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THE DEVELOPMENT
PERIODIC LAW
F. F\ VENABLE, F»ti.E>., F.C.S.,
Professor in the University of North Carolina.
EASTON, PA.: CHEMICAL PUBLISHING CO.
I8q6. /
ft 7
Copyright, 1896, by Edward Hart.
TABLE OF CONTENTS.
Prefatory Sketch
CHAPTER FIRST.
PROUT'S HYPOTHESIS AND THE DOEBEREINER TRIADS.
§2. The Unity of Matter— §3. Definition of Element— §4. The Atomic Weights — §5. Remarks of Roscoe on Dalton's First Table of Atomic Weights— §6. The Table of Thomson and Wol- laston — §7. The Table of Berzelius — §8. The Two Directions of the Work — §9. Prout's Hypothesis — §10. Prout's Second Paper — §11. Berzelius and Gmelin in Connection with Prout's Hy- pothesis— §12. The Examination of the Subject by Turner — §13. Penny's Results — §14. Dumas' Adhesion to Prout's Hypoth- esis— §15. The Extension of the Hypothesis — §16. Prout's La- test Views — §17. The Views of Meiuecke — §18. Prout's Views as to the Constitution of Matter — §19. Early Numerical Rela- tions— §20. The Triads of Dobereiner — §21. Dobereiner's Re- sumd of His Law — §22. The Slow Extension of these Views— §23. Berzelius on such Numerical Relations n-32
CHAPTER SECOND.
DUMAS AND THE PERIOD FROM 1850 TO i860.
§24. Slow Development of the Triad — §25. Dumas' Address be- fore the British Association — §26. The Effect of Dumas' Ad- dress— §27. Faraday's Views — §28. The Ascending Series of Kremers — §29. The Triads of Kremers — §30. Gladstone's Ar- rangement in the Order of the Atomic Weights — §31. The Ho- mologous Series of Cooke — §32. Kotikovsky and the Com- pound Nature of the Elements — §33. Low's Theory as to Com- position of the Elements — §34. The Extension of the Triad by Lennsen — §35. Elaboration of the Homologous Series by Du-
iv TABLE OF CONTENTS.
mas— §36. Double Parallelism of Dumas— §37. Dumas' Views as to the Compound Nature of the Elements — §38. The Dumas- Despretz Controversy— §39. Pettenkofer's Group Differences — §40. Comparison of the Elements with the Compound Radi- cals—§41. Odling's Triads — §42. Mercer's Comparison with the Organic Radicals— §43. The Revision of the Atomic Weights by Cannizzaro — §44. Lea uses the Atomic Weight Differences — §45. The Geometrical Ratios— §46. Other Regularities — §47. Physical or Absolute Atoms— §48. Dumas extends the Hypoth- esis of Prout — §49. Criticism of the Work of Dumas — §50. The Work Accomplished 33~62
CHAPTER THIRD.
THE IMMEDIATE FORERUNNERS OF THE PERIODIC LAW.
§51. The New Conditions — §52. Stas' Opposition to Prout's Hy- pothesis— §53. Numerical Relations— §54. Parallelism Revived — §55. The Pairing of the Elements — §56. Classification by the Atomicities — §57. Relations between the Atomic Weights and the Densities — §58. Brodie's Ideal Chemistry — §59. Brodie's Conception of the Genesis of the Elements — §60. The Telluric Screw of de Chancourtois — §61. The Work of Newlands — §62. The Law of Octaves — §63. Explanation of the Existence of Tri- ads— §64. Criticism of Newland's Law--§65. Character of the Work of de Chancourtois and Newlands — §66. The Remarks of Crookes upon the Priority Claims — §67. The First Table of Lothar Meyer — §68. Hiurich's Deductions from the Spectrum of the Elements — §69. The Pantogen of Hinrichs 63-90
CHAPTER FOURTH.
THE ANNOUNCEMENT OF THE PERIODIC LAW.
1869-187I.
§70. Periodic Law — §71. Mendel£eff's First Paper — §72. Mende- leeff's Horizontal Table — §73. Important Features of the Sys-
TABLE OF CONTENTS. V
tem — §74. MendeleefP s Claims as a Discoverer — §75. The Re- ception Accorded the Discovery — §76. The Evolution of Mey- er's Table— §77. Meyer's Table of 1864 — §78. Meyer's Table of 1868— §79. Meyer's Table of 1870— §80. Mendeleeff's Tables of 1871 — §81. Meyer's Later Tables — §82. Meyer's Curve of the Atomic Volumes — §83. The Failure to Recognize the Import- ance of the Daw — §84. The Criticism of Berthelot — §85. Men- deleeff's Reply — §86. Ostwald's Criticism 91-117
CHAPTER FIFTH.
DEVELOPMENT OF THE SYSTEMS.
1870-1880.
§87. A Return to Numerical Regularities — §88. Growth in the Belief in Unity of Matter — §89. Baumhauer's Spiral Arrange- ment— §90. Additional Work of Newlands — §91. The Synoptical Table of Gibbes — §92. Wiik's Arrangement — §93. The Primal Element of Simmen — §94. Wachter's Numerical Regularities — §95- Dockyer's Hypothesis as to the Compound Nature of the Elements — §96. Berthelot's Discussion of Dockyer's Hypothe- sis— §97. Crookes' Views as to the same — §98. Zangerle's Nu- merical Relations — §99. Dersch's Numerical Relations — §100. Zangerle's Primal Elements — §101. Criticism of Meyer and Seu- bert — §102. Meyer's Ideas as to the Elements — §103. Groshans on the Nature of the Elements — §104. Other Authors during this Period 1 19-149
CHAPTER SIXTH.
THE DEVELOPMENT OE THE NATURAL LAW.
1880-1885.
§105. Revival of Prout's Hypothesis — §106. Meyer and Seubert's Review of Dumas's Work — §107. Mallet's Views Regarding the Hypothesis of Prout — §108. The Views of Clarke — §109.
vi TABLE OF CONTENTS.
Crookes' Views as to this Hypothesis — §110. Meyer and Seubert on Prout's Hypothesis — §111. Groshans on Prout's Hypothesis — §112. Bay ley's Attempt at Showing the Connection between the Atomic Weights and the other Properties of the Elements — §113. Gladstone's Address before the British Association — §114. Hartley on Spectroscopic Evidence as to the Nature of the Elements — §115. Hartley's Criticism of Lockyer — §116. Nu- merical Relations of Fedaroff — §117. Laurie on the Physical Properties — §118. Gerber's Modification of the Hypothesis of Prout — §119. Mills' Equation for Calculating the Atomic Weights — §120. Carnelley's Study of the Relations of the Phys- ical Properties — §121. The New Law of Groshans — §122. Pe- lopidas Compares the Elements with the Organic Radicals — §123. The Spiral of v. Huth— §124. Berthelot's Theory as to Primal Matter — §125. Carnelley on the Periodic Law and the Occurrence of the Elements — §126. Carnelley on the Cause of the Periodic Law — §127. Spring's Diagram 151-179
CHAPTER SEVENTH.
THE DEVELOPMENT OF THE NATURAL LAW.
1885-1890.
§128. Rydberg on the Nature of Periodicity — §129. Relations be- tween the Atomic Weight Differences Observed by Rydberg — §130. Reynolds' Diagram Representing the Periodic Law — §131. Crookes' Modification of this Diagram — §132. Crookes' Genesis of the Elements — §133. Dulk upon Gravitation and the Atomic Weights — §134. Phipson's Outlines of a new Atomic Theory — §135. Reed's Graphical Representation of the Rela- tion between Valence and Atomic Weight — §136. Griinwald's Mathematical Spectrum Analysis — §137. Ames' Criticism of Griinwald — §138. Griinwald's Definition of Chemical Atoms — §139. Thomsen's Views as to Unity of Matter — §140. Flavitz- ky's Functions for Periodicity — §141. Numerical Regularities observed by Bazaroff — §142. Livermore's Classification — §143.
TABLE OF CONTENTS. Vll
An Atomic Hypothesis by Pearson— §144. Stoney's Logarith- mic Law of the Atomic Weights— § 145 . New Relations between the Atomic Weights by Delauney — §146. Haughton's Geomet- rical Illustration of the Periodic Law — §147. Hartley's Defini- tion of Atomic Weight — §148. Stransky's Numerical Relations — §149. Remsen on the Nature of the Elements — §150. Mende- leeff's Faraday Lecture — §151. Buehler's Theory as to the Na- ture of Matter 181-232
CHAPTER EIGHTH.
THE DEVELOPMENT OF THE NATURAL LAW.
I 890- I 896.
§152. The Controversy over the Standard — §153. Kronberg's Iso- morphism of the Atoms — §154. Tchitcherine's System — §155. Sutherland's New Periodic Property — §156. Carnelley's Alge- braic Expression of the Periodic Law — §157. Wendt's Evolu- tion of the Elements — §158. Bassett's Tabular Expression of the Periodic Relations — §159. Wilde on the Origin of the Ele- ments— §60. New Numerical Relations by Adkins — §161. Meu- sel on the Oneness of the Elements — §162. Preyer's Genetic System — §163. Wislicenus on the Nature of Matter — §164. A New Periodic Table by Deeley — §165. Palmer's Views as to the Nature of the Elements — §166. Meyer on the use of the Sys- tem by Teachers — §167. Hinrich's True Atomic Weights — §168. Rang's Periodic Arrangement — §169. A New System by Traube — §170. Venable's Modified Arrangement — §171. Thomsen's Ra- tional Atomic Weights — §172. Thomsen's Systematic Group- ing of the Elements — §173. Thomsen's Group of Inactive Ele- ments— §174. The System of de Boisbaudran — §175. Blan- shard's Cross Analogies — §176. Solubility and Genesis of the Elements — §177. The Melting Points as a Clue to Genesis — §178. The Position of Argon and Helium in the System — §179. Victor Meyer on the Problems of the Atoms — §180. Lothar Meyer's Account of the Inception of the Periodic System —
Vlll TABLE OF CONTENTS.
§181. Lea on the Color of the Ions — §182. Flavitzky's Function for Deduction of Properties — §183. Tutton's Comparisou of Iso-
morphous Salts 233-284
Index to Literature 285-308
List of Authors 309-312
General Index 313-321
PREFATORY SKETCH.
This work is intended as a study of the development of the natural law underlying the relations of the ele- ments and their properties to one another. It is to be used for purposes of reference and of study and not as a mere history of the subject. The errors and repetitions of the writers upon this subject in the past few years have abundantly proved the necessity for some such gathering and systematizing of thework of former years. It is, in the main, an out-of-the-way sort of literature and the difficulty of gathering it increases with the lapse of time. The growing interest in this natural law speaks well for the progress of the science in the future. More and more it is becoming recognized as the basis of the science, and the hope of the solution of some of the greatest problems which the chemist has to face seems to lie in it. The reproach that chemistry is not, in the fullest sense, a science will continue just so long as chemists content themselves with raking together the straws of facts, gleaners many of them in a harvested field, and neglect the "weightier matters of the law." The gathering of facts is good, gleaning is good, but contentment with such gains means stagnation.
The task has been undertaken in the hope of arousing interest in this matter and of aiding in the further de- velopment of the still incomplete system. No excuses are offered for the imperfections of the work. It could not be other than imperfect. The task has been most
2 PREFATORY SKETCH.
difficult, and the limitations of the writer have been felt at every turn. It has been done as conscientiously and impartially as was possible. Doubtless many authors will find cause for disagreement with the treatment ac- corded their work. The reception of Newland's L,aw of Octaves, by the L,ondon Chemical Society, and many other instances of mistaken judgment, show how difficult it is to weigh these matters fairly and wisely.
Since there may be some who do not care to make a study of the whole subject, but would like to take a con- nected glance over it, this preface will be turned into an historical sketch of the law's development, omitting the mass of details to be found in the remainder of the work. Such a sketch may prove useful to others also.
Before the atomic theory was formulated, numerical relations were proposed by Richter, the founder of Stoi- chiometry, between the equivalents obtained by him for the various bases and acids. This mathematical work of his served but little purpose beyond bringing the whole subject of his equivalents into some disrepute. Only a few years passed after the publication of the first tables of atomic weights before their inter-relation be- came a subject of speculation and research. In 1815 we have Prout pointing out the strange fact of their close approximation to whole numbers and boldly rounding them off into such. If they were integral multiples of hydrogen, he reasoned, then this might be the primal matter and all elements made up of it. The " Multi- plen-fieber" quickly took possession of the chemical world, even of conservative, level-headed workers such
PREFATORY SKETCH. 3
as Berzelius. Enthusiastic support was given it by the English chemists especially and, when Berzelius after- wards became its great antagonist, Thomson and others busied themselves in its defense. The newly organized British Association devoted its fresh energies to an exam- ination into the condition of the various sciences and, among other inquiries, set on foot one as to the grounds for believing in what was then called and has been often so called since, Prout's L,aw. The result of this inquiry was adverse to the "law" and it would have been dropped, in all probability, had it not been taken up by Marignac, Dumas, and the French chemists, with cer- tain modifications rendered necessary by the more per- fect knowledge of the atomic weights. Probably no other hypothesis in chemistry has been so fruitful of excellent research as this much discussed hypothesis of Prout.
Meanwhile, a different style of numerical regularity had been brought to the notice of chemists. In 1817, Dobereiner first noticed a strange grouping of analogous elements into threes, or triads as they soon came to be called. The intermediate member of such a triad showed itself to be a mean of the other two in atomic weight and other properties. Dobereiner was at first in- clined to think that this could only mean that the inter- mediate element was a compound of the other two. His effort at arranging all of the elements into triads failed. Still he did the science great service in arranging the elements accordingto their analogies andtosome extent a c- cording to their atomic weights. It was a great lightening
4 PREFATORY SKETCH.
of the task of both teacher and student and hence found ready entrance into the text-books, especially that of Leopold Gmelin, the most influential chemical writer of the times.
For twenty years, little was added to the work of Dobereiner. Little could be done with the imperfect and incomplete tables of the atomic weights then in use. Dumas and others had been busy in the revision of many of these constants and his mind was thus espec- ially drawn to their numerical regularities. At the meeting of the British Association at Ipswich in 1851, he delivered a lecture, embodying his ideas as to the possible composite nature of the elements and giving in- stances of remarkable relations existing between their atomic weights. This attracted the earnest attention of chemists everywhere. Reports of the lecture were pub- lished in the scientific journals of various countries. Hopes were aroused in very conservative chemists that the dissociation of the so-called simple bodies, which for half a century had been looked upon as made up of un- decomposable atoms, was a possible achievement of the near future. It would transport one to dreamland at once to think of what could be accomplished if once the secret of the composition and dissociation of these ele- ments was in the grasp of the chemist.
A diligent company of thinkers, workers, and also visionary speculators sprang up. The most prominent characteristic of the work of the period was the digging out of arithmetical regularities and relations between the numbers representing the atomic weights. Strict accord
PREFATORY SKETCH. , 5
was not demanded. Approximations ruled the day, and the reputed laws discovered were justified by the appeal to the laws of probabilities. It was easy to calculate out, as De Morgan did, that the probabilities were greatly against such and such a number of approximate coincidences occurring by accident. But little attention was paid to the other properties of the elements and their connection with the atomic weights, though in many cases the isomorphism of salts was made use of as determining the analogies of the elements. The triads of Dobereiner were completed and pushed far beyond the speculations of their author. There were efforts at com- bining them into enneades and securing a net-work of elements. Algebraic formulas were sought for, by means of which it would be possible to calculate the various atomic weights. The regularities observed among the homologous series of organic chemistry were appealed to in the hope of solving the mystery of the singular regularities which undoubtedly existed. For one must not think of these workers, some of them chem- ists of great reputation, as being entirely misled. Of course a great variety of relations are always to be ob- served between sixty odd numbers taken out of a little more than two hundred, especially if one is not over partic- ular in insisting upon exact coincidences. There are in- teresting numerical relations actually existing between these atomic weights, first noticed at the time of which we are speaking and still without any plausible explanation. In this period will be found the triads of Kremers, Lennsen, and Odling ; the homologous series of Cooke,
6 PREFATORY SKETCH.
Dumas, and Mercer ; the double parallelism of Dumas'; and the atomic weight differences of Dumas, Pettenkofer, and Lea. There was also the first attempt at arranging the atomic weights in an ascending series according to their increasing magnitude. This was by Gladstone, and is looked upon now as one of the fundamental fea- tures of the periodic system. No results were obtained at that time by this arrangement because the atomic weights used were very faulty, a large number of them being placed at about half the values at present assigned to them. It is not surprising that the hopes first aroused as to any valuable results flowing from these speculations were disappointed, and with the disap- pointment seems to have come a general discrediting in the public mind of all such work. Chemists of note ap- parently dropped the subject, some wrote anonymously, and really meritorious work was received either with silence or ridicule. It is only just to state that, so far as any hopes of the immediate solution of the problem of the constitution of the elements was concerned, Dumas had been careful to discourage them.
The first gleam of hope of an improved condition of affairs came through the introduction of more accurate atomic weights by Cannizzaro. Williamson aided in the introduction of these in England. With these it became possible to see relations which had been ob- scured before. An arrangement of the atomic weights in an ascending series now revealed something of that periodicity which has since proved such a valuable thought to inorganic chemistry. The first to arrange
PREFATORY SKETCH. 7
them in this way was the French engineer and mineralo- gist de Chancourtois. His Telluric Screw contained much of the essential truth that lies in the periodic law. Along with it, there was of course, error and confusion with useless detail. It is easy to see in this, now, the germs of Mendeleeff's later discovery. Chemists of the day, however, were not in a position to sift out the false, and hence the whole scheme received little or no atten- tion, and remained hidden in the publications of the French Academy of Sciences, to be unearthed a quarter of a century afterwards, by two French chemists.
Following this came the presentation of the I^aw of Octaves by Newlands, before the London Chemical So- ciety. Here the ascending series and the periodicity were still more clearly brought out. There was much less of the false and less of confusing detail. A thought, which was largely lacking in the work of the previous decade, begins to appear here. That is, the dependence of the properties upon the atomic weights. The same is true of the system of de Chancourtois. And yet, possi- bly because of the fanciful name given by Newlands im- plying a unity of his system with that of music, the So- ciety accorded him chiefly ridicule for his effort, and it took them twenty years, or more, to find out their mis- take.
Almost at the same time with the announcement of Newland's law, Meyer published his first work upon the Modern Theories of Chemistry, a work destined to a life of many editions and much fame and usefulness, and in this he gave the first of his tables of the atomic
8 PREFATORY SKETCH.
weights, the precursor of his periodic system. This certainly failed to give even as clear an idea of periodi- city as the table of Newlands, and required a great deal of evolution before it could bear much resemblance to the completed table. Almost at the same time we have the announcement by Hinrichs that the properties of the elements are functions of their atomic weights and that the unity of matter was as real as the unity of force. These were the precursors of the periodic law. They failed of recognition for many reasons, though two chief ones can be assigned ; first the public was wearied with,
I and distrustful of, such speculations ; secondly, they were incomplete, and in some respects, overweighted with error.
