (1) Gases prepared by wet way; (2) vigorous 
 reactions by projection into water; (3) dry actions accompanied 
 by the decrepitation of crystals; (4) 2Na + (moist), feeble 
 ionization; (5) reactions with incandescence, such as flames, or 
 combustion of metals in Og or Cl^', (6) reactions with lumines- 
 cence, such as the oxidation of P and of quinine sulfate. 
 
 The case may be summed up by stating that we have no 
 definite evidence as yet of the production of ionization or the 
 setting free of electrical charges by any homogeneous gas 
 reaction at ordinary temperature, but that in the case of hetero- 
 geneous reactions or gas reactions at higher temperature we have 
 undoubted cases of the liberation of charges, which may, how- 
 ever, not be directly the result of the chemical action, but the 
 secondary result of some accompanying physical occurrence. 
 
 The determination of ionization produced in gaseous explo- 
 sions has been undertaken by Haselfoot and Kirkby ^^ for elec- 
 trolytic hydrogen and oxygen at 80 mm. pressure, and for 
 ozoimide (HN3) by Kirkby and Marsh.*^ In the former case 
 the M/N ratio was about 10^ and in the latter about 100 times 
 smaller. The explosion method has the disadvantage that what- 
 ever charges are liberated by the reaction are produced suddenly 
 in large quantity so that the attainment of saturation current 
 might be very difficult. However, from the small N/M ratio 
 found it may be fairly concluded that the total liberation of 
 charge is small compared with the number of molecules reacting, 
 
 »»M. Broglie and L. Briznrd. Le Radium 7, 1G4-9 (1910). 
 
 «E. E. Haselfoot and P. J. Kirkl)y, Phil. Mag. (G) 8, 471-81 (1904). 
 
 *ip. J. Kirkby and J. E. Marsh, Proc. Roy. Soc. 87A, 90-99 (1913). 
 
THE RADIOCHEMICAL EFFECTS 131 
 
 because, if N were anything like the same order of magnitude as 
 M, the fields used would have drawn a greater number of ions 
 than was observed to the electrodes before recombination could 
 have occurred. 
 
Chapter 10. 
 Photochemical Equivalence Law. 
 
 54. Einstein's Application of the Quantum Theory to Photo- 
 chemical Action. 
 
 The inclusion of this subject, which does not properly form 
 a part of the present monograph, has a two-fold object: (1) to 
 enable a comparison between certain points of similarity which 
 this branch of photochemistry shares with the other radiochemi- 
 cal effects which have been discussed in the foregoing chapters; 
 and (2) to present the experimental investigations which have 
 been brought to bear upon a test of the photochemical equivalence 
 law since the appearance of the standard works on photo- 
 chemistry. 
 
 It has been recognized by physicists for some time that the 
 idea of the continuity of light as expressed by Maxwell's theory 
 suffices for the explanation of optical phenomena, but that cer- 
 tain other phenomena, such as ionization by light, photolumi- 
 nescence, and "dark radiation," require the introduction of an 
 atomistic conception of radiant energy. This step was taken by 
 Planck in his quantum theory according to which energy is 
 radiated or absorbed only in integral units equal to hv, in which 
 h is the Planck's constant (6.547 x 10"^^ erg. sec.) and v is the 
 frequency of vibration. Einstein ^ has proposed the application 
 of Planck's quantum theory to photochemical phenomena in the 
 following form: N = Q/hv, in which Q is the absorbed heat 
 required for the production of the chemical action, N is the 
 number of molecules dissociated by light of the frequency v. 
 
 In attempting to apply Einstein's law to actual photochemical 
 reactions it is necessary to keep in mind that it applies only to 
 the primary light reaction. As will be seen later, secondary 
 reaction may intervene in such a way that the total quantity 
 
 »A. Einstein, Ann. d. Physik (4) 37, 832-8; 38, 881-4; 888 (1912). Aiso 
 ma. (4) 17, 132-48 (1905). 
 
 132 
 
PHOTOCHEMICAL EQUIVALEifCE LAW 133 
 
 of chemical action resulting from the primary action may be 
 either equivalent to it, or greatly in excess or deficiency, depend- 
 ing upon circumstances. In general it is not possible to measure 
 the quantity of primary reaction directly, but only through the 
 production of some secondary reaction. In order, therefore, that 
 the test of the equivalence required by Einstein's photochemical 
 law shall have any significance it is necessary to be able to 
 measure a secondary reaction which is really equivalent to the 
 primary. From the terminology of photochemistry the term 
 acceptor has been used to designate the substance acted on by 
 the product of the primary light reaction. Evidently the first 
 requisite in testing the photochemical equivalence law is an 
 acceptor which will give a measurable secondary reaction that is 
 equivalent to the primary. There is as yet no theory according 
 to which the action of a given acceptor toward a given primary 
 product can be predicted. It is necessary in each case to try by 
 experiment. Early failures to find "suitable" acceptors for the 
 reactions investigated have rather retarded progress, but as 
 experience is accumulated a more rapid development of the 
 subject may be expected in the future. 
 
 55. Experimental Tests of the Law of Photochemical Equiv- 
 alence. 
 
 Warburg - was one of the first to undertake experiments in 
 this direction and was followed by Bodenstein, Lewis, and yet 
 more recently by Nernst, his co-workers, and others. The results 
 of the earlier work were summarized in 1913 by Bodenstein.^ 
 The following Table XV gives a list of reactions according to 
 Bodenstein which he terms "primary light reactions," in which 
 the number of molecules (M) acted on in the primary action are 
 either equal to hv or exceed it by small multiples. They may 
 be regarded as cases in which Einstein's law is at least approxi- 
 mately applicable. 
 
 At the time that Bodenstein made the classification pre- 
 sented in Table XV he was of the opinion that the primary light 
 reactions are the result of direct action of the positively charged 
 ions left after the removal of an electron from the molecule. As 
 
 " E, Warburg, Extended series of papers in the Sitzb. Berlin Akad. Wisa. 
 See later refs. 
 
 »M. Bodenstein, Zeit. pJiys. Chem. 85, 333 (1913). 
 
134 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELEC^ROi^S 
 
 
 TABLE XV 
 
 
 Primary Light Reactions According 
 
 to Bodenstein 
 
 Reaction 
 
 Authority Absorption 
 
 hv/M 
 
 2HI = H2 + I2 
 
 B.* weak 
 
 ? 
 
 30, = 203 
 
 weak 
 R.^ W.« strong 
 
 lfor203 (measd.) 
 
 2NH3 = N2 + 3H2 
 
 RJ W.« strong 
 
 4 (measd.) 
 
 2H3O = 2H, + 0, 
 
 Not yet measd. without photochemical re 
 combination. 
 
 Anthracene— > 
 
 
 1 to 0.7 (calcd.) 
 
 dianthracene 
 
 L. & W.° medium 
 
 3 (calcd. by B.) 
 
 Decomp. Levulose 
 
 B. & G.^'^ medium 
 
 1.4 (calcd.) 
 
 C,H,NO,CHO^ 
 CeH.NOCOOH 
 
 W. &K." medium 
 strong 
 
 9 (calcd.) 
 
 SX = Sfx 
 
 W.^2 medium 
 
 4 to 5 (calcd.) 
 
 Quinine oxidation by- 
 chromic acid 
 
 L. & F." medium 
 
 1.5 (calcd.) 
 
 203 = 30, (by CI,) 
 
 W.^* medium 
 
 1.7 (calcd.) 
 0.8 (calcd. by B.) 
 
 already stated, on account of the experimental evidence to the 
 .contrary Bodenstein ^^ was forced to abandon his theory and to 
 adopt the idea of Stark ^^ that the primary light effect consists 
 in loosening the valence electrons in such a manner as to render 
 the molecule chemically active. This change of theory in no 
 way affects the applicability of Bodenstein's idea of primary 
 light reactions, for which he prescribes the following character- 
 istics: (1) Proportionality between the quantity of chemical 
 
 ♦M. Bodonstoin, Zoit. phys. Chrm. 22, 23 (1897) ; fil, 447 (1007). 
 
 •E, Uegoner, Ann. d. Phyaik (4) 20, 1033 (190fi). 
 
 «E. Warburg, Sitzh. Akad. Wise. Perlln, 1912, 216. 
 
 '' E. Rogonor, loc. cit. 
 
 «E. Warburg, Sitzh. Alad. ^Vi8s. Berlin, 1911, 74G ; 1912, 210. 
 
 •R. Luther and F. Welgert, Zcit. phys. Chcm., 51, 297; 53; 385 (1905). 
 
 "» I). Berthelot and II. (;audec'bon, Comp. rend. 15(5, 707 (1913). 
 
 " F. Wi'igcrt and L. Kuninicrcr, Ber. 4(), 1207 (1913). 
 
 "A. Wigand, Zvit. phys. Vhem., 11, 423 (1911). 
 
 '» R. Luther and G. S. Forbes, ihid., 41, 1 (1902) 
 
 '«F. Weigert, ihid., 80, 103; Zcit. Elcktrochim., 14, 591 (1908). 
 
 "M. Bodenstein, Zcit. Elckirochrm., 22, 53-01 (1916). 
 
 '•J. Stark, "Atonidynaniik," Leipzig. 1911. Vol. II. p. 207. 
 
I 
 
 PHOTOCHEMICAL EQUIVALENCE LAW 135 
 
 reaction and the absorbed energy — with a corresponding law 
 for reaction velocity. (2) Absence of influence of foreign sub- 
 stances, and (3) absence of influence of temperature, insofar as 
 they do not influence the absorption of light. (4) One molecule 
 reacting for each quantum of energy absorbed or for a small 
 number of the latter. 
 
 Under secondary light reactions Bodenstein classed those 
 which show a great excess over or deficiency from the require- 
 ments of Einstein's theory, and originally assumed that the excess 
 action is due to the multiplied effect of the free wandering elec- 
 trons, as already explained in the previous chapter. Upon being 
 forced to abandon this theory for the same reason as in the case 
 of the primary reactions, Bodenstein makes the assumption that 
 a molecule which has received light energy (in the form of 
 loosened valence electrons) does not lose it on combining with 
 another atom or molecule, but produces a compound which is 
 capable of imparting this energy to certain other molecules with 
 which.it comes into contact. To take the case of the Hg — Clg 
 reaction, he assumes that Clg is activated, combines with ordi- 
 nary H, molecules to form activated HCl which can impart its 
 activity to Clg and to O2 (to explain dissipation of activity by 
 inhibitors), but not to neutral gases like N2, nor to Hg. In the 
 following section will be presented a theory by Nernst assuming 
 atomization of CI2 as the primary action. Without any distinc- 
 tion at present as to which theory has greater probability, Boden- 
 stein's classification of the secondary light reactions has the 
 same experimental weight as it originally carried and is there- 
 fore given in the following Table XVI. 
 
 Luther and Goldberg ^^ have shown that in all the photo- 
 chlorinations investigated by them oxygen acts as an inhibitor, 
 and Bodenstein makes the generalization that oxygen inhibits all 
 the secondary photochemical reactions except those in which it 
 takes part as an oxydizing agent. The data of Bodenstein and 
 Dux ^^ on the kinetics of the photochemical interaction of hydro- 
 gen and chlorine served as a basis for Bodenstein's general photo- 
 chemical theory, which he then applied to other photochemical 
 reactions with the following modifications, which have been 
 
 "R. Luther and E. Goldberg, Zeit. phys. Chcm., 56, 43 (190G). 
 '8M. Bodenstein and W. Dux, ibid., 85, 297-328 (1913). 
 
136 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 transformed by the writer into terms corresponding to his later 
 theory instead of the original electronic theory: 
 
 (1) It is not always the substance primarily acted on by light 
 which becomes activated for the secondary reaction. 
 
 (2) The velocity of the secondary effective reaction is not 
 always excessively large compared with the ineffective reversion 
 of the primarily affected substance to its original form. 
 
 (3) The secondary reaction is not always so great that the 
 primary one can be neglected in comparison, as in the case of 
 hydrogen and chlorine. 
 
 (4) Oxygen inhibition can be absent in case oxygen is the 
 substance activated in the secondary reaction. 
 
 (5) Other substances can act as inhibitors and either take 
 the place of or act jointly with oxygen. 
 
 In Table XVI the reactions are divided by Bodenstein into 
 three classes: I. Those in which oxygen acts as inhibitor. II. 
 Those in which oxygen is one of the components of the reaction 
 and does not inhibit. III. Those in which the primary reaction 
 can not be neglected in comparison with the secondary reaction. 
 lo refers to the light absorption by A, the substance primarily 
 acted on. B is the substance activated in the secondary reaction. 
 C is in some cases a third reacting substance, dx/dt indicates 
 velocity of chemical reaction in the usual differential form. 
 
 Recently a more rigorous test of Einstein's photochemical 
 equivalence law has been made by Nernst ^^ and Frl. Pusch.^^ 
 Nernst emphasizes the necessity of paying attention to the pri- 
 mary reaction and of choosing an acceptor which neither multi- 
 plies nor diminishes the products of the primary action, but 
 directly transforms them into the equivalent quantity of finally 
 measured product. Frl. Pusch found hydrogen to be a very 
 unsuitable acceptor in its reaction with bromine, the amount of 
 action falling far short of theory. In an experiment with solar 
 radiation of ten hours' duration, the quantity of bromine com- 
 bined was 0.02 g., where 2.3 grams were predicted by theory. In 
 experiments with a "nitra" (nitrogen filled) lamp as source of 
 light, it was found that heptane, hexane and toluene all combine 
 with bromine at a rate greater than theory, but hexahydroben- 
 
 »»W. Nernst, Zeit. Elektrochem., 24, 33r>-G (1918). 
 «»Frl. L. Pusch, ibid., 24, 33G-9 (1918). 
 
PHOTOCHEMICAL EQUIVALENCE LAW 
 
 137 
 
 ^ o 
 
 .< o ^ o o 
 
 ^>. O I o o 
 
 ^ ^ b 
 
 ss 
 
 o o o 
 o o o 
 
 to 
 P o 
 
 
 o 
 
 '^ 
 
 ^n, 
 
 
 
 
 lod 
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 q 
 
 o 
 ' + 
 
 B 
 
 PhO 
 
 WW 
 
 
 1^ -^ 
 
 ^^ 
 
 
 
 m 
 
 o. d 
 
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 O 
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 11 
 
 
 n 
 
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 IN 
 
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 1 
 
 
 M C> 
 
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 H 
 
 C3 
 <a3 
 
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 so 
 
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 o 
 
 
 C4 
 
 o 
 p 
 
 o 
 
 §°d 
 
 N 
 
 1— 1 
 1 
 
 CD 
 
 
 
 o 
 
 hH 
 
 1^ 
 
 
 CI 
 
 CI 
 
 
 C4 
 
 00 
 CI 
 
 r-l 
 CO ^ 
 
 .|-H N 
 
 CO W 
 
 
 
 ^ PQ 
 
 P4 
 
 w 
 
 m 
 
 
 
 ^ 
 
 
 Plh Ph 
 
 
 
 
 
 
 
 
 
 
 
 
 q, 
 
 
 
 
 
 
 
 
 
 So 
 
 Ph 4- 
 
 Wq 
 
 
 
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 ^ 
 
 s 
 
 d" 
 
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 -§> 
 
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 bD 
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 CI 
 
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 + 
 
 d' 
 
 CO 
 
 II 
 
 
 
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 c 
 
 1—! 
 
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 + 
 
 1—1 t— ' 
 
 
 
 
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 >^ 
 
 X 
 
 s 
 
 ^^ 
 
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 M 
 
 w 
 
 o 
 
 p 
 
 o* 
 
 s 
 
 '^ u 
 
138 THE CHEMICAL EFFECTS OP ALPHA PARTICLES AND ELECTRONS 
 
 h 
 
 .^ 
 
 <-- CO 
 fl « • 
 
 II .-^ 
 
 o 73 
 
 rg*^ 
 
 o 
 o 
 
 
 
 O 
 
 eo g 
 
 o 
 
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 m 
 
 ^4 
 
 o 
 
 W5 ^-v 
 
 00 «o 
 
 <N 
 
 00 
 
 =3 ss. ^ 
 
 •" g »1 
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 itPQ 
 
 + 
 
 pq 
 
 o 
 
 + 
 
 
 CI CO 
 
 2 § 
 
 00 |co 
 
 to ^ w 
 
 .si 
 
 (-1 rH 
 
 
 
 l5 
 
 rsi a 
 
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 ^ is 
 
 m Nj 
 
 m K !_; 
 
 S w £ 
 s a s 
 
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 Ah r 
 
 ^ S"^*? 
 
 
 
 ^ 
 
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 « 
 
 rc: 
 
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 Gi 
 
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 00" 
 
 1 
 
 to 
 
 10 
 
 <- 
 
 
 ■e 
 
 
 
 •<-» 
 
 
 
 rO 
 
 x 
 
 
 
 IS3 
 
 1 
 
 ^ 
 
 
 
 i-3 ~ d -^ "n 
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 « 8 
 
 
 K^M^ 
 
 ptH U fa 
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 Sill 
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 8 S & 
 
PHOTOCHEMICAL EQUIVALENCE LAW 
 
 139 
 
 zene appeared to be a suitable acceptor, and the following results 
 were obtained by Frl. Pusch for several different exposures. 
 
 TABLE XVII 
 
 Test of Photochemical Equivalence Law, According to Frl. Pusch 
 Reaction: Bromine + Hexahydrobenzene. 
 
 
 Milligrams of Bromine Combined 
 
 Hours 
 
 (Found) 
 
 Calcd, 
 (Einstein's Law) 
 
 8.25 
 22.33 
 20.25 
 24.25 
 24.00 
 
 2.08 
 5.95 
 6.72 
 5.66 
 5.82 
 
 1.82 
 5.38 
 5.10 
 5.70 
 5.51 
 
 Since the appearance of Bodenstein's classification, Warburg 
 has tested the applicability of Einstein's law for a number of 
 additional reactions. For the decomposition of ozone *^ he finds 
 that, in dilute mixtures where the total pressure is one atmos- 
 phere, the secondary reaction furnishes a new confirmation of the 
 law. Photolysis in aqueous solution was examined in the case of de- 
 composition of nitrates to nitrites *^ using three wave lengths sep- 
 arately of the zinc arc: A, = 0.214, 0.257, and 0.274^, respectively. 
 The reaction was faster in slightly alkaline than in acid solution, 
 was independent of the cation and of the degree of electrolytic 
 dissociation. Einstein's law was not followed, the reaction being 
 greater for short than for long wave lengths. The effect of the 
 solute was suggested as the probable cause. The conversion of 
 isomers was examined for the reactions: maleic -^ fumaric acid 
 and the reverse action.*^ The chemical action found was about 
 4-13% of theory. The rate for maleic -^ fumaric increased with 
 increase of X but in a much greater ratio. The rate of the 
 reverse reaction showed the opposite effect, thus contraverting 
 
 I 
 
 *o E. Warburg, Bcr. Berlin Akad. Wiss. 
 "E. Warburg, ihid., 1918, 1228-4G. 
 *2E. Warburg, iMd., 1919, 960-74. 
 
 1913, 644-59. 
 
