Nobel Lecture*, December 12, 1909
It has pleased no less than surprised me that of the many studies whereby I have sought to extend the field of general chemistry, the highest scientific distinction that there is today has been awarded for those on catalysis. The award has pleased me because in my innermost being I used to, and still do, consider this part of my work the one in which the personal quality of my method of work is most definitely shown up and which I therefore have more at heart than all the others. The award surprises me because it was not until a very much later period that I expected for this work the recognition on which I dared to place my hopes. It gives me a very high opinion of the unerring instinct with which the authorities of the Nobel Foundation perform their fine, no less than difficult and responsible task, that their judgement coincides with the one that I myself after most earnest self-examination must take; and since I cannot expect anyone to have a more thorough knowledge of my work than I myself, this proves that those authorities have acquired such a sure grasp of their function that in the future, too, the whole of international science can look forward to their decisions with confidence.
There is no need for me to point out that these comments do not refer to the choice of my person, but only to the choice of the work after the decision as to person. The first issue is not for me to judge; all that remains for me here is to accept the accomplished fact with all the profound, heart-felt gratitude which such recognition on the part of the most competent body, notably that of one's own colleagues, cannot fail to arouse. Amongst the many happy moments of what has been a life filled with a profusion of gratifying occasions, I am aware of only one which I can compare with the present occasion, and that is the first scientific recognition ever which I received publicly at the very outset of my career. Together with the recognition conferred on me today it forms the two high-lights of these experiences since even for the future I can expect nothing greater.
It is not quite a year ago that I wrote in a different context: "I myself have no cause for complaint whatsoever about lack of recognition of the scientific work which I have been so happy to perform in the field of general chemistry; yet the purely intellectual achievement of conceiving catalytic phenomena as accelerations of possible processes which are in progress, whereby the whole vast field of catalysis was first opened to exact study, lay at the time so far outside general scientific thought that where the broader masses of scientists are concerned it is today still at the incubation stage, notwithstanding the passing of some twenty years. I presume that subsequently this advance will become so naturally part and parcel of the overall context of scientific thought that, compared with before, the gap will cease to be apparent at all and I shall be deprived of that measure of personal glory to which I am justly entitled by virtue of this advance in theory. Yet this will not upset me any further since in the meantime I have come to regard such matters as object studies in the reactions of the collective psyche".
That I have fortunately been proved wrong in that prediction demonstrates how far I underestimated that as science progressively developed and as its nature and attributes became more and more familiar, mankind's appreciation and acceptance of scientific progress has steadily accelerated. Whereas in former centuries it was a commonplace for a scientist not to be understood until long after his death, in our day this time-lag has almost entirely disappeared, no less so than most of the active opposition formerly placed in the way of free research by powers which feared that their rule would be threatened by the growth of Science. Whereas, for example, research workers were, at one time, obliged to endeavour to ensure that their theories did not contradict those of the Church, nowadays, in contrast, the Church is at pains to prove that its teachings are compatible with those of Science. In other words, the Church acknowledges Science as the higher authority.
Similarly, an advance has been achieved within Science itself, namely the readier recognition of purely theoretical achievements. When Röntgen discovered X-rays, his name, linked with this discovery, was carried throughout the whole of the civilized world within a matter of only a few weeks, as the experimental fact of irradiating objects that are opaque to normal light is so remarkable that everybody immediately felt, although not always appreciated, its implications. Yet when Willard Gibbs discovered the phase rule, which is of much more universal, hence of far greater, importance, nobody at all recognized its implications at first and about twenty years elapsed before it was sufficiently understood to be accepted into Science's regular stock of chemical laws. This second case was a purely intellectual or abstract achievement for which even the special branch of Science which it concerned was so ill-prepared that to some extent it had to be educated to accept it, a task discharged, as is well known, by Van der Waals and his pupils. And this education was not successful until the vast experimental significance of this concept had been demonstrated in specific experimental studies.