When Mendeleeff, in 1869, announced the new "Natural System," as he at first called it, one keen- sighted observer reported it as something that would prove interesting and probably useful, but no great stir
1 was created, such as was noticed at the delivery of Du- mas' address. In a very short time appeared the almost identical system of Meyer, evolved from his earlier tables but modified somewhat by his study of the table of Men- deleeff. To these two men the Royal Society of Eng- land gave the highest medal in its gift as the discoverers of the greatest law of modern chemistry. To one, or both, the credit undoubtedly belongs. They were both in ignorance of the previous work of de Chancourtois and of Newlands and they presented the system in such a shape that it was useful for many purposes and could be put to the test as to its truth and value. Still the
PREFATORY SKETCH. 9
system aroused little comment and was threatened with the same fate of dust and oblivion which had befallen the systems of earlier writers. After several years of neglect, even on the part of its authors, attention was drawn to the system once more by the fortunate fulfil- ment of certain bold predictions made by Mendeleeff in his table. The discovery of scandium and gallium and their fitting into the predicted places, with atomic wreights and other properties coinciding with those pre- dicted for them, gave a newimpetusto the study of these tables and their use in the class-room. Many results have sprung from this. Increased diligence has been observed in the revision of faulty atomic weights ; new interest has been shown in the advancement of the knowledge of inorganic chemistry ; the inter-relation of the elements has become so clear that one is forced to the conclusion that they are composite in nature, even though the nature of the relationship is unknown, and no immediate hope is held out of solving the problem. The question of the variability of the atomic weights, suggested by Marignac and discussed by Cooke, Schiitz- enberger, Boutlerow, and others, seems untenable in the light of the periodic system and so too with the hypothe- sis of Prout, at least in its original form, presenting hydrogen as the original element. This hypothesis had been laid to rest by the wonderfully accurate atomic weight determinations of Stas, but was revived again by its old defender, Dumas, to receive a fitful sort of dis- cussion for a few years and be accorded a tentative, half- way support on the part of a few distinguished chemists.
IO PREFATORY SKETCH.
Its original features have now been lost and it has be- come identified with the theory of the unity of matter and the idea of the composite nature of the elements. In this form it is simply one of the natural deductions from the periodic law, although Mendeleeff would discourage all such dreams and denies that they are to be justly de- duced from his law.
Those who read the later pages of this work will see how far from complete this periodic system is. Its im- perfections are many, but they are outweighed by its virtues and the truths which it so well presents. That there can be a better presentation of them is most likely ; that it is just beginning to reveal all of the truths which it is capable of revealing is also true. It demands of the chemist careful study. The close of this century calls loudly for another Lavoisier, who shall interpret the facts won by such hard toil and place the science on the right track for another century of brilliant progress and dis- covery.
The Development of the Periodic Law.
CHAPTER I.
i. Prout's Hypothesis and Doebereiner's Triads. —
The study of the development of the natural arrange- ment of the elements, the gradual crystallization of the ideas concerning the laws underlying the numerical re- lations of the atomic weights into definite form, is one of great importance to the science of chemistry. Like other secrets wrested from nature, this has been no sud- den discovery, but is the result of the thought and labor of many years. In speaking of this development, it should be clearly understood that it is not to be consid- ered complete, nor that the process of evolution is fin- ished, nor that the natural system stands before us to-day in its full and perfect form. Much progress has been made, but there is growth in these ideas, and hence it is incumbent upon chemists to make a more thorough study of what has been done and so prepare themselves to aid in further progress. The natural system has already become the central fact of the science. It has dispelled many errors, it has inspired much true work, it points to the solution of some of the greatest problems which we have to face.
The study of this development will be pursued chron- ologically, and though there is at times much tempta- tion to follow up some special idea, as that of the triads, and bring together in one place all work referring to it,
12 THE PERIODIC IvAW.
there will be only a few brief excursions of the kind. It would seem that there is some great fascination con- nected with the search after numerical relations among the atomic weights. From the very first the possible dis- covery of some mysterious law or the dream of the Unity of Matter has lured on investigators and dreamers. Prout was the first one to point out a numerical relation on which he based his famous hypothesis. To show the material with which he worked, it will be necessary to discuss the early tables of atomic weights.
2. The Unity of Matter. — The question as to the na- ture of matter is one of the great world-problems con- stantly attracting and eluding man's research. For centuries the mind of man has dwelt on this problem without success, beyond certain plausible, yet unsatis- factory speculations, and still he is not willing to give up the problem as one beyond his powers of solution. The trend of thought has been toward simplification, a reduction of matter to its simple components and a unification in one primal component if possible, thus bringing matter into line with the great unities of the universe.
The Greek dream of atoms has found justification and fulfilment in the research and learning of this century. The old-world idea of unity or of a primal element has its followers at the present day who believe we are verg- ing upon such discoveries as will confirm that also, going deeper into the nature of matter than the material, pon- derable atoms. This is a close approach to the Pytha-
DEFINITION OF ELEMENT. 13
gorean idea of the infinite divisibility of matter yet should not be confused with it as some have done.
Dalton's revival of the atomic hypothesis at the begin- ning of this century gave additional meaning and im- portance to Lavoisier's definition of the elements, and from that time we have these two ideas, element and atoms, forming the very basis of the science of chemis- try. These ideas have not been introduced without some opposition, some confusion and lack of clearness of definition, but they have successfully fought their way and become more clearly defined.
As the century draws to its close the thought is gain- ing ground that these elements are not really simple bodies, but that their material atoms are composed of other forms of matter, and the hope rises that through these the way may be traced to the old elusive primal matter.
3. Definition of Element. — With increasing knowl- edge the exact definition of an element has become more and more difficult. The observation of the phenomena of allotropism overthrew the older definitions. Perhaps the one given by Patterson Muir (218, p. 6)1 is the most satisfactory. "The notion of the elements that has been attained after long continued labor is that of certain distinct kinds of matter, each of which has properties that distinguish it from every other kind of matter, no one of which has been separated into portions unlike one another and unlike the original substance, and
iThe figures in parentheses refer to Index to Literature at the end of the volume.
14 THE PERIODIC LAW.
which combine together to produce new kinds of matter that are called compounds." Again he speaks of the term being used more and more to designate certain groups or assemblages of associated properties (218, p. 31). It is one of the objects of these pages to sum up all that has been said about the numerical inter-relations of the atoms of these elements, and show just how much ground the speculations as to a primal matter have for their basis. The literature on the sub- ject is difficult of access ; there much is ignorance as to this literature, and a knowledge of it may save chemists from much repetition and from useless vagaries.
4. The Atomic Weights of Dalton. — The concluding paragraph of a paper read by Dr. John Dalton before the Literary and Philosophical Society of Manchester, Octo- ber 21, 1S03, upon "The Absorption of Gases by Water and other Liquids" is as follows :
"The greatest difficulty attending the mechanical hy- pothesis, arises from different gases observing different laws. Why does water not admit its bulk of every gas alike ? This question I have duly considered, and though I am not yet able to satisfy myself completely, I am nearly persua- ded that the circumstance depends upon the weight and number of the ultimate particles of the several gases, those whose particles are lightest and single being least absorbable, and the others more, accordingly as they in- crease in weight and complexity. (Subsequent exper- ience renders this conjecture less probable) . An inquiry into the relative weights of the ultimate particles of bodies is a subject, as far as I know, entirely new : I
THE ATOMIC WEIGHTS. 1 5
have lately been prosecuting this inquiry with remarkable success. The principle cannot be entered upon in this paper: but I shall just subjoin the results, as far as they appear to be ascertained by my experiments."
DALTON'S "TABLE OF THE RELATIVE WEIGHTS OF THE ULTIMATE PARTICLES OF GASEOUS AND OTHER BODIES."
Hydrogen i
Azot • 4
Carbone 4
Ammonia 5
Oxygen 5
Water 6
Phosphorus 7
Phosphoretted hydrogen 8
Nitrous gas 9
Ether 9
Gaseous oxide of carbone 9
Nitrous oxide 13
Sulphur 14
Nitric acid 15
Sulphuretted hydrogen 15
Carbonic acid 15
Alcohol 15
Sulphureous acid 19
Sulphuric acid 25
Carburretted hydrogen from stagnant water 6
Olefiant gas 5
This was the first attempt at a table of the atomic weights. Elements and compounds are considered to- gether and the numbers given are, of course, very faulty. Richter's earlier table of the equivalents of various sub- stances can scarcely be considered in the same light as
16 THE PERIODIC LAW.
Dalton's. These were mainly acids and bases and it was purely a stoichiometrical table.
In the year 1808 appeared Dalton's New System of Chemical Philosophy . In this he gives a table of the atomic weights of thirty-seven substances, again taking hydrogen as the unit and standard.
5. Remarks of Roscoe on Dalton's First Table of Atomic Weights. — Doubtless many chemists have won- dered how these first atomic weights were determined. Dalton's paper was read, as we have seen, before the Manchester Literary and Philosophical Society on Oc- tober 21, 1803, and was published in 1805. There is rea- son to believe that the numbers were obtained after the paper was read, says Roscoe (93), and inserted before its publication. Dalton gives no detailed explanation of how these actual numbers were arrived at.
In 1 8 10, in his New System of Chemical Philosophy, he explains in some cases how he arrived at these weights but he had then made considerable changes in the num- bers.
Roscoe very ingeniously attempts to trace the origin of these original numbers. He is struck by the clearness of perception of truth which enabled him to argue cor- rectly from inexact experiments. " In the notable case, indeed in which Dalton announces the first instance of combination in multiple proportions the whole conclusion is based upon an erroneous experimental basis. If we repeat the experiment, as described by Dalton, we do not obtain the results he arrived at. We see that Dalton's
TABLES OF THOMSON AND WOLLASTON. 1 7
conclusions were correct, although in this case it appears to have been a mere chance that his experimental results rendered such a conclusion possible."
6. The Tables of Thomson and Wollaston. — In 1810 Thomson gave in his System of Chemistry, a table of the equivalents for 23 acids and bases. Wollas- ton's Table of Equivalents published in 1814 was a de- cided improvement upon the preceding, as he made use of the best available work of other chemists, notably of Berzelius. Instead of taking hydrogen as the standard, he used oxygen giving it the equivalent 10.
WOIXASTON'S TABLE, 1814.
Hydrogen 1.32
Oxygen 10.00
Water 11.32
Carbon 7.54
Sulphur 20.00
Phosphorus 17.40
Nitrogen 17-54
Chlorine 44.1
Oxalic acid _• • 47.0
Ammonia 21.5
Sodium 29. 1
Potassium 49. 1
Magnesia 24.6
Calcium 25.46
Strontium 63.0
Baryta 97.0
Iron 34.5
Copper 40.0
Zinc 41.0
Mercury 125.5
Lead 129.5
Silver 135.0
1 8 THE PERIODIC LAW.
Only the most important of the equivalents are given in the above table as selected by Kopp.1 Elements and compounds are given together, Wollaston declining to consider these as atomic weights and desiring to avoid the difficulties and inconsistencies of Dalton's rules.
7. The Table of Berzelius. — Between the years 18 10 and 18 1 8 Berzelius published in the Memoirs of the Stockholm Academy a number of determinations of atomic weights. His first complete table was published in 18 1 5 and was as follows :
BERZELIUS' TABLE, 1815.
Oxygen 100.0
Phosphorus !67-5
Fluorin 60.0
Carbon 74.9
Hydrogen 6.64
Molybdenum 601.6
Wolframium 2424.2
Antimony 1613.0
Platinum 1206.7
Mercury 2531.6
Copper 806.5
Cobalt 732.6
Lead 2597.4
Iron 693.6
Manganese 711. 6
Magnesium 3T5-5
Strontium 11 18.1
Sodium 579-3
Sulphur 201 .0
Muriaticum 139-6
Boron 73.3
1 Gesch., ii, p. 376.
THE TWO DIRECTIONS OF THE WORK. 1 9
Berzelius' Table, 1815. (Continued.)
Nitricum 70.5
Arsenic 839.9
Chromium 708.1
Tellurium 806.5
Silicon 304.3
Gold 2483.8
Silver 2688.2
Nickel 733-8
Bismuth 1774.0
Tin J470.6
Zinc 806.4
Aluminium 343.0
Calcium 510.2
Barium 1709. 1
Potassium 978.0
In this table the bodies muriaticum, fluoricum, and nitricum are hypothetical bodies, Berzelius supposing that by union with oxygen they yielded the acids hydro- chloric, hydrofluoric and nitric. These were therefore left out of the table given by Berzelius in 1826, and, furthermore, he introduced many corrections in this subsequent table. This was, then, the condition of the atomic weights and represents the extent of the knowledge concerning them when the first speculations as to the numerical relations existing between them ap- peared and the first hypothesis based 011 these was formed.
8. The Two Directions of the Work. — The knowl- edge of these important constants of nature led very speedily to attempts at deducing numerical regular- ities and relations along two lines. First there were
20 the; periodic law.
the efforts of Prout and Meinecke to show that these numbers were all multiples of one common unit of weight : secondly, Dobereiner blazed the way for a host of followers in discovering numerical relationships between the atomic weights of similar elements or those of the same family, and later on of the dissimilar ones.
9. Prout's Hypothesis. — In the year 181 5, there ap- peared (1) an anonymous article upon the subject of the relations between the specific weights of bodies in the gaseous condition and their atomic weights. An abstract of this article follows and attention is especially to be drawn to the modest manner in which the author pro- pounds his theory.
' ' The author of the following essay submits it to the public with the greatest diffidence ; for though he has taken the utmost pains to arrive at the truth, he has not such confidence in his abilities as an experimentalist as to induce him to dictate to others far superior to himself in chemical acquirements and fame. He trusts, how- ever, that some one will undertake to examine it and thus to verify or refute its conclusions. If these should be proved erroneous, still new facts may be brought to light, or old ones better established by the investigation ; but if they should be verified, a new and interesting light will be thrown upon the whole science of chemis- try."
His observations were founded on Gay-Lussac's "Doctrines of Volumes." Three tables are given: Table I containing the specific gravities of various sub-
PROUT'S SECOND PAPER. 21
stances, H being i, O being 10, etc. Table II gives the specific gravities of the compounds with oxygen. Table III gave the specific gravities of the compounds with hydrogen.
' ' I had often observed the near approach to round numbers of many of the weights of the atoms before I was led to investigate the subject. Dr. Thomson ap- pears also to have made the same remark. It is also worthy of observation that the three magnetic metals as noticed by Dr. Thomson, have the same weight, which is double that of azote. Substances in general of the same weight seem to combine readily and somewhat to resemble one another in their nature."
"On a general review of the tables, we may notice :
i. That all the elementary numbers, hydrogen being considered as i, are divisible by 4, except carbon, nitro- gen and barium, and these are divisible by 2, appearing therefore to indicate that they are modified by a higher number than that of unity or hydrogen. Is the other number sixteen or oxygen, and are all substances com- pounded of these two elements ?"
His other deductions have no bearing upon the mat- ter in question.
10. Prout's Second Paper.— In 18 16, Prout published another paper (2) correcting a mistake in the one just quoted. In it he expresses the following views :
' ' If the views we have ventured to advance be correct, we may almost consider the Ttpcory vky of the ancients to be realized in hydrogen ; an opinion by-the-by, not
22 THE PERIODIC LAW.
altogether new. If we actually consider this to be the case, and further consider the specific gravities of bodies in their gaseous states to represent the number of vol- umes condensed into one, or in other words, the number of the absolute weights of a single volume of the first matter {npcdty vky) which they contain, which is ex- tremely probable, multiples in weight must always indi- cate multiples in volume, and vice versa, and the spe- cific gravities or absolute weights of all bodies in a gaseous state must be multiples of the specific gravity or absolute weight of the first matter {npoory vXy), be- cause all bodies in a gaseous state which unite with one another, unite with reference to this volume."
It soon became known that the author of these papers was Dr. William Prout, a physician, and afterwards a chemical author of some prominence. His views attracted general attention and in so far as they referred to the atomic weights being multiples of that of hydro- gen, and hence hydrogen being the primal element, they were looked upon with favor, more especially in England.
ii. Berzelius and Gmelin in Connection with Prout's Hypothesis. — The hypothesis of Prout was supported by Thomson in England, and it soon had many adherents. Thomson's experimentsin supportof it (8) were very un- satisfactory however, and were insufficient as evidence to confirm it. It was received by some in both France and Germany, but met with strong opposition on the part of others, and was especially antagonized by Berzelius, (though he at first regarded it favorably) . Berzelius gave
EXAMINATION OP THE SUBJECT BY TURNER. 23
in 1825, a table of carefully determined atomic weights of the elements which differed in many cases widely from those used by Prout and Thomson. He also urged very strongly against the practice of rounding off the fractions of atomic weights into whole numbers. As Hoffman says : "He could not persuade himself that the numerical relations of these values betokened an inner connection of the elements nor yet a common ori- gin. On the contrary, he was of the opinion that these apparent relations would disappear more and more as these values were more accurately determined. For him therefore, there existed as many forms of matter as there were elements : in his eyes the molecules of the various elements had nothing in common with one another save their immutability and their eternal existence."
Yet in 1827, ( 10) Gmelin gives in two parallel columns the atomic weights of Berzelius, with their fractions (oxygen being taken as 100), and the same weights rounded off into the whole numbers (hydrogen being the standard).
He adds : "It is surprising that in the case of many substances the combining weight is an integral multiple of that of hydrogen, and it may be a law of nature that the combining weights of all other substances can be evenly divided by that of the smallest of them all."
12. Examination of the Subject by Turner. — In
1829, (11) Turner, who was then an adherent of the hypothesis, began a revision of the work of Thomson. Later, in 1832, he was specially delegated by the British
24 THE PERIODIC LAW.
Association to inquire into and report upon this ques- tion. The basis of the work of Thomson had been the determination of the atomic weight of barium. This Turner critically revised and decided that Thomson's work was erroneous and that of Berzelius correct. In Turner's report in 1833 (12) he gave up the support of the hypo thesis.
13. Penny's Results. — In 1839 (13) Penny attacked this question from a different standpoint. If the atomic weights were represented by whole numbers, then their differences should also be integers. In a series of experiments upon potassium chlorate and potassium nitrate, he showed that this was not the case. He withdrew his support from the theory and thus, in its home, it was losing ground. But the failing theory was destined to be revived and brought vigor- ously to the front again in the laboratories of France.
14. Dumas' Adhesion to Prout's Hypothesis. — At
this time a number of excellent workers were busied upon the revision of the atomic weights. Among them may be mentioned Pelouze, Marignac, Erdmann, Marchand, Svanberg, Peligot, and others. In many cases the numbers obtained by them did not differ greatly from whole numbers, and influenced by their work, as well as by his own numerous determinations, Dumas, in 1840, revived the hypothesis of Prout. His views were strengthened in 1842 (14) by the re-determination of the ratio of carbon to hydrogen, carried out by his pupil Stas and himself, which was shown to be almost exactly
)
PROUT'S LATER VIEWS. 25
12 : i. This was followed by his work upon oxygen and nitrogen, giving their ratios as very nearly 16 : 1 and 14 : 1 respectively.
15. The Extension of the Hypothesis. — The atomic weight of chlorine had proved a great stumbling block to the supporters of Prout's hypothesis. No revision changed it materially from 35.5. Copper and lead and some other elements gave similarly trouble- some fractions. To overcome this Marignac suggested in 1844 that half the atomic weight of hydrogen be used as the unit and thus bring chlorine within the list of integral multiples. The idea was taken up by Dumas with enthusiasm, but he found it necessary to go a step further and take one-fourth the atomic weight as the unit. This was in 1858 and will be spoken of later. Erdmann and Marchand are to be classed among the Proutians at this time, and indeed, according to Berze- lius (9-b) specially exerted themselves to find confirma- tory evidence for the theory.
16. Prout's Later Views.— It is interesting to quote from a later work of the author of this hypothesis (3, p. no) and see how his views stood the stress of the heavy conflict waged for and against them.