140 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 the Einstein law. The effect of concentration was not great. 
 Further tests in the case of ammonia decomposition ^^ showed 
 that either the law does not apply or that much ammonia is 
 reformed. The application of the law was also not successful 
 for the photolysis of HBr.** 
 
 56. Comparison of Photochemical Equivalence Law and Ionic- 
 Chemical Equivalence. 
 
 Reference to Tables VII, XV and XVI will show that we have 
 the same kinds of variation between theory and experiment both 
 in photochemical and in a ray reactions. In both we have a 
 number of experimentally investigated reactions in which agree- 
 ment with theory is as good as could be expected in the present 
 status of experimentation. We also have in both cases large 
 departures from theory in either direction. On account of these 
 points of similarity the question naturally presents itself as to 
 whether the mechanism of reaction is not identical for the two 
 different forms of radiation. 
 
 The most striking case of greatly excessive action among 
 those hitherto investigated by a radiation has been shown to be 
 that of hydrogen and chlorine where reaction exceeds theory by 
 something like 10*. Among the photochemical reactions we find 
 the same reaction exceeding theory by 10®. Bodenstein {lac. cit.) 
 has expressed the view that the same mechanism must control 
 both reactions. It would be of great interest to measure the 
 increasing activity of hydrogen-chlorine mixtures with different 
 forms of radiation to see whether the reactivity increases in the 
 same proportion for all. 
 
 To explain the mechanism by which such large excess over 
 theory can be attained, we have first the free electron theory of 
 Bodenstein, which had to be abandoned as an explanation of 
 photochemical effects, on account of the experimental demonstra- 
 tion of the absence of free electrons; but which may still hold 
 for the a ray reactions, unless it be admitted with "Bodenstein, 
 that by analogy the same mechanism must hold for both. Sec- 
 ond, we have the theory of loosened electrons of Stark for which 
 Bodenstein has made the assumption that the light energy is 
 retained after reaction and is imparted to other molecules, ren- 
 
 «E. Wnrburjr, lirr. Berlin A had. Wiss., 1914, 872-85. 
 " E. Warburg, ibid., 1916, 314-29. 
 
PHOTOCHEMICAL EQUIVALENCE LAW 141 
 
 dering them active. While there may be some question as to the 
 probability of this theory, it has the advantage of very general 
 applicability. In the following section it will be seen that Nernst 
 has proposed an atomistic theory to account for the hydrogen- 
 chlorine reaction, which is based on purely thermodynamic con- 
 siderations. While it has great probability for that specific reac- 
 tion it appears to be inapplicable directly to the other cases of 
 excessive reaction. W. C. M. Lewis has proposed a radiation 
 theory which is discussed in § 58. 
 
 The cases in which large deficiencies from theory are observed 
 have all been explained up to the present by immediate reversal 
 of the primary reaction. In this sense, an acceptor is a substance 
 which combines with the products of the primary reaction with- 
 out allowing them to recombine among themselves. On the 
 other hand, the additional condition must be imposed upon a 
 ''suitable" acceptor, from the standpoint of photochemical equiv- 
 alence, that it shall not by any other process multiply the output 
 of the primary reaction. 
 
 57. Mechanism Proposed by Nernst for the Hydrogen-Chlor- 
 ine Photo-Reaction. 
 
 Nernst has recently applied his heat theorem *^ to calculate 
 the following heats of reaction: 
 
 CI + CI = CI2 + 106,000 cal. 
 
 H + H = H2 + 100,000 cal. 
 
 CI + H2 =: HCl + H + 25,000 cal. 
 
 H + CI2 = HCl + CI + 19,000 cal. 
 
 and H + CI = HCl + 125,000 cal. 
 
 From the known absorption of chlorine for light of different 
 wave lengths it can be calculated by the quantum theory within 
 what spectral region chlorine can be dissociated into atoms. 
 The calculation shows that this can be accomplished by the 
 wave lengths known to produce chemical combination of hydro- 
 gen and chlorine and the assumption of the existence of free CI 
 atoms for the propagation of the photo-reaction is therefore 
 justified. The heat of reaction shows that the combination of 
 a CI atom with a Hg molecule and the subsequent splitting of 
 
 «W. Nernst, Sitzh. Berlin Akad. Wiss., 1911, Go-90 ; also "Gruudlagen d. 
 neuen Warmesatzes" (1918), p. 133. 
 
142 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 this unstable product to HCl and a free H atom take place with 
 a large heat evolution, and therefore in the direction of sponta- 
 neous reaction according to the chemical free energy. Moreover, 
 when a free H atom (just produced by the foregoing reaction) 
 unites with a CI2 molecule we again have a reaction of the same 
 nature. The CI atom liberated by the latter reaction brings us 
 back to the original system, and a cycle has been completed 
 which may repeat itself indefinitely, except for the cross reaction 
 of H and CI atoms, and for the inhibitive effect of oxygen, which 
 is assumed to remove the free CI atoms from the field of action. 
 By this purely thermodynamic method Nernst explains the multi- 
 plied secondary reaction in a mixture of Hg and CI2, which 
 accounts for the large departure from Einstein's law through the 
 action of free atoms. In further support of the theory, Nernst 
 calculates that a similar continuous cycle in the case of hydrogen 
 and bromine is impossible, because one of the steps, Br + Hg, 
 would not proceed spontaneously on account of a negative heat 
 of reaction, —15,000 cals. And of course it is well known that a 
 mixture of H2 + Brg is not light sensitive at ordinary tempera- 
 ture. The further application of this or similar mechanisms to 
 explain other cases of excessive action has not been attempted, 
 but it is not without interest to note that in the only other two 
 cases where the M/N value is as high as 10^ (Table XVI), we 
 have halide and hydrogen present in the system. 
 
 58. General Radiation Theory of Chemical Action. 
 
 In an extended series of investigations, Lewis and his co- 
 workers ^® have proposed a radiation theory of chemical action 
 which appears to be of fundamental importance in chemical 
 kinetics, and which also has afforded additional confirmation of 
 the applicability of Einstein's law. A general review of Lewis's 
 theory and his deductions from it is pertinent to the subject of 
 the present chapter. 
 
 It has long been recognized that the usual positive tempera- 
 ture coefficient of chemical reaction, which is of the order of a 
 
 *«A. Lamble and W. C. McC. Lewis, Journ. CJtcm. Soc. Lond., 105ji , 2330-42 
 (1914); 107,, 233-48 (1915). R. H. Callow and Lewis, ihid., 109,-, 55-07 
 (1916). R. O. Griffith and Lewis, ihid., 109,, 67-83 (1910). Lewis, ihid., 109„, 
 796-815 (1916). R. O. Griffith, A. Lamble and Lewis, ihid.. Ill,, 389-95 (1917). 
 Lewis, ihid., 11,, 457-09; 111,,, 1086-1102 (1917); 113, 471-92 (1918); 115, 
 182-93 (1919) ; Rep. Brit. Assoc. (1915), p. 394. 
 
PHOTOCHEMICAL EQUIVALENCE LAW 143 
 
 2 to 3 fold increase for an interval of 10*^0., can not be explained 
 by the mere increase of kinetic energy of the reacting molecules. 
 It has also been rather generally assumed that the molecules, 
 before they react, must in some way be activated, and that this 
 process is the one influenced by increase of temperature. 
 
 In 1889 Arrhenius *^ deduced a relation based on the assump- 
 tion of a mass action equilibrium between active and inactive 
 molecules, of the form: d log k/d T = A/T^, in which k is the 
 velocity constant of chemical action, T is the absolute tempera- 
 ture, and A is one half of the energy required to change 1 Mol 
 of inactive to active modification. This formula has since been 
 shown to be of very general experimental applicability, although 
 its theoretical basis is no longer tenable for the following reasons. 
 The conception of Arrhenius, or indeed any other theory that 
 attempts to explain velocity of reaction as controlled by tempera- 
 ture, leads directly to the consideration of the effect of catalysts, 
 and that of Arrhenius to the prediction that the temperature 
 coefficient should be diminished in a homogeneous system by 
 the increase of the concentration of the catalyst. This predic- 
 tion has not been confirmed by later work, including that oif 
 Lewis, who found that the temperature coefficient of the rate of 
 hydrolysis of methyl acetate is independent of the concentration 
 of acid. Recent work of Taylor *^ in the laboratory of Arrhenius 
 has cast further doubt upon the existence of "active" molecules 
 (in the sense of Arrhenius). 
 
 In 1914 Marcelin*^ treated the effect of temperature on 
 velocity of reaction as a purely physical one dependent on 
 the increase of the internal energy of the reacting molecule, 
 and arrived at a formulation similar to that of Arrhenius: 
 d logk/dT = E/RT^, in which E is defined as the critical energy 
 that must be absorbed by the molecule to render it active. Lewis 
 suggests that E be called the critical increment to emphasize 
 that it is the excess energy that must be absorbed by the acti- 
 vated molecules above the average energy possessed by all 
 molecules. 
 
 Rice^° has developed in more exact mathematical form 
 the same equation: d logk/dT == (V «-¥„,+ 1/2 (RT) )/KT\ in 
 
 1*^ Sv. Arrhenius, Zeit. phys. Chem., 4, 226-48 (1889). 
 " H. S. Taylor, Mcdd. Vetemkcipsakad. NoJ)cUnst. 2, No. 34 (1912). 
 *»R. Marcelin, Comp. rend. 158, 161 (1914). 
 •oj. Rice, Rep. Brit. Assoc. (1915), p. 397. 
 
144' THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 which Y^ is the mean value of the potential energy of the mole- 
 cules and V^ is the critical value which must be attained before 
 chemical reaction ensues. Rice's formulation was used by Lewis 
 in the development of the radiation theory applied to catalysis 
 and later to chemical action in general. The application to 
 catalysis has been adopted and explained by Rideal and Tay- 
 lor." 
 
 Lewis {loc. cit.) advances the hypothesis that the energy 
 increment is imparted to the molecule by means of infra- 
 red radiation, and that the Einstein Law is applicable to 
 the energy absorption. The energy increment can be calcu- 
 lated directly from the temperature coefficient, as follows: 
 logkgs/kgg = E/R( 1/298— 1/308). For the hydrolysis of methyl 
 acetate the coefficient for a 10° interval at ordinary temperature 
 is about 2.5, from which E is calculated to be 16,800 cals. per 
 g.mol., or 1.03x lO'^^ergs per single molecule. From Einstein's 
 law Lewis calculates that for the infra-red radiation of X := 7.5^ 
 for methyl acetate (Coblentz ^^), hv should be 0.262 x 10"^^ gj-gg^ 
 or that 4hv should suffice to furnish the required energy E. Con- 
 versely Lewis has calculated from the velocity of the H ion 
 (electrolytic) and its probable free path that it would have a 
 vibration frequency falling in the region of the known absorption. 
 
 Lewis's suggestion that catalysis is in general a radiation 
 phenomenon is supported by the theory of Trautz °^ and later by 
 that of Kriiger,^* who showed that the processes of solution, 
 solution pressure, solubility and electrolytic dissociation can be 
 explained on the basis of radiation, which in turn can be related 
 to the dielectric constant of the solvent. According to Lewis's 
 conception the function of a catalyst is to absorb the infra-red 
 radiation of the chemical system and to transfer the energy to 
 the reacting molecule. In this sense catalysis is evidently but a 
 special case of chemical reaction, where the absorption is accom- 
 plished by the catalyst instead of by the reacting substance 
 itself. All reactions taking place in a solvent must be regarded 
 as catalytic. 
 
 A still further step has been taken by Lewis (loc. cit.) in 
 
 »'E. Rldeal and H. S. Taylor, "Catalysis in Theory and Practice" (1919), 
 p. 58 et acq. 
 
 w W. W, Coblentz, Pub. Carnegie Inst., Washington, 1905, 35. 
 MM. Trautz, Zcit. xriss. Phot., 4, IGO (1906). 
 "H. KrUger, Zcit. ElcJctrochcm., 17, 453 (1911). 
 
 i 
 
I 
 
 PHOTOCHEMICAL EQUIVALENCE LAW ' 145 
 
 applying his theory to uncatalyzed homogeneous gas reactions. 
 Strictly, Einstein's law is applicable only when n (index of 
 refraction) = 1, which is true only in the case of gases. Lewis's 
 theory applies to bimolecular homogeneous reactions of the type 
 2HI = H2 + 12, with a fairly good agreement with the Einstein 
 law. Heterogeneous (contact) catalysis can also be explained 
 by Lewis's theory on the basis of Langmuir's ^^ hypothesis regard- 
 ing the spacial distribution of molecules and atoms at the inter- 
 face between two phases. The energy increment is lowered at 
 the contact surface, which is in agreement with the lower tem- 
 perature coefficients of heterogeneous chemical reactions. 
 
 Lewis ^^ has recently pointed out the anomalous case of mono- 
 molecular homogeneous gas reactions, which differ from the bimo- 
 lecular reactions in the pronounced failure of Einstein's law. 
 The value of the velocity constant for the rate of dissociation of 
 PH3 observed by Trautz and Bhandarkar ^^ is about 10^ greater 
 than calculated by Lewis from Einstein's law on the assump- 
 tion of continuous absorption. For discontinuous absorption the 
 discrepancy becomes still greater. In view of the approximate 
 agreement for bimolecular, reactions this great departure for 
 monomolecular reactions is all the more notal^e. 
 
 Baly ^^ has applied the quantum theory to spectroscopic and 
 fluorescent phenomena. According to his theory a molecule may 
 absorb radiation by quanta of a given frequency and radiate a 
 larger number of quanta as a result of chemical action at a lower 
 frequency. Chemical action, excessive from the standpoint of . 
 Einstein's law, can then be explained by re-absorption of- this 
 internal radiation, a process that will result in further chemical , 
 action that may be multiplied to very large quantities from one 
 quantum primarily absorbed. Baly proposes this explanation for 
 the large excess observed in the thermal decomposition of phos- 
 phine and also for the photochemical decomposition of hydrogen 
 peroxide and hydrolysis of acetone.^^ , 
 
 It should be mentioned that Perrin ^° independently arrived , 
 
 "I. Langmuir, Journ. Amer. Chem. 8oc. 38, 2221 (1916). 
 
 ^W. C. McC. Lewis, Phil. Mag. (G) 39, 2G-31 (1920). • , 
 
 57 M. Trautz and D. S. Bhandarkar, Zeit. anorg. Chem. 106, 95 (1919) 
 
 WE. C. C. Baly, Phil. Mag. (6) 40, 1-15; 15-31 (1920). 
 
 6«V. Henri and R. Wunnser, Com/), rend. 15(5, 1012 (1913). 
 
 *»J. Perrin, Ann. de Physique (9) 11, 5-108 (1919). 
 
146 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 at a general radiation theory of chemical action which is very 
 similar to that of Lewis. 
 
 The type of radiation that is involved in Lewis's theory is 
 very different from the corpuscular forms that are treated in 
 this monograph and also from those of the usual photochemical 
 effects. In the infra-red absorption the energy increment is not 
 a large fraction of the chemical energy of the reaction, whereas, 
 in the case of the corpuscular and photochemical radiation effects, 
 the energy applied is usually largely in excess of the net chemical 
 energy involved in the reaction. 
 
 With reference to the emission of infra-red radiation by chem- 
 ical reactions, the recent work of David ^^ should be cited, who 
 has shown that the explosive combination of oxygen with coal 
 gas and with hydrogen results in the emission of radiation of 
 wave lengths X = 2.8^i and 4.4pi. Although the temperature of 
 reaction in the experiments of David is estimated at 1200°, he 
 is of the opinion that the radiation is due to the chemical action 
 and not to temperature effect. 
 
 Further contributions to the radiation theory of chemical ac- 
 tion have been very recently made by Langmuir,^^ Rideal,"^ 
 Lindemann ^* and Tolman.®^ Langmuir makes a fundamental in- 
 quiry into the basis of the radiation hypothesis of chemical ac- 
 tion and concludes (1) that it has not been satisfactorily demon- 
 strated that the radiation emitted by a chemical action, as cal-. 
 culated from the temperature coefficient, falls in the absorption 
 region of the system; (2) that the total radiation is not nearly 
 sufficient to account for chemical activation and that the radia- 
 tion hypothesis is untenable. Langmuir believes that the in- 
 ternal energy of the molecule is the ultimate source of its acti- 
 vation. Lindeman points out (as does Langmuir also) that ac- 
 cording to the radiation hypothesis many reactions should be 
 photo-sensitive which fail to exhibit this effect; Tolman adopts 
 the view of Lewis, Perrin and Marcelin that the similar form 
 of the Arrhenius equation and the Wien radiation law justifies 
 the radiation hypothesis of chemical action. Tolman employs 
 
 "W. T. David, Phil. Mag. (6) 39, 66-83; 84-95 (1920). Trans. Roy. Soc. 
 Lond., 211, 375; Proc, 85, 537 (1911). 
 
 ~I. Lnngmuir, J. Am. Chem. Soc, 42, 2190-2205 (1920). 
 "Eric K. Rideal, Phil. Mag. (0) 40, 461-6 (1920). 
 •*F. A. Lindemann, ihid. (6) 40, 671-4 (1920). 
 »P, C. Tolman, J. A^n. Ch^m. Soc, 42, 2506-?8 (1980), 
 
PHOTOCHEMICAL EQUIVALENCE LAW 147 
 
 the principles of statistical mechanics to develop the Rice- 
 Marcelin equation and also makes many other applications im- 
 portant to chemical kinetics. Rideal employs a formula of 
 Langmuir and Dushman to develop the equation for velocity of 
 
 dn -hy 
 
 reaction: -— = y.e kt , in which n is the number of molecules 
 dt 
 
 reacting per second, v is the frequency, and all other symbols 
 having the usual meaning. Applying this to the decomposition 
 of PHg, the velocity constant is calculated to be 3.5 x 10"^, the 
 same order of magnitude as that observed 10.2 x 10"^. 
 
 Daniels and Johnston ^^ have recently investigated the ther- 
 mal and photochemical decomposition of gaseous NgOg. The 
 thermal action is monomolecular and proceeds at room tempera- 
 ture. The critical increment as calculated from the temperature 
 of the velocity of decomposition is independent of the tempera- 
 ture. Its value, 24,700 calories, indicates according to the radi- 
 ation theory that the reaction should be catalyzed by light of 
 wave length = 1.16^1. Photochemical investigation failed to con- 
 firm this prediction. Light in the region 400— 460np, does accel- 
 erate the decomposition, but only in the presence of NOg. The 
 interesting theory is proposed that the catalytic effect of NO2 
 is due to its absorption of blue light over a wide spectral range 
 and that through fluorescence, radiation is emitted in the infra- 
 red region where its absorption lines coincide with those of NgOg, 
 causing decomposition of the latter. Experimental evidence of 
 the actual fluorescence of the NO2 and of the decomposition of 
 N2O5 by radiation in the infra-red region remains to be obtained. 
 
 80 F. Daniels and E. H. Johnston, J. Am. Chem. Soc., 43, 53-81 (1921). 
 
Chapter 11. : 
 
 Positive Eays and Eecoil Atoms. 
 
 59.' General Nature of Positive Rays. 
 
 In 1886 it was observed by Goldstein^ that if he used a per- 
 forated cathode in examining electrical discharge through air at 
 low pressure, luminous beams of rays could be seen traversing the 
 space back of the cathode, t. e. on the side away from the anode, 
 which apparently came through the channels in the cathode. 
 On account of their mode of formation or demonstration Gold- 
 stein called them "canal" rays. It has since been shown that 
 they are the positively charged gaseous ions which, at low gas 
 pressure, attain sufficient velocity toward the cathode or nega- 
 tive pole to carry them through the perforations into the space 
 behind, where they can be observed by means of phosphorescent 
 screens or by their action on the photographic plate. 
 