Of course there were even greater difficulties fifty years previously when Berzelius made similar scientific advances in chemistry. We may refer to this great scientist as the good spirit of this building.1 Here he spent the largest and most important part of his busy life while for the second time (his predecessor being Linné), he established the scientific hegemony of his country in Europe. From here he sent into the world those annual reports dealing with his science in which as an honest appraiser he put every item discovered by the research of his day into its proper perspective and thus for the first time brought out its value and significance. It was here through purely intellectual effort that he achieved incomparably more for his Science than he was able to achieve with all his pains in his simultaneous capacity as a tireless experimenter.
Nevertheless, it would have been difficult for him to have achieved this degree of esteem and influence of his judgement had he not beforehand in practically all sectors of his science first examined the nature of things in person, and if in his hands the simplest tools had not through proper and varied use become ever-flowing springs of fresh knowledge. The profusion of his experimental discoveries, the meaning of which was as understandable to his contemporaries as their number was baffling, led to his being acknowledged the unchallenged master of chemistry and to his even greater gift of formulating concepts being first conceded, then enthusiastically recognized, and finally renounced. But why, later, when his electrochemical theory of chemical compounds was considered completely vanquished by the unitary theory of the biased organic chemists, were the concepts of positive and negative elements which he had formulated an unchallenged, even determinative, factor in the writings of those selfsame triumphing opponents? The reason was the simple fact that those concepts summed up a truth, the force of which asserted itself even when time had eroded away the ephemeral element. And these very same new concepts which had become decisive for the triumphing theories, i.e. isomerism and constitution, were formulated by the thinker whose theories his short-sighted opponents thought they had everywhere disposed of and vanquished.
In Berzelius, therefore, we have above all else to honour a master in the art of formulating chemical concepts and it is no wonder that he has a decisive bearing on the concept formulation with which we are concerned today. Even the term catalysis which, after being for long misunderstood, nay despised, is now back in favour, we owe to Berzelius.
For a deeper insight into this task of penetrating into scientific conceptions, a task which is still far too little known and to which far too little attention is still paid, we shall first consider a case where something concrete was obtained at the very outset. This is the concept of isomerism.
In the first quarter of the nineteenth century the experimental proof for the interdependence of the composition and properties of chemical compounds resulted in the theory that they are mutually related, so that like composition governs like properties, and conversely. The well-known fact that the form of a specific substance, e.g. water, and hence its properties can alter without a change in composition was disposed of by the formal view that a physical, not a chemical, process was involved. As though that disposed of the actually existing difference in properties for the same composition ! Nevertheless, these differences are governed by variations in temperature and pressure and (with certain limitations) it is true to say that under given external conditions the properties of a substance of given composition are invariably the same.
Then, in the 1830's, substances were quickly discovered one after another which, even under the same external conditions, had quite dissimilar properties while analysis showed them to be identical in chemical composition. Wöhler's in many ways successful studies of cyanic acid gave the same analysis results for this compound as Liebig had found in his analysis of fulminic acid (which at the time made him a world-famous chemist at the age of barely twenty). The two young scientists had failed to notice it but it struck Berzelius when, in his conscientious and concise manner he abstracted the two papers for his annual report.
There is no need for me to go into the familiar story of how isomerism was discovered; I should like to single out just one point. When the common fact became apparent that like composition can be accompanied by substantially dissimilar chemical properties, Berzelius acquired the equipment to investigate experimentally such a case as thoroughly as he could. In an admirable study of racemic acid and its salts he then established these facts with the maximum precision and raised the concept of isomerism to the status of a fully authenticated scientific concept. Since that time, notwithstanding the enormous advance of our knowledge about this very subject, it has not materially altered but only been expanded in the original sense. Even the then still completely hypothetical view that the differences in properties came about because "the atoms were assembled in different ways" has remained absolutely intact and the differences of opinion subsequently concerned only how the various "assemblies" are to be envisaged and represented.