' ' It may be observed that we have spoken as if the atomic weights of bodies were related to one another by multiple and were all multiples of some common unit. Now this opinion has been maintained by some, while it has been denied by others, who, admitting that multiples in weight are necessary to the union of similar molecules,
26 THE PERIODIC UW.
both chemically and cohesively, will not admit that mul- tiples are necessary to the union of dissimilar molecules. The matter is one which in the present imperfect state of chemistry, can hardly be determined by experi- ment ; for what with the difficulty or rather impossibility of procuring bodies in a perfectly isolated form, and the unavoidable imperfections of all chemical processes, we can scarcely hope to approach within the necessary limits of precision."
17. The Views of Heinecke. — Meinecke has been mentioned by some as having, independently of Prout, announced the same views at about the same time. This may have arisen from the fact that Ostwald, in the first edition of his "Allgemeine Chemie," refers to Meinecke's " Chemische Messkunst," which was pub- lished in 1 8 15. The proper citation is given in the second edition of this work and refers to a period three years later. The citation (4) is as follows :
"It is noteworthy that the number of hydrogen is a divisor of the remaining stoichiometrical numbers. That this should be absolutely correct in the case of those simple bodies which have been most accurately deter- mined, and that in the case of most of the others it should accord as nearly as could be expected for difficult analyses, is certainly not to be looked upon as an accident, but rather it is to be assumed that the numbers of all simple bodies, and consequently of all compound sub- stances, form integral multiples of the value of hydrogen. There are also deeper theoretical grounds to speak for
PROUT'S VIEWS AS TO MATTER. 27
this. This combined with the calculations based on volumes furnish the chief means for the accurate deter- mination of these chemical magnitudes."
18. Prout's Views as to the Constitution of Hatter.
— It is pertinent to the subject to append here Prout's views as to the constitution of matter.
"Although we have thus rendered it probable that the molecules of bodies, considered at present as elemen- tary, are immediately compounded of many others, more or less resembling them ; yet it is obvious that there must be a point at which these and other elements exist in a primary and ultimate form, and beyond which, if the elements can be supposed to be subdivided, they must become something altogether different. In this respect, therefore, the views we have advanced accord greatly with the views at present entertained, and the only respect in which our views differ is in supposing that the self-repulsive molecule as it exists in the gaseous form, does not represent the ultimate molecule, but is composed of many sub-molecules. With respect to the nature of the sub-molecules of these bodies, which we at present consider to be elements, as for instance of oxy- gen, they may naturally be supposed to possess the most intense properties. Indeed such sub-mole- cules may be imagined to resemble in some degree all imponderable matters, heat, etc., not only by their extreme tenuity, but in other characters also ; and this very intensity of property and character may be reason- ably considered as one, if not the principal reason, why
28 THE PERIODIC LAW.
they are incapable of existing in a detached form.
19. Early Numerical Relations. — Leaving now the hypothesis of Prout, let us consider other numerical relations among the atomic weights than their divisi- bility by some common factor.
Before the atomic theory was formulated by Dalton, we have Richter's table of equivalents (in 1798) exhibiting the mass relations when an acid is neutralized by certain bases. Richter was very strongly of the opinion that his constants were subject to special laws, particularly if arranged in the order of their magnitude.
Strictly speaking, the first notice of numerical rela- tions existing between the atomic weights of the elements, apart from the question of their being multiples of the weight of hydrogen, was that which Prout deduced from his table, namely, that they were all divisible by four, except three, which were divisible by two. Of course, Prout' s table was very crude and imperfect.
20. The Triads of Dobereiner. — It is to Dobereiner that the credit is due for drawing attention to the first striking regularities. He observed the fact that certain related elements occurred in threes, the cen- tral one having a mean atomic weight and mean properties between the other two. These were called the Dobereiner Triads. The first publication con- cerning them did not come from Professor Dobe- reiner himself, but from a letter of Professor Wur- zer's, describing the work of Dobereiner at Jena (5). He says that Dobereiner, working upon celestite, found
dobereiner's resume of his law. 29
the stoichiometrical value of strontium to be 50. This is the mean of calcium, 27.5, and barium 72.5, (the then accepted atomic weights). Hence, for a moment, he questions the independent existence of strontium. Still more remarkable is the fact that the specific gravity of strontium sulphate is the mean of calcium sulphate and barium sulphate. He was led to believe celestite to be a mixture of anhydrite and heavy spar.
A little later (6) Dobereiner published a brief paper bearing upon this subject. In it he says :
Noteworthy relations are revealed when one examines the stoichiometrical values of the chemical elements and compounds arranged in series.
1 . Those most often found in plants have the smallest values and are the most abundant. The highest values are less widely distributed.
2. Those corresponding in many physical and chemi- cal properties, as iron, cobalt and nickel, have almost the same stoichiometrical value.
3. Compounds which have like equivalent numbers are also most alike in chemical constitution.
21. Dobereiner's Resume of His Law. — For nearly a decade there is silence upon this subject. Dobe- reiner's next publication seems to have been called forth by the new and accurate atomic weight determina- tions of Berzelius in 1825. He writes (7) of his having prophesied in his lectures that perhaps the atomic weight of bromine would be the arithmetical mean of those' of chlorine and iodine and rejoices in the confirmation of
30 THE PERIODIC LAW.
this by the determination of Berzelius. Bromine had just been discovered. He had also twelve years earlier placed strontium as very nearly the arithmetical mean between calcium and barium, and sodium between lithium and potassium. For the group of phosphorus and arsenic the middle factor is lacking. If sulphur, selenium and tellurium belong together, which is to be assumed from the fact that the specific gravity of selen- ium is the mean of the specific gravities of sulphur and tellurium, then selenium is the mean factor in the mat- ter of atomic weights.
Fluorine, he says, does not belong to the same group of salt- formers as chlorine, etc., but doubtless to one which bears the same relation to this group as the alka- lies to the alkaline earths. He further attempts to show in this grouping the intensity of the chemical attraction. Hydrogen, oxygen, nitrogen and carbon, he says, seem to be isolated, and the fact that nitrogen is the mean between oxygen and carbon cannot be considered as meaning anything since no analogy exists between these elements.
The third member is lacking between boron and sili- con, beryllium and aluminium, yttrium and cerium. Magnesium stands quite alone. Iron and manganese have chromium as their middle factor. Other possible groups are mentioned, but he hesitates to express his opinion regarding several where the properties are poorly deter- mined and the analogies indistinct.
The important fact is that he recognized it as a law of nature that the elements occurred in groups of threes,
BERZEUUS ON SUCH NUMERICAL RELATIONS. 3 1
the middle factor being the arithmetical mean of the other two in atomic weight and in properties.
22. The Slow Extension of these Views. — This idea was taken up by other chemists who tried, as the knowledge of the elements increased, to complete the unfinished triads and to observe other analogies. These triads played quite an important part in Gmelin's Hand Book of Chemistry, the most influential text-book of chemistry during the second quarter of this century. With this exception not much notice was taken of them.
23. Berzelius on Such Numerical Relations. — In
1845, Berzelius writes (9-b): "On examining the tables of atomic weights it will be found that many bodies have an equal or almost equal atomic weight, as for instance, chromium and iron, nickel and cobalt; platinum and iridium ; gold and osmium ; many have also a weight twice as large as the others, for instance, silicon and boron ; tungsten and molybdenum ; magne- sium and lithium, etc., the atomic weights of oxygen and sulphur, selenium and tellurium are in the ratio of 1, 2, 5 and 8 ; add to this those which seem to be multi- ples of the equivalent of hydrogen ; thus it is seen that between bodies of a certain similarity of properties, cer- tain weight relations obtain. It could easily happen that a revision of these numbers would separate them further from one another or from their seeming relations, and it is therefore useless at present to speculate upon such relations. They could easily lead to false assump- tions."
CHAPTER II.
DUMAS AND THE PERIOD FROM 185O TO i860.
24. Slow Development of the Triads. — For more than twenty years little was added to the work of Dobereiner and no new ideas were developed. This was in part due to imperfections in the determinations of the atomic weights and ignorance as to whether they should be written as had been done by Berzelius, or many of them doubled as was done by Gerhardt.
Further, the whole question of atomic weights was in much doubt and numerical speculations concerning them would have had little meaning during this period. The first high wave of hope and expectancy following upon the introduction of the idea of atoms and the tables of their weights was succeeded by a corresponding period of doubt and difficulty. Graham made no dis- tinction between the atomic weights of Dalton and the equivalents of Wollaston, and much later Laurent devotes several pages to discussing the merits of the various terms : equivalents, proportional numbers, and atomic weights.
25. Dumas' Address before the British Association. — The first to take up once more the dropped thread was Dumas (16). He had devoted his chief energies to atomic weight determinations and had erected a lasting monu- ment to himself in his determination of the atomic weights of carbon and the ratio of hydrogen and oxygen in water, besides a number of other determinations. In 1 85 1 he delivered a lecture before the British Associa- tion at Ipswich, which aroused the greatest interest
34 THE PERIODIC LAW.
among chemists, and with this lecture began the most prolific decade in this style of research down to the present.
This address of Dumas' was made without notes and the reports of it lack completeness. It seems to have been drawn out in a discussion following a report pre- sented by Faraday. The larger portion of it was gath- ered together with some later papers of his and appeared in a connected form in 1859. In this address he drew attention to the triads of Dobereiner, without, how- ever, mentioning this author's name, and suggested that in a series of bodies, if the extremes are known, then by some law the intermediate bodies might be discovered, and said that a suspicion arose as to the possibility of the intermediate body being com- posed of the extremes of the series and thus processes of transmutation might be hoped for. In so far as con- cerned the composite nature of the intermediate ele- ments he but reiterated the early suspicion of Dobe- reiner. He then alluded to the possibility that such metals as were similar in their relations and could be substituted one for the other in certain compounds, might also be found transmutable one into the other. Dumas spoke of the idea of the ancients as to the trans- mutation of metals and their desire to change lead into silver and mercury into gold ; but these metals do not appear to have the requisite similar relations to render these changes possible. He then passed to the changes of other bodies, such as the transmutation of the dia- mond into black lead under the voltaic arc, etc.
After elaborate reasoning and offering many analogies
FARADAY'S VIEWS. 35
from his stores of knowledge as to chemical analysis and reactions, Dumas expressed the opinion that the law of the substitution of one body for another in groups of compounds might lead to the transformation of one group into another at will ; and that we should endeavor to devise means to divide the molecules of one body of one of these groups into two parts, and also the molecules of a third body, and then unite them, and probably the intermediate body might be the result.
The facts of associated occurrence in nature of such bodies as cobalt and nickel, chlorine, bromine and iodine were taken as possible evidence in favor of trans- mutation.
26. The Effect of Dumas' Address. — These views of Dumas led to a number of experiments by Despretz, and a lively discussion between these two chemists some years later. This will be referred to at the proper time. A more immediate result followed his taking up of the triads of Dobereiner and pointing out additional regu- larities of that kind. This was a fruitful field and a strangely fascinating one to a man who once enters upon it. In the next few years we have a number of well- known chemists engaged upon this work.
27. Faraday's Views. — It is perhaps well to show by a quotation from Faraday (20) how this conservative and distinguished worker looked upon the opinions advanced by Dumas. In his lecture upon chlorine, bromine and iodine (pp. 158, 159, 160), he says :
' ' When we come to examine the combining powers of
36 THE PERIODIC LAW.
the three, as indicated by their respective equivalents or atomic weights the same mutual relation will be ren- dered evident. This circumstance has been made the basis of some beautiful speculations by M. Dumas — speculations which have scarcely yet assumed the con- sistence of a theory, and which are only at the present time to be ranged among the poetic day dreams of a philosopher : to be regarded as some of the poetic illum- inations of the mental horizon, which possibly may be the harbinger of a new law."
He then considers the triads of salt-makers, of alka- lies, of alkaline earths, and the sulphur triad, and con- tinues : ' ' Thus we have here one of the many scientific developments of late origin, which tend to lead us back into speculations analogous with those of the alchemists. Already have we seen that it is possible for one body to assume, without combination, two distinct phases of manifestation, therefore such of the so-called elements as are subject to allotropism, are not the unchanging enti- ties they were once assumed to be ; and now we find, after our attention has been led in the direction, that the triad of chlorine, bromine, and iodine not only offers a well-marked progression of certain chemical manifesta- tions, but that the same progression is accordant with the numerical exponents of their combining weights. We seem here to have the dawning of a new light, in- dicative of the mutual convertibility of certain groups of elements, although under conditions which as yet are hidden from our scrutiny." •
THE TRIADS OF KREMERS. 37
28. The Ascending Series of Kremers. — One of the
first to follow in the footsteps of Dumas was Kremers (18) who pointed out the existence of certain regu- larly ascending series among the elements. Thus, when we take certain analogous non-metals as 0 = 8 ; S = 16; Ti= 24.12; P = 32; Se = 39.62, etc., we see that there is a regular difference of eight between them. Now many metals lie in between these as Mg= 12.07 between O and S ; Ca= 20 between S and Ti ; Fe = 28 between Ti and P, etc. Divide these by four and the non-metals give an even number and the metals an uneven. A fundamental element with the atomic weight four can therefore be assumed. This multiplied by an even num- ber gives a non-metal, by an uneven it gives a metal. In salts, then, looked at from a dualistic point of view, the acid is an even multiple of four and the base is an uneven one, and this, in the opinion of the author, lends strength to his hypothesis of the fundamental element. Kremers gives a table of these non-metals, their atomic weights, and their factors (multiples of 4) and also the metals falling in the intermediate spaces. To this latter fact he seems to attach a good deal of importance. He includes among his non-metals several bodies now re- garded as metals.
39. The Triads of Kremers. — In later communications (29), he follows up the old idea of triads and of the probable composite nature of the intermediate elements. From his examination of various compounds he de- duces the law : "If two different bodies mix and form a
38 THE PERIODIC LAW.
homogeneous whole the intensity of the physical pro- perties of these mixtures is as a rule modified."
By this he means that instead of the product having exactly intermediate properties, these properties are modified at all temperatures save one. For instance, in examining the question whether the solubility of the salts of the intermediate member of a triad form the means of the solubilities of those of the extremes, he finds this to be true for a certain definite temperature only. He was of the opinion that the differences ob- served in the atomic weights of middle members of triads from the calculated were due to the temperature at which the determinations were made, and that only at one temperature could exactly agreeing compounds be obtained.
From the consideration of compounds this law is transferred to elements, and he examines a number of the properties in connection with the triads. This was an attempt at placing the doctrine of triads upon a firm experimental basis, if such a thing were possible. Dobereiner had suggested it as holding good for some elements, but did not know whether it could be ex- tended to all. It had been extended to many, but there were still a number of doubtful ones. Kremers united some of the triads into what he called conjugated triads. His study of the properties led him to doubt the con- stancy of the atomic weights.
His theory of conjugated triads may be explained a little more in detail. One of these ran in this way :
GLADSTONE'S ARRANGEMENT. 39
Li= 7, Na= 23, K= 39.
Mg=24, Zn = 4.o, Cd=ii2.
Ca = 40, Sr=87.5, Ba=i37.
In these triads we have the following proportions : Ivi : Na : K as 7 : 23 : 39 as I4 : Mg : Ca.
This close agreement is not found in every case, how- ever. It was claimed that there were eight of these con- jugated triads, and each twenty-seven elements can be arranged in space in the form of a cube. Of these cubes there are again three or a triad ; one positive, one nega- tive and one intermediate. The number of the possible elements is then a power of three, probably three raised to the fourth power.
Kremers at first thought that this cubic triad repre- sented the natural arrangement of the elements. This view he gave up later (1863), and with it the doctrine of the triads in the strict sense.
30. Gladstone's Arrangement in the Order of their Atomic Weights. — In 1853 Gladstone (21) published an article on the relation between the atomic weights of analogous elements. In this he arranged the elements in the order of their atomic weights, using the numbers given in L,iebig's Jahresberichte for 185 1. A few years later this method of arranging them brought out the main features of the natural law, but the numbers used by Gladstone are too faulty to show any noteworthy regularity. Still it is interesting to note that he is the first to arrange them in this order. He observed noth- ing striking in these numbers except the number of
40 THE PERIODIC UW.
them congregated around 28 and 52, and that there was only one between 80 and 99, and then followed a group of four.
Prof. DeMorgan helped him to calculate the probability of such occurrence being accidental, and found that the odds were 250 to one against the same number occurring six times in the sixty elements. Taking the elements next by groups, as given in Gmelin's Handbook, Glad- stone found the numerical relations to be of three kinds.
1 . The atomic weights of analogous elements are the same.
2. The atomic weights of analogous elements are in multiple proportions.
3. The atomic weights of analogous elements may differ by certain regular increments.
In the first class fall Cr, Mn, Fe, Co, Ni with atomic weights approximating 28 ; Pd, Rh, and Ru approxi- mating 52 : and Pt, Ir, and Os approximating 99.
In the second class we see the platinum group double the palladium group, and gold double platinum. Again he gives O = 8 and S = 16; and B = 10.9 and Si = 21.3 as examples. A group consisting of Ti, Mo, Sn, V, W, and Ta is cited as having atomic weights which are all multiples of 11. 5.
In the third class we have elements with intermediate properties occupying intermediate positions. Li, 6.5 ; Na, 23 ; K, 39.2.
The first kind of analogy he compared with allotropism if that were carried out through all the compounds of an element.
HOMOLOGOUS SERIES OF COOKE. 4 1
The second is to be compared with polymerism in or- ganic chemistry.
The third is analogous to the homologous series in organic chemistry.
He regarded the doctrine of triads as to some extent a natural law, but the existence of these triads was to him an unsolved problem.
31. The Homologous Series of Cooke. — In the follow- ing year Professor Josiah P. Cooke (22) published a very detailed study of these numerical relations. He thought that the doctrine of triads as given by Dumas was only a partial view of the subject, since these triads are only parts of series similar in all respects to the homologous series of organic chemistry, in which the differences be- tween the atomic weights is a multiple of some whole number. In so far as he pointed out that these triads broke up natural groups of elements, he struck a fatal blow to the doctrine of triads.
All the elements, he said, may be classified into six series, in each of which the number whose multiples form the differences is different and may be said to characterize the series. In the first it is nine, in the second, eight, in the third, six, in the fourth, five, in the fifth, four, and in the last, three. The elements are fur- ther arranged in series according to the strength of their electro-negative properties, or in other words, as their affinities for oxygen, chlorine, sulphur, etc., increased, while those for hydrogen decrease, as we descend. He found the difficulty with most of the classifications, exist-
42 THE PERIODIC EAW.
ing at that time, to be that they were too one-sided, based upon one set of properties to the exclusion of others. If there were any fundamental property common to all elements, the law of whose variation was known, this might serve as the basis of a correct classification. Pro- fessor Cooke laid special stress upon the correspondence of his grouping with the homologous series of organic chemistry.
The elements of any one of the six series form similar compounds and produce similar reactions ; moreover they resemble each other in another respect in which the members of the organic series do not, their crystal- line forms are the same, or, in other words, they are isomorphous. As one general symbol will express the composition of the whole organic series, so a simple algebraic formula will express the atomic weight, or, if you may please so to term it, the constitution of a series of elements.
In the first series the atomic weights gradually in- crease from oxygen downward and admit of a general expression, which is 8 -j- ng. This series is comparable to the formic acid series. For the next series the generic formulas are 8-\-n8 and4 + w8. Thus this series is divided into two sub-series, in which there are marked analogies. There seems to be no proof of isomorphism between the sub-series.
For the next or six-group the formula is 16 -\- ni2. Oxygen is placed at the head of each one of these three groups because 'its atomic weight seemed to be the nucleus of all three." In other cases also we find the
COMPOUND NATURE OF THE ELEMENTS. 43
same element occurring in more than one group. The five-series is the shortest of them all, containing only three elements. Its formula is 6 -j- 725. The four-series is much the largest of all, containing what are known as the heavy metals. This is divided into two sub-series with the two formulas 4 -j- n\ and 2 -f- n/\. The three- series and last is composed of hydrogen and the alkalies, only three of which were known at that time. The for- mula here is 1 -f- n$.