 In 1898 Wien ^ demonstrated the deflection of the canal rays 
 by a strong magnetic field. Since this time J. J. Thomson ^ has 
 conducted a series of investigations which have resulted in dis- 
 coveries of the greatest importance both to physics and chemis- 
 try. It has been recommended by Thomson* that the more 
 correctly descriptive term, positive rays of electricity, be used 
 instead of canal rays. 
 
 Thomson * has elaborated a technique to determine by means 
 of deflection in a combined magnetic and electrostatic field the 
 e/m value of each type of positive ray. The effects due to the 
 superposition of the electric and magnetic fields simultaneously 
 applied have been analyzed by Thomson in the following way: 
 If the forces are applied parallel to the axis of z, the y and z 
 defiections of the particle are given by the two equations: 
 
 IE. Goldstein, 8Uzb. Aknd. Wias., Berlin, 1886, p. G91 ; Wied. Ann., 04, 38 
 (1898). 
 
 «W. Wien, Verh. deut. phya. Qea., 17, .. (1898). 
 
 •J. J. Thomson, Phil. Mag. (G) 21, 225-49 (1911) ; 24, 209-53 (1912). 
 
 *J. J. Thomson, "Rays of Positive Electricity" (1913). 
 
 148 
 
POSITIVE RAYS AND RECOIL ATOMS 149 
 
 y = e/mv.A and z = e/mv-.B, in which A and B depend only on 
 the strengths of the magnetic and electrical fields, respectively, 
 and the distance of the projection from the point of deflection, 
 and can be made constant for a given experiment. In the absence 
 of any field all positive rays would pass through the narrow 
 aperture in the cathode and be recorded on the photographic 
 plate at the same spot x = 1, the distance of the plate from the 
 source. Under the selective action of the two forces the particles 
 are sorted out and no two strike the plate at the same spot unless 
 they are moving with the same velocity and have the same e/m 
 value. By combining the two equations just given above we 
 have: v = y/z.B/A and e/m = yVz-B/A^. The first shows that 
 y/z is constant for all particles moving with a given velocity v, 
 no matter what their charge or mass is, and, therefore, will all 
 lie on the plate in a straight line passing through the undeflected 
 position of the particles. The second equation shows that for 
 the same kind of particles, y Vz is constant no matter what their 
 velocity; hence, all particles of the same kind will trace on the 
 plate a parabola with its vertex at the undeflected position of 
 the particles. Each parabola will represent a different kind of 
 particle. This principle has been used by Thomson and his 
 co-workers as a method of positive ray analysis, which will be 
 described in the following section. 
 
 60. Thomson's Method of Positive Ray Analysis. 
 
 Thomson's experimental method has been very fully described 
 in his ''Rays of Positive Electricity." The latest modiflcation 
 of the apparatus, termed mass-spectrograph, has recently been 
 thoroughly described by Aston.^ Only a few of the most 
 important experimental features will be mentioned here before 
 passing on to a consideration of the results. A very large 
 spherical bulb (20 cms. diameter) is employed for the discharge 
 between the anode and cathode in order to favor the passage of 
 current at very low pressure. A silica anticathode is used which 
 has the advantages of infusibility and of giving no disturbing 
 X radiation. The two cathode slits which give direction to the 
 beam of positive rays are of aluminium 2 mm. long and 0.05 mm. 
 wide. The space between the slits 10 cms. long is kept at the 
 
 •F. W. Aston, Phil. Mag. (6) 39, 611-2G (1920). 
 
150 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRON^ 
 
 highest possible vacuum by a side tube of charcoal immersed in 
 liquid air. Beyond the slit system is the electrical field, 200 to 
 500 volts, between two flat brass surfaces 2.8 mms. apart and 5 
 cms. long. Beyond the electrical field is the magnetic field in 
 which the rays pass between the pole pieces of a large DuBois 
 magnet of 2500 turns, the faces of which are circular, 8 cms. in 
 diameter and 3 mms. apart. The current for the magnet is pro- 
 vided by a set of large accumulators. A current of 0.2 ampere 
 jiist brings the H lines onto the plate, while 5 amperes just 
 bring the singly charged Hg lines into view. The camera cham- 
 ber is provided with a special plate holder arranged so that the 
 plate can be shifted for several different exposures without open- 
 ing the chamber. Exposures from 2iO seconds for the H lines, up 
 to 30 minutes or more are required. The discharge in the large 
 chamber is maintained by means of a large induction coil with 
 a Hg coal-gas break. 100 to 150 watts are passed through the 
 primary circuit, and the bulb itself takes 0.5 to 1.0 milliampere 
 at 20,000 to 50,000 volts. 
 
 The measurement of the photographic plates to determine 
 the mass of the positive rays is made by means of a special 
 comparator capable of measuring in two directions. Theoreti- 
 cally an unknown mass may be determined from one known on 
 the same plate, but practically, greater accuracy is obtained by 
 bracketing the unknown with several known lines just as in 
 ordinary spectral line measurements. 
 
 The photographic method does not yield an insight into the 
 relative quantities of the different rays. This has been accom- 
 plished by Thomson by substituting for the camera a Wilson 
 tilting electroscope to determine the total charge under the 
 following conditions. The condenser into which the positive rays 
 are received is provided with a parabolic slit, which in principle 
 might be moved to any part of the field to admit rays of a given 
 mass for quantitative measurement by means of their charge. 
 Instead of actually moving the slit it is made stationary and the 
 rays of different masses are successively brought to it by varying 
 the magnetic field strength. 
 
 Thomson has determined the various types of ions which are 
 produced in different gases. The variety of ions for a given sub- 
 stance is very large compared with electrolytic ions. Certain 
 characteristics have been pointed out by Thomson which are 
 
I 
 
 POSITIVE RAYS AND RECOIL ATOMS 151 
 
 very useful in determining what mass is represented by a given 
 m/e value. Multiple charge is found only in the case of atoms." 
 Molecules either of elements or of compounds have not been found 
 to be multiply charged with either sign.^ The heavy atoms show 
 multiple charge to a higher degree than do the lower ones. 
 There is no apparent relation between the chemical properties 
 of the element, such as valence and the number of charges. 
 Mercury can have as many as eight charges, oxygen, nitrogen, 
 and neon two; hydrogen never more than one, which is the only 
 element examined for which no multiple charges have ever been 
 found. 
 
 61. Isotopes of Neon. 
 
 As early as 1912 Thomson obtained some evidence by the 
 positive ray method of the existence of particles of mass 22 in 
 neon gas. Aston ^ has recently determined the mass spectra of 
 neon by the positive ray method with an accuracy of 1 in 1000 
 parts. The measurements show conclusively that neon consists 
 of two isotopes of masses 20 and 22, in the proportion of about 
 nine of the former to one of the latter, which accounts for the 
 observed atomic weight 20.2. There is also a faint indication of 
 a third isotype of mass 21 in a proportion estimated as less than 
 1%. If this third isotope proves to have real existence it will 
 constitute a very interesting continuation of the system of triads 
 like iron, nickel and cobalt, which was predicted in 1895 by 
 Reynolds,® purely from analogy with the three other well known 
 groups of triads. 
 
 Attempts have been made by Lindemann and Aston® to 
 separate the two modifications of neon by fractional distillation 
 and by fractional diffusion through pipe-clay. Later Linde- 
 mann ^° discussed the theory of the separation and decided that 
 the negative result obtained was the one to have been expected 
 under the experimental conditions, in the case of fractional dis- 
 tillation. The fractional diffusion resulted in an apparent differ- 
 ence of density of about 0.7%, while an automatic method 
 
 'Except in case of fluorides of boron and silicon. (F. W. Aston, PMl. 
 Mag. (6) 40, 630 (1920). 
 
 'F. W. Aston, Phil. Mag. (6) 39, 449-55 (1920). 
 
 « E. Reynolds, Nature, Marcli 21, 1895. 
 
 •F. A. Lindemann and F. W. Aston^ PMl. Mag. (6) 37, 523-35 (1919). 
 
 10 F. A. Lindemann, iMd., 38, 173-81 T1919). 
 
152 THE CHEMICAL EPFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 started in 1914 gave a difference of only 0.3%. It can therefore 
 be said at the present time that the diffusion method in the case 
 of neon has given positive results but the differences are too small 
 to be conclusive. 
 
 62. Discovery of Other New Isotopes by Aston. 
 
 Still more recently Aston ^^ has extended the search for iso- 
 topes by the positive ray method to other elements. His investi- 
 gations have yielded results which, while absolutely astounding 
 to chemists in one sense, must be regarded as having been fore- 
 shadowed by Front's ^^ hypothesis more than one hundred years 
 ago. At the time of writing (Oct., 1920) eighteen elements have 
 been examined by Aston with the following results, H, He, C, 
 N, O, F, F, and As give a pure mass spectrum indicating but 
 one isotope, as would be expected from their whole number 
 atomic weights. The results for the other elements can be seen 
 in the following Table XVIII. The case of bromine is of par- 
 ticular interest. Although its atomic weight (79.92) is quite close 
 to 80, there appears to be no isotope of the mass 80 at all, but 
 two isotopes in almost equal quantities of 79 and 81. 
 
 As the atomic weights of the elements increase it becomes 
 more difficult to get a definite resolution of isotopes of masses 
 differing by one or two units, since the percentage difference is 
 small. The whole number rule on the basis of O = 16 has not 
 hitherto been departed from in any case except hydrogen. This 
 may be related to the absence of electrons in the hydrogen 
 nucleus. At any rate it seems very well established that the 
 departures of the ordinary atomic weights from unity is to be 
 accounted for by a mixture of whole number isotopes. The 
 occurrence of isotopes appears to become more common among 
 the elements of higher atomic weight; apparently, there are more 
 complex than simple elements. The influence this is likely to 
 have in practical and theoretical chemistry has been expressed 
 by Aston {lac. cit.) as follows. "The very large number of dif- 
 ferent molecules possible when mixed elements unite to form 
 compounds would appear to make their theoretical chemistry 
 
 « F. W. Aston, Nature, 105 ; p. 8 ; p. 54G ; pp. 617-19 (1920). Phil. Mag. (6) 
 89, 611-25; 40, 628-34 (1920). 
 
 "W. Ostwald, Grundri88 d. allgemcinen Chemie (1899), p. 41. S. L, Blge- 
 low, "Theoretical and Pliysical Chemistry" (1912), p. 87. 
 
POSITIVE RAYS AND RECOIL ATOMS 
 
 TABLE XVIII • 
 
 153 
 
 Isotopes ^^ of the Ordinary Elements According to Positive Ray 
 Analysis by Aston'^^ 
 
 Element 
 
 H 
 He 
 B 
 C 
 
 N 
 
 
 
 F 
 
 Ne 
 
 Si 
 
 P 
 
 S 
 
 CI 
 
 A 
 
 As 
 
 Br 
 
 Kr 
 
 X 
 
 Hg 
 
 Atomic 
 
 Atomic 
 
 Number 
 
 Weight 
 
 1 
 
 1.008 
 
 2 
 
 3.99 
 
 5 
 
 10.9 
 
 6 
 
 12.00 
 
 7 
 
 14.01 
 
 8 
 
 16.00 
 
 9 
 
 19.00 
 
 10 
 
 20.2 
 
 14 
 
 28.3 
 
 15 
 
 31.04 
 
 16 
 
 32.06 
 
 17 
 
 35.46 
 
 18 
 
 39.88 
 
 33 
 
 74.96 
 
 35 
 
 79.92 
 
 36 
 
 82.92 
 
 54 
 
 130.2 
 
 80 
 
 200.6 
 
 Minimum 
 
 No. of 
 
 isotopes 
 
 1 
 
 1 
 
 2 
 
 1 
 
 1 
 
 1 
 
 1 
 
 2 
 
 2 
 
 1 
 
 1 
 
 2 
 (2) 
 
 1 
 
 2 
 
 6 
 
 5 
 (6) 
 
 Mass in the Order of 
 Intensity 
 
 1.008 
 
 4 
 
 11,10 
 
 12 
 
 14 
 
 16 
 
 19 
 
 20,22,(21) 
 
 28, 29, (30) 
 
 31 
 
 32 
 
 35, 37, (39) 
 
 40, (36) 
 
 75 
 
 79, 81 
 
 84, 86, 82, 83, 80, 78 
 
 (128, 131, 130, 133, 135) 
 
 (197-200), 202, 204 
 
 almost hopelessly complicated, but if, as seems likely, the sepa- 
 ration of isotopes on any reasonable scale is to all intents 
 impossible, their practical chemistry will not be affected, while 
 the whole number rule introduces a very desirable simplification 
 into the theoretical aspects of mass." 
 
 The attempts of Lindemann and Aston to separate the two 
 modifications of neon have already been referred to. A number 
 of experiments to this end have already been carried out with 
 other elements, and doubtless in the future we may expect much 
 activity in the same direction. It also appears highly desirable 
 that a series of very accurate atomic weight determinations 
 should be made of the complex elements from different sources to 
 
 " A list of the radioactive isotopes will be found in Appendix, Table B. 
 "F. W; Aston, Phil. Mag. (G) 40, 633 (1920). 
 
154 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 ascertain if the isotopes always occur mixed in the same pro- 
 portion. 
 
 No attempt to separate isotopes has as yet been conclusively 
 successful. In the case of radioactive and ordinary lead, Rich- 
 ards and Hall ^^ obtained wholly negative results by the use of 
 fractional crystallization. Harkins^^ and his co-workers have 
 been engaged in the attempt to separate chlorine by diffusion 
 and have obtained encouraging though not finally positive results. 
 The theoretical aspects of the separation of chlorine by various 
 methods have been the subject of much recent discussion.^^ 
 
 Bronsted and v. Hevesy ^® report the separation of mercury 
 into two fractions by distillation, one having a density 0.999980, 
 the other of 1.000031, compared with that of the original as 
 unity. 
 
 63. General Properties of Recoil Atoms. 
 
 The treatment of the chemical action produced by recoil 
 atoms does not fall under the title either of a particles or elec- 
 trons, but since the emission of a radiation and, to a much smaller 
 degree, of (3 radiation is always accompanied by recoil, and since 
 it has recently been shown that the recoil atoms are capable of 
 producing chemical action, it appears appropriate to treat the 
 subject briefly in the present monograph. Before proceeding to 
 the chemical effects it will be necessary to consider the more 
 general characteristics of recoil atoms. 
 
 When a radioactive atom emits an a particle in a given direc- 
 tion the parent atom, or atomic residue, receives an impulse in 
 the opposite direction, which has very aptly been termed recoil. 
 The atom receiving the recoil is termed the recoil atom. Recoil 
 atoms were first studied by Miss Brooks,^^ by Hahn,^^ and by 
 Russ and Makower ^^ as a means of separating the recoiling 
 radioactive substance in a pure state. 
 
 ^T. W. Richards and N. F. Hall, Joum. Amer. Chem. Soc. 39, 531-41 
 (1917). 
 
 '«W. D. Harkins, Science, 51, 289 (1920). 
 
 "T. R. Merton and H. Hartley, Nature, 105, 104 (1920) ; W. D. Harkins, 
 iiid., 105, 230 ; D. L. Chapman, ihid., 105, 487 ; 642 ; F. Soddy, ibid., 105, 516 ; 
 A. F. Core, ibid., 105, 582. 
 
 '■J. N, Bronsted and G. v. Hevesy, Nature, 106, 144 (1920). 
 
 "Miss H. T. Brooks, Nature, July 21, 1904. 
 
 "O. Hahn, Verh. deut. phys. Qea., 11, 55 (1009). 
 
 " S. Russ and W. Makower, Proc. Roy. Soc. 82A, 205 (1909). 
 
I 
 
 POSITIVE RAYS AND RECOIL ATOMS 155 
 
 Rutherford ^^ has shown that when a particle of mass m is 
 ejected with velocity v from an atom of mass M, the residual 
 atom of mass M-m recoils with a velocity V, according to the 
 relation (M-m) V = mv. In the case of Ra A of atomic weight 
 218 (Table I) the expulsion of the a particle of mass 4 at a 
 velocity of 1.82 x 10^ cms. sec."^ results in a recoil atom of Ra B 
 with a velocity of 3.4 x 10^ cms. sec."^. This velocity is sufficient 
 to ionize a gas in which the recoil radiation- takes place, as 
 has been shown by Wertenstein.^^ The velocity and kinetic 
 energy of the recoil atoms may be calculated to be about 1/50 
 to 1/60 that of the corresponding a particles. The fraction in 
 
 each case is equal to ^hf -o^ 
 
 ^ M-m. 2* 
 
 Wertenstein,^^ in the laboratory of Mme. Curie, has made 
 the most exhaustive investigation of recoil atoms yet under- 
 taken. He has called the recoil atoms from Ra A a particles. 
 They have a range in air at atmospheric pressure of 0.14 mm., 
 and in hydrogen of 0.83 mm. This range in air is about 1/350 
 that of the a particle ; and since the kinetic energy of the a par- 
 ticle is 1/50 that of the a particle, it is evident that the expendi- 
 ture of energy by the a particle is about seven times as great per 
 length of path as that of the a particle. This does not mean that 
 the ionization is seven times as great, because the proportion of 
 energy expended in producing ionization is somewhat smaller in 
 the case of a particles, but Wertenstein found that the ionization 
 produced by a particles becomes in maxima about five times as 
 great as that of a particles over the same path. 
 
 This knowledge of recoil atoms will suffice at least for a pre- 
 liminary survey of what may be expected if they produce chem- 
 ical action in anything like the same proportion to their ionizing 
 powers that a particles do. The two most prominent properties 
 to be kept in mind are their very limited range and their great 
 intensity of action within that range. In a vessel of infinitely 
 large volume in which the a particles would expend all their 
 energy in the gas system without striking the wall, the compara- 
 tive effect of the recoil atoms would be less than 2%, or very 
 
 "E. E. Rutherford, "Radioactive Substances and Their Radiations" (19.13), 
 p. 174. 
 
 23 L. Wertenstein, Comp. rend. 152, 1057 (1911). 
 
 2* Meyer and v. Schweidler, "Radioaktivitat" (191G), p. 139, 
 
 ?' li. Wertenstein, Thcsw, paris, 1913, 
 
156 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 small. On reducing the volume or pressure, the effect of the 
 easily absorbed recoil atoms remains constant, while the a par- 
 ticles expend part of their energy in the wall, which part was 
 shown in Chapter VI to be ineffective in producing chemical 
 action. As the volume is further diminished the a particles 
 have still shorter paths and the effect of the recoil atoms becomes 
 relatively greater and greater. In very small volumes and at 
 low pressures it is evident that the ionizing and chemical effects 
 of the recoil atoms would exceed the effect of a particles by sev- 
 eral fold. That this is exactly the case found experimentally with 
 respect to chemical action will be shown in the following section. 
 
