A new era in chemistry; some of the more important developments in general chemistry during the last quarter of a century

Preface

Although the development of chemistry has taken place more or less by leaps and bounds, it is difficult to fix an exact date as the beginning of the “New Era.” The year 1887 marks the appear¬ ance of the first volume of the Zeitschrift fur physikalische Chemie,” and in this volume the epoch-making papers by Van’t Hoff, on the “Rela¬ tions between Solutions and Gases,” and of Arrhe¬ nius on the “Theory of Electrolytic Dissociation” appeared. This date, 1887, is therefore taken as the beginning of the “New Era,” which is, then, a quarter of a century old.

It is, however, clearly recognized, that there is a difference between the chemistry of twenty-five years ago- and that of today. That this is really a difference in kind, is not always clearly understood either by those who have watched the development during that period, or by those who have not studied chemistry long enough to have the necessary perspective.

It has seemed desirable to point out as clearly as possible in what this difference consists; how these new developments were brought about and by whom. This is the object of this little work.

IV

PREFACE

My apology for adding another book to the lit¬ erature of chemistry, is that I have lived during the “New Era/’ have known well most of the men who have been instrumental in bringing it about, and have been a student of the three leaders in this movement — Van’t Hoff, Arrhenius and Ostwald.

Baltimore," June, 1913

Harry C. Jones

Chapter I Page

Condition of Inorganic Chemistry before Mendeleeff ... 1

Hypothesis of Prout . 3

Periodic system of Mendeleeff and Lothar Meyer .... 4

Organic Chemistry in 1887 . 8

Type Theory of Dumas . 9

Work of Kekule . 9

Celebration in honor of Kekule ’s Benzene Hypothesis . . 12

Beginning of a Science of Chemistry . 17

CHAPTER II Development of the Law of Mass Action . 19

Importance of a generalization . . . 19

Earlier views on mass action . 20

Berthollet . 21

Work of Rose . 21

Dulong . 22

Wilhelmy . 23

Berthelot and Saint Gilles . 23

Pebal and Than . 24

Williamson . 25

Discovery of the law of mass action by Guldberg and Waage 27

CHAPTER III The Energy Changes that take place in Chemical

Reactions . 31

Chemists first studied material changes . 31

Work of Julius Thomsen on thermochemistry . 32

Work of Hess . 33

VI

PAGE

Thermochemical work and deductions of Berthelot . 34

Berthelot’s chemical mechanics and statics . 38

Criticism of the law of maximum work . 40

Chapter IV

Van’t Hoff, Le Bel and Guye and the Origin of Stereo¬ chemistry . 44

Work of Van’t Hoff . 44

Van’t Hoff and the geometry of molecules . 45

Observation of Pasteur . 46

The relation pointed out by Le Bel . 49

Van’t Hoff and stereochemistry . 53

Symmetry of methane . 54

Shape of a molecule of methane . 55

Tetrahedral carbon atom . 56

Asymmetrical tetrahedral carbon atom . 56

Stereochemistry of carbon and other elements . 57

The qualitative suggestion of Van’t Hoff made quanti¬ tative by Guye . 59

Testing Guye’s hypothesis . 61

CHAPTER V The Phase Rule of Willard Gibbs . 66

The definition of phase and component . 66

One component and two phases . 67

One component and three phases . 68

One component and four phases . 70

Chapter VI

Chemical Dynamics of Van’t Hoff and Chemical Equi¬ librium of Le Chatelier . 74

Van’t Hoff’s conception of chemistry . 75

Van’t Hoff on reaction velocities . . 76

Le Chatelier on chemical equilibrium . 80

Effect of temperature . 81

Effect of pressure . 81

Analogy between mechanical and chemical equilibria ... 81 vii