Cooke caught a glimpse of one great truth, and that was that we must not merely separate out here and there so-called related elements, but must grasp the fact that there is a relationship even between the apparently dis- similar. He says that one of the most remarkable facts brought out by his system of tabulation is the ' ' affilia- tion of the series." " Many of the elements, while they manifestly belong to one series, have properties which ally them to another." He concludes, that this table shows that the chemical elements may be classified in a few series similar to the series of homologues of organic chemistry ; secondly, that in these series the properties of the elements follow a law of progression ; and finally that the atomic weights vary according to a similar law, which may be expressed by a simple algebraic for- mula.
32. Kotikovsky and the Compound Nature of the Ele- ments.— In this same year (1854), Kotikovsky (23) took up the idea of the compound nature of the elements suggested by Dumas, and attempted to prove the truth
44 THE PERIODIC LAW.
of this by a singular mode of reasoning and without ex- perimental proofs. It has not been possible to get at the original article, nor has it been deemed necessary to make a very extended search for it. Following the lead of Priestley and the phlogistic chemists, he assumed the presence of hydrogen in all combustible bodies. He develops a simple appearing system of chemistry in which there are no troublesome exceptions to his rules, because all facts which do form exceptions are stated otherwise and made to accord. He gives no proof of how he found these to be different from what is com- monly accepted. The following example of his mode of reasoning will suffice: " Water = 18 can not contain oxygen — 32 because no part can weigh more than the whole."
S3- Low's Theory as to the Composition of the Ele- ments.— Low (25) held that hydrogen and carbon were the original constituents of many of the elements. Thus he regarded N as C2H2 and O as CHH, etc. As experimental evidence he offered the fact that potas- sium or sodium melted under rock-oil became oxidized, and this he regarded as a making of oxygen.
Since hydrogen and carbon (atomic weight 6) had at that time lower atomic weights assigned them than any other elements, and since they were capable beyond all the others of entering into combination with one another, he assumed that all elements are composed of the two. Or, to state the proposition more generally, all bodies may be derived from hydrogen and carbon or from the
COMPOSITION OF THE ELEMENTS. 45
principles, elements, or matter, of which hydrogen and carbon are themselves formed.
He examined in detail the various elements and en- deavored by appeal to experiments and analogies to show- how they were made up of one another and all composed of hydrogen and carbon. The relations existing among organic substances were adduced in support of the theory.
Further, he criticised the reasons for holding certain bodies to be elementary and a demonstration was given of how all elements might be built up of, say, two bodies, A and B. Of the nature of the ultimate atoms or parti- cles we " know and can know nothing." "We infer that they have weight and extension." "We cannot conceive a body to have weight and extension, and the parts of which it is formed to be destitute of weight and extension, however far we suppose the division to be car- ried." The conception of Boscovich of the atom as in- finitesimally small and hence a mathematical point, or of the philosopher as merely a resisting point, and hence all matter to be but a system of forces is not the idea of the chemist who regards it as a " particle of matter."
L,ow believed that it was unjust to regard bodies as simple or elementary merely because we are unable to de- compose them by the means at our disposal. Induction and analogy should be relied upon as well as experi- ment. Without them experiment would fail to conduct us to the discovery of natural laws. "It would be justice to regard a body as compound when we are not able to prove it to be simple." Many things show that the two arbitral classes, elements and compounds, are not to be
46 THE PERIODIC LAW.
divided by so wide a chasm as a " distinct corpuscular constitution."
"Davy, in the early period of his chemical inquiries, was conducted to the opinion that sulphur and phos- phorus, which give off hydrogen under the influence of voltaic action, might be compound. He even expressed the opinion, that all simple bodies might be compound and resoluable into hydrogen and some unknown base. He never, however, pursued his own hypothesis to its consequences, and at length he seems to have abandoned it altogether."
34. The Extension of the Triads by Lennsen.— Lenn- sen, in 1857, (26) returned to the doctrine of the triads and is almost the last one to attempt the development of this line of speculation. He endeavored to extend the triads to all of the elements, grouping them by their physical and chemical characteristics. He formed, in all, twenty triads, thus including the sixty best known ele- ments. Mercury formed the uniting member, appear- ing in the tenth and again in the twentieth triad. The first ten triads contained the non-metals and acid-form- ing metals ; those from eleven to twenty contained the metals, He noted a further intimate relationship be- tween the triads. Thus, for each three triads we have the middle members forming a new triad, and, there- fore, the three triads formed what he called an enneade. This is, of course, a very similar idea to the conjugated triads of Kremer's. He saw, however, that the division into triads was not entirely satisfactory. The middle
HOMOLOGOUS SERIES OF DUMAS. 47
member did not always present in every respect the in- termediate characteristics. He then suggested a divi- sion into diads with the third member forming a link or binding member. The triads, K, Na, Li ; Ba, Sr, Ca ; Mg, Zn, Cd ; became diad K, Na, and link L,i ; diad Ba, Sr, and link Ca ; diad Mg, Zn, and link Cd, and so on for the others. He laid especial stress upon the analogous salts of these diads crystallizing with the same amount of water.
Other properties, as the color of the salts, color given to flame, etc., were also brought to bear in effecting this division.
35. Elaboration of the Homologous Series by Dumas. — In the latter part of the year 1857, Dumas (27) took up again the subject of the numerical regularities of the atomic weights and this time not from the point of view of the triads but of the homologous organic series. He made use of the formula devised by Cooke, a + nd. The facts that organic radicals are not always produced by addition but sometimes by substitution and again that there are certain series of radicals where the fundamental molecule itself changes as well as the bodies added to or substituted in it, are especially emphasized. In comparing the equivalents of the elements he noted that the halogens do not form a simple progression. The relation between their equivalents is, however, ex- hibited by the scheme a, a -\- d, a-\-2d-\-d', 2a-\-2d-\- 2d'. Thus F— 19 ;C1= 19+ 16.5; Br = 19 + 2(16.5) + 28; I = 2(19) + 2(16.5) + 2(28). And so for the nitrogen group; N=i4; P=i4+i7; As= 14+17+44; Sb=
48 THK PERIODIC LAW.
I4-J-I7 + 88; Bi = 14+ 17+ 176. Similar series are given for C, B, Si, and Zr ; as well as for Sn, Ti, and Ta. For the oxygen group we have the series a, 2a, 5a, 8a, or a, a-\-d, a-\-^d, a-{-jd. Taking the latter as preferable from analogy , 0=8; S = 8-(-8; Se = 8 -|— 32 ; Te = 8-|-56. A common difference of eight also connects the following : Mg= 12 ; Ca = 12 -j- 8 ; Sr=i2+32; Ba=i2+56; Pb=24+8o. The fol- lowing have a common difference of sixteen : L,i = 7 ; Na = 7 -+- 16 ; K = 7 + 32. Mo, W, Cr, and V form a similar series with the difference 22.
36. Double Parallelism of Dumas. — A few months after this Dumas brought out his idea of double paral- lelism. He made the following comparison :
N=i4 P = 3i As=75 Sb=i22
F = i9 Cl=35.5 Br = 80 I =127 On adding 108 to the number for nitrogen we get that for Sb, and on adding it to F we get I, and so the addi- tion of 61 gives us respectively As and Br. These facts teach the propriety, he says, of arranging the metals in series that shall show a double parallelism, for such a classification brings to view the various analogies exist- ing between these elements. In fact, when arranged by natural families, each of the elements is in proximity to two others, belonging to two related families ; and these related families occupy the two lines next to that con- taining the metal selected forcomparison. Finally each metal is surrounded in such a table by four others, which are united to it by analogies of different kinds and more or less close.
COMPOSITION OP THE ELEMENTS. 49
37. Dumas' Views as to Compound Nature of the Elements. — In a further communication he draws this comparison between the elements and the other bodies in nature. The compounds which the three kingdoms offer for our study are reduced by analysis to a certain number of radicals which may be grouped in families. Secondly, the characters of these families show incontestable analogies. But the radicals of min- eral chemistry differ from the others in that if they are compound they have a stability so great that no known forces are capable of producing decomposition. The analogy authorizes the inquiry whether the former may not be compound as well as the latter. It is necessary to add, he says, that the analogy gives us no light as to the means of causing this decomposition and if it is ever to be realized it will be by methods or forces yet unsus- pected.
In 1859, Dumas (34) collected and published in one article the more important parts of his work upon the numerical relations of the atomic weights, laying special stress upon the probably composite nature of the ele- ments.
38. The Dumas=Despretz Controversy as to the Com- position of the Elements. — This idea of the composite nature was combatted by Despretz (35), who per- formed a number of experiments to determine, if possi- ble, whether the elements could be looked upon as vary- ing modifications or condensations of one and the same material or whether they were compounds of unknown constituents. For instance, he found that copper sul-
50 THE PERIODIC UW.
phate gave at the beginning and end of its electrolysis the same body, copper, with the same characteristics. So too by fractional precipitation of copper with hydro- gen sulphide or with sodium carbonate he got only one substance. The same was true of lead nitrate when fractionally precipitated by means of sodium carbonate. Electrodes were sunk in melted lead and the metal ex- amined at the positive and negative end. Both were identified with ordinary lead. Zinc, on being fractionally distilled, yielded zinc only and the same was true of chlorine. These suffice to give the character of his ex- periments. He thought he could conclude that the ele- ments consisted of peculiar elementary material, un- changeable in its nature and properties and that they were by no means the same matter in different molecular condition.
Dumas replied that Despretz's methods were inade- quate to solve this question and that no just conclusions could be drawn from them.
Despretz defended the correctness of his researches. He volatilized Cu, Bi, and Ag in a stream of hydrogen by the white heat of a furnace and more rapidly by a strong galvanic current and showed that these vol- atilized metals gave the same compounds as be- fore. He also showed that Fe, Cu, Bi, and Ag gave out no hydrogen nor other gas at a white heat.
It does seem as if this work of Despretz was one of supererogation as Dumas had distinctly stated in his speculations upon the composite nature of the metals that their decomposition, if ever accomplished, would be
PKTTENKOFER'S GROUP DIFFERENCES. 5 1
by means and methods yet unsuspected. Dumas' reply to such criticism as these was a very easy one.
39. Pettenkofer's Group Differences. — Pettenkofer (30), in pursuing this subject of the regularities in the weights, first criticized the doctrine of triads. That the equivalent of a body, he says, should form a mean between two very similar bodies is certainly only something ac- cidental. One can compare F, CI, and Br as well as CI, Br, and I and then the mean relation does not appear.
He maintains that a remarkable relation does appear, however, when one examines the numerical differences between certain natural groups of elements, these differ- ences seeming to be nearly multiples of one and the same number. He examines the alkalies, alkaline earths, chromium group, and sulphur groups and finds the num- ber to be eight. ThusLj=7+2X 8=Na+2X8=K. Another number, five, is found for the halogens and for the C, B, Si group; also by the group N, P, As, andSb it seems to be made up of 5 and 8.
He regards the occurrence of these differences approx- imating eight as too frequent to be accidental, thus making use of the style of argument which he had rejected in the case of the triads. By taking eight as the difference and using some member of each group as the unit he calcu- lates out the atomic weights for the group. A table is given in which the atomic weights are thus calculated and compared with the observed weights and the differ- ences are also tabulated. He did not think that the fact that this number eight was the one then regarded as the atomic weight of oxygen should have any meaning.
52 THE PERIODIC LAW.
40. Comparison of Elements with Com pound Radicals.
— He further compared the elements with the organic radicals and thought that the metals would come to be regarded as compound radicals. He thought the whole matter could be stated briefly thus :
1. The equivalents of the inorganic elements, which form natural groups, show among themselves such constant differences as the equivalents of organic com- pound radicals which belong to natural groups.
2. The simple inorganic elements can therefore be re- garded from the standpoint of the compound organic radicals.
The difference-numbers are not always the same number or its multiples but are to be looked upon as built up of two numbers and their multiples, thus the 18 of the nitrogen group is 2 X 5 + 8.
Pettenkofer made a claim for priority that he had de- livered a lecture upon these difference-numbers one year before Dumas' brilliant address. More work was needed upon the atomic weights to enable him to complete his confirmation of the supposed law. He had applied to the Royal Society of Munich for aid which had been denied him and he had therefore given the work up. This claim was justified so far as his ideas concerning difference-numbers and compound radicals were con- cerned. The trend of the work, however, was different, and Pettenkofer's was almost unknown while the influ- ence of Dumas' speculations was widely felt.
4i. Odling's Triads. — Odling (28) should be men-
COMPARISON WITH ORGANIC RADICALS. 53
tioned as another of the followers of the doctrine of triads. He made these the basis of a system of the elements which he arranged according to their physical and chemi- cal characteristics, into natural families. In several cases he included more than one triad in the same family. These natural groupings of the elements were based upon the properties of the elements other than the atomic weights and may be regarded as a development of the families already recognized. For this all properties must be considered. Two elements forming a large number of compounds of analogous composition with marked similar- ity of properties must be grouped together. If a marked general accordance is found a discrepancy in some parti- cular property is to be overlooked. This grouping re- quires a careful and thorough discussion of the proper- ties as far as they are known. Such a classification is likely to be upset by increased knowledge of the proper- ties. The groups are mainly triads though several are larger. The intermediate terms of the triads are pos- sessed of intermediate atomic weights and properties. The mean differences or increments of atomic weights in the different groups were noted. He spoke of the larger groups as triads with which were associated analogous elements having atomic weights approximately one half that of the first member or double that of the last member of the triad. Sometimes there occur what he calls twin elements.
42. Mercer's Comparison with the Organic Rad= icals. — Mercer (31), in a paper before the British As- sociation, pointed out many numerical relations and
54 THE PERIODIC LAW.
differences between groups of elements. He carried out more fully the comparison with the organic radicals. In the alkaline group, L,i = 7 corresponds to H ; Na = 23 corresponds to C2H3 ; K = 39 corresponds to C4H5. He made use of some of the difference-numbers of Pettenkofer and also noted that the difference between the nitrogen group and the halogens is 5 ; N = 14, F=i9, &c. Hence F = 5-fN; Br=5 + As. Again 42 = <3; 43 = Mg; 44 = S ; 45=Ca; 410 = Se; 4n = Sr; 4l6=Te; 4,, = Ba ; 4+ 3=L,i ; 45 + 3 = Na ; 4, + 3=K. Let us take as a further example one of his groups. C = 6or 5+1 = 6 = ab+b = CH+H. B = 5 + 6mior52+i = 2 ab+b = 2CH+H=Methyl Si= 53+6= 2ioi"54+ 1 =4ab-r-b = 4CH + H=Ethyl Zr=55 + 6 = 3ior56+i = 6ab + b=6CH+H=Propyl A number of such groups are given. There is ap- pended what is called a table of the Atomic Parallels, which is the first attempt at representing the atomic weights in a diagram. The atomic weights from the ordinates. Then the oxygen group is repre- sented by three straight lines, the first beginning at 8 and ending at 16, the second beginning at six- teen and going to 40, the third beginning at 40 and going to 64. For the magnesium group these lines began at 12, 20, 44 respectively and ended at 64. The foot note states : "oxygen and magnesium groups, showing the steps or differences between each member; they are parallel except that Mg is raised up 4. Similar parallels are given for the nitrogen and chlorine groups." From his tables of the groups compared with the organic
REVISION OF THE ATOMIC WEIGHTS. 55
radicals Mercer deduced a general formula as an expres- sion for the atomic weights of single groups of elements ; as mx or mx-\-y, where x andjv are constant for the same group.
43. The Revision of the Atomic Weights by Canniz- zaro. — In i860 and the year or two following, M. Carey Lea published a number of articles bearing upon the numerical relations of the equivalents. As they were continuations of the same general search, though in a rather scattering fashion, for some law or laws underlying these relations they will be mentioned to- gether. Preliminary to this mention, however, it must be stated that the atomic weights were now in a much more satisfactory condition. As has been seen from the quotations already made from various workers, there was very little uniformity in the usage as regards these numbers. Some took one authority, some another, and the numbers differed widely and were quite far removed in many cases from those at present in use. So great was this confusion and discord that a meeting, inter- national in character, was called in i860 to meet at Karlsruhe to come to some agreement with regard to their definite and fixed representation. The unitary theory represented by Cannizzaro gained much ground yet it was evident that no full agreement could be arrived at.
Cannizzaro's views afterwards prevailed. They were based on the conceptions of Avogadro, Gerhardt and Regnault and withstood all criticism. His idea of atoms was the smallest portion of an element which enters into
56 THE PERIODIC LAW.
a molecule of its compounds and his table of the atomic weights was the first that gave such approximately cor- rect values as admitted of an insight into the underlying laws.
44. Lea uses the Atomic Weight Differences. — Lea began his first paper with the remark (39) : " Increas- ing accuracy in the determination of the chemical equivalents of the simple bodies seems to destroy more and more the numerical relations once supposed to exist between the equivalent numbers of certain series of elements nearly related to each other by their properties. Yet it can be demonstrated that such relations exist." The first part of Lea's work referred to the numerical differences between the atomic weights of the elements of the same group or family. Thus he formed a descend- ing series begining with Sb 120 and having a regular de- crease of 45. In this way he hit very nearly the atomic weights of the other elements of the group. But he did not stop there going on to a number of negative equiva- lents and remarking upon the cases where they happened to coincide with known positive atomic weights. He found the difference between the elements of the mercury group and so also for the magnesium group. The difference 45 is found between the two groups of the platinum metals. Between a number of elements, not easily classed together, he observed that the difference was nearly twice 44. And so for certain acid-forming ele- ments, as Sn, Ti, Mo, &c, a variety of relations are brought out by adding or subtracting 44.
The elements C, B, and Si are united as follows : (C)
THE GEOMETRICAL RATIOS. 57
12, (B) ii, (Si) 21 = 44. Here he is misled by a faulty determination of the equivalent of silicon. The same difference is detected in several other cases. After tracing these differences, he remarks that this number 44-45 plays an important part in the science of stoichio- metry and the relations which depend upon it are sup- ported, in some cases at least, in a remarkable manner, by analogies of atomic volume. These analogies are pointed out in a series of tables. The author concludes that this relation extends to 48 of the known elements, to all whose equivalents are well known except the group O, S, Se, and Te "substances which stand alone and unmistakably apart from the other elements." This same difference 44 is beginning again, in these later days, to attract attention in considerations of the atomic weights. L,ea did not make much use of the negative equivalents given by him in his tables, still they were criticized. So in a subsequent paper (40) he met these criticisms by the statement that these numbers with the negative sign were mere mathematical abstractions and of course did not mean "less than nothing." Considered in connec- tion with the operations by which they were produced, they are full of significance.
45. The Geometrical Ratios. — Another paper (45) was devoted to what he called geometrical ratios. He first offered as an explanation of the arithmetical relations, al- ready discussed, the hypothesis that the common differ- ence in a series of elements might represent the equivalent number of a substance, as yet undetermined, which by
58 THE PERIODIC LAW.
its combination in varying proportions gave rise to the successive terms of the series.
He noted that if we take two substances and examine the ratio which subsists between the numbers repre- senting their atomic weights, we may find, in certain cases, that it is identical with the ratio subsisting between the atomic weights of two other substances and so on through a considerable number of elements. The ratio between the atomic weights, for instance, of O and N is that of four to seven, so likewise is that between Zr and K ; or K and Ba. He then gave a table in which the elements are arranged according as they give this oxygen-nitrogen ratio of f-, and a second table for the carbon-nitrogen or f ratio.