 64. Chemical Reaction Produced by Recoil Atoms. 
 
 In § 43 the influence of the size of the reaction vessel on the 
 rate and extent of the combination of hydrogen and oxygen in 
 equivalent proportions mixed with radium emanation was dem- 
 onstrated. The general law found experimentally and based in 
 principle upon the average path of a particles in the reaction 
 
 vessel is for spheres: log P/Po/Eofe-^' — 1) = 84.1/0^, in which 
 Po is the initial pressure of electrolytic gas in mm. of Hg, P the 
 pressure of the same at any time t, Eo is the initial quantity of 
 radium emanation in curies, e"^^ expresses the rate of decay of 
 emanation, and D is the diameter of the spherical reaction vessel 
 in cms. The expression was shown to be true for spheres with 
 diameters up to about 10 cms. containing electrolytic mixture 
 not exceeding one atmosphere pressure. On attempting to apply 
 the kinetic equation represented by the left hand side of the 
 equation just given, to the case of a sphere of diameter as small 
 as 1 cm., it was found that a velocity constant could not be 
 obtained as in the case of larger spheres (Table XI). The 
 experimental data of Lind ^^ are shown in Table XIX for a 
 sphere of about 1 cm. diameter which should have, according to 
 the general relation for larger spheres, a value of velocity constant 
 (k^i/X) of 90.4, but, as will be seen, the value of the first measure- 
 ment was 104.6, which rose as the reaction progressed to a value 
 of 220.5. If the velocity constant be calculated for each separate 
 interval, as explained in § 45, the rise of the (k^/X) ' becomes still 
 more marked, as may be seen in the table. But the time intervals 
 
 JOS. C. Lind, Journ. Amcr. Chem. Soc. 41, 533 (li)ll)). 
 
POSITIVE RAYS AND RECOIL ATOMS 
 
 157 
 
 are still too large. To avoid this, Curve 1 in Fig. 7 was plotted 
 with pressure as ordinates and time as abscissae. The interpo- 
 lated values of P in Table XIX were then taken from the curve 
 from which the values of (k^,/A)' in the last column were cal- 
 culated. Curve la in Fig. 7 shows the course of the normal 
 pressure reduction by a rays alone in larger vessels, as calculated 
 from the general equation. 
 
 TABLE XIX 
 
 Effect of Recoil Atoms in Producing an Abnormal Rate of Com- 
 bination of Hydrogen and Oxygen in a Small Sphere 
 
 Vol. = 0.470 c. c. 
 
 Diam. = 0.9647 cm. Eo — 0.04234 curie. 
 Normal k\i/l = 90.4. 
 
 Actual Data 
 
 Calculated from 
 Actual Data 
 
 Interpolated Data 
 
 Days 
 
 Hrs. 
 
 P. in 
 mm. Hg 
 
 k\i/k 
 
 (k\i/ir 
 
 Days 
 
 Hrs. 
 0.0 
 
 P. 
 
 (k\i/iy 
 
 
 
 0.0 
 
 507.8 
 
 
 
 
 
 507.8 
 
 
 
 
 
 
 
 
 
 6.0 
 
 425.0 
 
 95.6 
 
 
 
 15.67 
 
 310.3 
 
 104.6 
 
 104.6 
 
 
 
 
 12.0 
 
 18.0 
 
 354.0 
 290.0 
 
 102.7 
 117.1 
 
 
 
 19.90 
 
 271.2 
 
 105.9 
 
 111.2 
 
 1 
 1 
 
 0.0 
 6.0 
 
 233.0 
 187.0 
 
 134.4 
 141.6 
 
 
 
 23.67 
 
 235.1 
 
 111.4 
 
 142.9 
 
 1 
 
 1 
 
 12.0 
 
 18.0 
 
 150.7 
 123.0 
 
 145.0 
 
 148.8 
 
 1 
 
 15.33 
 
 135.4 
 
 121.4 
 
 139.0 
 
 2 
 2 
 
 0.0 
 6.0 
 
 96.0 
 73.0 
 
 182.4 
 210.9 
 
 1 
 
 19.00 
 
 119.0 
 
 123.4 
 
 148.7 
 
 2 
 2 
 
 12.0 
 18.0 
 
 51.5 
 33.0 
 
 278.9 
 377.6 
 
 2 
 
 5.00 
 
 76.7 
 
 134.8 
 
 195.0 
 
 3 
 3 
 
 0.0 
 3.0 
 
 19.5 
 14.0 
 
 461.7 
 594.3 
 
 3 
 
 0.33 
 
 18.8 
 
 181.3 
 
 349.6 
 
 3 
 3 
 
 6.0 
 9.0 
 
 9.9 
 7.5 
 
 646.0 
 528.5 
 
 3 
 
 15.42 
 
 5.0 
 
 220.5 
 
 483.3 
 
 3 
 3 
 
 12.0 
 15.42 
 
 5.7 
 5.0 
 
 535.1 
 228.3 
 
 To ascertain whether the abnormality observed for the 1 cm. 
 sphere could be accounted for by the action of recoil atoms added 
 to that of a particles, the following analysis of the results was. 
 
158 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 made. If 90.4 is the normal velocity constant for a particles, 
 180.8 will represent a velocity where the action of recoil atoms 
 is just equal to that of a particles under the same conditions. 
 By plotting the (k|x/X)' values from the last column of Table 
 XIX as Curve 2 of Fig. 7, it was found that (kjx/X)' becomes 
 equal to 180.8 at a gas pressure of 118 mms. At any other pres- 
 sure the proportion of chemical action being produced by each 
 type of radiation can be estimated on the following basis: 
 
 1. That the chemical effect of the recoil atoms remains con- 
 stant down to a very low pressure at which they also begin to reach 
 the wall in large proportion without being stopped by the gas. 
 
 / 2 
 
 T/MS IN Days for all Curves 
 Fig. 7. 
 
 2. That the chemical effect of the a particles will at all pres- 
 sures be proportional to the pressure. 
 
 For example, at 118 mms. the two effects are equal to each 
 other and one can arbitrarily place each equal to 118. At any 
 other pressure, 50 mms. for example, the recoil atom effect, which 
 
I 
 
 POSITIVE RAYS AND RECOIL ATOMS 169 
 
 for convenience will be called the R effect, would still have the 
 value 118; the a effect now will have the value 50; the combined 
 effect is 168; the abnormality factor, or the ratio of the observed 
 abnormal effect to the normal <x effect, will be (R + a)/a = 
 168/50 = 3.36. Table XX shows this same analysis carried to 
 its upper and lower limits. 
 
 Comparison of the last two columns of Table XX shows that 
 the general trend of the experimental and calculated values of 
 the velocity constant (kpi/^) ' is the same. The calculated values 
 will be found plotted in Curve 2 of Fig. 7 as +, the interpolated 
 values taken from Table XIX as O . The agreement between 
 theory and experiment is satisfactory. The maximum value 
 found, 632, when divided by the normal a value 90.4, shows that 
 the maximum ratio (R + a) /a is 6.99. According to Wertenstein 
 {loc. cit.) the maximum ionization due to recoil atoms from 
 Ra A is five times that of the a particles over the same path, 
 which would be a combined ionization six times that of the a 
 particles alone. Remembering that Wertenstein's statement 
 refers to recoil atoms from Ra A alone, while with emanation 
 we are dealing with three different sets of a particles, the agree- 
 ment is perhaps as good as could be expected. At least one must 
 be convinced that recoil atoms cause the combination of hydro- 
 gen and oxygen at ordinary temperature, and approximately in 
 the same proportion to their ionizing powers as in the case of a 
 particles. 
 
 At first thought it must appear surprising that the chemical 
 effect of recoil atoms can be observed at fairly large pressures. 
 One must consider, however, that the radius of the reaction bulb 
 is only 4.8 mms., and that the average path within the spherical 
 bulb is only about 6/10 of this, or about 2.9 mms.; moreover, the 
 range of the a particle in the electrolytic mixture will be about 
 0.3 nam. at standard pressure (calculated from Wertenstein's 
 measurements for air and for hydrogen), and would be still 
 greater for recoil atoms of Ra C. These facts, considered together 
 with the intensity of the energy expense by recoil atoms, make it 
 evident that the pressure and bulb dimensions at which the 
 chemical effect of recoil atoms manifests itself are quite con- 
 cordant with Wertenstein's ionization data. 
 
 Finally it should be inquired whether the chemical effect of 
 recoil atoms will not also be observed in larger spheres at low 
 
160 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 pressure. The answer must be affirmative, with certain reserva- 
 tions. By referring to Table XI it will be seen that for the 2- 
 centimeter sphere there is an unmistakable tendency for k|x/X 
 to increase slightly toward the end of the reaction, which tend- 
 ency would be brought out much more distinctly by calculating 
 for (kjx/X)'. However, the quantity of gas to be acted on in 
 larger spheres, beginning with normal pressure, is so much greater 
 than in a 1-cm. one, that before low pressures are attained, the 
 emanation is nearly exhausted and the effect on the k\i/k value 
 is largely masked. 
 
 TABLE XX 
 
 Analysis of the Recoil Atom Effect (R) and the a Ray Effect (a) 
 in Causing Electrolytic Hydrogen and Oxygen to Combine 
 in a 1 cm. Sphere 
 
 R effect = constant =118. a effect proportional to pressure = P. 
 
 a = P (mm. Hg) 
 
 R + o. 
 
 (R + «;/« 
 
 (k\i/iy 
 
 Calcd. 
 
 (h\i/iy 
 Found 
 
 
 
 
 (Curve 2) 
 
 10 
 
 128 
 
 (12.80) 
 
 ... 
 
 
 20 
 
 138 
 
 6.90 
 
 622 
 
 632 
 
 30 
 
 148 
 
 4.93 
 
 444 
 
 446 
 
 40 
 
 158 
 
 3.95 
 
 356 
 
 376 
 
 50 
 
 168 
 
 3.36 
 
 303 
 
 350 
 
 60 
 
 178 
 
 2.97 
 
 268 
 
 292 
 
 70 
 
 188 
 
 2.69 
 
 242 
 
 267 
 
 80 
 
 198 
 
 2.48 
 
 223 
 
 240 
 
 90 
 
 208 
 
 2.31 
 
 208 
 
 223 
 
 100 
 
 218 
 
 2.18 
 
 195 
 
 204 
 
 110 
 
 228 
 
 2.07 
 
 186 
 
 192 
 
 120 
 
 238 
 
 1.98 
 
 177 
 
 182 
 
 130 
 
 248 
 
 1.91 
 
 172 
 
 166 
 
 140 
 
 258 
 
 1.84 
 
 166 
 
 162 
 
 160 
 
 268 
 
 1.79 
 
 161 
 
 153 
 
 200 
 
 318 
 
 1.59 
 
 143 
 
 133 
 
 250 
 
 368 
 
 1.47 
 
 132 
 
 118 
 
 300 
 
 418 
 
 1.39 
 
 125 
 
 112 
 
 400 
 
 518 
 
 1.29 
 
 116 
 
 100 
 
 500 
 
 618 
 
 1.24 
 
 113 
 
 95 
 
 600 
 
 718 
 
 1.19 
 
 107 
 
 ... 
 
POSITIVE RAYS AND RECOIL ATOMS 161 
 
 The almost vertical drop in Curve 2, Fig. 7, after passing the 
 maximum is due to practical exhaustion of the electrolytic gas 
 mixture. The experimental method employed was the same as 
 that described in § 42, and is not applicable to extremely low 
 pressures with accuracy. It would be very interesting to exam- 
 ine this reaction, using a refined pressure method in order to 
 investigate more precisely the course of the reaction near its 
 end. Theoretically the abnormality factor should continue to 
 rise until the gas is completely exhausted. 
 
Chapter 12. 
 Atomic Disintegration by a Particles. 
 
 65. Scattering and Impacts of a Particles. 
 
 The great potency of the a particle as an agent in the produc- 
 tion of chemical action has been frequently emphasized in pre- 
 ceding chapters. The reactions treated up to the present have 
 been of ordinary molecular character. Very recently Rutherford 
 has demonstrated conclusively for the first time that under cer- 
 tain conditions the a particle is capable of producing a much more 
 fundamental chemical change, namely, the disintegration of the 
 atom into new kinds of atoms. Although such changes are spon- 
 taneously taking place among the radioactive elements, Ruther- 
 ford has presented the first evidence that can be accepted with- 
 out doubt, of the artificial disintegration of the atom. These 
 intra-atomic reactions fall very properly within the confines of 
 radiochemistry. It will therefore be attempted to give a brief 
 non-mathematical description of Rutherford's work which led 
 up to and proved absolutely this discovery of preeminent 
 importance. 
 
 The investigations of Rutherford and his co-workers in Man- 
 chester and more recently in Cambridge of the phenomena 
 accompanying the passage of a particles through matter have 
 been remarkably successful in furnishing insight into the question 
 of atomic structure. As has been pointed out, the flight of the 
 a particle of high velocity carries it in a straight line through 
 a large number of molecules or atoms, which are ionized by the 
 removal of a single electron from each molecule encountered. 
 The a particle suffers no deflection in the ordinary encounter, 
 but has its velocity gradually diminished until it is no longer 
 able to produce ionization. Toward the end of its path, when 
 its velocity is much reduced, the a particle is more subject to 
 deflection or scattering, and occasionally it experiences a very 
 large deflection or is actually turned backward in its path. The 
 
 162 
 
ATOMIC DISINTEGRATION BY a PARTICLES 163 
 
 great rarity of the occurrence of the large deflections led, as has 
 already been pointed out, to the Rutherford-Bohr atomic model 
 according to which most of the atomic mass is centered in an 
 extremely minute nucleus with a positive charge equal to the 
 atomic number of the atom, which for the heavier elements is 
 somewhat less than half the atomic weight. 
 
 The large deflections or reversals of the a particle are then 
 attributed to a close impact of the particle with the nucleus of 
 the atom encountered. These impacts were first investigated 
 using thin sheets of the heavier metals. The law governing the 
 deflection or scattering was worked out by Geiger and Marsden,^ 
 on the basis of repulsion inversely with the square of the distance 
 from point charges. The experimental scattering was in good 
 agreement with this theory and it was calculated that the direct 
 impact represents an approach of the a particle to the nucleus 
 within about 3 x 10"^^ cm. in the case of heavy atoms. 
 
 The case for light atoms is different in two important respects. 
 First, on account of the smaller nuclear charge the repulsion of 
 the positively charged a particle is much less than in the case 
 of heavy atoms, and the a particle is therefore able to approach 
 much closer to the nucleus, approximately ten times as close. 
 This close approach on impact produces radical differences in 
 the result of the repulsion which will be described later. Second, 
 on account of the smaller mass of the nucleus of light atoms 
 they are repelled to greater distances than the heavy ones. 
 Under favorable circumstances the light atoms are projected 
 forward at a velocity which carries them beyond the range of the 
 impelling a particle and can be detected and counted by the 
 scintillation method. This opens new possibilities for their inves- 
 tigation, which have been utilized by Rutherford as will be 
 recounted in the following paragraphs. 
 
 Darwin ^ has shown that the law of scattering and repulsion 
 predicts that all the light atoms up to and including oxygen 
 should be capable of being repelled by a doubly charged a par- 
 ticle to a distance exceeding the range of the a particle in the 
 same medium, provided that the atom repelled has a single 
 positive charge. Evidently, if the repelled atom has a double 
 charge, no atom heavier than helium could be repelled beyond 
 
 iH. Geiger and E. Marsden, Phil. Mag. (6) 25, 604 (1913). 
 *C. G. Darwin, PJiil. Mag. (6) 27, 499 (1914). 
 
164 THE CHEMICAL EFFECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 the range of the a particle, without borrowing energy from some 
 other source. It was to test this prediction that Rutherford 
 undertook the experiments which have led to other highly sig- 
 nificant conclusions. 
 
 66. Swift Hydrogen Atoms. 
 
 In the case of the repulsion of a hydrogen atom as the result 
 of an intimate impact with an a particle, we have a case of great 
 simplicity in some respects. On account of its having but a 
 single electron it is impossible for the nucleus of the hydrogen 
 atom to carry more than a single positive charge. On account 
 of its elemental nature there is little probability of the hydrogen 
 atom being changed or disrupted by impact with an a particle. 
 On the theory of impact one should expect a hydrogen atom to 
 be set into swift motion as the result of a direct nuclear encoun- 
 ter with an a particle, with a velocity 1.6 times that of the a 
 particle. The range to be expected for the swift hydrogen atom 
 would be about four times that of the a particle, and its kinetic 
 energy 0.64 of the energy of the a particle. Marsden ^ found that 
 the passage of a particles through hydrogen did produce a large 
 number of faint scintillations on a zinc sulfide screen which 
 could be detected far beyond the range of the a particle. Ruther- 
 ford* has made a very detailed study of the subject which con- 
 firmed the theoretical predictions. The swift H atoms have a 
 range in hydrogen of 100 cms., about four times that of the a 
 particle in the same gas. The nimiber projected straight forward 
 by an <x particle of range 7 cms. is 30 times greater than required 
 by the simple theory of scattering. The probable explanation is 
 the distortion of the nucleus by such close approach, which was 
 about 3 x 10"^^ cm., or approximately the same as the diameter of 
 an electron. The direction of the swift H atoms is mainly the 
 same as that of the a particle, and the velocity of different par- 
 ticles is uniform. On reducing the velocity of the a particle the 
 direction of the H atoms becomes more varied, approaching the 
 requirements of the law of scattering as to distribution, but still 
 exceeding theory in number. In traversing one cm. of hydrogen 
 about lO'* a particles produce one swift H atom, which means 
 
 »E. Marsden, Phil. Mag. (G) 27, 824 (1914). E. Marsden and W. C. 
 Lantsberry, ibid., 30, 240 (1915). 
 
 *E. E. Rutherford, Phil. Mag. (C) 37, 537-61; 5G2-71 (1919). 
 
ATOMIC DISINTEGRATION BY a PARTICLES 165 
 
 that out of 10^ hydrogen atoms ionized, only 1 is set into swift 
 motion as the result of a direct nuclear impact. 
 
 Since the nuclear impact is an atomic phenomenon, the long 
 range swift atoms can be produced by radiating either the ele- 
 ment or any compound of it. This fact has proved a source of 
 some embarrassment in the case of hydrogen, since it is very 
 difficult to remove water vapor and possibly other compounds 
 containing hydrogen from the field of action. As a consequence 
 every source of a radiation has been found to give some swift H 
 atoms continuously. So persistent is this phenomenon that it 
 has suggested the possibility of the emission of H particles from 
 the nucleus of the radioactive element itself in the same way that 
 a particles are emitted. Later evidence obtained by Rutherford 
 {loc. cit.) does not appear to support such an hypothesis strongly, 
 but the question is still regarded by Rutherford as a subject 
 requiring further investigation. 
 
 Both magnetic and electrostatic methods of deflection have 
 been used by Rutherford in examining the charge and velocity 
 of the swift H atoms. The charge was shown to be unipolar 
 positive, and the maximum velocity is 1.6 times that of the a 
 particle, as required by theory. 
 
 67. Experiments of Rutherford with Other Light Atoms. 
 
 After obtaining such important results with hydrogen Ruther- 
 ford ^ proceeded to investigate the propulsion of some of the 
 other light atoms to distances beyond the range of the a parti- 
 cle. Assuming singly charged particles as the result of impact, 
 it was predicted from Darwin's formulation that the swift nitro- 
 gen atom ought to have a range 1.33 times that of the a particle 
 producing it, and that oxygen should similarly have the value 
 1.12. Both of these gases were examined by Rutherford, who 
 found numerous scintillations beyond the a range in the region 
 7-9 cms. from the source, which in number corresponded closely 
 to that found in the hydrogen experiments, indicating that the 
 nature of the impact was similar. The range found for nitrogen 
 was approximately that predicted by theory. In the case of 
 oxygen the range was not very different from that found for 
 nitrogen. This value greater than theory was rather puzzling, 
 
 •E. E. Rutherford, Phil. Mag. (6) 37, 571-87 (1919). 
 