Chapter VII Page

The R6le of Osmotic Pressure in the Analogy between

Solutions and Gases . 84

Generalizations discovered by Van’t Hoff . 84

Lecture by Van’t Hoff . 84

Pfeffer’s measurements of osmotic pressure . 89

Artificial semipermeable membranes . 90

Law of Boyle for osmotic pressure . 91

Law of Gay-Lussac for osmotic pressure . 93

Principle of Soret . . . 95

Avogadro’s law applies to the osmotic pressure of solutions 98

Gas pressure and osmotic pressure . 100

Van’t Hoff saw the above relations from a few imperfect

data . 101

Measurements of osmotic pressure by H. N. Morse and

coworkers . . 102

Results obtained by Morse . 105

Exceptions to the above relations . 108

Formulation of gas laws as applied to osmotic pressure 110

CHAPTER VIII Arrhenius and the Theory of Electrolytic Dissociation 112

Theories of electrolysis — theory of Grotthuss . 113

Williamson’s theory of solution . . . 115

Clausius’ theory of electrolysis . 117

Arrhenius proposes the dissociation theory . 118

Reception of the dissociation theory . 121

Certain applications of the dissociation theory . 123

Meaning of the term acid . . 124

No undissociated compound an acid . 126

Why are hydrogen ions acidic? . 128

Meaning of the term base . 130

Constant heat of neutralization of strong acids and strong

bases . 131

Explanation of constant heat of neutralization . 132

Heat of neutralization of weak acids and weak bases . . . 133

Hydrogen and hydroxyl ions always combine when in the presence of one another . 134 viii

PAGE

Law of the thermoneutrality of salts . 137

Properties of mixtures of electrolytes and non-electrolytes . 139

The meaning of substitution in chemistry . 140

Ions are the active agents chemically . 142

CHAPTER IX The Solvate Theory of Solution and the Importance of

Solutions for Science in General . 145

Generalizations of Van’t Hoff and Arrhenius . 145

Criticism of the generalizations of Van’t Hoff and Arrhenius 147

Origin of the solvate theory of solution . 148

Work of Jones and Ota . 149

Work of Jones and Knight . 150

Work of Jones, Chambers and Frazer . 151

Explanation of results by Jones . 151

Work of Jones and Getman . 152

Evidence for hydration in aqueous solution . 152

Work of Jones and Bassett . 153

The solvate theory . 155

Spectroscopic evidence for the solvate theory . 155

What is meant by absorption of light? . 156

What we mean by color in solution . 157

Bearing of the absorption of solutions on the solvate theory 157

The grating spectroscope . 158

Work of Jones and Uhler . 159

Work of Jones and Anderson . 159

Work of Jones and Strong . 161

The radiomicrometer spectroscope . 163

Work of Jones and Guy . 164

The present solvate theory and the older hydrate theory of

Mendel^eff . 166

Bearing of the solvate theory of solutions . 167

Importance of solution for chemistry in particular and for science in general . 168

CHAPTER X The Work of Wilhelm Ostwald in Inaugurating the

New Era in Chemistry . 172

Ostwald the experimenter . . . 173

IX

PAGE

Dilution law . 174

Ostwald ’s modification of Kohlrausch’s law . 176

Ways in which ions are formed . 177

Absorption of light by solutions . 180

Ostwald’s theory of indicators . 182

Allotropy . 183

Oxygen and ozone . 184

Sulphur . 186

Chemical action without contact . 188

Faraday’s law and chemical valence . 192

Catalyzers . 196

True and pseudocatalyzers . 196

Autocatalyzers . 197

Catalysis and the chemical industries . 197

Fixation of nitrogen . 197

Characteristics of Ostwald the experimenter . 198

Ostwald the founder and organizer of a school of chemistry 200 The founding of the Zeitschrift fur physikalische Chemie 201