A different mode of expressing these relations is gotten when instead of adopting the equivalent of one element as oxygen or hydrogen as a permanent unit, we suc- cessively make those of the left-hand members of the proportion the units, say ioo, then of course all the right-hand members will have the equivalent 175, or for the second ratio some different number will be gotten.
46. Other Regularities. — These ratios are traced in
sundry ways for many elements. The author did not
regard them as having any very evident explanation.
He further traced various obscure relationships in the
group of the halogens, thus: I = 10 CI — 12 F; Cl =
12 Br — 7I . , , . 1 • t_ • •
— etc., etc. A table is also given, beginning
2
with Mg= 12, and using oxygen as an increment, and the coincidences with known elements are noted, and
PROUT'S HYPOTHESIS. 59
also another table beginning with 0=8 and using the same increment. The author very aptly added that it is difficult to fix the exact importance to be attached to the various numerical regularities hitherto observed among the atomic weights, some being mere casual co- incidences, and sometimes relations remarkably exact and symmetrical may exist between the atomic weights of bodies which show no analogies in their general properties.
47. Physical or Absolute Atoms.— In a last paper (45) the author makes use of the work of Gustav Tchermak, on the subject of the law of volumes of liquid chemical compounds, in which he maintains that many of the substances usually classed as elements, comport themselves as compound bodies and that it is possible to determine from their physical properties the number of "physical" or absolute atoms which he supposes are contained in a chemical atom of such a body. This theory L,ea combines with some of the numerical rela- tions formerly noted by him.
48. Dumas' Extension of Prout's Hypothesis. — Dumas had taken up and put new life into the hypothesis of Prout in 1840. A little later he had adopted with en- thusiasm the suggestion of Marignac that the hypothesis be extended to the half- atom of hydrogen. In 1859 he reiterated his adhesion to the hypothesis and extended it still further to the fourth atom of hydrogen, this having become necessary because of more accurate determina- tions and the certainty that fractional atomic weights would have to be used for some of the elements. He
60 THE PERIODIC UW.
found twenty-two atomic weights to be whole multiples of hydrogen ; seven atomic weights were multiples of the half atomic weights : and three were multiples of the fourth atom.
Further he found that analogous bodies have identical atomic weights or those with very simple relations be- tween them. And again, the equivalents of elements in the same family furnish laws analogous to those fur- nished by the numbers representing the equivalents of organic radicals belonging to the same natural series.
He formulated the two following propositions.
i. The natural classification of non-metallic bodies is based on the character of the compounds which they form with hydrogen, on the ratio in volumes of the two elements which combine, and in the mode of conden- sation.
2. The natural classification of the metals and in gen- eral, of the bodies which do not unite with hydrogen, should be based on the character of the compounds which they form with chlorine, and so far as possible on the ratio in volumes of the two elements which combine and the mode of condensation.
49. Criticisms of the Work of Dumas. — Schneider (33) regardep the work of Pettenkofer and Dumas as important steps toward the upbuilding of a natural sys- tem. He criticised the propositions of Dumas in detail, differing with him especially as to several elements having the same atomic weight. He pointed out further that the extension of the hypothesis of Prout to the fourth of an atom of hydrogen really deprived it of all
THE WORK ACCOMPLISHED. 6 1
interest and value. The extension could just as well be carried out to the eighth of an atom and so ad infinitum.
Schafarik (38 ) thought that the observations of Dumas upon the atomic weights opened up brilliant glimpses. He regarded them as the last and clearest expression of a movement of the age. " If the simple bodies group themselves into series as do the organic still many blanks remain to be filled. But when one sees what Gerhardt's series have accomplished for the organic chemist he can not drive out similar expectations for the inorganic. And when once the series of simple radicals are full, we will surely learn to accomplish with them what we can already partially do for the compound radicals — build them up."
50. The Work Accomplished. — From the extracts which have been given, it has been seen that the decade from 1850 to i860 was one of great activity in the line of discovering all sorts of numerical relations between the atomic weights, a sort of blind groping, feeling that there was an underlying law to be discovered and reaching out after it without avail. It is not strange that many of the relations should have been very fanci- ful. Nor is it wonderful that they failed to see the law at the bottom of these regularities or the explanation of them. The natural law could not be discovered with such incorrect atomic weights as were at their service. Even with our approximately correct weights we are far from seeing the explanation of many of these same relations. The first attempt at arranging the elements in an ascending series according to the magnitude of the atomic weights, was in this decade. This was done by
62 THE PERIODIC LAW.
Gladstone, but failed of any important results, because of errors in the atomic weights. The first diagrammatic representation of the elements, based upon the atomic weights, fell also in this period, Mercer having made the first diagram. Lastly, the analogy to the compound radicals and homologous series was first noted and dis- cussed. Still, one must confess that the brilliant prom- ise of the beginning of the period was far from fulfilled, and it was perfectly natural that chemists generally, should begin to regard the whole subject with indiffer- ence or even with ridicule.
CHAPTER III.
THE IMMEDIATE FORERUNNERS OF THE PERIODIC LAW.
51. The New Conditions.— From i860 on, the way be- came clearer, and in the succeeding work we catch glimp- ses of the great natural law until at the close of the decade the law stands fairly stated. At first little attention was paid to the papers containing it, or they were even laughed at, for chemists had become tired of these endless symme- tries and regularitiesoffered without explanation and with- out use. We will see too that occasionally some returned to the same sort of speculations which characterized the sixth decade, oblivious of the changes which had come over the field of work. Two factors enter largely into the improvement in the character of the work of the period. Chemists were now in the possession of a fairly accurate set of atomic weights and a more extended knowledge of the elements and their compounds. Several elements were added to the list by means of the spectroscope and expectations were aroused that yet others might be discovered.
52. Stas' Opposition to Prout's Hypothesis. — The last serious conflict over this hypothesis took place be- tween Stas and Marignac from i860 to 1866. In order to test the truth of this hypothesis so earnestly con- tended for by his old master and co-worker, Dumas, Stas undertook a re-determination of many of the more im- portant atomic weights with a degree of care and accuracy never before attained. The atomic weight of silver was made the central factor in many of these determination.
64 THE PERIODIC UW.
Stas tells us (36) that when he undertook his researches he had " an almost absolute confidence in the correctness of Prout's hypothesis." He had indeed assisted Dumas in his memorable revision of the atomic weight of carbon which had done so much to reinstate this theory. As his newer researches progressed, doubts gradually arouse within him. His results for silver, chlorine, lead, potassium and other elements were clearly not in accord with the hypothesis in its original form and so he was forced to declare against the hypothe- sis. Marignac (37) reasoned from Stas' own results that Prout's Hypothesis was substantiated rather than dis- proved. He made use of the two stock arguments of the Proutians ; that Stas' numbers were very close approxi- mations to whole numbers and hence could be considered as such, and that those approximations were too num- erous to be accidental. This fatal error of rounding off fractions into whole numbers was the very thing which mislead Prout at the beginning and with him there was far more excuse for it. Marignac further said that should future determinations of other elements give simi- lar approximations he would feel assured of the existence of some fundamental cause which brought about the multiple relation of the atomic weights and subordinate causes which modified it. He thought that Prout's I^aw deserved to rank with that of Gay L,ussac or of Mariotte. In another place (61) Marignac speaks of Prout's L,aw as one of those not absolute but only approximate laws, like many other Natural Laws, and says in regard to the assumption of a primal matter, or protyle, that its
OTHER NUMERICAL RELATIONS. 65
atomic weight could be taken as small as might be nec- essary.
It could well be classed then with what Pettenkofer calls "the attractive and misleading simple laws of Nature." The " rounding-off " passion was called by Berzelius most aptly " Multiplen-Fieber."
53. Other Numerical Relations. — The craze for search- ing out such regularities as has been recorded in the previous chapter seems to have largely subsided. Most of the work from now on shows a marked difference in aim and method. There is mainly a striving after classification, not disjointed triads, nor unconnected families, but a continuous series of some sort. Besides most of the work now before us is tinged more or less with the idea of periodicity. Still there are a few of the old style of numerical relations to be mentioned. They can best be considered together.
In 1864 a short article appeared in the London Chemi- cal News (48) headed " Numerioal Relations of Equivalent Numbers" and signed " Studiosus." In this it was noted that the atomic weights of the elemen- tary bodies, with few exceptions, were either exactly or very nearly multiples of eight. This can be compared with the work of Dumas and Pettenkofer of which Stud- iosus seems ignorant.
Newlands opposed this generalization. The matter was further discussed by Noble (51) who disapproved of using the term "law", as Studiosus had done, for such relations. Some of these he said, were interesting, others were rubbish. Other brief notes on the subiect
66 THE PERIODIC EAW.
appeared from "Inquirer" and from "Studiosus", and there the matter rested. The fact that many writing upon these subjects concealed their identity under fictitious names would indicate that confidence had been lost in them and that they were looked upon with dis- favor.
54. Parallelism Revived. — Several years later (1869) an anonymous paper appeared (68) in the American Sup- plement to the London Chemical News. This paper con- sidered the parallelism of the elements in a different way from the Double Parallelism of Dumas and in a broader sense, though the ideas do not greatly differ. The diagram given is similar in some respects to some of the diagram- matic representations of the Periodic Law which appeared a number of years afterwards, though it is evident that this unknown author had no idea of the law in making his diagram. The prominent idea with him was the par- allelism, or pairing of the elements.
A central vertical line represented the increase in atomic weights and the different elements were placed along it at heights corresponding to their atomic weights and at such distances as to throw those of the same series in columns together.
"The atomic weights seem to arrange themselves on the diagonal, in parallel shelving lines; also there is a correspondence between the series of artiads andperissads which have the highest atomic weights, that is to sa)', Na, K, Rb, Cs, and Tl on the one hand and Mg, Ca, Sr, Ba, and Pb on the other, inasmuch as they form strong bases and peroxides but no suboxides or acids."
THE PAIRING OF THE ELEMENTS. 67
And so this parallelism was traced for the two series having the next highest atomic weights &c. Also special resemblances were pointed out between the ele- ments occupying corresponding places in the series as C and F, S and P, Ca and K, &c.
The author then observed that the regularity to be de- tected is certainly a very rude one but "considering that every different combination of molecular elasticities (as shown by spectral lines) must give a new set of proper- ties and considering that only about sixty elementary substances out of the myriads which might exist are known to us, we ought to expect no more accurate classification of them than could be made of the animal kingdom, if only sixty animals were known."
55. The Pairing of the Elements. — A short time before the appearance of the article just discussed, another (69) was published in the same journal, also anonymous, and dealing with a sort of parallelism.
Here, too, a table was given, in which the elements were arranged in two columns according to their even or odd valencies, and at the same time observing the order of their atomic weights. It was claimed that an inspec- tion of the table showed that the elements were brought into ' ' something like a natural relation with one another." "Where the atomic weights agree in the two columns there is a still further agreement between the corresponding elements ; the element of even val- ence is paired or mated with an element of odd valence. Probably for each column there is a progression of prop- erties from the top to the bottom, in the order and in the
68
THE PERIODIC EAW.
proportion of the numbers, and the discovery of such properties is a fair and open problem."
"Also, the column readily breaks up into smaller col- umns, or groups. The peculiar relation of the artiads and perissads in Group I is very striking. On one side are all the metals of the known alkalies and each is paired with a well-known alkaline earth."
"The standing out unpaired of H, N, P, As, Sb, and Bi, is very noticeable, for these are the only unmated perissads. There are many unmated artiads, and it is noticeable that many of them occur together. It is pos- sible that they may be filled by the discovery of new elements."
The author thought that more alkalies might be looked for.
|
Artiads. |
Perissads. |
Artiads. |
Perissads. |
||||
|
Gl |
9 |
H |
1 |
Co |
58.8 |
||
|
C |
12 |
Li |
7 |
Yt |
61.7 |
||
|
B |
11 |
Cu |
63-4 |
||||
|
N |
14 |
Zn |
65.2 |
||||
|
o |
16 |
F |
19 |
In |
72 |
||
|
Mg |
24 |
Na |
23 |
As |
75 |
||
|
Al |
27.4 |
Se |
79-4 |
Br |
80 |
||
|
Si |
28 |
Sr |
87.6 |
Rb |
85.4 |
||
|
P |
3i |
Zr |
89.6 |
||||
|
S |
32 |
CI |
35-5 |
Da |
93-6 |
Cs |
94 |
|
Ca |
40 |
K |
39- 1 |
Mo |
96 |
||
|
Ti |
50 |
Ru |
104.4 |
||||
|
Cr |
52.2 |
V |
5i-4 |
Rh |
104.4 |
||
|
Mn |
55 |
Pd |
106.6 |
Ag |
108 |
||
|
Fe |
56 |
Cd |
112 |
||||
|
Ni |
58.8 |
Eb |
112. 6 |
||||
|
&c |
•> |
&c |
•> |
&c, |
&c. |
ATOMIC WEIGHTS AND DENSITIES. 69
|
THE SMAI.I, GROUPS. |
||
|
I. |
||
|
u |
Gl |
|
|
Na |
Mg |
|
|
K |
Ca |
|
|
&c. |
II. |
&c. |
|
F |
O |
|
|
CI |
S |
|
|
Br |
Se |
|
|
I |
III. |
Te |
|
Ag |
Pd |
|
|
Au |
Pt |
|
|
Pb |
Tl |
&c.
56. Classification by the Atomicities. — It should be mentioned in this connection that in 1864 Williamson (50) had presented before the Royal Institution a " Classification of the Elements in Relation to their Atomicities." Much credit is due Williamson for assist- ing in the introduction of Cannizzaro's views concerning the atomic weights among English chemists and in sug- gesting the same changes in Gerhardt's system, which had been chiefly used up to that time. This put a new and fairly correct table in the hands of chemists.
57. Relation between the Atomic Weights and Den= sities. — A new line of research was struck out by Fleck (58) in 1864 by his work upon the " Relations Between the Chemical Equivalents and the Densities of Bodies." Intimations of some sort of connection between the atomic weights and the properties lie, of
7<D THE PERIODIC UW.
course, in the idea of the triads and in much of the pre- ceding work, but they were not clear. Here we have a distinct search for such relations, though not a very suc- cessful one. The day was still some distance off when the dependence of the properties upon the atomic weights would come to be recognized.
Fleck found that the simple bodies, or elements, form several groups in which the relation of the equivalents to the square of the density is invariable, and these con- stant volumes are generally entire multiples of the value borne to potassium.
58. Brodie's Ideal Chemistry. — This is perhaps the best place to mention the efforts of Brodie (66) to sub- stitute a new chemical theory and system in opposition to the atomic theory. It appeared as a long article of one hundred pages in the Journal of the London Chemical Society, and was discussed and antagonized by many authors, as Jevons, Williamson, Odling, Kekule, Ward, Crum-Brown, and others.
The paper is a speculative one and is referred to here because of the attention aroused by it, because it is quoted by later authors, and because of its bearing upon that side of the subject of this treatise, which was often adverted to in the earlier speculations and which under- lies much of the thought and work upon the Periodic L,aw, namely, the composite nature of the elements.
Brodie discussed first the inadequacy of the chemical symbols. He suggested as a foundation for a new and more correct principle the unit of each body in a gaseous condition, viz., that unit of gaseous weighable matter
BRODIK'S IDEAL CHEMISTRY. 71
which fills a space of 1000 cc. at o° and 760 mm. pres- sure.
This unit of mass, empty, may be designated I. Now let S designate the operation by which the unit of mass is filled with the unit of weight, then S3I would mean this unit of mass filled with a stuff of three times the condensation, etc. Such a system of symbols would give at the same time the operation and its result. The symbol of the compound is at the same time the symbol according to which the combination took place. The following may be taken as examples :
|
Unit of mass = I |
s=t, |
|
H = a |
H2S = at |
|
0=x2 |
|
|
H20 = ax |
S03=tx3 |
|
H202 = ax2 |
H2S04 = atx4 |
Thus the hypothesis is made that the symbol of hydro- gen be a, and hydrogen is formed by one of the above- mentioned operations. Then oxygen (x) represents two operations ; the same also of water.
This use of symbols, according to Brodie, should give us an insight into the nature of matter. There are, he thinks, different classes of elements.
1. Those which were formed by one operation (as H and Hg.)
2. Those in whose formation two similar operations were carried out.
3. Those which must be designated compound (as CI out of a, and an unknown element c.) In these com- pound elements we come across units of unknown ele-
72 THE PERIODIC LAW.
ments, as c, i, n. Whether these exist or not, Brodie does not profess to know. Their unit symbols answer every condition of real existence. Perhaps they were once free upon the earth, but have become indissolubly combined upon its coolings. Brodie says he does not aim at proving the existence of a primal matter, but only to make the existence of these compound elements probable.
It is scarcely necessary to subject such speculations to criticism.
59. Brodie's Conception of the Genesis of the Elements. — With regard to the existence of these elements, out of which our present elements are made up, he says :
' ' We may conceive that in remote time or in remote space, there did exist formerly, or possibly do now exist, certain simpler forms of matter than we find on the sur- face of our globe, a} %, e, v} and so on. We may con- sider that in remote ages the temperature of matter was much higher than it is now, and that these other things existed then in the state of perfect gases, separate ex- istences, uncombined.
" We may then conceive that the temperature began to fall, and these things to combine with one another and to enter into new forms of existence, appropriate to the circumstances in which they were placed. * * * We may further consider that as the temperature went on falling, certain forms of matter became more perma- nent and more stable, to the exclusion of other forms.
TELLURIC SCREW OF DE CHANCOURTOIS. 73
We may conceive this process of the lowering of the tem- perature going on, so that these substances, when once formed, could never be decomposed, in fact, that the resolution of these bodies into their component elements could never occur again. You would then have some- thing of our present system of things.
"Now, this is not purely an imagination, for when we look upon the surface of our globe, we have actual evi- dence of similar changes in Nature. When we look at some of the facts which have been revealed to us by the extraordinary analyses which have been made of the matter of distant worlds and nebulae, by means of the spectroscope, it does not seem incredible to me that there may even be evidence, some day, of the indepen- dent existence of such things as x andjy."
It is perhaps not so very surprising that such baseless speculations as these should have received more atten- tion and more approval than the L,aw of Octaves of Newlands. Where boundless space and limitless possi- bilities are taken into consideration, no proof is possible and none can be required, and such free flights of the imagination are always attractive to certain minds.
60. The Telluric Screw of De Chancourtois. — It is to
De Chancourtois, an engineer and geologist, that the credit of being the first to devise a symmetrical arrange- ment of the elements is generally given. He may in some measure be regarded as the originator of the periodic law, though his work lay unnoticed for thirty years and the periodic law was developed independently
74 THE PERIODIC LAW.
of it. In 1862 (46) he presented to the French Acad- emy of Science a paper on a " Natural Classification of the Simple or Radical Bodies entitled the Telluric Screw (Vis Tellurique)." Several communications fol- lowed and it was all finally put in the form of a lithographic table which summed up all his ideas and was accompanied by certain general considerations on the numerical character of the simple bodies, as well as on the verifications which spectral analysis might furnish. In this paper is found the very explicit asser- tion as " the first general conclusion from his work." " Les proprietes des corps so?it les pivpriStes des nom- bres." The most important part of the Periodic L,aw is that the properties of the elements are determined by and are dependent upon the atomic weights. De Chancour- tois' statement is obscure but may be looked upon as conveying in part the same idea.