166 THE CHEMICAL EFFECTS OF AlPHA PARTICLES A^D ELECTRO^ 
 
 but Rutherford was inclined to believe that the swift particles 
 were in both cases the singly charged oxygen or nitrogen atoms. 
 The improbability of this assumption was pointed out by 
 Fulcher,® who showed that the propulsion of a singly positively 
 charged atom of nitrogen (or oxygen) involves the assumption 
 that the other orbital electrons are carried with the swift atom. 
 According to Fulcher's contention the forces binding these remote 
 electrons to the nucleus are not sufficient to overcome their initial 
 inertia at the moment of impact, when they would have to take 
 on a speed of 10^ cm. sec.-^ in less than 10~^^ sec. According to 
 Fulcher the remaining electrons would either be left behind ini- 
 tially or soon be brushed off by contact with other molecules of 
 the gas traversed. The swift particles could not be nitrogen or 
 oxygen atoms without electrons, for such multiply charged atoms 
 would have shorter ranges than were observed. Fulcher suggests 
 that the swift particles are a rays produced by the disruption of 
 nitrogen by the impact. Of course doubly charged helium atoms 
 could not be projected beyond the range of the bombarding a 
 particle unless they got additional energy from some other source. 
 Fulcher suggested that the impact results in the explosion of the 
 nitrogen atom so that the internal atomic energy becomes avail- 
 able, just as in the case of the radioactive changes. This would 
 represent a type of "artificial radioactivity" which will be dis- 
 cussed in § 69. The only difficulty of Fulcher's assumption lay 
 in its failing to explain the uniform direction of the swift parti- 
 cles in the direction of the a particle. The result of an atomic 
 explosion would be expected to cause the ejection of a particles 
 in any direction according to the law of chance. The probability 
 of atomic disruption by a particles had already been established 
 for nitrogen in another way by Rutherford, which will be con- 
 sidered in the following section. 
 
 68. Decomposition of Nitrogen and Oxygen. 
 
 In June 1919 Rutherford ^ reported the observation of an 
 anomalous effect in nitrogen bombarded by a rays. A closed 
 metal box containing an intense source of Ra C at 3 cms. from 
 the end was provided with an opening in the end covered with a 
 silver plate of stopping power equivalent to 6 cms. of air. The 
 
 •G. S. Fulcher, Science r»0, 582-4 (1919). 
 »E. E. Rutherford, Phil. Mag. (6) 37, 581-7. 
 
ATOMIC DlSlKTEaRATlON BY a PARTICLES 167 
 
 ZnS screen was placed just outside the opening at 1 mm. dis- 
 tance. The number of "natural" scintillations on this screen, 
 owing to some unavoidable source of swift H atoms, is increased 
 by exhausting the box. On admitting dry air or CO2, the num- 
 ber of scintillations is diminished in the ratio to be expected from 
 the increase of stopping power of the gas column. But if nitrogen 
 is admitted the number of scintillations increases. Nitrogen from 
 different sources was tried and various attempts were unsuccess- 
 ful in explaining the phenomenon without assuming that H atoms 
 were being bombarded from nitrogen atoms by a rays. The 
 observed range of the swift particles was too great for them to 
 have a mass greater than that of the H atom ; the effect seemed to 
 depend on the presence of nitrogen and to be proportional to its 
 concentration, so that no other conclusion was left open except 
 that nitrogen is disrupted by a ray bombardment and that one 
 of the products of the disruption is the swift H atom. 
 
 Upon going to Cambridge, Rutherford^ continued his work 
 on the nuclear constitution of atoms, and devised a comparison 
 method of examining the magnetic deflection of the swift parti- 
 cles in order to estimate the mass. The results of the experiments 
 confirm that the long range particles from nitrogen are particles 
 with the same mass as the H atom, as Rutherford had previously 
 supposed. The investigation of the shorter range particles from 
 oxygen and nitrogen has in part confirmed the predictions of 
 Fulcher. In both cases they appear to be doubly charged helium 
 atoms and not the singly charged atom of nitrogen or oxygen; 
 but instead of having the usual mass 4 of the He atom, a mass of 
 3 was found which according to Rutherford represents an isotope 
 of helium. In the case of oxygen no very long range particles 
 corresponding to those of hydrogen and nitrogen are found, and 
 Rutherford suggests that the oxygen nucleus is composed of four 
 helium atoms of mass 3 and one of mass 4 and two nuclear or 
 binding electrons giving a net positive charge of 8. In the case of 
 nitrogen we have two different modes of disruption, one giving 
 swift doubly charged atoms of helium of mass 3, the other giv- 
 ing swift H atoms of mass 1. Since the number of the former 
 exceeds the latter by five to ten fold, Rutherford assumes that 
 the two modes of disruption are independent of each other and 
 do not occur simultaneously from the same atom. The nuclear 
 
 "E. E. Rutherford, Bakerian Lecture, Proc. Roy. Soc. 97A, 374-400 (1920). 
 
16S THE CHEMICAL EPEECTS OF ALPHA PARTICLES AND ELECTRONS 
 
 structure of nitrogen proposed by Rutherford is four doubly 
 charged, helium atoms of mass 3 and two singly charged H atoms 
 of mass 1 and three binding electrons giving a net positive charge 
 of 7. If the H atoms have an interior position in the nucleus 
 with reference to the He atoms, as Rutherford suggests, this 
 might account for the greater frequency of the disruption accom- 
 panied by expulsion of a swift He atom. 
 
 69. Artificial Radioactivity. 
 
 The experimental results of Rutherford just discussed in § 68 
 appear to confirm Fulcher's prediction (§ 67) that the shorter 
 range swift particles from nitrogen (and also those from oxygen) 
 are not the singly charged N and atoms, but are doubly charged 
 He atoms (of mass 3). Rutherford estimates that the gain in 
 energy of motion resulting from the impact must be at least 8%, 
 even though the subsequent motion of the disintegrated nucleus 
 and of the bombarding a particle be neglected. Evidently this 
 additional energy is derived from the internal atomic energy 
 of the disrupted atom, and we have direct proof of Fulcher's 
 "artificial radioactivity." If the excess energy utilized by the 
 swift particle is in reality not more th|in 8% of the energy of 
 the bombarding a particle, Fulcher's difficulty of explaining the 
 uniform direction of the swift particles can perhaps be dismissed. 
 There is no evidence that the atomic nucleus is entirely disrupted, 
 and Rutherford inclines to the view that only a single particle 
 is ejected from each atom and discusses the possible isotopic 
 modifications of atoms of lower atomic weight which remain as 
 the result of the loss of a single atom in the two types of disrup- 
 tion. As yet there is experimental evidence only of the swift 
 particles of range longer than the a particle and we have no 
 direct evidence as to the nature of the residue. 
 
 Rutherford points out that the amount of disintegration is 
 exceedingly small. If in the case of nitrogen only one a particle 
 in 300,000 succeeds in getting near enough to the nucleus to 
 liberate a swift H atom with sufficient velocity for it to be 
 detected, the entire a radiation from a gram of radium, if wholly 
 absorbed in nitrogen, would generate only about 5 x 10"* mm.* of 
 hydrogen per year. It is quite possible however that much dis- 
 integration takes place through the liberation of particles of 
 
ATOMIC DISINTEGRATION BY a PARTICLES 169 
 
 slower velocity which can not be detected. It is also possible 
 that high velocity electrons possess sufficient energy to bring 
 about such a disintegration, because their close approach to, the 
 nucleus would be accompanied by an attraction instead of a 
 repulsion. In this case we should expect to find the effect pos- 
 sibly more pronounced in the case of the atoms of high atomic 
 number than of lower. It is possible that some of the inert gases 
 found by various authorities by spectral methods may have 
 resulted from intense electronic bombardment of the electrodes. 
 The results of further experiments in this direction may be 
 awaited with a great deal of interest. Rutherford does not con- 
 sider it impossible that penetrating X rays may have sufficient 
 energy to cause atomic disintegration. 
 
 It may not be without interest to observe that the discovery 
 of radioactivity came about as the result of the search for the 
 spontaneous emission of X rays. We now have the situation 
 reversed; having discovered radioactivity and the spontaneous 
 disintegration of the atom, we turn back to its artificial dis- 
 ruption, and enter upon an era of renewed activity in the quest 
 of "transmutation." 
 
170 
 
 APPENDIX 
 
 APPENDIX 
 Table A. Decay of Radium Examination According to L. Kolowrat 
 
 Time 
 
 Quantity 
 
 
 Time 
 
 Quantity 
 
 A 
 
 Time 1 
 
 Quantity 
 
 
 
 Remaining 
 
 A 
 
 
 
 Remaining 
 
 
 
 Remaining 
 
 A 
 
 Days 
 
 Bra. 
 
 0.00 
 
 Days 
 
 Hrs. 
 
 0.00 
 
 Days 
 
 Hrs. 
 
 0.00 
 
 
 
 
 1.00000 
 
 375 
 
 
 11 
 
 0.76913 
 
 575 
 
 
 8 
 
 0.47592 
 
 353 
 
 
 0.5 
 
 0.99625 
 
 372 
 
 
 12 
 
 0.76338 
 
 570 
 
 
 6 
 
 0.46533 
 
 345 
 
 
 1 
 
 0.99253 
 
 742 
 
 
 13 
 
 0.75768 
 
 567 
 
 
 9 
 
 0.45498 
 
 337 
 
 
 2 
 
 0.98511 
 
 736 
 
 
 14 
 
 0.75201 
 
 562 
 
 
 12 
 
 0.44486 
 
 330 
 
 
 3 
 
 0.97775 
 
 730 
 
 
 15 
 
 0.74639 
 
 557 
 
 
 15 
 
 0.43496 
 
 323 
 
 
 4 
 
 0.97045 
 
 726 
 
 
 16 
 
 0.74082 
 
 554 
 
 
 18 
 
 0.42528 
 
 315 
 
 
 6 
 
 0.96319 
 
 719 
 
 
 17 
 
 0.73528 
 
 549 
 
 
 21 
 
 0.41582 
 
 308 
 
 
 6 
 
 0.95600 
 
 715 
 
 
 18 
 
 0.72979 
 
 545 
 
 
 
 
 0.40657 
 
 3004 
 
 
 7 
 
 0.94885 
 
 709 
 
 
 19 
 
 0.72434 
 
 542 
 
 5 
 
 4 
 
 0.39455 
 
 2915 
 
 
 8 
 
 0.94176 
 
 703 
 
 
 20 
 
 0.71892 
 
 537 
 
 5 
 
 8 
 
 0.38289 
 
 2829 
 
 
 9 
 
 0.93473 
 
 699 
 
 
 21 
 
 0.71355 
 
 533 
 
 5 
 
 12 
 
 0.37158 
 
 2745 
 
 
 10 
 
 0.92774 
 
 693 
 
 
 22 
 
 0.70822 
 
 529 
 
 5 
 
 16 
 
 0.36059 
 
 2664 
 
 
 11 
 
 0.92081 
 
 688 
 
 
 23 
 
 0.70293 
 
 525 
 
 5 
 
 20 
 
 0.34994 
 
 2585 
 
 
 12 
 
 0.91393 
 
 683 
 
 2 
 
 
 
 0.69768 
 
 522 
 
 6 
 
 
 
 0.33960 
 
 2509 
 
 
 13 
 
 0.90710 
 
 678 
 
 2 
 
 1 
 
 0.69246 
 
 517 
 
 6 
 
 4 
 
 0.32956 
 
 2435 
 
 
 14 
 
 0.90032 
 
 672 
 
 2 
 
 2 
 
 0.68729 
 
 514 
 
 6 
 
 8 
 
 0.31982 
 
 2363 
 
 
 15 
 
 0.89360 
 
 668 
 
 2 
 
 3 
 
 0.68215 
 
 509 
 
 6 
 
 12 
 
 0.31037 
 
 2293 
 
 
 16 
 
 0.88692 
 
 663 
 
 2 
 
 4 
 
 0.67706 
 
 504 
 
 6 
 
 16 
 
 0.30019 
 
 2225 
 
 
 17 
 
 0.88029 
 
 657 
 
 2 
 
 6 
 
 0.66698 
 
 490 
 
 6 
 
 20 
 
 0.29229 
 
 2160 
 
 
 18 
 
 0.87372 
 
 653 
 
 2 
 
 8 
 
 0.65705 
 
 489 
 
 
 
 
 0.28365 
 
 2096 
 
 
 19 
 
 0.80719 
 
 648 
 
 2 
 
 10 
 
 0.64726 
 
 482 
 
 
 4 
 
 0.27527 
 
 2034 
 
 
 20 
 
 0.86071 
 
 643 
 
 2 
 
 12 
 
 0.63763 
 
 475 
 
 
 8 
 
 0.26714 
 
 1974 
 
 
 21 
 
 0.85428 
 
 639 
 
 2 
 
 14 
 
 0.62813 
 
 468 
 
 
 12 
 
 0.25924 
 
 1915 
 
 
 22 
 
 0.84789 
 
 633 
 
 2 
 
 16 
 
 0.61878 
 
 461 
 
 
 16 
 
 0.25158 
 
 1859 
 
 
 23 
 
 0.84156 
 
 629 
 
 2 
 
 18 
 
 0.60957 
 
 454 
 
 
 20 
 
 0.24414 
 
 1804 
 
 
 
 
 0.83527 
 
 624 
 
 2 
 
 20 
 
 0.60050 
 
 447 
 
 8 
 
 
 
 0.23693 
 
 1751 
 
 
 1 
 
 0.82903 
 
 620 
 
 2 
 
 22 
 
 0.59156 
 
 440 
 
 8 
 
 4 
 
 0.22993 
 
 1699 
 
 
 2 
 
 0.82283 
 
 614 
 
 3 
 
 
 
 0.68275 
 
 432 
 
 8 
 
 8 
 
 0.22313 
 
 1649 
 
 
 3 
 
 0.81669 
 
 611 
 
 3 
 
 8 
 
 0.56978 
 
 422 
 
 8 
 
 12 
 
 0.21654 
 
 1600 
 
 
 4 
 
 0.81058 
 
 605 
 
 3 
 
 6 
 
 0.55711 
 
 413 
 
 8 
 
 16 
 
 0.21014 
 
 1553 
 
 
 5 
 
 0.80453 
 
 601 
 
 3 
 
 9 
 
 0.54471 
 
 404 
 
 8 
 
 20 
 
 0.20393 
 
 1507 
 
 
 6 
 
 0.79852 
 
 597 
 
 3 
 
 12 
 
 0.53259 
 
 395 
 
 9 
 
 
 
 0.19790 
 
 1462 
 
 
 1 
 
 0.79255 
 
 592 
 
 3 
 
 15 
 
 0.52074 
 
 386 
 
 9 
 
 4 
 
 0.19205 
 
 1419 
 
 
 8 
 
 0.78663 
 
 588 
 
 3 
 
 18 
 
 0.50916 
 
 378 
 
 9 
 
 8 
 
 0.18637 
 
 1377 
 
 
 9 
 
 0.78075 
 
 583 
 
 3 
 
 21 
 
 0.49783 
 
 369 
 
 9 
 
 12 
 
 0.18087 
 
 1326 
 
 
 10 
 
 0.77492 
 
 579 
 
 4 
 
 
 
 0.48676 
 
 361 
 
 9 
 
 18 
 
 0.17291 
 
 1268 
 
 I 
 
APPENDIX 
 
 171 
 
 Table A. 
 
 APPENDIX— (Con fiTiwed) 
 Decay of Radium Examination According to L. Kolowrat 
 
 Time 
 
 Quantity 
 
 
 Time 
 
 Quantity 
 
 
 Time 
 
 Quantity 
 
 
 
 
 Remaining 
 
 A 
 
 
 
 Remaining 
 
 A 
 
 
 
 Remaining 
 
 A 
 
 Days 
 
 Hrs. 
 
 e-^' 
 
 0.00 
 
 Days 
 
 Hrs. 
 
 0.00 
 
 Days 
 
 Hrs. 
 
 0.00 
 
 10 
 
 
 
 0.16530 
 
 1212 
 
 14 
 
 16 
 
 0.07136 
 
 0519 
 
 21 
 
 12 
 
 0.02086 
 
 01496 
 
 10 
 
 6 
 
 0.15803 
 
 1159 
 
 15 
 
 
 
 0.06721 
 
 0489 
 
 22 
 
 
 
 0.01906 
 
 01367 
 
 10 
 
 12 
 
 0.15107 
 
 1108 
 
 15 
 
 8 
 
 0.06329 
 
 0461 
 
 22 
 
 12 
 
 0.01742 
 
 01250 
 
 10 
 
 18 
 
 0.14442 
 
 1059 
 
 15 
 
 16 
 
 0.05961 
 
 0434 
 
 23 
 
 
 
 0.01592 
 
 01142 
 
 11 
 
 
 
 0.13807 
 
 1013 
 
 16 
 
 
 
 0.05613 
 
 0409 
 
 23 
 
 12 
 
 0.01455 
 
 01044 
 
 11 
 
 6 
 
 0.13199 
 
 0968 
 
 16 
 
 8 
 
 0.05287 
 
 0385 
 
 24 
 
 
 
 0.01330 
 
 00954 
 
 11 
 
 12 
 
 0.12619 
 
 0925 
 
 16 
 
 16 
 
 0.04979 
 
 0362 
 
 24 
 
 12 
 
 0.01216 
 
 00872 
 
 tl 
 
 18 
 
 0.12063 
 
 0885 
 
 17 
 
 
 
 0.04689 
 
 0341 
 
 25 
 
 
 
 0.01111 
 
 00797 
 
 12 
 
 
 
 0.11533 
 
 0846 
 
 17 
 
 8 
 
 0.04416 
 
 0321 
 
 25 
 
 12 
 
 0.01015 
 
 00728 
 
 12 
 
 6 
 
 0.11025 
 
 0809 
 
 17 
 
 16 
 
 0.04159 
 
 0303 
 
 26 
 
 6 
 
 0.00928 
 
 00637 
 
 12 
 
 12 
 
 0.10540 
 
 0773 
 
 18 
 
 
 
 0.03916 
 
 02809 
 
 27 
 
 
 
 0.00775 
 
 00532 
 
 12 
 
 18 
 
 0.10076 
 
 0739 
 
 18 
 
 12 
 
 0.03579 
 
 02567 
 
 28 
 
 
 
 0.00647 
 
 00444 
 
 13 
 
 
 
 0.09633 
 
 0701 
 
 19 
 
 
 
 0.03271 
 
 02346 
 
 29 
 
 
 
 0.00541 
 
 00371 
 
 13 
 
 8 
 
 0.09072 
 
 0660 
 
 19 
 
 12 
 
 0.02990 
 
 02144 
 
 30 
 
 
 
 0.00452 
 
 
 13 
 
 16 
 
 0.08543 
 
 0622 
 
 20 
 
 
 
 0.02732 
 
 01960 
 
 40 
 
 
 
 0.000747 
 
 
 14 
 
 
 
 0.08046 
 
 0586 
 
 20 
 
 12 
 
 0.02497 
 
 01791 
 
 50 
 
 
 
 0.000123 
 
 
 14 
 
 8 
 
 . 0.07577 
 
 0552 
 
 21 
 
 
 
 0.02282 
 
 01637 
 
 
 
 o 
 
 0.00000 
 
 
172 
 
 APPENDIX 
 
 
 9 
 
 I 
 
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 CS 
 
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 08 
 
 
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 c8 
 
 
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INDEX OF SUBJECTS 
 
 Absorption, of a rays, 32, 33 ; of j8 
 rays, 41 ; of 7 rays, 45 ; of hydrogen 
 in glass under a radiation, 112 ; of 
 xenon (chemical?), 127; infra-red of 
 methyl acetate. 144. 
 