Text-books by Wilhelm Ostwald . 204

Lehrbuch der allgemeinen Chemie . 204

Grundriss der allgemeinen Chemie . 205

Grundlinien der anorganischen Chemie . 207

Wissenschaftlichen grundlagen der analytischen Chemie . . 209

Physiko-chemische Messungen . 209

Thermodynamische Studien von Willard Gibbs . 209

Klassiker der exakten Wissenschaften . 210

Elektrochemie ihre Geschichte und Lehre . 211

Overthrow of Scientific Materialism . 211

Energetics . 212

CHAPTER XI Investigations by the Students and Coworkers of

Wilhelm Ostwald . 215

Apparatus of Beckmann . 215

Beckmann thermometer . 217

Freezing-point apparatus . 218

Boiling-point apparatus . 218

Molecular weights of dissolved substances . 220

X

TAGE

Dissociation of electrolytes . 221

Investigations of Paul Walden . 222

Liquid sulphur dioxide . 223

Liquid hydrocyanic acid . 223

Abnormal electrolytes . 224

Organic solvents . 224

Work of Walter Nernst . 225

The primary cell . 225

Solution-tensions of the metals . 227

Solubility investigations . 229

Thermodynamics . 230

Electrochemical Investigations of M. Le Blanc . . . 230

Decomposition values of ions . 231

Decomposition values and the theory of electrolysis . . . 232

Older theory of electrolysis . 232

Older theory of electrolysis erroneous . 233

New theory of electrolysis . 235

Decomposition values and the electrolysis of acids .... 236

Decomposition values and the electrolysis of bases .... 237

Decomposition values and the electrolysis of salts .... 238

Primary and secondary decomposition of water in electrol¬ ysis . 240

Work of Georg Bredig on Colloidal Suspensions . . . 242

Method of making colloidal suspensions of the metals . . . 242

Colloidal suspensions of the metals are catalyzers .... 243

Preparation of colloidal suspensions . 245

Why ions are necessary for precipitation . . . 246

Precipitation not the natural condition in chemistry. . . . 247

Colloidal solution and colloidal suspension . 248

Colloidal chemistry . 249

Molecular Weights of Pure Liquids . 249

Method of Ramsay . 250

Method of Longinescu . 250

Work of Haber . 251

Solid Solutions . 252

Diffusion in mixtures of solids . 253

Lowering of vapor tension and freezing-point in solid solu¬ tions . 253

Kinds of solids which can form solid solutions . 253

Work of A. A. Noyes . 255

Free ions in solution . 255 xi

PAGE

Conductivities at higher temperatures . 256

Hydrolysis at high temperatures . 256

Work op Richards . 257

CHAPTER XII The Electron and Radiochemistry . 259

Earlier view of the atom . 259

The electron . 259

Constancy of the ratio s . 260

The cathode particle . 262

What is the corpuscle? . 262

Mass and inertia due to the electrical charge . 263

The Electron . 264

“The Overthrow of Scientific Materialism” . 265

The electron theory of matter . 265

The atom in terms of the electron theory . 266

Rouland’s conception of the atom . 267

The electron theory and electrolytic dissociation . 268

Meaning of intrinsic energy . 269

The electron theory and the periodic system . 270

Radiochemistry . 271

Discovery of the X-ray . 271

X-rays and phosphorescence . 271

Discovery of radium . 272

Meaning of radioactivity . . . 273

Alpha particles . 273

The spinthariscope . 274

The Beta particles . 275

The Gamma rays . 275

Properties of radium . 275

Heat energy produced by radium . 276

Whence comes the heat liberated by radium? . 278

Origin of solar heat . 280

Is there radium in the sun? . 280

Radium the source of some terrestrial heat . 281

The emanation . 282

Radium emanation produces helium . 282

Production of an element . 284

Not transmutation . 285 xii CONTENTS

PAGE

Heat produced by the radium emanation . 286

Induced radioactivity . 287

Radioactive matter being unstable decays, and is also pro¬ duced . 287

Uranium X . 288

Thorium X . 289

Explanation of Radioactive Phenomena . 290

The more important properties of radioactive substances 290 The older conception of the atom cannot explain radio¬ activity . 290