The fundamental idea of the Telluric Screw consisted in writing the values of the atomic weights along the generatrix of a vertical cylinder, the circular base of which was divided into sixteen equal parts, sixteen be- ing the atomic weight of oxygen. If we then trace upon the cylinder a helix with an angle of forty-five degrees to its axis, each point of the helix may be considered as the characteristic point of a simple body, the atomic weight of which, proportional to the corresponding length of the spiral, will be read upon the generatrix which passes by this point. At each turn, the helix re- turns on one and the same perpendicular at distances from the summit of the cylinder which are multiples of
TELLURIC SCREW OF DE CHANCOURTOIS. 75
sixteen, and mark the bodies whose atomic weights con- form to this condition.
"In the same manner the various points of intersection of the helix with any of the sixteen principle genera- trices, traced from the divisions of the circular base, correspond to elements whose atomic weights differ among themselves by sixteen, or by a multiple of sixteen. Lastly , if after having developed the cylinder upon a plane which transforms the helix into a series of straight parallel segments, we join by a straight line any two points taken upon two segments, after coiling up, this right line will produce a secondary helix, and the inter- sections of this latter with the various turns of the prin- cipal helix will mark bodies for which the differences of the atomic weights will be multiples of a constant quan- tity. In this manner the Telluric Screw, by simply drawing right lines, enables us to show numerical rela- tions which it would have been less easy to detect by a mere inspection of the numbers."
"The relation of the properties of the bodies are mani- fested by simple relations of position of their character- istic points : and then, each of the helices carried through two characteristic points and passing by several other points, or merely in their proximity, shows relations of properties of a certain kind, the analogies or the con- trasts being manifested by certain numerical orders of succession like the immediate sequence or the alterna- tions at diverse periods."
De Chancourtois thus gives a classification of the ele- ments according to their atomic weights and indicates
76 THE PERIODIC LAW.
the idea of periodicity. He says, " We cannot refrain from remarking the predominance of the number 7 in the types of the groups occupying the spiral which are best filled out."
In his pamphlet, published in 1863, he speaks of ' ' direct developments of the system which enable us to perceive at the same time approximations of the series of numerical characteristics to the series of musical sounds, and to that of the bands and rays of the spec- trum."
For this resume of the work of de Chancourtois I am indebted to L,ecoq de Boisbaudran and A. de -L,ap- perent (198), and Crookes (199). It has been compared with the original. In their critique of the work they say that they are far from pretending that the theory of the screw is free from faults, and that the author had not grafted upon his work many considerations which it would have been better to leave out. Several approxi- mations were inaccurate or were strained, and some of them evince too free a use of the imagination. De Chan- courtois started out with the idea that in the natural series the differences between the atomic weights ought to be constant. Gaps were filled up by imagining new varieties of known simple bodies which he called Secondary Characters, and this often led him to mistaken ana- logies.
61. The Work of Newlands. — A second worker, to whom credit is due as to one who grasped some of the truths of the Periodic Arrangement, was John A. R.
THE WORK OF NEWLANDS. 77
Newlands. His work followed immediately upon that of de Chancourtois, but was quite independent of it. His first paper (47) was devoted to the consideration of some numerical relations between the atomic weights. These relations were in part along the line of the old triads, thus zinc was pointed out as the mean between magnesium and cadmium, copper between cobalt and zinc. In the group of the alkalies, one of lithium and one of potassium made two of sodium ; one of lithium and two of potassium made one of rubidium, etc. Sim- ilar relations were observed for other groups. He also endeavored to show a certain kind of symmetry when the lowest member of a group was subtracted from the next higher member and when the lowest member of a triad was deducted from the highest. These were not very obvious. In his first work he used the old atomic weights but speedily abandoned them for those of Cann- izzaro.
In a second paper (53) he gave a table containing the elements arranged in the order of their atomic weights. In a side column the differences between these weights were given, each being deducted from the one next higher in the scale. He failed to find any regularity in these differences, in fact the table was made to disprove the supposed law of one " Studiosus," who had maintained that the atomic weights of the elementary bodies were, with few exceptions , either exactly or very nearly multiples of eight, and whose work has been already mentioned. This has been claimed as the first arrangement of the elements in the order of their atomic weights, but
78 THE PERIODIC LAW.
was preceded by nearly ten years by the arrangement of Gladstone, in which, however, the atomic weights were so faulty that no regularities were discovered, and it is also antedated by the arrangement of de Chan- courtois. The remainder of his paper was devoted to a discussion of some triads and he noted the recurrence of the number sixteen as the difference number between the first and second numbers of some of the best known triads.
62. The Law of Octaves. — It was in a third paper (54), published a month later, that he began to pay attention to the possibilities of his new arrangement of the elements in the order of their atomic weights. In that paper he stated that if these elements are numbered 1, 2, 3, &c, "it will be observed that elements having consecutive numbers frequently either belong to the same group or occupy similar positions in different groups." "The difference between the number of the lowest member of a group and that immediately above it is 7 ; in other words, the eighth element starting from a given one is a kind of repetition of the first, like the eighth note of an octave in music. The differences between the numbers of the other members of a group are frequently twice as great; thus in the nitrogen group, between N and P there are seven elements ; between P and As 13 ; between As and Sb, 14 and between Sb and Bi, 14."
At the close of the paper, he referred again to his triads, and spoke of the apparent existence of triads where the middle members were unknown and also the possibility of Mn, Fe, Co, Ni, and Cu, being the centres of triads whose extremes were unknown or unrecognized. On
EXISTENCE OP TRIADS. 79
the discovery of indium, he hastened to suggest a place for it among the triads and also in his new system (55).
One year after his first announcement of the new system of the atomic weights in numerical order, New- lands published a paper (56), giving his discovery a name and proclaiming it to be a "law." The paper was entitled " On the Law of Octaves." In the table which he gave, he transposed some of the elements so as to bring them into their proper groups. He observed that elements belonging to the same group " usually" appear on the same horizontal line. He next declared that ' ' all the numerical relations among the equivalents pointed out by M. Dumas and others, including the well- known triads, are merely arithmetical results flowing from the existence of the Law of Octaves." Pursued by what might well be called, in his case and in many others, a mania for hunting out arithmetical relations, he tried to discover some sort of relationship between the numbers given the elements as they fall in their places in the system and their atomic weights.
63. Explanation of the Existence of Triads. — He offered (57) as an explanation of the existence of triads the fact that, "in conformity with the Law of Octaves, elements belonging to the same group generall)T have numbers differing by seven or by some multiple of seven. That is to say, if we begin with the lowest member of a group, call- ing it 1, the succeeding members will have the numbers 8, 15, 22, 29, &c respectively. But 8 is the mean between 1 and 15 ; 15 is the mean between 8 and 22 &c. and therefore as an arithmetical result of the Law of Octaves
80 THE PERIODIC LAW.
the number of an element is often the exact mean of those of two others belonging to the same group and consequently its equivalent also approximates to the mean of their equivalents."
Newlands' Table of the elements, as given in 1866, is reproduced here.
Elements Arranged in Octaves.
No. No. No. No.
H 1 F 8 CI 15 Co and Ni 22
Li 2 Na 9 K 16 Cu 23
|
8 |
n. |
|
• 9 |
K |
|
10 |
Ca |
|
11 |
Cr |
|
12 |
Ti |
G 3 Mg 10 Ca 17 Zn 24
Bo 4 Al 11 Cr 18 Y 25
C 5 Si 12 Ti 19 In 26
N 6 P 13 Mn 20 As 27
O 7 S 14 Fe 21 Se 28
Br 29 Pd 36 Te 43 Ptandlr.-so
Rb 30 Ag 37 Cs 44 Os 51
Sr 31 Cd 38 BaandV..-45 Hg 52
Ce and La. 32 U 39 Ta 46 TI 53
Zr 33 Sn 40 W 47 Fb 54
Di and Mo 34 Sb 41 Nb 48 Bi 55
RoandRu.35 I 42 Au 49 Th 56
In order to allow for certain elements which have their atomic weights very close together, as cobalt and nickel, Newlands modified his law thus ; ' ' The numbers of analogous elements, when not consecutive, differ by seven, or by some multiple of seven."
|
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82 THE PERIODIC UW.
64. Criticisms of Newlands' Law. — Dr. Gladstone objected to the arrangement on the score of no room being left for elements which might still be discovered. Further there seemed to be about as close an analogy between the elements in the last vertical column as be- tween those in any horizontal line. Professor G. F. Foster condemned the arrangement because of the distance placed between manganese and chromium or iron and cobalt and nickel.
In reply to the criticism of Gladstone, Newlands said that the fact that such a simple relation existed now was presumptive proof that it would continue to exist no matter how many elements should be discovered. The difference in the numbers of the analogous elements might be altered to eight or any conceivable number without destroying the simple relation between the num- bers of analogous elements.
Very little attention was paid to this work of Newlands. In fact it was allowed to drop completely out of sight as was the somewhat similar work of De Chancourtois. It was not brought to light again until after the system of Mendeleeff had become famous.
65. Character of the work of De Chancourtois and Newlands. — With regard to the work of these two, De Chancourtois and Newlands, it is certain they recognized the fact that periods of seven existed. They failed to extend the idea fully to properties other than the atomic weights. The arrangement of the elements in the order of their atomic weights had been tried a number of years before
DE CHANCOURTOIS' AND NEWUNDS' WORK. 83
the papers of these two workers appeared. De Chan- courtois seems to have had some glimpse of the de- pendence of the properties upon the atomic weights. These two investigators then really cover many of the im- portant points of the PeriodicLaw. Their failure to impress their views upon their contemporaries came from a lack of clearness of statement, from faulty atomic weights and arrangement, and from their complicating matters and obscuring the truth by useless and false speculations.
Mendeleeff (181) has criticised their work as fol- lows : "In such attempts at arrangement and in such views are to be recognized the real forerunners of the Periodic Law; the ground was prepared for it between i860 and 1876, and that it was not expressed in a deter- minate form before the end of the decade, may I suppose, be ascribed to the fact that only analogous elements had been compared (vid. M. Carey Lea) . The idea of seeking for a relation between the atomic weight of all the elements was foreign to the ideas then current , so that neither the Vis Tellurique of De Chancourtois, nor the Law of Octaves of Newlauds, could secure anybody's attention. And yet both De Chancourtois and Newlands, like Dumas and Strecker, more than Lennsen and Pettenkofer, had made an approach to the Periodic Law and had discovered its germs.
"The solution of the problem advanced but slowly, be- cause the facts, and not the law, stood foremost in all attempts ; and the law could not awaken a general in- terest so long as elements, having no apparent connection with each other, were included in the same octave."
84 THE PERIODIC LAW.
66. Remarks of Crookes upon the Priority Claims. —
With regard to the claim of priority advanced for De Chancourtois and Newlands Crookes says (199) "The Periodic Law, it must be remembered, when first announced was not immediately accepted. When Mr. Newlands read his memoir before the Chemical Society it by no means met with a very enthusiastic reception. One gentleman present even inquired, sarcastically, whether the author had ever arranged the elements according to the order of their initial letters.
"Then came the announcements by Professors Mende- leeff and L,. Meyer of their independent and simultaneous discovery of the same truth. The details were quickly circulated and discussed in the scientific press, and the respective merits of the two savants was for a time a bone of contention. Professor Mendeleeff said : It is possible that Newlands has prior to me, enunciated something similar to the Periodic Law, but even this cannot be said of Iy. Meyer.
When the successful attempt was made to vindicate the claims of Newlands as the first discoverer, the ques- tion was thoroughly rediscussed. But none of the savants who entered into the question ever breathed the name of De Chancourtois. His memoirs were at all times accessible in the Comptes Rendtis. But no one found in them that meaning which M. de Boisbaudran and de L,apperent now assert. They certainly contain a pro- posal to classify the elements with reference to their atomic weights. But we may be permitted to doubt
FIRST TABL,E OF I^OTHAR MEYER. 85
whether they can be fairly considered as the germ of the Periodic Law.
1 ' In going over old researches we often find in them matter which we may now regard as a forecast of subse- quent discoveries ; but there is no sufficient evidence that the author disentangled such matter from accom- panying speculations. In the memoir (of de Boisbaudran and de Lapperent) we find an admission that such has been the case with the writings of M. De Chancourtois." 67. The First Table of Lothar Meyer. — In the year 1864, that is, two years before the presentation of New- lands'paper before the Chemical Society of London, con- taining his Law of Octaves, but about the time of his first publication, Lothar Meyer published the first edition of his ' 'Modern Theories of Chemistry' ' (59) and in it gave a table of the elements arranged horizontally according to their atomic weights, so that analogous elements stood under one another and the change of valence, along with that of atomic weight, could be easily observed. Besides, the difference numbers between these weights, taken horizontally, were also given. Some elements were not included in the list and others were given inaccurately, thus impairing the value of the table. The second, third and fourth series are given here as illustrations, iv. in. 11. 1. 1. 11.
O 16.0 F 19.0 Na 23.05 Mg 24.0
16.07 16.46 16.08 16.0
S 32.07 CI35.46 K 39.13 Ca 40.0
46.70 44.51 46.30 47.6
Se 78.8 Br 79.97 RD85.40 Sr87.6
49.50 46.80 47.60 40.5
|
2. Ser. |
C 12.0 |
N 14.04 |
|
Diff. |
16.5 |
16.96 |
|
3- Ser. |
Si 28.5 |
P 31.0 |
|
Diff. |
44-45 |
44.00 |
|
4. Ser. |
|
As 75.0 |
|
44-45 |
45.60 |
86 THE PERIODIC LAW.
It is clear from the part of the table given that the idea of the natural families, already well known, was the predominant one, and that the numerical order of the atomic weights was subordinated to it. Thus the four first elements form a series and then the others are in sixes. Some elements are omitted and vacant spaces are left in other cases. In the fourth series, we have the first member omitted in order that analogous elements may fall properly. No places were found in the table for copper, silver and gold, and other elements. There is certainly less evidence of periodicity in this arrange- ment than in the preceding one of Newlands and yet underlying the system, though probably unrecognized or unappreciated by even the author at the time of its publication, are the" two great principles of the ascending series of atomic weights and the stated recurrence of elements with similar properties. It was Meyer's first attempt, imperfect and incomplete, but sufficient to start that brilliant thinker along the right road and lead him ultimately to the great discovery. The complete table of 1864 will be given later on.
68. Hinrichs' Deductions from the Spectra of the EIe= ments. — Following up his hypothesis of one primary form of matter, first announced twelve years before, Hinrichs called the recent developments in spectroscopy to his aid in the investigation. Making use of the Plucker and Ditscheiner's determinations of the wave lengths in various spectra of the metals, he drew the following con- clusions (from thirteen elements considered).
THK PANTOGEN OF HINRICHS. 87
' ' The dark lines of the elements are equidistant throughout the spectrum, but of varying intensity, many not being observed (or observable) at all; the intervals between the observable lines are expressible as simple multiples of the equal distance indicated by all."
Further, by considering the spectra of seven elements, he found that the ' ' dark lines of the elements are related to the atomic dimensions, considering the elements com- posed of one single primary element, Urstoff."
He concluded by promising a series of articles which should show that, " the properties of the chemical elements are functions of their atomic weights" and that, "the unity of matter is as real as the unity of force. ."
These are indeed remarkable statements, coming as they do three years before Mendeleeff announced, in his Periodic L,aw the dependence of the properties upon the atomic weights, and almost in the same language.
69. The Pantogen of Hinrichs. — This theory, Hinrichs states, was first communicated to various learned men and academies of Europe in 1856 and 1857. It may be stated, beforehand, that Hinrichs is a believer in the Proutian Hypothesis as extended by Marchand and Dumas. This pantogen is the constituent of the various elements. Atoms of pantogen he called ' 'pan atoms. " It is necessary to consider them as material points, without any hidden occult property. When combined, these atoms (all equal) are at definite distances. Those of three atoms form a regular triangle. Chemical elements whose atoms are made up of such figures are called Trigonoides
THE PERIODIC LAW.
Phosphoides
aA Tetrgomoioes
THE PANTOGEN OF HINRICHS. 89
(corresponding to non-metals.) Four panatoms form a square and elements whose atoms are composed of such figures are called Tetragonoides (metals). Elements are thus classified according to the form of their atoms. The Trigonoides and Tetragonoides form the true orders of the elements. These orders are divided into families and the families into species or elements. The families can be expressed by an algebraic equation. Thus the "phosphoides" will be Ph = m (p). These are the ele- ments N, P, As, Sb, Bi. In the equations given, p is a regular hexagon. For the halogens, or as they are called by the author, "chloroides," the equation is Ch= (I)-|-tn. p where m=5.
In the organic series . (homologous) he saw the proto- types of the elements.
His chart of the elements is here reproduced. The radii in this mark the genera and the spiral cutting them, according to the order number, marks the elements, the distance of the species from the centre being proportional to its atomic weight. n as the symbol of pantogen, is placed at the centre of the chart.
It is evident from this citation from Hinrich's Program der Atomechanik that it bears little relation to the Periodic Law. The author states in a later publication that it contains, explicitly stated, all that is true in the Periodic Law. He is a vigorous critic and opponent of this law, however, and may mean by this statement that he regards very little of it as true. The leading facts of his system seem to be drawn from of the Proutian Hy- pothesis of the composite nature of the elements and the
go
THE PERIODIC LAW.
old well-recognized families, falling in the two imper- fect divisions of non-metals and metals.
The diagram which he gave is undoubtedly the pre- cursor of the spiral arrangement of Baumhauer and others, although the fundamental ideas are not identical.
CHAPTER IV.
THE ANNOUNCEMENT OP THE PERIODIC LAW. I 869-1871.
70. Periodic Law. — We come now to the period of the announcement of the Periodic Law. The numerical relations already given form an important part of the Nat- ural Law which one may believe will in time be recog- nized as something higher and broader than what is now known as the Periodic Law. Some of these regularities are doubtless fanciful, the importance of others is not yet fully understood and all are too often overlooked in the prominence ascribed to the ascending series of atomic weights and their regular periodicity. Much credit is due to the early investigators who worked over the strange coincidences and connections between these important physical constants.
71. Mendeleeff's First Paper. — The first paper sum- ming up all the more important principles of the Peri- odic Law was one laid by Mendeleeff before the Russian Chemical Society in March 1869. (70.) The conclu- sions reached in that paper were as follows :
1. The elements, if arranged according to their atomic weights, exhibit an evident periodicity of properties.
2. Elements which are similar as regards their chem- ical properties have atomic weights which are either of nearly the same value (e.g., platinum, iridium, osmium) or which increase regularly (e.g., potassium, rubidium, caesium) .
3. The arrangement of the elements, or groups of ele- ments, in the order of their atomic weights corresponds
92 THE PERIODIC LAW.
to their so-called valences as well as, to some extent, to their distinctive chemical properties — as is apparent, among other series, in that of lithium, beryllium, barium, carbon, nitrogen, oxygen and iron.
4. The elements which are most widely diffused have small atomic weights.
5. The magnitude of the atomic weight determines the character of the element just as the magnitude of the molecule determines the character of a compound body.
6. We must expect the discovery of many yet unknown elements, for example, elements analogous to aluminium and silicon, whose atomic weight would be between 65 and 75.
7. The atomic weight of an element may sometimes be amended by a knowledge of those of the contiguous elements. Thus, the atomic weight of tellurium must lie between 123 and 126, and cannot be 128.
8. Certain characteristic properties of the elements can be foretold from their atomic weights.
" The aim of this communication will be fully at- tained if I succeed in drawing the attention of investi- gators to those relations which exist between the atomic weights of dissimilar elements which, as far as I know,
1 have hitherto been almost completely neglected. I
believe that the solution of some of the most important
problems of our science lies in researches of this kind."
The chief trouble about this first paper of Mendeleeff
\ lay in the imperfections of his table, which is here given in full. The arrangement was only partially according
mendeleef's horizontal table.