Whereas here we have a concept which has persisted in essentially unchanged form right up to the present and which appears destined for a very long life yet on its original basis, Berzelius was less fortunate with another. The explanation lies in the fact that the sum total of the knowledge in the field discussed above is still today at the same period of its development because no new fundamental ideas have sprung up despite vast development in breadth. With the other concept, catalysis, a decisive change has set in meanwhile whereby the problem itself has acquired a new basis. This has meant that all the peculiarities belonging to that earlier epoch have simultaneously had to be laid aside and thus in the light of the new science, chemical kinetics, the concept has acquired an essentially different emphasis. Yet it should be pointed out at once that Berzelius revealed his genius by actually formulating his concept almost as purely and as perfectly as possible under the particular conditions.
Important fundamental laws governing the genesis of any science are involved here and hence a few words about these general phenomena will not be out of place. It is not just of general, epistemological importance to have a more precise knowledge of these phenomena but also of very great practical importance because it substantially facilitates estimating the particular state of any science, hence the inevitable discussions can be settled and shortened, and progress to some extent made independent of chance, i.e. organized.
We know from biology that new forms of organisms simulate their primitive form as closely as possible at first, even though obliged to exist under changed internal and external conditions. Hence they invariably take with them into their new mode of life a certain number of forms and characteristics which are superfluous, detrimental even, for the new state. It is contrary to the nature of organic evolution for such "rudimentary" organs or characteristics to be shed at once. On the contrary they have to be carried for quite a long time and are only discarded after long and difficult evolution.
The cause of this obviously inefficient state of affairs lies in a general characteristic which may be termed the law of biological inertia and which is a determining factor in the chronological events associated with biological phenomena, in the same way as the mechanical law of inertia determines dynamic phenomena. In the final analysis the law of biological inertia is based on the common attribute of living creatures, the sweeping importance of which was first recognized by Ewald Hering and which has been termed memory in the widest sense, i.e. the law is based on the fact that living creatures (as distinct from inorganic structures) experience or perform a process more easily, quickly or perfectly, the more frequently they have been subjected to it. After each such process the organism is in a certain sense altered, whereas the inorganic structure is normally reversible, i.e. once the former conditions have been restored it reverts exactly to its earlier state.
Accordingly, the same characteristic also occurs with all special activities of the organisms. Thus, we meet them again in the new concepts in science which are invariably so formulated as to simulate as closely as possible the existing concepts and therefore from the time of their formation and the ideas then prevailing they absorb a greater or lesser number of "rudimentary" elements which it is the difficult and laborious task of subsequent research to eliminate. For the furtherance of science it is therefore extremely important to recognize the rudimentary elements of an existing concept which are destined to disappear. Normally they are the ones which appear particularly appropriate to the thinking of the era, since the ephemeral and hypothetical aspects come closer to this as a rule than the fundamentally general aspect which invariably necessitates a much more penetrating process of abstraction.
Referring now to the formulation of the catalysis concept, it must first of all be pointed out that in the days before Berzelius no one at all had ever conceived and felt that the individual phenomena which we have since learnt to regard as special cases of a general event were related. On the contrary they were put down as isolated facts which, although their existence had to be acknowledged since they had been ascertained by reliable observers, for the time being could only be taken note of and nothing further. A remarkable thing here is that certain of these phenomena, e.g. the formation of dextrin and sugar from starch by boiling with acids (the acid not changing permanently) had been known ever since the close of the eighteenth century and developed into large-scale industries, it being quite typical of technology not to wait at all until Science has tidied up a thing theoretically before applying it. On the contrary, it is usually ample for a start if the actual process mechanism is known in sufficient detail to enable the process to be conducted as desired and, if possible, quantitatively controlled too. Both conditions applied to the action of acids on starch.
Berzelius was induced to group this phenomenon together with a number of other, seemingly dissimilar, phenomena under a single concept as a result of a work performed by his pupil, Mitscherlich, who had studied in detail the transformation (also known technically) of alcohol into ether under the action of 50% sulphuric acid and had equally found that no consumption of the sulphuric acid occurs during the process. Admittedly, the reaction ceases after a time but that is due only to secondary reactions (oxidation of the alcohol by the sulphuric acid) which play no direct part in the formation of ether.