 Acceptor, photochemical, 133. 
 
 Acetone, photo-hydrolysis of, 136, 145. 
 
 Actinium series, 23. 
 
 Active, deposit, — equilibrium with 
 emanation, 25 ; — properties, 35 ; 
 
 — heat evolution, 65 ; centers of 
 luminescence, 54 ; — recovery theory 
 of, 54 ; deposit, diffusion and loca- 
 tion of, 105 ; — hydrogen, 112 ; 
 
 — molecules, 143 ; — non-existence 
 of, 143. 
 
 Alkaline halides, decomposition of by 
 penetrating rays, 62 ; — sulfides, 
 phosphorescence of, 57. 
 
 Alpha Particle, positive charge, 22 ; 
 corpuscular nature. 22 ; as chemical 
 agent. 22, 73, 92, 97 ; kinetic energy, 
 26 ; identity of from various sources, 
 26 ; range, end of, 27 ; in minerals, 
 51 ; radiometric determination of 
 range, 77 : velocity, 28 ; equation of, 
 31 ; unit ionization by, 29, 81, 116 ; 
 enumeration of, 31, 79 : distribution 
 in time and space, 36 ; ionization 
 curve of. 30. 79 ; stopping power 
 toward, 32, 33 ; change of valence 
 by emission of, 42 ; heat of absorp- 
 tion, 65 ; decomposition of ammonia 
 by, 73, 85, 93, 97 ; of other gases, 
 85, 92, 93, 97 ; ozonization by, 75, 
 85, 113 ; thin bulbs, penetrable by, 
 76, 80 ; number from radium, 79 ; 
 average path of in spheres, 82 ; syn- 
 thesis of hydrogen chloride by, 85 ; 
 equilibrium of water when radiated 
 by, 91, 104 ; specific ionization of 
 gases by, 92 ; comparison of chem- 
 ical effect of penetrating rays with 
 that of. 112: thermal theory of 
 chemical effect, 116 ; recoil atoms 
 from, 154 ; atomic disruption by, 
 162; scattering by, 163. 
 
 Ammonia, decomposition by a particles, 
 72. 85, 93, 98 ; by electrical dis- 
 charge, 126 ; equilibrium of, 72. 73. 
 
 Analysis, positive ray method, 149 ; of 
 chemical effect of recoil atoms, 157. 
 
 Anthracene, photochemical polymeriza- 
 tion of, 134. 
 
 Argon, two isotopes of, 153. 
 
 Arsenic, simple element, 153. 
 
 Atom, radioactive disintegration, 21, 
 24 ; -ic weight change by emission 
 of an a particle, 24 ; -ic number, 
 45 ; -istic theory of photosynthesis 
 of hydrogen chloride, 141 ; Front's 
 hypothesis, 151 ; law of whole num- 
 ber atomic weights, 152 ; recoil, 154 ; 
 chemical action by recoil, 156 ; im- 
 
 Eact of a particles with light and 
 eavy — , 163 ; disruption of, 22, 
 
 162 ; of nitrogen and oxygen, 166 ; 
 swift hydrogen — , 164 ; from nitro- 
 gen, 166 ; nuclear structure of, 167 ; 
 quantity of disruption, 168 ; gain in 
 energy by disruption, 167 ; multiply 
 charged — s, 150. 
 
 Barium, effect on color of fused ra- 
 dium chloride, 49 ; — sulfide, phos- 
 phorescence, 57. 
 
 Beta particle. See also Penetrating 
 rays. Nature of, 22 ; properties, 40 ; 
 change of valence by emission of, 
 42 : number of from radium, 42 ; 
 unit ionization by, 42 ; chemical ac- 
 tion of, 47 ; coagulation of colloids 
 by, 47 ; heat of absorption, 65 ; syn- 
 thesis of hj'drogen chloride by, 85, 
 119. 
 
 Bleaching of dyes, 138, 
 
 Boron, two isotopes of, 153, 
 
 Bromine, photo-bromination of toluene, 
 138 ; of hexahydrobenzene, 138 ; of 
 hydrogen not similar to that of 
 chlorine, 142 ; two isotopes of, 152. 
 
 Canal rays. See also Positive rays. 
 Discovery of, 148, 
 
 Carbon, tetrachloride — radiochemical 
 action on, 63 ; dioxide, decomposition 
 by a particles, 85, 93, 121 ; mon- 
 oxide, reduction by hydrogen (em- 
 anation), 90; decomposition by o 
 particles, 97 ; no isotopes of, 153, 
 
 Catalysis, 143 ; over-emphasis in radio- 
 chemistry, 19 ; action of a rays non- 
 catalytic, 59 ; radiation theory of, 
 144. 
 
 Chemical action, by o particles, 73, 92, 
 97, 110, 122 ; by penetrating rays, 
 47 ; in gases by electrical discharge, 
 43 ; of emanation, kinetic equation, 
 95, 99 ; , of a rays, ther- 
 mal theory of, 115, 116 ; ionization 
 by, 128-9 ; radiation theory of, 142, 
 145 ; by a recoil, 156. 
 
 Chemical effect, of penetrating rays, , 
 47 ; of radium emanation, 65, 72, 89, 
 95 ; of electrical discharge in gases, 
 43. 123 ; of recoil atoms. 156 ; tables, 
 157, 160. See also Chemical Action. 
 
 Chlorine, from radium (barium) chlo- 
 
 . ride, 48 ; combination with hydrogen, 
 by a rays, 85 ; by j8 and 7 rays, 85, 
 119 ; by X rays, 129 ; photochemical, 
 118, 132, 141 ; inhibition of, 119 ; 
 separation of isotopes of, 154. 
 
 Chloroform, radiochemical action on, 
 64. 
 
 Collision, ionisation by, 43, 124. 
 
 Colloidal, coagulation by j8 and 7 rays, 
 47; coloration theory, 50, 
 
 Color, and luminescence by radium, 52 ; 
 loss of and thermoluminescence, 53 ; 
 change from brown to violet by heat- 
 ing, 52, See also Coloration. 
 
 173 
 
174 
 
 INDEX OF SUBJECTS 
 
 Coloration, of salts, 47 ; by radium, 50 ; 
 
 colloidal theory of, 51 ; of minerals, 
 
 51, 52 ; of glass, 51. 
 Corona, ozonization by, 81, 125 ; active 
 
 hydrogen in, 112. 
 Corpuscular nature of a particle, 21. 
 Crystal structure by 7 ray method, 44. 
 Curie, definition of, 25. 
 Cylinder, average of a particles in, 83. 
 
 Decay, constant (X) of radioactive 
 substances, 23 ; of luminosity of zinc 
 sulfide, 54. 
 
 Decomposition table of Radium emana- 
 tion. Appendix A ; of radium salts, 
 47 ; inorganic by penetrating rays, 
 63 ; organic, 64 ; of water by polo- 
 nium, 75 ; by radium solution, 60, 
 75, 85 ; of hydriodic acid by pene- 
 trating rays, 63 ; of water by em- 
 anation, 68, 87, 113, 120; of gases 
 by emanation, 85, 93, 97; of hj- 
 driodic acid by a rays, 85 ; of solid 
 salts by ^ and 7 rays, 86 ; of am- 
 monia by electrical discharge, 125 ; 
 thermal of phosphine, anomalous, 
 145; of atoms, 22, 162, 167; of 
 nitrogen and oxygen by a rays, 166 ; 
 of nitrogen pentoxide, 146. 
 
 Dehydration, of radium salts, 49. 
 
 Deposit, active-rate of diffusion, 105 ; 
 location of, 105. 
 
 Diameter, of sphere, — influence on 
 chemical action produced by radium 
 emanation, 100. 
 
 Diffraction of X rays by crystals, 44. 
 
 Diffusion of active deposit, 105. 
 
 Disintegration, of quartz by radium 
 ravs, 49 ; of atoms by a particles, 
 162, 166. 
 
 Dyes, bleaching of, 138. 
 
 Einstein photochemical equivalence, 
 132; tests of, 133, 136, 146; excess 
 of chemical action, 119. See also 
 Equivalence and Photochemistry. 
 
 Electrical, deflection of o rays, 22 ; of 
 positive rays, 150 ; of swift hydrogen 
 atoms, 165 ; discharge in gases, 37 ; 
 discharge, ozonization by, 124 ; de- 
 composition of ammonia by, 126 ; 
 combination of hydrogen and oxygen 
 by, 125 ; chemical effect of, 123 ; 
 — charge, production by chemical ac- 
 tion, 128. 
 
 Electron, -ic nature of /3 particle, 22; 
 variable mass of, 41 ; — theory of 
 photochemical action, 119 ; loosening 
 of valence -s by light, 134, 140; 
 possibility of atomic disruption by, 
 168. See also Therm-electron. 
 
 Emanation (radium), equilibrium with 
 active deposit, 25 ; properties of, 35 ; 
 chemical effect of, 65, 66 ; decom- 
 position of water, ice and water 
 vapor by, 69. 87, 120; action of on 
 hydrogen, 85 ; on oxygen, 72, 85 ; 
 determination of by 7 radiation, 77 ; 
 purification of, 79 ; effective in re- 
 duction of carbon monoxide by hy- 
 drogen, 90 ; kinetic equation for 
 action of — on gases, 95, 99 ; effect 
 of volume on chemical efficiency of, 
 101 ; disappearance of — from spec- 
 trum tubes, 127 ; decay table. Ap- 
 pendix, Table A. 
 
 Energy, radiant, 17 ; kinetic, concen- 
 tration in the a particle, 22 ; of 
 Ionization, 29; radiated by various 
 rays, 42; utilization, chemical of 
 
 penetrating rays, 01 ; small in photo- 
 chemical action, 123 ; of a rays in 
 chemical action, 122 ; of recoil 
 atoms, 155 ; of swift hydrogen atoms, 
 163 ; gain in by artificial radio- 
 activity, 168. 
 
 Enumeration, of a particles, 31, 79 ; of 
 )8 particles, 42. 
 
 Equilibrium, radioactive, 24 ; of am- 
 monia (emanation), 72; of hydro- 
 gen, oxygen, and water (emanation), 
 91, 104. 
 
 Equivalence, ionic-chemical, 75, 82, 85, 
 90, 114; exceptions to, 117, 120; of 
 ozonization and ionization, 80 ; 
 photochemical, 132, 133, 138, 146. 
 
 Esters, radiochemical formation and 
 decomposition, 63. 
 
 Excess, of hydrogen from decomposi- 
 tion of water by radium, 48 ; by em- 
 anation, 61 ; influence of — of hy- 
 drogen or oxygen on rate of syn- 
 thesis of water, 107-10 ; of chemical 
 action over ionization, 118 ; of ion- 
 ization over chemical action, 120 ; 
 over theory of photochemical action, 
 136, 140. 
 
 Explosion, ionization by, 130 ; infra- 
 red radiation in, 146. 
 
 Faraday's Law, applicable to decom- 
 position of water by polonium, 75 ; 
 to ozonization by a rays, 80 ; In- 
 applicable to ozone formation, 124, 
 and ammonia decomposition by elec- 
 trical discharge, 126. 
 
 First order reaction, 24, 145. 
 
 Fluorine, simple element, 153. 
 
 Fumaric acid, radiochemical action on, 
 63, 139. 
 
 Gamma Rays, nature, 22 ; properties, 
 44 ; heat of absorption, 65 ; deter- 
 mination of emanation by. 77. 
 
 Gas, -es, specific ionization and stop- 
 ping power for a particles, 32 ; dis- 
 appearance from discharge tubes, 39, 
 127 ; evolution from radium salts 
 and solutions, 48 ; chemical action 
 of electrical discharge in, 43, 123 ; 
 
 — pipette (Ramsay), 66; kinetic 
 equation for chemical action of em- 
 anation on, 95, 99 ; — reactions and 
 explosions, ionization by, 129, 130: 
 
 — ions, variety of. 81 ; rate of 
 recombination of, 117. 
 
 Glass, coloration by radium, 53 ; ab- 
 sorption of hydrogen in under o 
 radiation. 112 ; thin — capillaries 
 and bulbS, 76, 87. 
 
 Half life period of radioactive ele- 
 ments, 23 ; relation to half period of 
 chemical action by emanation. 70. 
 
 Heat evolution, continuous from ra- 
 dium, 20 ; quantity of from radium, 
 65 ; quantity of from a, i3, and 7 
 rays, 65. 
 
 Helium, a particle, 22 ; accumulation 
 from radioactive change, 24 ; simple 
 element, 153 ; — particles of mass, 
 3, 167. 
 
 Hydrogen, excess of decomposition of 
 water by radium, 48 : by emanation, 
 80 ; action of emanation on, 61, 72, 
 85, 111 : combination with oxygen, 
 72, 85, 89, 97. 99, 101, 107 ; in elec- 
 trical discharge, 125 ; — -oxygen 
 equilibrium (emanation), 91, 104; 
 influence of excess of on synthesis 
 
INDEX OF SUBJECTS 
 
 175 
 
 of water, 109 ; — chloride, synthesis 
 of by a rays, 85. 135, 137, 141 ; by 
 /3 and y rays, 85, 119 ; by X rays, 
 129; by light, 128, 132; — iodide, 
 photolysis of, 134; decomposition of 
 by a rays, 86 ; — pero^de, syn- 
 thesis, 62 ; energy utilization of 
 penetrating rays in synthesis of. 61 ; 
 photolysis of, 188, 201 ; — .sulfide, 
 decomposition by emanation, 93, 
 121 ; inhibition of photochemical ac- 
 tion of — and chlorine, 118 ; tri- 
 and mono-atomic, active, 112 ; re- 
 duction of carbon monoxide by — 
 (emanation). 90; absorption in glass 
 under a radiation, 112 ; simple ele- 
 ment, 153 ; swift — atoms, from 
 hydrogen, 164 ; from nitrogen, 167. 
 
 Ice, decomposition by a rays, 88, 120. 
 
 Increment of internal energy (chem- 
 ical), 143. 
 
 Infra-red, radiation in chemical action, 
 142, 145 ; — absorption of methyl 
 acetate, 144. 
 
 Inhibition, of photochemical interac- 
 tion of hydrogen and chlorine, 119 ; 
 general by oxygen of photo-reactions, 
 135. 
 
 Interference, of X rays in crystals, 44. 
 
 Iodide, photolysis of hydrogen — , 134 ; 
 decomposition of -s by jS and 7 rays, 
 62. 
 
 Iodoform, phot-oxidation of, 138. 
 
 Ionization. See also Ions. — by o 
 particle, 27 ; curve of, 30, 136 ; by 
 collision, 39, 43, 124 ; Townsend's 
 formula, 43 ; — formula of Duane 
 and Laborde, 66, 83, 85 ; by therm- 
 electrons, 43 ; specific — of gases by 
 a particle, 92 : — theory of chemical 
 action, 74, 124 ; calculation of, 78, 
 
 83 ; , evaluation of M/N, 
 
 103 ; unit — by a and jS rays, 29, 42, 
 80, 116 ; — by chemical action, 128, 
 130 ; by recoil, 155. 
 
 Ions, energy to produce one pair of, 
 29 ; ionic-chemical equivalence. 75, 
 115, 140 ; cluster — , 81 ; variety of 
 gas — , 81, 150 ; rate of recombina- 
 tion of gas — , 117 ; absence of in 
 chemical action, 128. See also Ion- 
 ization. 
 
 Isotopes, analysis of by positive rays, 
 149 ; of neon, 151 ; of various ele- 
 ments, 152 ; separation of, 151, 153 ; 
 of helium, 167 ; by atomic disrup- 
 tion. 168 : radioactive — , Appendix, 
 Table B, 172. 
 
 Kinetic, -s of radioactive transforma- 
 tion, 23 ; energy of a particle. 26 ; 
 -s of gas reactions (radiochemical), 
 94 ; equation of, 95 ; application, 99 ; 
 — equations, 107 ; -s of water svn- 
 thesis (by emanation), 100. 107; 
 chemical -s and radiation, 147 ; en- 
 ergy of recoil atoms, 155. 
 
 Krypton, six isotopes of, 153. 
 
 Lambda, decay constant, definition of, 
 23. 
 
 Lead, attempt to separate isotopes of, 
 154. 
 
 Lenard rays, ozonization by, 80, 123. 
 See also Electrons. 
 
 Levulose, photolysis of, 134. 
 
 Luminescence, blue of fused radium 
 salts, 50 ; and color by radium, 51, 
 53 : active centers of. 54 ; decay, 54, 
 and recovery, of in zinc sulfide, 54. 
 
 Magnetic deflection, of a particles, 22 ; 
 of j3 particles, 41 ; of positive rays, 
 148 ; of swift hydrogen atoms, 167. 
 
 Maleic acid, radiochemical action on, 
 63, 139. 
 
 Manometric measurement of the ve- 
 locity of gas reactions, 65. 
 
 Mass, of electron variable, 41 ; — 
 spectrograph, 149 ; — spectra, 151 ; 
 of swift particles from hydrogen, 
 nitrogen and oxygen atoms, 167. 
 
 Mercury, effect of hydrogen and oxygen 
 on, in presence of radium emanation, 
 111 ; isotopes of, 153 ; separation, 
 154. 
 
 Meso-thorium, life period, 55 ; in lu- 
 minous material, 55. 
 
 Mica, pleochroic rings in, 52. 
 
 Minerals, coloration of, 50, 52 ; range 
 of a rays in, 51 ; pleochroic rings 
 and geological age of, 51 ; photo- 
 electric effect in, 50, 52. 
 
 Molecules, active, 143. 
 
 Monatomic, character of radioactive 
 transformations, 23, 25 ; hydrogen, 
 112. 
 
 Neon, isotopes of, 151; triad (?), 151, 
 153. 
 
 Nitro-benzaldehyde, radiochemical con- 
 version to acid, 63. 
 
 Nitrogen, simple element, 153 ; disrup- 
 tion of, 166 ; swift hydrogen atoms 
 from, 167 ; swift helium atoms from, 
 167 ; decomposition of nitrous oxide 
 by a rays, 85, 93; of — pentoxide, 
 147. 
 
 Number, of a, 31, j3, 41, and 7 rays 
 from radium, 42 ; atomic — , 45. 
 
 Order of reaction, first, 24. 
 
 Oxygen. See also Ozone, Ozonization, 
 and Phot-oxidation. Combination 
 with hydrogen, by emanation, 72, 85, 
 97, 99, 101, 107 ; by electrical dis- 
 charge, 125 ; effect of emanation on 
 — in the presence of mercury. 111 ; 
 effect of excess of — in the syn- 
 thesis of water by emanation, 110 ; 
 inhibition by, 135 ; simple element, 
 153 ; disruption and swift particles 
 from, 165. 
 
 Ozone. See also Ozonization. Forma- 
 tion by a rays, 80 ; photolysis. 1,36. 
 
 Ozonization, by a rays, 76, 80, 85, 123 ; 
 bv Lenard rays, 80, 123 ; in corona, 
 124 ; photochemical, 134 ; theory of, 
 123. 
 