The election theory and radioactivity . 291

Heavier atoms more radioactive . 291

Alpha particles tend to come off first . 293

The chemical atom unstable . 294

All atoms probably radioactive . 294

Origin of radium . 294

Radium produced indirectly from uranium . 295

Ionium . 295

Supposed transmutation of certain elements . 296

Importance of physics and mathematics for chemistry . . . 297

Appendix . 299

MENDELflEFF . 299

Kekule . 299

Gibbs . 301

Ramsay . 302

Van’t Hoff . 303

Arrhenius . 307

Ostwald . 309

Index . 313

Chapter I

The science of chemistry has not developed continuously from the beginning. Some one dis¬ covered a generalization or made a fertile sugges¬ tion, and this guided the experimental work in chemistry for quite a period of time. The aim was to test the generalization or suggestion in question, to see how much truth was contained in it, or of how wide-reaching or far-reaching signifi¬ cance it was.

Then some one would announce another generaliza¬ tion, and the active chemists of the time would turn to the testing of it ; and this would often change the entire trend of chemical work and chemical thought. Examples of this condition of things are the periodic system of Mendel6eff and Lothar Meyer, and the benzene hypothesis of Kekul6.

Condition of Inorganic Chemistry before Men - delee ff. — During the half century prior to 1869 a large number of chemical elements had been dis¬ covered. These had for the most part been isolated and their properties studied. They had been allowed to combine with one another, and the composition and properties of the various compounds formed had been the objects of investigation.

After Dalton proposed the atomic theory, these elementary substances were regarded as made up of ultimate units or atoms; and one of the leading problems of the chemist was to determine the relative weights or masses of these atoms. This was made possible especially by Avogadro, who proposed his hypothesis in 1811.

It was, however, soon found that one element often combines with another element in more than one proportion. This led to what appeared to be hopeless confusion in the determining of atomic weights, by simply analyzing the compounds contain¬ ing the elements in question. If the compound contained one atom of one element united with one atom of another element, the determination of the relative amounts of the two elements in the compound would give at once their relative atomic weights.

When, however, one atom of one element com¬ bined with an unknown and indeterminable number of atoms of the other element, the problem of determining relative atomic weights by chemical analysis alone became hopeless.

It was the Italian chemist, Cannizzaro, who showed much later, how the hypothesis of Avogadro can be used to solve the problem of the relative atomic weights or masses of the chemical atoms.

The atomic weights of many of the best-known chemical elements were worked out with a high degree of accuracy, considering the crudity of the methods available for such work at that period, especially by Stas.

Chemists began to study these figures representing the relative atomic weights of the atoms. They soon came to feel that there is some close relation between the atomic weights of the different ele¬ ments and their physical and chemical properties. A number of attempts were made to find such a relation.

Hypothesis of Prout . — The most serious and meritorious of these was the view advanced by Prout in 1815. If the most accurately determined atomic weights were expressed in terms of hydrogen as one, it was observed by Prout that they are all very nearly whole numbers. This he interpreted as due to the fact that all of the elements are made up of hydrogen. Their atoms are simply stable groups of hydrogen atoms, the number of such atoms in the atom of the element in question being expressed by the atomic weight of the element in terms of hydrogen as one. It was, however, soon found that there are elements whose atomic weights are not whole numbers in terms of hydrogen as unity, but are whole numbers and a half. It was then proposed by Marignac to halve the hydrogen atom, and consider all of the other atoms as built up of half hydrogen atoms.

Elements were then found whose atomic weights were unity and a quarter. It was then proposed to quarter the hydrogen atom, and to use this as the fundamental unit of which the atoms of all other substances were made.

Having once begun to divide the hydrogen atom the process could be continued indefinitely; and, consequently, the hypothesis of Prout soon fell into disrepute.

We shall see that the difficulty was that they did not subdivide the hydrogen atom often enough, or they would have been essentially where we are today with respect to the ultimate unit of matter.

The hypothesis of Prout is a generalization of great importance in the history of chemistry, whether it is rigidly true or not. It was the first compre¬ hensive, rational attempt to correlate atomic weights and other physical and chemical properties of the elements.