93
II
to the size of the atomic weights. They were arranged in vertical series and some of the atomic weights were incorrect.
i
B B C N O F N
72. Mendeleeff's Horizontal Table. — Mendeleeff used other arrangements of the elements in this first paper, one of which has been generally accepted as the most convenient mode of expressing the Periodic Law, though the vertical rows are placed horizontally and the hori- zontal series then become vertical.
|
Mendeleeff's Table. |
1869 |
||||||||
|
Ti |
50 |
Zr |
90 |
? |
180 |
||||
|
V |
5i |
Nb |
94 |
Ta |
182 |
||||
|
Cr |
52 |
Mo |
96 |
W |
186 |
||||
|
Mn |
55 |
Rh |
104.4 |
Pt |
I97;4 |
||||
|
Fe |
56 |
Ru |
104.4 |
Ir |
198 |
||||
|
Ni,Co |
59 |
Pd |
106.6 |
Os |
199 |
||||
|
Cu |
634 |
Ag |
108 |
Hg |
200 |
||||
|
Be |
9-4 |
Mg |
24 |
Zn |
65.2 |
Cd |
112 |
||
|
B |
11 |
Al |
27.4 |
? |
68 |
Ur |
116 |
Au |
197 |
|
C |
12 |
Si |
28 |
? |
70 |
Sn |
118 |
||
|
N |
14 |
P |
3i |
As |
75 |
Sb |
122 |
Bi |
210 |
|
O |
16 |
S |
32 |
Se |
79-4 |
Te |
128? |
||
|
F |
19 |
CI |
35-5 |
Br |
80 |
I |
127 |
||
|
Na |
23 |
K |
39 |
Rb |
85.4 |
Cs |
133 |
Tl |
204 |
|
Ca |
40 |
Sr |
87.6 |
Ba |
137 |
Pb |
207 |
||
|
? |
45 |
Ce |
92 |
||||||
|
?Er |
56 |
La |
94 |
||||||
|
?Y |
60 |
Di |
95 |
||||||
|
?In |
75-6 |
Th |
118 |
|
Li |
Na |
K |
Cu |
Rb |
Ag |
Ca |
.. |
Tl |
|
Be |
Mg |
Ca |
Zn |
Sr |
Cd |
Ba |
.. |
Pb |
|
B |
Al |
Ur |
Bi |
|||||
|
C |
Si |
Ti |
Zr |
Sn |
||||
|
N |
P |
V |
As |
Nb |
Sb |
Ta |
||
|
O |
S |
Se |
Te |
W |
.. |
|||
|
F |
CI |
Br |
.. |
I |
.. |
94 THE PERIODIC I.AW.
73. Important Features of the System. — Mendeleeff also brought out the idea that all the elements can be ar- ranged in one single unbroken series made up of consec- utive periods. He said " The system can be arranged in the form of a spiral and in this the resemblances prin- cipally appear among the members of every other series."
He especially emphasized the idea of periodicity. He said afterwards (117): "The repetition of the word peri- odicity shows that from the very beginning I held this to be the fundamental property of my system of the ele- ments."
In his paper upon atomic volumes a few months later, (71) he said that his system expressed not only the chemical relationship of the elements but also corres- ponded with the division into metals and non-metals, made a distinction between the valences, brought to- gether similar elements of different groups, explained the resemblance of the series of the elements to the homologous groups, set aside hydrogen as a typical ele- ment, placed near together those elements which are most widely distributed in nature and which accompany each other, showed the faultiness of Prout's hypothesis, and pointed out the relations between the elements con- formable to their reciprocal affinities. Lastly he pointed out the relations existing between the specific gravities and specific volumes of the different series of elements, arranged by this system.
74. Mendeleeff's Claim as a Discoverer. — As to his claims as a discoverer, Mendeleeff says later, very truly, that no natural law is discovered all at once. Many
RECEPTION ACCORDED THE DISCOVERY. 95
might claim share in the discovery as bringing their contributions of fact orthought, but he is rightly to be regarded as the discoverer or creator, who has discerned not only the philosophical side but also the real, and who has known how to throw such light upon the matter that every one can convince himself of its truth.
He stated that the earlier works upon the numerical relations of the atomic weights were known to him, ex- cepting those of De Chancourtois and Newlands, and that he was principally indebted to Lennsen and Dumas. " I have studied their researches and they aroused me to seek for a true law . " (117.)
In the elaboration of his law he counted Carnelley as the only one who had added anything new to it, referring to Carnelley's work upon the melting points and mag- netic properties. In this statement he considered only that which had been done up to 1880. As to Lothar Meyer, he denied to him any part in the discovery of this law, conceding only that his graphic representation had made certain properties somewhat clearer.
75. The Reception Accorded the Discovery. — It was in March of 1869 that Mendeleeff announced his law to \ the Russian Society. In August he presented before the Russian Association of Naturalists a paper upon the | bearing of his law upon the volumes of simple bodies. ' In November a further paper appeared from him extend- ing the application of the new system.
Richter, in a letter from St. Petersburg, October 17, 1869,(77) mentioned Mendeleeff's presentation of his sys- tem before the Russian Chemical Society and added: ' ' Ich
96 THE PERIODIC LAW.
glaube dass diese interessanten Formulirung nicht ver- fehlen werden, Ihre Aufmerksamkeit zu erregen." While it is perfectly true that this and the publication of Meyer, to be mentioned next, did attract attention, the notice given them was not at all in accordance with the greatness of the discovery. It is evident that their importance was not recognized and, it may be added, is not fully realized even yet. So far as can be judged at present, the lecture of Dumas at Ipswich created a much greater stir among chemists, was discussed more and led more immediately to others undertaking work along the same or similar lines.
76. The Evolution of /lever's Table.— The discussion between Mendeleeff and Meyer as to the relative merits of their claims to the authorship of the Periodic Law is one of longstanding and has been somewhat hotly waged by the principals and by their supporters.
Meyer's claims are based upon his table, published in 1864 and already given. Further, something less than a year after Mendeleeff, he devised a system of the elements which contained the principal features of the Periodic Law. This system will be discussed a little later on. Meyer stated that it was an expansion of his earlier table and was worked out in entire ignorance of the similar work of Mendeleeff which had appeared in the Russian language some months previously. Before his article was published, however, he saw an abstract of Mendeleeff's article in the Zeitschrift fiir Chemie (N. F. Bd. V. 405.) Such being the state of the case, Meyer claims credit only for points in which he believed he had
MEYER'S TABLE OF 1 864. 97
improved upon the table of Mendeleeff, or differed from it. In his original article he said that his table was es- sentially identical with the one given by Mendeleeff.
77. Meyer's Table of i864. — For purposes of comparison Meyer's first table is here given in its complete form. It will be observed that there are two portions. One of twenty-eight elements in six vertical rows and a second of sixteen in five rows. There is a manifest struggle be- tween the desire to arrange the elements according to the atomic weights and at the same time to have them fall according to their analogies in families. It is well to note the significance attached to the difference-num- bers, a signifiance not yet understood nor appreciated. Meyer's First Table. 1864.
|
4 val. |
3 val. |
2 val. |
1 val. |
1 val. Li 7.03 |
2 val. (Be 9.3) |
|
Diff. .... |
16.02 |
(14-7) |
|||
|
C 12.0 |
N 14.4 |
O 16.OO |
F 19.0 |
Na 23.5 |
Mg 24.0 |
|
Diff. 16.5 |
16.96 |
16.07 |
16.46 |
16.08 |
16.0 |
|
Si 28.5 |
P 31-0 |
S 32.0 |
CI 35-46 |
K 39.13 |
Ca 40.0 |
|
Diff. ^44-45 |
44 -o |
46.7 |
44-51 |
46.3 |
47.0 |
|
|
As 75.0 |
Se 78.8 |
Br 79.97 |
Rb 85.4 |
Sr 87.0 |
|
Diff. *H 44.55 |
45-6 |
49-5 |
46.8 |
47.6 |
49.0 |
|
Sn 117.6 |
Sb 120.6 |
Te 128.3 |
1 126.8 |
Cs 133.0 |
|
|
Diff. ^44.7 |
Af443-7 |
35-5 |
|||
|
Pb 207.0 |
Bi 208.0 |
(Tl 204.0?) |
Ba 137. 1 |
||
|
4 val. |
4 val. |
4 val. |
2 val. |
1 val. |
|
|
f Mn 55.1 \ Fe56.o |
Ni 58.7 |
Co 58.7 |
Zn 65.0 |
Cu 63.5 |
|
|
(49-2 |
|||||
|
DifN |
45-6 |
47-3 |
46.9 |
44-4 |
|
|
1 48.3 |
|||||
|
Ru 104.3 |
Rh 104.3 |
Pd 106.0 |
Cdni.9 |
Ag 107.94 |
|
|
Diff. 3J^ 46.0 |
AfJ. 46.4 |
¥ 46.5 } |
H- 44-5 |
1f^-44-4 |
|
|
Pt 197.1 |
Ir 197. 1 |
Os 199.0 Hg 200.2 |
Au 196.7 |
98 THE PERIODIC LAW.
78. fleyer's Table of 1868. — Lately Seubert, the pupil and friend of Meyer, has published an account (239) of a paper which has come to light since the death of its distinguished author and which shows the indepen- dence of Meyer in his work. This was a preliminary suggestion of his System, an elaboration of his work of 1864, written out and handed to his friend and successor in the chair of chemistry at Eberswald, Professor A. Remele, in July 1868. Meyer first learned of its pre- servation when Remele showed it to him in 1893 after his lecture before the German Chemical Society upon the Periodic Law. He then expressed regret that he had not published it in 1868, even though incomplete. This table is fuller and shows many differences from the earlier one. Fifty-two elements are given and in fifteen vertical rows. There are many imperfections in it. Thus there is no place for boron in it and aluminium is put down twice because of evident doubt as to its proper location. Even then its proper place is missed. Imper- fectly known atomic weights also cause some trouble in the arrangement. Every one must admit that there is a wide step between this table and the one given by Meyer after the publication of Mendeleeff .
MEYER'S TABI.E OF l868.
99
|
H ll ^ 11 ° Ji ^ H °w as |
NO |
n H| JO ON |
" |
|
|
ir u^-sH p° 00 ^ 8 00 |
0 |
3" ^S g IT bo 55 io B 5 it 1! 11 -H> |
||
|
£ S S | 00 - ^ |
H |
J Pi! no J' m <£ M w 0 °* H -*»• °° O |
h bo |
00 |
|
illlliMH&JIM |
to |
II W H °°Jl V£) -£* O 00 |
ii 6j |
*. |
|
c*> V O N . M O |
00 |
3 00 •^1 |
Ol |
|
|
p . -1 ■ 5f' "r1 b CTv |
■*> |
« !■ M ,ON On4>-J OH ^1"Tno *■ |
ON |
|
|
i!°li°g £? W NO 0 b b |
a |
MM 0 -£■ - 0 io • "° |
^4 |
|
|
1 |
hj 00 XJi » to ^NO 0«» W«j "0 T* ^^ ^ |
h?.Sn0 00 !° """ O |
00 |
IOO THE PERIODIC EAW.
70. fleyer's Table of 1870. — Lothar Meyer's article upon the ' ' Nature of the Elements as Functions of their Atomic Weights" (81) appeared in the year 1870, although written, as he says, in December 1869. The table there given is an expansion (116) of his table published in 1864. It is distinguished from it in that the consecutive atomic weights are not arranged horizontally but vertically as in one of the tables of Mendeleeff. He had tried to arrange all the elements in that first table but had been unable to do so because of the numerous erroneous atomic weights. When these were corrected he saw the possibility of arranging all of the elements into one table in accordance with the size of the atomic weights. Although Mendeleeff did say that the weights might be ordered in one single spiral, he did not do this and could not have attached much im- portance to such an arrangement. In fact it was not possible to so arrange them with the series as first given by him and with the false atomic weights included in his table. Meyer observed, (116) " had Mende- leeff then attached any importance to the formation of a single series he would have, without doubt, chosen other values for these elements. Mendeleeff did not hesitate to "correct" the value of the atomic weights by his table and to insert unknown ones when necessary." A close examination of Mendeleeff' s first table will show a struggle between a desire to have a single series ac- cording to atomic weights and still to get the analogous elements to fall info periods. The regular recurrence of the periods is brought out better by Newlands in his
MENDELEEFF'S TABLE OF 1871. IOI
scheme though Newlands had more inaccuracies of atomic weights to contend with and less knowledge of the analogies between the elements. Meyer's table is much clearer than that of Mendeleeff and brings out the series of analogous elements better. It is given on page 102.
One claim made by Meyer for this table, is the dis- covery of what he called double periodicity. This is shown in the table where we see that elements of analo- gous properties recur in every other column and not in the immediately adjacent ones, thus giving two series of analogous bodies. As has been already shown by the quotation from Mendeleeff's first article the two rec- ognized that the analogy was apparent principally be- tween the members of every other series. These he distinguished later as the "matched and unmatched" series.
80. Mendeleeff's Table of 1871. — Mendeleeff's table given in 1871 (74) was a great improvement over his first. He gave in fact two tables, one giving the hori- zontal and the other the vertical mode of arrangement. These tables follow on pages 103 and 104.
102
THE PERIODIC LAW.
|
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1 So ^ |
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H J Hjijl 1 § |
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N ob a, |
2 B II |
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t/> |
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104 THE PERIODIC LAW.
|
Mendeleeff's Tabi,e II. |
|||||
|
Gr. Ser. i. |
2. |
4- |
6. |
8. |
10. |
|
I. |
W7 |
K39 |
Rb85 |
Cs 133 |
10 |
|
II |
Be 9.2 |
Ca 40 |
Sr87 |
Ba 137 |
|
|
III. |
B 11 |
?Sc |
Yt8g? |
Dii39? |
Er 175? |
|
IV. |
C 12 |
Ti48 |
Zr 90 |
Ce 141 |
La 180 ? |
|
V. |
N 14 |
v 51 |
Nb 94 |
?2 |
Ta 182 |
|
VI. |
O16 |
Cr52.S |
Mo 96 |
? |
W 184 |
|
VII. |
F 19 |
Mnss |
|||
|
VIII |
Fe 56 |
Ru 103 |
Os 194 |
||
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Co 58.6 |
Rh 104 |
•• |
Ir 195 |
||
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Ni 58.6 |
Pd 106 |
•• |
Pt 197 |
||
|
I. H i |
Na 23 |
Cu 63.5 |
Ag 108 |
Au 197 |
|
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II. |
Mg 24 |
Zn 65 |
Cd 112 |
3 |
Hg 200 |
|
III. |
Al 27.3 |
Ga 69 |
In 113 |
Tl 204 |
|
|
IV. |
Si 28 |
??? |
Sn 118 |
.. |
Pb 204 |
|
V. |
P31 |
As 75 |
Sb 120 |
.. |
Bi 208 |
|
VI. |
S32 |
Se 79 |
Te 125 ? |
|
|
|
VII. |
CI 35-5 |
Br 80 |
I 127 |
|
Th Ur
231
240
In a foot note it was stated that possibly Di had an atomic weight of 146 and would occupy place marked 2. In another note he spoke of Carnelley's having assigned Norwegium to place 3. These tables contain the Peri- odic L,aw as it is known to us. They have not been very materially altered, though they have been corrected in minor points. The work since has been mainly one of elaboration. The credit for the expansion and filling out of the Periodic I,aw, its extension to the other proper- ties of the elements and the bringing of the various com- pounds of these elements into consideration also, has been almost entirely due to the skill and knowledge of Mendeleeff. He was bold and successful in his proph- ecy of new elements and their properties, and also as to
MEYER'S LATER TABLES. 105
changes in properties then generally accepted. Many, though not all, of these prophecies have been fulfilled.
81. rieyer's Later Tables. — Lothar Meyer, in the later editions of his " Modern Theories of Chemistry" has given his table in a changed and improved form. He says of this table (3d ed. p 292):
1 ' If one will think of this table as rolled upon an up- right cylinder so that the right side shall touch the left, thus nickel joining itself directly to copper, palladium to silver and platinum to gold, one will get as is easy to be seen, a continuous series of all the elements arranged in the form of a spiral and according to the size of the atomic weights. The elements which by this arrange- ment stand over one another form a natural group, or family, the members of which resemble each other in very unequal measure. In most of the groups four or five of the seven or eight members are more nearly re- lated to one another than to the remaining three which again show a great similarity to one another. In the second vertical column, beginning with Li, the five light alkali metals are very much alike, while the three heavy metals agree with one another in many properties; with alkali metals, however, only in single points, as in the isomorphism of many of the compounds and in their ability to unite with a single atom of a halogen.
Li 7-OI
15-93
Na 22.99
16.04
K 39-03
24.15
Cu 63.1J
Rb
85.2
22.5
IO7.66 25.0
Cs
132-7
165
Au I96.2
Be
9.08
14.86
Mg 23-94
Ca 39-91
Zn 64.88
Sr 87-3
Cd
in. 7
Ba
136.86
170
Hg 199. J
226
B IO-9
16.14
Al 27.04
16.93
Sc 43-97
? Y 89.6
23.8
In H3-4
Yb 172.6
Tl 203.7
230
C II.97
Si 28
Zr 90.4
27.4
Sn
H7-35
23.8
Ce 141. 2
176
Pb 206.39
?Th 231-96
N I4-OI 16.95
P
30.96
V
5i-i
23.8
As TA-9_
18.8
Nb
_93i7_
25-9
Sb 119. 6
25
Di 145
Ta
182
Ki 207.5
234
O
15.96
16.02
s
31.98
126.3
151
w
183.6
?4 239.8
F 19-06 16.31
|
52-45 |
Mn 54-8 |
|
26.48 |
|
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25.0 |
|
|
Se 78.87 17.0 |
|
|
Br 79.76 |
|
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19 |
|
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Mo 95-9 |
|
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? |
|
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3°-4 |
99 28 |
126.54
Fe 55-86
Co 58.6
Ni 58.6
|
Ru 103 -5 |
Rh 104. 1 |
Pd 106.2 |
|
Os. J95? |
Ir I92-5 |
Pt 194-3 |
TARDY RECOGNITION OP THE LAW. 107
In a similar manner each of the following columns can be separated into two groups, clearly different and yet related to one another in certain particulars."
82. fleyer's Curve of the Atomic Volumes. — Meyer was the first to give a graphic representation of this law. He devised a curve intended to show the dependence of the atomic volumes upon the atomic weights. The atomic weights were taken as the abscissae, the atomic volumes forming the ordinates. The curve uniting the tops of these ordinates gave a picture of the changes which the atomic volume experiences with increasing atomic weight.
83. The Failure to Recognize the Importance of the Law. — As has been said, the Periodic Law soon attracted attention, but its importance does not seem to have been generally recognized at first, nor was it widely accepted as a law. In fact for several years it nearly dropped out of sight and it was only the lucky discovery of some new elements, thus fulfilling certain predictions of Mende- leeff , that brought it prominently before the chemical world. How long it would otherwise have laid unnoticed can only be guessed at.
In 1879, the London Chemical News translated from the Moniteur Scientifique and republished Mendeleef's article on the ' ' Periodic Law of the Chemical Ele- ments," because "considerable attention has been drawn to M. Mendeleeff's memoir in consequence of the newly discovered elements, gallium and scandium, being nearly identical with the predicted elements eka-alumi- nium and eka-boron."
io8
the; periodic law.
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TARDY RECOGNITION OP THE LAW. IO9
Mendeleef said in his introductory note to the article mentioned :
"Although seven years have passed since these thoughts absorbed my attention ; although other occu- pations have withdrawn my attention from the problem of the elements which was always getting nearer solu- tion ; in short, although I might wish to put this ques- tion otherwise than I did seven years ago, still I keep to the same firm conviction that I formerly had on the im- portance and value of the theorems on which my memoir is based. Several occurrences have aided to make some of the logical consequences of the Periodic Law popular.