 Path, average of a rays, calculation, 
 82 ; influence on chemical activity of 
 radium emanation, 100. 
 
 Penetrating rays, from radium, 34 ; 
 chemical action of, 47, 61. 112 ; en- 
 ergy utilization in synthesis of hy- 
 drogen peroxide, 61 ; decomposition 
 of hydriodic acid, 63 ; of water by, 
 114 ; synthesis of hydrogen chloride 
 by, 85, 119. 
 
 Phosgene, photo-synthesis of, 138. 
 
 Phosphine, anomalous decomposition 
 of, 145. 
 
 Phosphorescent, alkaline earth sul- 
 fides, 57 ; zinc sulfide, 54 ; willemite, 
 57. 
 
 Phosphorus, simple element, 153. 
 
 Photochemical, reduction of ferrous 
 sulfate, 63 ; small energy utilization 
 in — action, 123 ; — equivalence, 
 132, 138, 145 ; comparison with 
 
176 
 
 INDEX OF SUBJECTS 
 
 ionic-chemical equivalence, 140 ; 
 
 — interaction of hydrogen and 
 chlorine, 136: inhibition of, 118; 
 synthesis of phosgene, 138 ; ozoniza- 
 tion, 134 ; bromination of toluene, 
 138 ; of hexahydrobenzene, 139 ; the- 
 ory of — action, 140 ; decomposition 
 of nitrogen pentoxide, 147. See also 
 Photochemistry and Photolysis. 
 
 Photochemistry, texts of, 7 ; relation 
 of to radiochemistry, 18 ; comparison 
 with a ray effects, 57 ; — of hydro- 
 gen-chlorine reaction, 118, 132 ; of 
 primary, 134, and secondary light 
 reactions, 137. 
 
 Photo-electric effect and coloration of 
 minerals, 50, 52. 
 
 Photolysis, of ammonia, hydriodic acid 
 gas, levulose, ozone, 134 ; of hydro- 
 gen peroxide, ozone, 136 ; of hydro- 
 gen bromide, 140. 
 
 Phot-oxidation, of quinine, 137 ; of 
 iodoform and hydrogen iodide, 137. 
 
 Pleochroic rings in mica, 52. 
 
 Polonium, a particles from, 36 ; decom- 
 position of water by, 75. 
 
 Positive, charge of a particle, 22 ; 
 
 — rays, 148 ; analysis by. 149 ; 
 method of, 149 ; magnetic deflection 
 of, 148 ; isotopes discovered by, 151. 
 
 Potassium, radioactivity of, 24 ; — 
 iodide (acid), decomposition by o 
 rays, 86. 
 
 Primary light reactions, 133 ; Table of, 
 134. 
 
 Prout's Hypothesis, renewed impor- 
 tance of, 151. 
 
 Qualitative and quantitative radio- 
 chemical effects, 46. 
 
 Quantum theory, 132, 136. 
 
 Quartz, disintegration by radium rays, 
 49. 
 
 Radiation, forms of, 18, 21 ; continu- 
 ous emission by radium, 20 ; emana- 
 tion as source of, 65 ; theory of 
 chemical action of, 142 ; — theory 
 of catalysis, 144 ; distribution of — 
 in time and space, 37; infra-red 
 
 — in explosions, 146. See also o. 
 P, 7, positive and Lenard rays and 
 recoil atoms. 
 
 Radioactivity, theory of, 20, 21 ; phe- 
 nomena of, 21 ; series of, 23 ; — of 
 potassium and rubidium, 24 ; radio- 
 active equilibrium, 25 ; standards 
 
 and units of, 25 ; , isotopes 
 
 resulting from. Appendix, Table B, 
 172 ; "artificial" — , 166, 168. 
 
 Radiochemistry, definition, 17 : relation 
 to photochemistry, 18 ; problems of, 
 74. 
 
 Radio-thorium, life of and use in lu- 
 minous material, 55. 
 
 Radium. See also Emanation and 
 Radiation. Discovery of radiations, 
 20; equilibrium with emanation. 25; 
 
 — family, Table I, 28 ; standards, 
 26 ; number of a, 31, /3, 42, and y 
 rays from, 42 ; — salts and solution, 
 gas evolution from, 47 ; precautions 
 In sealing — in tubes, 48 ; — lu- 
 minous paint, 54 ; recovery of lu- 
 minosity in, 54 ; disintegration of 
 quartz by — , 49 ; coloration l)y, 50 ; 
 l)lue luminescence of fused — salts, 
 50 ; decomposition of water in — 
 pplVtloR, 59, 75, 85, 
 
 Radium A, B, C, D, E, F, properties, 
 36 ; heat from Ra A and Ha C, 65. 
 
 Range, of a particle, 27 ; end of, 27 ; 
 in minerals, 51 ; radiometric deter- 
 mination of, 77 ; of swift atoms, 163. 
 
 Recoil, from a particles, 23, 154; en- 
 ergy and velocity of — atoms, 155 ; 
 chemical action of, 156. 
 
 Reflection of X rays by crystals, 44. 
 
 Roentgen rays. See X rays. 
 
 Rubidium, radioactivity of, 24. 
 
 Salts, coloration of by radiation, 47 ; 
 of radium, gas evolution from, 48 ; 
 decomposition of in solution, 03 ; in 
 solid state, 86. 
 
 Saturation current, as a measure of 
 ionization, 37. 
 
 Scattering, of /3 particles, 41 ; of a 
 particles, 163. 
 
 Scintillation, of zinc sulflde by a rays, 
 53 ; by swift particles from hydro- 
 gen, 164 ; nitrogen and oxygen, 163, 
 166. 
 
 Secondary light reactions, 132; table 
 of, 136. 
 
 Separation of isotopes, 154. 
 
 Sidot's blende, 54. See also Zinc Sul- 
 flde. 
 
 Silent discharge, 124. See also Elec- 
 trical discharge. 
 
 Silicon, two isotopes of, 153. 
 
 Solids, chemical effect of radiation on, 
 86, 121. 
 
 Solution, radium-gas evolution from, 
 48 ; decomposition of water in, 86. 
 
 Sphere, average path of a particles in, 
 82 ; influence of size on chemical ac- 
 tion of emanation, 100. 
 
 Standard, radium, 26. 
 
 Stopping power toward a particles, 32, 
 33 ; Table II, 33. 
 
 Sugar inversion, radiochemical, 63. 
 
 Sulflde, alltaline- earth, phosphorescent, 
 57 ; zinc, phosphorescent, 54. 
 
 Sulfur, simple element, 153. 
 
 Synthesis, of hydrogen chloride by a 
 rays, 85 ; by ^ and y rays, 119 ; by 
 X rays, 128; by light, 118, 136; of 
 water, ammonia, and hydrogen bro- 
 mide by emanation. 72. 85, 89, 97, 
 99, 116; of water by electrical dis- 
 charge, 125. 
 
 Temperature coeflicient, of radiochem- 
 ical action on water, 61 ; on potas- 
 sium iodide, 63 ; on hydrogen sulflde. 
 ammonia, and nitrous oxide, 93 ; of 
 reaction velocity, 143. 
 
 Theta ((?), average life period, deflni- 
 tion, 24. 
 
 Therm-electrons, ionization by, 43. 
 
 Thermoluminescence, and loss of color, 
 52. 
 
 Thorium series, 23. See also Meso- 
 and Radio-thorium. 
 
 Toluene, radiochemical action on, 64 ; 
 photo-bromination of, 138. 
 
 Tube, X ray of Coolldge, 40, 45; thin, 
 o ray-penetrable, 76, 80. 
 
 Ultra-violet light, chemical effects of, 
 68. 
 
 Unit, -s of radioactivity. 26 ; — Ioniza- 
 tion by a particles, 29 ; by )3 and y 
 rays, 42. 
 
 Uranium, series, 28; Table I, 28; 
 equilibrium in, 24. 
 
INDEX OF SUBJECTS 
 
 177 
 
 Valence, change of by emission of a 
 and /8 particles, 42 ; — electrons, 
 loosening of by light, 134, 140. 
 
 Velocity, equation of a particle, 31 ; of 
 
 gas reactions by manonietric 
 
 method, 65 ; of diffusion of active 
 deposit, 105 ; abnormal of phosphine 
 decomposition, 144; of recoil atoms, 
 155 ; of swift hydrogen atoms, 163. 
 
 Water, excess hydrogen from decom- 
 position of by radium, 48 ; by emana- 
 tion, 61 ; synthesis, 72 ; decomposi- 
 tion by emanation, 69, 89, 113, 120 ; 
 by electrical discharge, 125 ; by po- 
 lonium, 75 ; by radium in solution, 
 59, 75 ; synthesis of by emanation, 
 89, 97, 99, 117 ; — vapor, decomposi- 
 tion by emanation, 87, 120 ; equilib- 
 
 rium with hydrogen and oxygen 
 (emanation), 91, 104. See also Ice. 
 Willemite, phosphorescence of, 56. 
 
 X rays, discovery, 20, 44 ; properties, 
 44 ; ionization by shock in — tube, 
 39 ; interference, diffraction and re- 
 flection by crystals, 44 ; structure of 
 crystals by, 44 ; — tube of Coolidge, 
 40, 45 ; characteristic, synthesis of 
 hydrogen chloride by, 129. 
 
 Xenon, absorption of by electrodes 
 (chemical?), 127; five isotopes of, 
 153. 
 
 Zinc sulfide, pure, non-luminescent, 70; 
 decay of luminosity in, 54 ; recovery 
 of luminosity in, 54. 
 
INDEX OF AUTHORS 
 
 Anderegg, F. O., ozonization In the 
 
 corona, 125. 
 Arrhenius, S., active molecules, 143. 
 Aston, F. W., positive ray analysis, 
 
 149 ; isotopes of neon, 151 ; of other 
 
 elements, 152. 
 Aston, F. W. See Lindemann, F. A., 
 
 151. 
 
 V. Bahr, B., photolysis of ozone, 
 137. 
 
 Baly, E. C. C, Einstein's Photochem- 
 ical Law, 145. 
 
 Bancroft, W, D., colloidal coloration, 
 50. 
 
 Barkla, C. G., characteristic X radia- 
 tion, 45. 
 
 Baslcerville, C. See Kunz, G. P., 57. 
 
 Becquerel. H., discovery of Becquorel 
 rays, 20, 44 ; chemical action of /3 
 and 7 rays, 47. 
 
 Benrath, A., photochemistry, 7. 
 
 Bergwitz, K., decomposition of water 
 by polonium, 75. 
 
 Berth clot, D., and Gaudochon, H., pho- 
 tolysis of levulose, 134. 
 
 Bhandarkar, D. S. See Trautz, M., 
 145. 
 
 Bigelow, S. L., first order reactions, 24 ; 
 Front's Hypothesis, 152. 
 
 Bloch, Ij., ionization by chemical ac- 
 tion, 129. 
 
 Bodenstein, M., synthesis of hydrogen 
 chloride by a rays, 85, 119 ; photo- 
 chemical equivalence, 132 : primary 
 light reactions, 134 ; secondary light 
 reactions, 137 : photolysis of hydro- 
 gen iodide, 134 ; theory of photo- 
 chemical action, 134. 140. 
 
 Bodenstein, M., and Dux. W., photo- 
 synthesis of hydrogen chloride, 135, 
 137. 
 
 Bodiander, G. See Rungo. G., CO. 
 
 Bohr, N., atomic model, 27. 
 
 Boll, M., photochemical action, 137. 
 
 Boll, M.. and Job. P., photo-hydrolysis 
 of chloroplatinic acid, 137. 
 
 Bragg, W. n., radioactivity, 8 ; kinetic 
 energy of a particle, 20 ; ionization 
 curve of a particle, 30, 103 ; stop- 
 ping power for a particle, 32, 33 : 
 first calculation of ionic-chemical 
 equivalence, 75 ; specific ionization 
 of gases by o particles, 92. 
 
 Bragg, W. II., and Bragg, W. L., crys- 
 tal structure, 44. 
 
 Bragg, W. H., and Klooman, R. D., 
 Identity of a particles, 20. 
 
 Bragg, W. L., reflection of X rays by 
 crystals, 44. 
 
 Bragg. W. L. See Bragg. W. IT., 44. 
 
 Brizard, L. See Broglle. Af.. 130. 
 
 Broglie. M.. and Brizard, li.. absence 
 of ionization by chemical action, 
 130. 
 
 Bronsted, J. N., and v. Hevesy, G., 
 separation of isotopes of mercury, 
 154. 
 
 Brooks, IT. T., recoil from o par- 
 ticles, 154. 
 
 Bruner, L., and Czernicki, S., photo- 
 bromination of toluene, 138. 
 
 Bunsen, R., and Roscoe. IT. E., photo- 
 synthesis of hydrogen chloride, 
 118. 
 
 Callow, R. H., and Lewis, W. M. McC, 
 radiation in chemical action, 142. 
 
 Cameron. A. T., and Ramsay, W., chem- 
 ical effects of emanation, (50 ; ap- 
 paratus, 66-9 ; synthesis of water by 
 emanation, 85, 97 ; decomposition of 
 ammonia, hydrogen chloride, and 
 carbon dioxide by emanation, 85 ; 
 synthesis of ammonia by emanation, 
 85, 98 ; decomposition of carbon 
 monoxide by emanation, 97. 
 
 Campbell, N. R., and Ryde, .T. W. H., 
 disappearance of gas in electrical 
 discharge, 128. 
 
 Campbell, N. R., and Wood, A., radio- 
 activity of potassium and rubidium, 
 24. 
 
 Chapman, D. L., theory of isotopic 
 separation, 154. 
 
 Chapman, D. L., and Gee, F. IT., photo- 
 synthesis of phosgene, 138. 
 
 Chapman, D. L., and MacMahon, P. S., 
 inhibition of photochemical action, 
 119. 
 
 Coblentz. W. W., infra-red absorption 
 of methyl acetate, 144. 
 
 Collie, J. N., absorption of xenon 
 (chemical?), 127. 
 
 Coolidge, W. D., X ray tube, 40, 45. 
 
 Core, A. F., theory of isotopic separa- 
 tion, 154. 
 
 Creighton, IT. J. M., and McKenzie, A. 
 G., decomposition of hydriodic acid 
 by penetrating rays. 03. 
 
 Curie, P., and Curie, Mme. P., colora- 
 tion of glass, 47. 
 
 Curie, P.. and Debierne, A., gas evolved 
 by radium salts and solutions. 48. 
 
 Curie. P.. and Laborde, A., theory of 
 radioactivity. 20. 
 
 Curie, Mme. P., radioactivity. 8, 24 ; 
 corpuscular nature of a particle, 22 ; 
 radium standards. 20, 59 ; lumines- 
 cence and color, 51 ; energy of pene- 
 trating rays chemically utilized, 61 ; 
 ionic chemical equivalence. 75. 
 
 Curie, Mme. P. See Curie, P., 47. 
 
 Czernicki, S. See Bruner, L., 138. 
 
 Daniels, F., and Johnston, E. II., de- 
 composition of nitrogen pentoxide, 
 147. 
 
 Darwin, C. G., X radiation, 45 ; scat- 
 tering of a particles, 163. 
 
 178 
 
INDEX OF AUTHORS 
 
 179 
 
 David, W. T., infra-red radiation in 
 chemical reaction, 146. 
 
 Davies, J. H., decomposition of am- 
 monia by electrical discharge, 126. 
 
 Davis, C. W., pure zinc sulfide, non- 
 luminous, 56. 
 
 Debieme, A., excess of hydrogen in de- 
 composition of water, 48; decom- 
 position of radium solution, S5 ; dif- 
 fusion of active deposit, 105 ; de- 
 composition of water by penetrating 
 rays, 114 ; thermal theory of a ray 
 chemical effect, 116. 
 
 Debierne, A. See Curie, P., 48. 
 
 Doelter, C, coloration of minerals by 
 radium, 50. 
 
 Draper, J. W., photochemical action, 
 118. 
 
 Duane, W., end of range of a particle, 
 27 ; thin a ray bulbs, 76. 
 
 Duane, W., and Scheuer, O., decom- 
 position of water by emanation, 60, 
 86 ; excess hydrogen from, 61 ; extra- 
 polation of ionization by emanation, 
 84 ; decomposition of water, ice, and 
 water vapor, 85-9, 120. 
 
 Duane, W., and Hu, K.-P., X radia- 
 tion, 45. 
 
 Duane, W., and Laborde, A., ionization 
 formula, 66, 84. 85, 86. 
 
 Duane, W., and Shimizu, T., X radia- 
 tion, 45. 
 
 Duane, W., and Wendt, G. L., active 
 hydrogen, 112. 
 
 Dux, W. See Bodenstein, M., 135, 137. 
 
 Einstein, A., photochemical equivalence 
 law, 132. 
 
 Fajans. K.. change of valence by a or 
 $ radiation. 42 : radioactive isotopes, 
 Appendix, Table B. 
 
 Falckenberg, G., decomposition of am- 
 monia by electrical discharge, 126. 
 
 Fall?, K. G., first order reactions, 24. 
 
 Flamm, L., and Mache, H., calculation 
 of ionization by emanation, 83. 
 
 Fletcher, A. L. See Joly, J., 52. 
 
 Fletcher, H. See Millikan, R. A.. 42. 
 
 Forbes, G. S, See Luther, R., 134. 
 
 Friedrich, W., Knipping, P., and Laue, 
 M., crystal diffraction, 44. 
 
 Fulcher. G. S.. atomic disruption and 
 artificial radioactivity, 166, 168. 
 
 Gaudechon, H. See Berthelot, D., 134. 
 
 Gee, F. H. See Chapman. D. L., 138. 
 
 Geiger, H., ionization curve of o par- 
 ticle, 30 : velocity equation of a 
 particle, 31. 
 
 Geiger, IT. See Malcower, W., 77. 
 
 Geiger, H., and Marsden, E., scatter- 
 ing of a particles, 163. 
 
 Geiger, H. See Rutherford, E. E., 22, 
 36. 
 
 Giesel, F., coloration of salts, 47. 
 
 Goldberg, B. See Luther, R., 135. 
 
 Goldstein, E., coloration by cathode 
 rays, 51 ; discovery of canal rays, 
 148. 
 
 Gottschalk. V. H. See Millikan, R. A., 
 29. 81, 116. 
 
 Griffith. R. O., Lamble, A., and Lewis. 
 W. C. McC, radiation in chemical 
 action, 142. 
 
 Griffith, H. O.. and Lewis, W. C. McC, 
 radiation in chemical action, 142. 
 
 Ilaber, F., and Just, G., ionization by 
 chemical action, 129, 
 
 Hahn, O., recoil from a particle, 154. 
 
 Hall, N. F. See Richards, T. W., 154. 
 
 Harkins, W. D., separation of isotopes 
 of chlorine, 154. 
 
 Hartley, H. See Merton, T. R., 154. 
 
 Haselfoot, E. E., and Kirkby, P. J., 
 ionization in gas explosions, 130. 
 
 Henri, V., and Wurmser, R., photo- 
 hydrolysis of acetone, 137, 145 ; pho- 
 tolysis of hydrogen peroxide, 137. 
 
 Hess, V. F., and Lawson, R. W., num- 
 ber of )3 particles from radium, 42 ; 
 of a particles, 79. 
 
 Hess, V. F. See Meyer, S., 65. 
 