Periodic System of Mendeleeff and Lothar Meyer . — The English chemist, Newlands, in 18641 had at¬ tempted to arrange all of the elements in a table in the order of their increasing atomic weights, begin¬ ning with hydrogen. He observed that every eighth element is related, and arranged the elements in groups of eight, whence the so-called “ octaves of Newlands.” This arrangement, although very defective, was important in that it attempted to correlate the properties of all of the then known elements, and their atomic weights.

A generalization which fits the facts much better, was the periodic system of the Russian, Mendeleeff, and the German, Lothar Meyer. Mendeleeff in i Chem. News., 10, 96 (1864); 12, 83 (1865).

1869 1 published his now famous periodic table of the elements, and Lothar Meyer discussed his arrangement of the elements, which was essentially the same as that of Mendeleeff, in 1870. 2

This arrangement of the elements in the order of their increasing atomic weights3 is too familiar to require detailed discussion in the present connec¬ tion. When all of the elements are thus arranged in groups of seven, the closely allied elements fall in the same vertical columns.

This system, although full of imperfections, is a wonderfully fruitful generalization. The number of relations brought out by it is simply legion. Its value as a generalization is largely due to its comprehen¬ sive nature. It comprized not only all of the ele¬ ments known when it was proposed, but it contained places for many elements unknown at that time.

Mendeleeff, guided by his generalization, predicted the existence of certain elements which have since been discovered. He not only predicted the exist¬ ence of the then unknown elements, but from the elements in the table to the left and right of the unknown element in question, and above and below this element, he announced the properties of the unknown element. He foresaw not only the physical and chemical properties of the element, but the composition and properties of the com-

3 See author’s “Elements of Physical Chemistry,” 4th edition, published by the Macmillan Company, N. Y.

pounds which it would form with other chemical elements. These predictions went even into such details as the color and specific gravity of the element itself, and the color and specific gravity of its compounds. As is well known, a large number of these predictions made by Mendeleeff have since been verified with surprising accuracy and in in¬ credible detail. A number of the predicted elements have been discovered, and have been found to have the calculated atomic weights. Their compounds have been made, and the properties of these com¬ pounds found to agree with those foreseen for them with surprising accuracy.

When a scientific generalization is announced, the least that can be expected of it is that it should be able to account for all, or nearly all of the facts which it is meant to correlate. A generalization is, however, of greater value in science when it can, in addition, predict the existence of facts then unknown and have these facts subsequently dis¬ covered. The generalization in question then be¬ comes a working hypothesis, as it is rightly termed. It suggests new lines of work, and in this way leads to the development of the science in question.

The periodic system of Mendeleeff and Lothar Meyer was not only able to account for most of the facts of general chemistry, that were known at the time it was proposed; but was able to predict new and unknown facts, and to have these predictions subsequently verified.

This generalization exercised for a time a dominant influence in chemistry for each of the above reasons. Before it was proposed, general chemistry was a more or less disconnected mass of facts, which had been brought to light as the result of nearly a century of experimental work. Certain relations had been pointed out between certain of these facts. These relations were, for the most part, of limited scope, and were not of any very fundamental sig¬ nificance. When the periodic system was proposed, we had a comprehensive generalization which covered the facts of chemistry in general.

Furthermore, it was a working hypothesis; pre¬ dicting undiscovered facts and suggesting new lines of work, which were taken up by both chemists and physicists.

The impression made by the periodic system upon chemists, imperfect and defective as this system was, was deep-seated. It dominated the thought and the work in general chemistry for quite a period after it was proposed. It may be said to have been the philosophy of general chemistry from the time it was announced until 1887 ; when another sugges¬ tion was made, as we shall see, which shared with the periodic system the attention of chemists and which is even more important.

The periodic system, then, converted general chemistry from pure empiricism into system; but it did not do more than make of chemistry a system¬ atic branch of natural science. It never did, and it never could convert chemistry into a branch of exact science.