1st. The law I announced has been considered as a repetition in another form of what has been already said by others. It is now certain that the Periodic Law offers consequences that the old systems had scarcely ventured to foresee. Formerly it was only a grouping, a scheme, a subordination to a given fact ; while the Periodic Law furnishes the facts and tends to strengthen the philosophic question which brings to light the mys- terious nature of the elements. This tendency is of the same category as Prout's Law, with the essential differ- ence that Prout's Law is arithmetical and that the Peri- odic Law exhausts itself in connecting the mechanical and philosophical laws which form the character and glory of the exact science. It proclaims loudly that the nature of the elements depends above all on their mass, and it considers this function as periodic. The formula of the law might be changed ; a greater appreciation of this function will be found, but I believe that the origi- nal idea of the periodic law will remain."
IIO THE PERIODIC LAW.
It is undoubtedly true, as has been said, "the dis- covery of gallium may be considered as the inaugura- tion of the Periodic Law."
84. The Criticism of Berthelot. — From what has been said, it will be seen that one must look into the second decade after the announcement of the law for criticisms of it. Some of these may be quoted as showing the character of the reception accorded it.
An adverse criticism from Berthelot will first be given. The French have been especially slow in acknowledging the merits of the discovery. Somewhat strangely Ber- thelot's critique is placed in his Origins of Alchemy (145) where one would scarcely look for anything of that character, and so has escaped more general notice.
"It is known that certain general relations exist be- tween the atomic weights of the bodies, their atomic volumes and their different physical and chemical properties. These relations were studied long before the arrangement of the elements in parallel series. They result from the absolute atomic weights and not from any periodic differences. Yet, as these relations are the immediate consequence of the "atomic weights, the coincidences established between these come to light again necessarily when we consider their atomic volumes and all the other correlative properties of the chemical mass of the elements.
' ' This circumstance increases the convenience of the new table. It brings no new proof of the existence of the periodic series. It is necessary to guard against all illusion in that direction. L,et us examine the predic-
THE CRITICISM OF BERTHEEOT. Ill
tions deduced from the new classification. It is in this re- spect more than in any other that the system should prove interesting. In the arithmetical progressions which em- brace each family of elements, it is seen that certain terms are lacking. Between S= 32 and Se= 79 there should exist two intermediate terms 48 and 64. In the same way between Se = 79 and Te = 128, two terms are lacking, 96 and 112. Evidently these are to be filled in by unknown elements and there is an opening here for research. But as the number of these is too great, the authors of the system, in haste to fill the gaps in each family, have interpolated elements already known which are manifestly strangers to the family : such as Mo in- serted between Se and Te : W and U added in like man- ner to the series. To the series of L,i=7, H=i has been placed at the head and at the end Cu =63, Ag = 108 and Au = 197. All this trenches upon the fanciful.
' ' In the same way between CI and Br and between Br and I certain terms of the arithmetical progression are lacking. Here we have again hypothetical and to-be- discovered elements. Notice here that their properties are not undetermined. In fact the physical or chemical properties of an unknown element can be predicted and calculated when its atomic weight and family or analo- gies are given. This prediction is not a consequence of the theory of the periodic series. It results purely and simply, from the long-known laws and analogies which are independent of the new system.
"It is impossible not to draw the attention of the critic and of the philosopher to the convenient trick, by the aid
112 THE PERIODIC LAW.
of which the authors of the system have managed to in- clude not only all known but all possible substances. This trick consists in forming their table with terms which do not differ by more than two units, terms so bound together that no new body, whatever it may be, can fall outside the meshes of the net. The thing is the more assured since the periodic differences often admit in their applications to known atomic weights, of varia- tions of one to two units. We see that it is no longer a question of fractions of units which separate the multiples of hydrogen such as were raised as objections to the hy- pothesis of Prout and Dumas.
" Without excluding absolutely the conception of parallels, we must avoid attaching too high a scientific value to frames so elastic. Especially must we guard against attributing to it discoveries, past or future, to which it does not necessarily conduce in a precise and necessary manner. We might say, with all sincerity, that outside of the old natural families of the elements, known for a long time, there is little here but artificial groupings. The system of the periodic series has not, any more than the system of the multiples of hydrogen, furnished, up to the present, a certain and definite rule for discovering either the simple bodies found in late years or those which we do not yet know. None of these systems has given a positive method of fore-seeing, much less of synthetically forming, our elements.
"It is not that such systems have no use in the sci- ence ; they serve to arouse and sustain the imagination of investigators. They submit, with difficulty, to rest
THK CRITICISM OF BERTHEIvOT. 113
upon a purely experimental basis and push into the region of construction and of theories that spring from the desire for unity and causality inherent in the human mind. It would be too harsh, and useless besides, to wish to prescribe everything tentative of this nature. But such is the seduction exercised by these dreams, that it is necessary to guard against seeing in them the fun- damental laws of our science and the basis of its facts, under pain of falling again into a mystic enthusiasm parallel to that of the alchemist.
' ' Such conceptions are on the one hand too narrow and it thus invites to elevating them too high. At bottom, those who invoke the multiples of hydrogen and the per- iodic series, bind everything to the conception of certain atoms smaller than those of the reputedly simple bodies. But if it comes to demonstrating that the equivalents of the actual elements are rigorously multiples, the one of the other, or more generally, multiples of certain num- bers, forming the differences in determined arithmetical progressions, it results in this probable conclusion, that the actually simple bodies represent the unequal stages of condensation of the same fundamental material. This fashion of conceiving things has nothing which can be repugnant to a chemist versed in the history of his science.
" One can call to mind, as proofs, facts well-known to all and which are not without some analogy. Such are the multiple forms of carbon, an element which mani- fests itself in the free state in the most diverse forms and which gives rise to many series of compounds corres-
114 TH:E periodic law.
ponding in a certain manner with each of these funda- mental forms, as the compounds of an ordinary element correspond with that element. Carbon represents, in some sort, the common generator of an entire family of elements, differing in their condensation. One is brought to the same conclusion by a study of the hydro- carbons. The objection might be raised that the diver- sity of the properties of carbon should not be less than the diversity existing between the elements comprised in one family, those of the halogens or of the sulphur group, for instance. In reality S and Se never produce the same compounds in uniting with O, H, or N, and they cannot be regenerated by condensation of the most simple among them.
" To sum up, carbon viewed in its different states and degrees of condensation is equivalent in itself to an en- tire class of simple bodies. O, S, Se, and Te by the same reasoning could represent the different states of a common element. Further, ozone, a body of very sim- ple properties, and comparable therefore to a true ele- ment, has been really formed of oxygen, its existence to a certain extent justifying the preceding conjectures.
85. Mendeleeff's Reply. — It is best to quote here, from his Faraday lecture, (1S1) Mendeleeff's reply to this criticism of Berthelot. This also gives the author's views of the many attempts to make use of the Periodic L,aw in speculations concerning the original form or froms of matter. We shall come across many such speculations in the remaining pages of this work.
" Feeling that spectrum analysis will not yield a sup-
ostwald's criticism. 115
port to the Pythagorean conception, its modern promo- ters are bent upon its being confirmed by the Periodic Law. It is evident that the illustrious Berthelot has simply mixed up the fundamental idea of the Law of Periodicity with the ideas of Prout, the alchemist, and Democritus about primary matter. But the Periodic Law, based as it is on the solid and wholesome ground of experimental research, has been evolved indepen- dently of any conception as to the nature of the elements; it does not in the least originate in the idea of an unique matter ; and it has no historical connection with that relic of the torments of classical thought, and therefore it affords no more indication of the unity of matter or of the compound character of our elements than the Law of Avogadro, or the Law of Specific Heats, or even the conclusions of spectrum analysis. None of the advo- cates of an unique matter have ever tried to explain the law from the standpoint of ideas taken from a remote antiquity when it was found convenient to admit the ex- istence of many gods or of an unique matter."
86. Ostwald's Criticism.— Ostwald has the following criticism of the Periodic Law on pages 126 and 127 of his Lehrbuch der Allgemeinen Chemie (149).
' ' The numerous and unexpected developments which the Periodic Law has given us as to the relations of the atoms, one to another, should not make us blind to cer- tain difficulties which have arisen in its full application. Thus the discussion over the atomic weight of beryllium is not yet closed, since there are many reasons for not accepting the arrangement of the elements as given.
Il6 THE PERIODIC LAW.
Again elements are separated from one another which in the form of their compounds stand close together — as mercury and copper, with which it has more points of resemblance than with zinc and cadmium. Sodium is separated from the alkaline metals proper and placed with copper, silver, and gold. The silver here shows, at best, a relationship through the isomorphism of the water-free sulphate. Also the oxidation steps held up by Mendeleeff as characteristic or typical are neither the only ones, nor the lowest, nor yet the highest, indeed they are often unknown and incapable of existence.
"These objections are not raised to refute the Periodic Law. They are too few in number for that and stand opposed to too many favoring circumstances. They serve only to show that the law in its present form is only the beginning of a most promising line of thought. The idea of the analogy of the elements has still too much undetermined to permit of its definite use. There is still no numerical expression for it. Further, the rela- tion of multiple proportions to the Periodic Law remains to be examined. Mendeleeff shows justly that the views predominating at present as to the valence of the elementary atoms has real meaning only for the carbon compounds and falls into constant contradiction in the case of the inorganic compounds. It is to be hoped that a theory of chemical compounds which will suit both branches of chemistry will be developed out of the rela- tions of the multiple proportions to the Periodic Law. Lastly, it cannot be left without mention that in reflect- ing upon the causes of the Periodic Law the same meta-
ostwald's criticism. 117
physical consequences press forward which have served as starting points for the hypothesis of Prout and have been somewhat supported by the approximate and par- tial agreement of the same with experiment. If the properties of the elements prove to be functions of the atomic weights, the thought lies near to seek in these also the causes of the same, and the assumption of a primal matter, whose different states of condensa- tion define the differences of the elements, can hardly be set aside. These hypotheses are far reaching and far removed from sure foundation, but they accord with the general tendency of natural science."
CHAPTER V.
DEVELOPMENT OF THE SYSTEMS. 1870-1880. In the preceding chapter it was stated that but little was done to improve and extend the Periodic Law dur- ing the first years after its announcement. Its discoverers had dropped it for other work, Mendeleeff finding occu- pation in the study of the origin of petroleum and in various physico-chemical researches. Meyer (91) complained of the "present lack of system in in- organic chemistry ' ' and appeals for the putting forth of greater efforts in the development of this branch of chem- istry. He mentioned "the natural system of the ele- ments arranged according to their atomic weights with which he and Mendeleeff had been busying themselves of late years" as a step towards this development. The natural system should be the principle of the classifica- tion of inorganic compounds.
87. A Return to Numerical Regularities. — We will find in the record of this decade, therefore, chiefly independent and new systems and a recurrence of numerical regularities such as were pointed out almost ad nauseam in the period immediately following the lec- ture of Dumas. It is strange to see how indefatigable chemists have been along this line and how many differ- ent ' ' relations ' ' they have discovered between the six- ty odd numbers lying in the range of atomic weights between one and two hundred and forty.
120 THE PERIODIC LAW.
There seems from now on a more marked tendency toward the search after laws underlying these relations. In the earlier periods the discovery of isolated ' ' regulari- ties ' ' seemed to satisfy the investigator.
88. Growth in the Belief of the Unity of Matter.—
There is also from this time forward a very evident increase in the number of adherents to the philosophic theory of the Unity of Matter. There is a revival of the Proutian Hypothesis under various forms. The com- posite nature of the elements is more widely and boldly stated and discussed. The last question of the century shows a revulsion to this old hypothesis in so far as it teaches that the elements are compound, though the part of it referring to the multiple relations existing be- tween the atomic weights has been largely set aside.
89. Baumhauer's Spiral Arrangement. — In the year 1870, shortly after the appearance of the system of Men- deleeff and the table of Meyer, Baumhauer (90) sug- gested a mode of illustrating graphically the relation- ship between the elements and, possibly, the derivation, or nature, of the supposed simple bodies.
The fairly regular differences between the groups were given by Meyer in his earlier work. Baumhauer gives these differences as 16, 46, and 88-92. He then con- tinues :
" A clear view of the elements and, with that, the ex- planation of many peculiarities, is first obtained when one arranges them in accordance with increasing atomic weight in the form of a spiral, giving hydrogen the cen-
BAUMHAUER'S SPIRAL ARRANGEMENT. 121
tral position. Similar elements fall under one another. The ring-formed series in the spiral are called central, those reaching from center to peripheiy are radial. For the sake of greater simplicity seven chief radials are assumed, some of which are again split up into several others. Between the radial and central series numerous transitions show themselves which are to be explained by the preponderating influence of neighboring elements. Only when the relations to all neighboring members of the system appear for each element at the same time and with equal intensity will the whole furnish a perfect scheme.
' ' The relations to neighboring elements can be many and since they cannot be quantitatively determined, it is difficult, proceeding from the chemical properties of the element, to assign it its proper place in the system. Generally, however, the position of an element relative to the others can be determined by a closer observation of the clue given by its characteristics. The principle followed can be outlined as follows : Each element holds a position determined by its chemical characteristics, as a summary expression of which the atomic weight may be regarded, either upon the continuous series of a spiral arranged according to increasing atomic weight or be- tween the rings of the same. In the last case, as well as by each interposition upon the spiral itself, the chem- ical nature and the atomic weight of the element in question is dependent upon the nature and the atomic weight of neighboring elements. Thus one can calcu- late atomic weights for any blank positions upon the
122 THE PERIODIC UW.
spiral where an element is lacking. This can be only imperfectly done after passing the atomic weight 137 as so many of the vertical and side neighboring elements are lacking.
' ' The atomic weight and the chemical nature of an element stand in close connection with one another. Still this connection is not usually a simple one. On the contrary, the atomic weight of an element is com- posed of the atomic weights of others in just the measure in which its properties show themselves to be a complex of other elements. This idea can be brought under the general formula
A _ IB+mC+nD . . . I -\- m -\- n . . where A = the atomic weight of an element, B, C, D atomic weights of related elements, /, m, n certain coef- ficients. These last express the ratio of the magnitude of affinity of A with the elements B, C, D . . . . Ac- cording to this formula, quite different elements can have similar atomic weights whereby B, C, D, as well as /, m, n, have a different meaning in each separate case. Like elements also have almost identical weights where B, C, D, as well as /, m, n, change only in slight degree.
' ' The form of a spiral was chosen for the graphic representation of these facts only after many vain at- tempts at arranging the element in other ways which would express the facts equally well. The typical ele- ments fall upon the spiral and their atomic weights form an increasing series. They show relationship to one another and may perhaps in part be referred to still sim-
ADDITIONAL WORK BY NEWUNDS. 1 23
pier types. The elements appearing as medial members can be recognized from their many-sided characteristics.
" In this table the relation of the elements to one an- other is indicated by arrows in the more difficult cases.
The most distinguished chemists are united in the opinion that there exists one or a few primal elements and that our elements are at most modifications or com- binations of these. This idea is expressed in the table in the reduction of the complicated elements to certain types, and thus each series is represented by its initial member which has the lowest atomic weight. The other members differ from the first in their density. Al- most without exception the specific gravity increases from the center to the periphery of the spiral. We can therefore assume that all elements of any one typical series are only definite functions of the first member. Their atomic weight is gotten by the addition of a num- ber given by the building of the spiral.
" One can go a step further and look even upon these initial members as peculiar and to a certain degree indi- vidualized modifications of one and the same primal matter. This, however, is of course only speculation."
The diagram follows and needs no further explana- tion. Its resemblance to that of Hinrich's will be noted.
9o. Additional Work by Newlands. — In 1872 New- lands published his first priority claim (86). A little later, in a short note, (87) he drew attention to the oc- currence of the fourteen principal elements, which are most widely distributed and which appear to be essen-
124 THE PERIODIC LAW.
tial to vegetable and animal life. He observed that they comprise two representatives of each of the chief chemi- cal groups. In this he classed hydrogen and chlorine together and aluminium and iron.
In 1873 he made another priority claim before the London Chemical Society. In 1875 he gave another table to be used in text-books as a substitute for the old alphabetical lists, which have been hard to displace. In this he included the ordinal-number, to which he continued to attach importance, the symbol, the atomic weight, and the difference between each atomic weight and the one immediately preceding it. He drew atten- tion to the recurrence of analogous elements at every eighth interval and repeated his former comparison to the octaves in music. When the table was given a hori- zontal arrangement, in sevens and in sixteen columns, he remarked upon the quantivalence of the elements thus exhibited.
In 1878 (104) Newlands gave a table comparing the atomic weights derived from four different standards : Hydrogen, 1; Sodium, 10; Chlorine, 15, "nearly"; and Carbon, 5. Comparisons are made with the ordi- nal numbers. These need not be commented upon and the following brief notes of his will be passed over with bare mention.
1. He believed the atomic weights to be invariable.
2. It is possible that elements of higher atomic weight might contain those of lower atomic weight, but not the reverse.
3. If we view all matter as realty composed of various
ADDITIONAL WORK BY NEWLANDS. 1 25
modifications of one elementary substance, consisting of physical atoms, we may regard the atomic weight of each element as expressing the relative number of phys- ical atoms contained in the chemical atom. The same number of physical atoms differently arranged might form two or more distinct elements which might then be regarded as isomeric. Perhaps cobalt and nickel are thus related.
4. With regard to Prout's law ; the number of ele- ments whose atomic weights approach, within experi- mental errors, to exact multiples of hydrogen is far greater than it should be on the theory of probabilities.
5. It sometimes happens that the atomic weight of one element, when doubled, gives a number identical, or nearly so, with the atomic weight of another.
6. It frequently happens that out of three elements having common properties, the atomic weight of one ap- proaches the mean of the other two, as in the well-known triplet groups or triads.
7. Two atomic weights, taken from the lower part of the series, when added together frequently equal the atomic weight of some other element, though no general rule seems to be applicable to such cases.
8. Taking the three lowest known atomic weights, those of H, Iyi, and Be ; many of the higher atomic weights may be arithmetically derived from them by various combinations.
9. Taking a certain number of elements whose weight may be supposed to be consecutive, say the twenty-eight first, and arranging them in two columns, the first half
126 THE PERIODIC LAW.
in order of trie atomic weights and the second in reverse order, nearly a constant quantity will be gotten by add- ing together the corresponding members of the two col- umns, if the atomic weights corresponded to the natural order of numbers, or to some multiple of such order. As a matter of fact the numbers obtained vary consider- ably.
10. No simple relation could be worked out of the atomic weights under any other system than that of Cannizzaro, and if we attempt to introduce various equivalents of one element into the table they seem out of place, as do also the combining weights of quasi-ele- ments, such as ammonium or cyanogen.
ii. If any data, as specific heats or vapor densities, should prove ultimately to be without exception, either directly or inversely as the atomic weights, a list of ele- ments arranged according to such data would, of course, also show a Periodic Law.
12. Although all the elements yet discovered appear to take their places in accordance with the Periodic Law, it is quite conceivable that various series of elements may exist not very simply related to each other.
Newlands' mind ran on numbers — a mania for numer- ical relations. It was impossible for him ever to have developed the Periodic Law.
91. The Synoptical Table of Gibbes. — A "Synoptical Table of the Elements" was published by L. R. Gibbes in 1875, in the proceedings of the Elliott Society of Charles- ton (95). It purported to be a table prepared, two or three years before, for the illustration of his lectures to
THE SYNOPTICAL TABLE OF GIBBES.
127
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