 V. Hevesy, G., change of valence by o 
 or i8 radiation, 42. 
 
 V. Hevesy, G, See Bronsted, J. N., 
 154. 
 
 Higgins, W. F. See Patterson, C. C, 
 54. 
 
 Honigschmid, O., radium standards, 
 26 ; coloration of radium salts, 48 ; 
 disintegration of quartz by radium 
 rays, 49 ; blue luminescence of ra- 
 dium salts, 50. 
 
 Horton, F., ionization by therm-elec- 
 trons, 43. 
 
 Hu, K.-W. See Duane, W., 45. 
 
 Hull, A. W., crystal structure by X 
 rays, 45. 
 
 Job, P. See Boll, M., 137. 
 
 Johnston, E. H. See Daniels, F., 147. 
 
 Joly, J., range of a rays in minerals, 
 
 52 ; pleochroic rings and geological 
 
 age, 52. 
 Jorissen, W. P., and Ringer, W. E., 
 
 synthesis of hydrogen chloride by $ 
 
 and 7 rays, 47, 85, 119. 
 Jorissen, W, P., and Woudstra, H. W., 
 
 coagulation of colloids by iS rays, 47. 
 Just, G. See Haber, F., 129. 
 
 Kabakjian, D. H., theory of ozoniza- 
 tlon by electrical discharge, 124. 
 
 Kabakjian, D. H. See Karrer, E., 49. 
 
 Kalian, A., energy utilization of pene- 
 trating rays in chemical action, 61 ; 
 decomposition of hydrogen peroxide 
 by penetrating rays, 62 ; of alkaline 
 halides, 62 ; of organic and inorganic 
 substances, 63-4. 
 
 Karrer, E., and Kabakjian, D. H., blue 
 luminescence of radium salts, 49. 
 
 Kaufmann, W., mass of electron, 41, 
 
 Kelly, M. J. See Millikan, R. A., 29, 
 81, 116. 
 
 Kernbaum, M., formation of hydrogen 
 
 geroxide by radium 48, 60 ; excess 
 ydrogen in decomposition of water, 
 60. 
 
 Kirkby, P. J., chemical action in gases 
 by electrical discharge, 43, 125. 
 
 Kirkby, P. J. See Haselfoot, E. E., 
 130. 
 
 Kirkby, P. J., and Marsh, J. E., ioniza- 
 tion in explosive reactions, 130. 
 
 Kistiakowski, W., bleaching of dyes, 
 137. 
 
 Klatt, V. See Lenard, P., 57. 
 
 Kleeman, R. D., specific ionization of 
 gases by a particles, 92. 
 
 Kleeman. R. D. See Bragg, W. H., 26. 
 
 Kolowrat, L., table of decay of emana- 
 tion, Appendix, Table A, 170. 
 
 Knipping, P. See Friedrich, W., 44. 
 
 Kriiger, F., ozonization by Lenard rays, 
 80, 124 ; radiation theory In electro- 
 chemistry, 144. 
 
180 
 
 INDEX OF AUTHORS 
 
 Kiimniell, G., ionization in the photo- 
 chomioal svnthosis of hydrogen 
 cblnrUlf. 12S. 
 
 Kummorer. L. See Weigert, W., 134. 
 
 Kunz, G. F., and Baskerville, C, radio- 
 luminescence of gems, 57. 
 
 Kunz, J. See Rideal, E. K., 81, 125. 
 
 Laborde, A. See Curie, P., 20. 
 
 Laborde, A. See Duane, W., 66, 84, 
 85, 86. 
 
 Larable, A., and Lewis, W. C. McC, 
 radiation in chemical action, 142. 
 
 Landauer, S. See Wendt, G. L., 81, 
 112. 
 
 Langevin, P., rate of recombination of 
 gaseous ions, 117. 
 
 Langrauir, I., monatomic hydrogen, 
 112 ; arrangement of molecules at an 
 Interface, 145 ; radiation hypothesis, 
 146. 
 
 Lantsberry, W. C. See Marsden, E., 
 164. 
 
 Laue, W., interference of X rays, 44. 
 
 Laue, W. See Friedrich, W., 44. 
 
 Lawson, R. W. See Hess, V. F., 42, 
 79. 
 
 Learning, T. H., Schlundt, H., and Un- 
 derwood, J. E,, application of the 
 Duane and Laborde ionization for- 
 mula, 66. 
 
 Le Blanc. M., ionic-chemical equiva- 
 lence, 75 ; decomposition of ammonia 
 by electrical discharge, 126. 
 
 Le Blanc, Rf., and Vollmer, M., syn- 
 thesis of hydrogen chloride by X 
 rays, 128. 
 
 Lenard, P., and Klatt, V., phosphores- 
 cent alkaline earth sulfides, 57. 
 
 Lewis. W. C. McC, photochemical 
 equivalence, 133 ; radiation theory 
 of chemical action, 142 ; anomaly of 
 phosphine decomposition, 145. 
 
 Lewis, W. C. McC. See Callow, R. H., 
 142. 
 
 Lewis, W. C. McC. See Griffith, R. O., 
 142. 
 
 Lewis, W. C. McC. See Griffith, R. O., 
 and Lamble, A., 142. • 
 
 Lewis, W. C. McC. See Lamble, A., 
 142. 
 
 Lind, S. C, loss of color and thermo- 
 luminescence, 52 ; synthesis of wa- 
 ter by emanation, 71, 85 ; decom- 
 position of ammonia by one o par- 
 ticle, 73 ; ozonization by o rays, 76, 
 85, 124; thin a ray bulbs, 76; ra- 
 diometric determination of range of 
 a ray, 78 ; theory of ozone forma- 
 tion, 81 ; average path of a ray, 82 ; 
 synthesis and decomposition of hy- 
 drogen bromide by emanation. 86 ; 
 decomposition of hydriodic acid and 
 of solid salts, 86 ; equilibrium of 
 hydrogen and oxygen (emanation), 
 91, 104 ; kinetic equation for chem- 
 ical action of emanation on gases. 
 95 ; application of, 99 ; influence of 
 size of sphere on rate of water syn- 
 thesis (emanation), 101; location of 
 active deposit, 105 ; excess of com- 
 ponents In water synthesis (emana- 
 tion), 107; action of emanation on 
 pure hydrogen or oxygen. Ill ; ionic- 
 chemical equivalence, 115 ; chemical 
 action by recoil atoms of a particles, 
 156-160. 
 
 Lindemann, F. A., radiation hypo- 
 thesis, 146 : theory of separation of 
 Jsotopes, J5l. 
 
 Lindemann, F. A., and Aston, F. W., 
 separation of isotopes of neon, 151. 
 
 lioeb, L. B., cluster ions, 81. 
 
 Lunn, A. C, average path of a rays, 
 82. 
 
 Luther, R., photography and photo- 
 chemistry, 18. 
 
 Luther, R., and Forbes, G. S., phot- 
 oxidation of quinine. 134. 
 
 Luther, K., and Goldberg, E., inhibi- 
 tion, 135. 
 
 Luther, R., and Weigert, F., photo- 
 chemical polymerization of anthra- 
 cene, 134. 
 
 Mache, H. See Flamm. L., 83. 
 
 MacMahon, P. S. See Chapman, D. L., 
 119. 
 
 Makower, W., and Geiger, H., y ray 
 determination of emanation. 77. 
 
 Makower, W. See Russ, S., 154. 
 
 Marcelin, R., increment of Internal 
 energy, 143. 
 
 Marsden, E.. decay of luminosity of 
 zinc sulfide, 54. 
 
 Marsden, E. See Geiger, XL, 163. 
 
 Marsden, E., and Lantsberry, W. C, 
 long range hydrogen atoms, 164. 
 
 Marsh, J. E. See Kirkl)y, P. J., 130. 
 
 McKenzie, A. G. See Creighton, II. J. 
 M.. 63. 
 
 McKlung, R. K., rate of recombination 
 of gaseous Ions, 117. 
 
 Meitner, Frl. L., life of meso-thorlum, 
 55. 
 
 Mellor, J. W., chemical kinetic calcula- 
 tions, 108. 
 
 Merton. T. R.. and Hartley, H., theory 
 of separation of isotopes, 154. 
 
 Meyer, S., and Hess, V. F., disintegra- 
 tion of quartz by radium rays, 49 ; 
 heat evolution of radium, 65. 
 
 Meyer. S., and Przibram, K., photo- 
 electric effect and coloration of min- 
 erals, 50, 51. 
 
 Meyer. S., and V. Schweidler, E., radio- 
 activity, 8, 24 ; radium standards, 
 26 : energy and velocity of recoil 
 atoms, 155. 
 
 Millikan, R. A., and Fletcher, H., ion- 
 izntion by /8 particles, 42. 
 
 Millikan, R. A.. Gottschalk, V. H., and 
 Kelly, M. J., Ionization by a par- 
 ticles. 29, 81, 116. 
 
 Moore. R. B., use of meso-thorlum In 
 luminous paints, 55. 
 
 Moseley, H. G. J., number of j8 par- 
 ticles, 42 ; atomic numbers, 44. 
 
 Mof^.eley. H. G. J., and Robinson. H., 
 number of 7 rays from radium, 42. 
 
 Nernst, W.. photochemical equivalence, 
 133. 136; mechanism of photo-syn- ' 
 thesis of hydrogen chloride, 141. 
 
 Ostwald, W., photochemical researches 
 of Bunsen and Roscoe, 118 ; Prout's 
 hypothesis, 152. 
 
 Patterson, C. C, Walsh, J. W. T.. and 
 lliggins. W. F., radium luminous 
 paint, 54. 
 
 Perrin, J., radiation theory of chem- 
 ical action, 145. 
 
 Pinlus, A., ionization by gas reactions, 
 129. 
 
 Planck. M., quantum theory, 132. 
 
 Plotnikow. .T., photochemistry, 7 : phot- 
 oxidation of hydriodic acid, 137 ; of 
 io<Joform, 137, 
 
INDEX OF AUTHORS 
 
 181 
 
 Pohl, R., decomposition of ammonia by 
 electrical discharge, 126. 
 
 Prout, W., atomic hypothesis, 152. 
 
 Przibram, K. See Meyer, S., 50, 51. 
 
 Pusch, Frl. L., test of Einstein photo- 
 chemical law, 136, 138. 
 
 Ramsay, W., excess of hydrogen in 
 water decomposition by radium, 48, 
 60 : gas pipette, 66. 
 
 Ramsay, W. See Cameron, A. T., 
 66-9, 85, 97, 98. 
 
 Ramsay, W., and Soddy, F., decom- 
 position of radium solution, 75. 
 
 Reboul, G., ionization by chemical ac- 
 tion, 129. 
 
 Regener, E., photochemical ozonization, 
 134 ; photolysis of ammonia, 134 ; of 
 ozone, 137. 
 
 Reynolds, E., triad of neon, 151. 
 
 Rice. J., equation of energy increment, 
 143. 
 
 Richards, T. W., and Hall, N. F., in- 
 separability of isotopes, 154. 
 
 Rideal, E. K., radiation in chemical 
 kinetics, 146. 
 
 Rideal, E. K., and Kunz, J., ozoniza- 
 tion in the corona, 81, 125. 
 
 Rideal, E. K., and Taylor, tl. S., ca- 
 talysis, 144. 
 
 Ringer, W. E. See Jorissen, W. P., 47, 
 85, 119. 
 
 Roberts, L. D., average path of a par- 
 ticles in cylinders, 83. 
 
 Robinson, H. See H. G. J. Moseley, 
 42. 
 
 Roentgen, W. C, discovery of X rays, 
 20, 44. 
 
 Roscoe, H. E. See Bunsen, R., 118. 
 
 Ross, W. H., photochemical reduction 
 of ferrous sulfate. 63. 
 
 Royds, T. See Rutherford, E. E., 22, 
 76. 
 
 Runge, G.. and BodlSnder, G.. excess 
 hydrogen in water decomposition by 
 radium, 60. 
 
 Russ, S., and Makower, W., recoil 
 atoms from a particles, 154. 
 
 Russell, A. S.. change of valence by a 
 or )3 radiation, 42. 
 
 Rutherford, E. E., radioactivity, 8, 24 : 
 magnetic and electrical deflection of 
 a parficles. 22 ; atomic disruption, 
 22 ; radioactive equilibrium. 25 ; 
 atomic model. 27 ; energy of ioniza- 
 tion, 29 ; enumeration of a particles, 
 31 ; energy radiated by a, ^. and 7 
 rays. 42 ; disintegration of quartz by 
 radium rays. 49 ; pleochroic rings in 
 mica, 52 ; active centers of lumines- 
 cence. 54. 57 ; heat of absorption of 
 a, j8. and y rays, 65 ; 7 ray deter- 
 mination of emanation, 77 ; dis- 
 appearance of emanation in spec- 
 trum tubes, 127 ; momentum of a 
 recoil, 155 ; scattering of a particles, 
 162 ; swift hydrogen atoms. 164 ; 
 from nitrogen, 167 ; swift helium 
 atoms from oxygen and nitrogen, 
 167 ; helium atoms of mass, 3, 167 ; 
 gain in energy by atomic disruption, 
 166 ; quantity of. 168 ; unclear struc- 
 ture of nitrogen, oxygen, and car- 
 bon atoms, 167. 
 
 Rutherford. E. E.. and Goigor, IT., 
 charge of a particle. 22; distribution 
 of a radiation in time and space, 36. 
 
 Rutherford, E. E., and Royds, T., na- 
 ture of a particles, 22 ; thin a ray 
 papjllarjr, 76, 
 
 Rutherford, E. E., and Soddy, F., hy- 
 pothesis of atomic disintegration, 21, 
 24. 
 
 Ryde. J. W. H. See Campbell, N. R„ 
 127, 
 
 Sadler, C. A., characteristic X rays, 45. 
 
 Scheuer, O., calculation of ionization, 
 84 ; synthesis of water by emana- 
 tion, 85, 89 ; reduction of carbon 
 monoxide (emanation), 90, 
 
 Scheuer, O. See Duane, W., 60, 85, 86, 
 85-9, 120. 
 
 Schlundt, H. See Leaming, T. H., 66. 
 
 Schmidt, G. C. See Wiedemann, E., 
 57. 
 
 V. Schweidler, E. See Meyer, S., 8, 24, 
 26 155 
 
 Seboi*, J. ' See Stoklasa, J., 90. 
 
 Sheppard, S. E., photochemistry, 7. 
 
 Shimizu, T. See Duane, W., 45. 
 
 Siegbahn, M., X radiation, 45. 
 
 Soddy, F., change of valence by a or 
 P radiation, 42 ; theory of isotopic 
 separation. 154. 
 
 Soddy, F. See Ramsay. W., 75. 
 
 Soddy, F. See Rutherford, E. E., 21, 
 24. 
 
 Stark, J., loosening of valence elec- 
 trons, 134, 140. 
 
 Stoklasa, J., Sebor, J., and Zdobnicky, 
 v., reduction of carbon monoxide by 
 hydrogen (radium), 90. 
 
 Strong, W. W.. theory of ozone forma- 
 tion, 81, 123. 
 
 Strutt, R. J., positive charge of a par- 
 ticle, 22. 
 
 Taylor, IT. S., regulator for thin o ray 
 bulb, 79 ; synthesis of hydrogen chlo- 
 ride by a rays. 85, 119 ; non-exist- 
 ence of»active molecules. 143. 
 
 Taylor, H. S. See Rideal, E. K., 
 144. 
 
 Taylor, T, S., specific ionization of 
 gases by a rays, 92. 
 
 Thomson. J. J., positive rays, 148 ; va- 
 riety of gaseous ions, 81 ; absence of 
 ions in photo-synthesis of hydrogen 
 chloride. 128 ; analysis by positive 
 rays, 149. 
 
 Tian. A., nhotolysis of hydrogen perox- 
 ide. 137. 
 
 Tolman. R. C, radiation and chemical 
 kinetics, 146. 
 
 Townscnd. J. S., ionization by collision, 
 43. 124 ; rate of recombination of 
 gas ions. 117. 
 
 Trautz. M.. radiation theory of ca- 
 talysis. 144. 
 
 Trnutz, M.. and Bhandarkar, D. S., 
 decomposition of phosphine, 145. 
 
 Underwood, J. E. See Leaming, T. H., 
 66. 
 
 Usher, F. L., non-catalytic action of a 
 rays. 59 ; ammonia equilibrium (em- 
 anation), 72; decomposition of am- 
 monia and water by emanation, 85, 
 98 : absorption of hydrogen by glass 
 under a radiation, 112 ; decomposi- 
 tion of water by a and by P rays, 
 113. 
 
 Vollmer, M. See Le Blanc, M., 128. 
 
 Waentig, P.. phosphorescent alkaligp 
 parth s\ilfldps, 57, 
 
1S2 
 
 INDEX OF AUTHORS 
 
 Walsh, J. W. T., recovery of luminos- 
 ity of radium paint, 54 ; meso- 
 thorium luminous paint, 55. 
 
 Walsh, J. W. T. See Patterson, C. C, 
 54. 
 
 Walter, B„ life of radiothorium, 55. 
 
 Warburg, E., low energy utilization in 
 photochemical action, 123 ; inapplica- 
 bility of Faraday's law to ozoniza- 
 tion by electrical discharge, 124 
 test of Einstein's law, 132, 139; 
 photochemical ozonization, 134 ; pho 
 tolysis of ammonia, 134. 
 
 Weigert, P., photochemistry, 7 ; pho- 
 tolysis or ozone by chlorine, 134 ; 
 without chlorine, 137. 
 
 Weigert, F., and Kummerer, L., photo- 
 chemical conversion, 134. 
 
 Weigert, F. See Luther, R., 134. 
 
 Wellisch, E. M., cluster ions, 81. 
 
 Wendt, G. L., and Landauer, R. S., 
 cluster ions, 81 ; tri-atomic hydro- 
 gen, 112. 
 
 Wendt, G. L. See Duane, W., 112. 
 
 Wertenstein, L., a recoil atoms, 155, 
 159. 
 
 Wiedemann, E., and Schmidt, G. C, 
 phosphorescent alkaline earth sul- 
 fides, 57. 
 
 Wien, W., magnetic deflection of canal 
 rays, 148. 
 
 Wigand, A., photochemical transforma- 
 tion of sulfur, 134. 
 
 Wildermann, M., photo-synthesis of 
 phosgene, 138. 
 
 Winther, C, bleaching of dyes, 137. 
 
 Wood, A. See Campbell, N. R., 24. 
 
 W^oudstra, H. W. See Jorissen, W. P., 
 47. 
 
 Wourtzel, E. E., ammonia decomposi- 
 tion by one a particle, 73 ; extrapola- 
 tion of ionization, 84 ; decomposition 
 of hydrogen sulfide, ammonia, nitrous 
 oxide, and carbon dioxide by emana- 
 tion, 85, 93, 121 ; inapplicability of 
 thermal theory of a ray chemical 
 effect, 116 ; no synthesis of ammonia 
 by emanation, 85, 120 ; collision the- 
 ory or radiochemical action, 93. 
 
 Wurmser, R. See Henri, V., 137, 145. 
 
 Zdobnicliy, V. See Stoklasa, J., 90. 
 
 I 
 
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 Lind, S*C. 
 
 The chemical effects 
 of alpha particles and 
 electrons. 
 
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 UNIVERSITY OF CALIFORNIA 
 
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 ^Ve chmical effects 
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 «i on.t.rons.