Organic Chemistry in 1887 . — The condition of organic chemistry at the end of the period we are now considering was, in many respects, analogous to that of inorganic. It may be of interest to trace very briefly the more important steps in the develop¬ ment of the chemistry of carbon to the point where the new era in chemistry found it.

It is well known that the first organic compound was prepared artificially by Wohler in 1828. Am¬ monium cyanate, when allowed to stand, passed over spontaneously into urea.

Four years later, 1832, Liebig and Wohler pub¬ lished the results of their joint investigation on the radical contained in benzoic acid. They showed that benzoic acid, oil of bitter almonds and many of its derivations, contained a common group, C7H50, which, unchanged, passed from one of these com¬ pounds to another. This group thus behaved like the elements of inorganic chemistry, and they called it a compound element, or an organic element. Since it occurred in benzoic acid and its derivatives they called this radical “Benzoyl.” The discovery of an organic radical or element was of great im¬ portance, and this discovery dominated carbon chemistry for quite a period.

The next important advance in the chemistry of carbon was the discovery of the act of substitu¬ tion. A number of isolated observations had been made of what we today know as substitution, but it was the French chemist, Dumas,1 in 1834, who 1 Ann. Chim. Phys. [2], 56, 140 (1834).

first called attention to them. Laurent went much farther than Dumas,1 and formulated the rule that when say chlorine replaces hydrogen in a com¬ pound the chlorine takes the place of the hydrogen, and the chlorine substitution product must have properties analogous to the original compound. This aroused the opposition of Berzelius, whose electrochemical theory was apparently threatened by the relations between acetic acid and trichlorace¬ tic acid.2

Type Theory of Dumas. — A little later, in 1839, Dumas transformed the substitution theory into the type theory, which referred carbon compounds to certain definite and well-known chemical types, such as water, ammonia, etc. The fact was pointed out by Dumas, that when substitution of one atom or group by another takes place, the chemical type remains unchanged. He reached this conclusion especially from his study of the relations between acetic acid and trichloracetic acid. The three posi¬ tive hydrogens are replaced by what was supposed to be three negative chlorines, without changing the chemical type of the compound, but also without materially altering the properties of the compound.

Work of Kekule. — We now come to the work of one who was destined to play a most prominent part in the development of the chemistry of carbon —

2 See author’s “Elements of Physical Chemistry,” 4th edition, p. 350. (Macmillan Co., N. Y.)

August Kekule. Organic chemists had dealt thus far chiefly with the radicals or groups which can be passed unchanged from one compound to another. It was Kekule who first arrested attention to the now well-known fact that, to have a science of car¬ bon chemistry, we must go beyond or within the radicals to the atoms 1 of which they are composed. An attempt had already been made by Frankland, in 1852, to do the same thing for inorganic chemistry. The importance of this step for organic chemistry, as we shall see, cannot easily be overestimated.

The atoms present in these organic radicals must be united, and Kekule pointed out in 1859 that carbon must be regarded as a tetravalent element, having the power of combining with four hydrogen atoms, four chlorine atoms, or four uni¬ valent atoms in general ; and further, that a carbon atom has the power of combining with another carbon atom. This led to the so-called “ linking of carbon atoms.’ ’ If two carbon atoms combine, one combining unit of one combines with one combining unit of the other. Two such carbon atoms would, therefore, have six remaining combining units — would be hexavalent. From this fundamental con¬ ception Kekul6 was able to work out the constitu¬ tion of the aliphatic carbon compounds, essentially as it is today. A much greater work, however, remained for Kekule to do. There was a class of carbon compounds occurring in the natural oils which had a strong odor, and from this they were i Lieb. Ann., 104, 129 (1857).

called aromatic compounds. These compounds con¬ tained more carbon than the corresponding aliphatic compounds, and Kekule recognized that the sim¬ plest of them contain at least six atoms of carbon. He pointed out further, that the derivatives of the aromatic compounds have this in common; the chief product formed has at least six atoms of carbon.

Said Kekule, “ These facts justify the conclusion that in all aromatic substances there is one and the same atomic grouping, or, if you will, a common kernel, which consists of six carbon atoms.”

A brief paper of fourteen pages, dealing with this subject, was first published by Kekule in the Bulletin de la Society Chimique [3] 1, 98, (1865), dated Jan¬ uary 27, 1865. A far more comprehensive paper of sixty-eight pages appeared shortly after in Liebig’s Annalen,1 on February 6, 1866. In the latter paper Kekule proposed what has since come to be known as his “ benzene hypothesis.”

He suggested the two following formulas for benzene. Benzene is either a regular hexagon, with a carbon and a hydrogen at each solid angle, or it is a triangle.

d a

In the first figure1 every carbon and hydrogen would bear the same relation to the molecule. In the latter case, the three carbons at a, c and e would bear a different relation to the molecule from the three carbons at b, d and /. The study of the sub¬ stitution products led to the conclusion that three carbon atoms in benzene are different from the other three, and that, therefore, the second for¬ mula was the more nearly correct. This will be recognized to be nothing more nor less than the well-known hexagon formula, or the Kekul6 for¬ mula for the constitution of benzene.

a

It is difficult to overestimate the importance of this suggestion on the subsequent development of carbon chemistry. This was not only an hypothesis which accounted for the facts then known concerning the chemistry of the aromatic compounds, but it was far more than this; it was a working hypothesis, sug¬ gesting new lines of work in every direction. The result was that it became the dominant thought in organic chemistry for quite a period. Indeed, as we shall see, until the significance of chemistry in three dimensional space was recognized.

Celebration in Honor of Kekule’s Benzene Hypothe - sis. — So important did this suggestion prove to be that the German Chemical Society, in 1890, held a celebration 1 in honor of Kekule. There were present on this occasion a distinguished company of chemists. Adolf von Baeyer, Kekule’s oldest pupil, and who has subsequently done much work on the constitution of benzene, was the prin¬ cipal speaker. He pronounced a eulogium, dis¬ cussed briefly the work on the constitution of benzene, and then gave place to Kekule.

The address of Kekule 2 on this occasion is fasci¬ nating reading, and a few brief passages from it will be given.

“Some one has said that the benzene theory appeared like a meteor from the sky. It came absolutely new and uninitiated. The human mind does not work in this manner. Nothing has ever been thought of which is absolutely new, certainly not in chemistry.” . . . “We can never speak of anything being absolutely new.

“Some one has spoken of genius, and has desig¬ nated the benzene theory as the product of genius. I have often asked myself the question, What is the work of genius? What is genius? Some one has said that genius perceives the truth without knowing the proof of the truth. It has also been said that genius thinks by leaps and bounds. Gen¬ tlemen, the expanding mind does not think by leaps. This is not possible.”

Kekule then gave a brief account of how he dis¬ covered the benzene theory.

“ During my stay in London I lived for a long time in Clapham Road near the Commons. I frequently spent the evening with my friend, Hugo Muller, in Islington, on the other side of that enormous city. We talked about many things, but chiefly about our beloved chemistry. On one beautiful summer day, I traveled through the busy streets of that me¬ tropolis in the last omnibus, and as usual rode outside on the top of the omnibus. I began to dream. The atoms began to play antics before mine eyes. I had always seen each little particle in motion, but had never before succeeded in deter¬ mining the nature of their motion. That day I saw how two smaller ones often united to form a pair, how the larger ones seized two of the smaller ones, and how the still larger held three and even four of the smaller, and how they all moved in vortices. I saw how the greater formed a row, and how the smaller were drawn along at the ends of the chain. I saw what the old master Kopp, my honored teacher and friend, pictured in such a charming manner in his ‘molecular world/ but I saw it long before he did. The call of the conductor, ‘Clapham Road/ awaked me from my dreams but I spent a part of the night transferring to paper at least sketches of each of these dream pictures. Thus arose the structure theory.