The processes grouped together by Berzelius were: the transformation of starch into dextrin and sugar by acids (Kirchhoff, 1811); the same transformation by malt extract (Kirchhoff, 1814); the decomposition of hydrogen peroxide into water and gaseous oxygen in the presence of platinum, manganese dioxide, etc. (Thénard, 1818); the action of finely divided platinum on inflammable gas mixtures (Davy, 1817; and Döbereiner, 1823); the formation of ether by the action of sulphuric acid (Mitscherlich, 1834). The factor which Berzelius regarded as being common to all these processes was that the substances which interact to form the product (or else which decompose into their cleavage products) do not do so on their own or spontaneously but only after the addition of a certain substance which is not itself consumed. Mitscherlich had termed the process which he studied a chemical action by contact; Berzelius introduced the name catalysis instead, with the active but unconsumed substance being termed the catalytic substance or catalyst, and the cause underlying the phenomena catalytic force. Berzelius insisted categorically that it had not been his intention with this terminology to give an explanation of the group of phenomena. On the contrary he defined: The catalytic force actually appears to consist in the ability of substances to arouse the affinities dormant at this temperature by their mere presence and not by their affinity and so as a result in a compound substance the elements become arranged in another way such that a greater electrochemical neutralization is brought about.
In the ensuing controversy with Liebig, which has been described elsewhere and hence need not be repeated, Berzelius expressly drew attention to there being no assumptions underlying this definition which, as far as is feasible, is restricted merely to specifying the facts and deliberately and expressly avoids attempting to account for them. In reply to Liebig's hypothesis that a decomposing substance could induce the decomposition of other substances in contact with it, and after he had shown the examples cited by Liebig to be invalid, he continues: "We thus obtain a fictitious explanation by which we believe to have understood that which we cannot yet understand, and whereby the attention is diverted away from the matter to be explained which then remains all the longer unelucidated. I should like to repeat once again what I have stated so often before, namely that in Science fictitious, prematurely enunciated explanations invariably lead astray, and that the only method to obtain positive knowledge is to leave the incomprehensible unexplained until sooner or later the explanation emerges of its own accord from facts which are so plain that divided opinions about them can scarcely arise. Not to believe that there is more to be seen than can clearly and plainly be appreciated, and to regard the rest as material for further investigation, is a scientific principle which should not be violated but it is one which precisely those persons who are gifted with a lively mind and a fertile imagination find most difficult to follow".
The last phrase refers to Liebig whose other views were opposed more and more by Berzelius at the same period although with less justification than in the present case, for, owing to the acceptance of Liebig's clear but not rational views, catalysis reached a stage of almost complete stagnation. Knowledge of the experimental state of affairs where catalytic processes are concerned was increased only in occasional isolated instances where the facts were too obvious to be overlooked, and no further progress was made in understanding them.
One of those who ascertained new, relevant facts was, surprisingly, Liebig himself who in a masterly study, carried out jointly with Wöhler, on the decomposition of amygdalin into oil of bitter almonds and sugar by an apparently protein-like substance occurring in almonds which they termed emulsin, established a typical case of a very extensive series of catalytic phenomena, i.e. enzyme actions.
Already in 1833, however, Payen and Persoz had found that the transformation of starch into dextrin and sugar by malt discovered by Kirchhoff was attributable to the action of a special substance which can be extracted from germinated barley by water and purified by repeated precipitation with ethyl alcohol; they had also found that the activity is eliminated by heating to 100°C. Yet the multiple technical applications to which this discovery immediately gave rise had occupied their attention to such an extent that they did not arrive to study the general aspect of the phenomenon in more detail. This was taken in hand in the study by Liebig and Wöhler which Berzelius in his annual report referred to as the most important of the year and in which the recognized the analogy of the reported processes with the general catalytic processes which Liebig at any rate was not inclined to admit. In contrast to Berzelius, Liebig secured general acceptance of his theory of molecular collisions or vibrations, two circumstances being instrumental in bringing about this acceptance. On the one hand, in contrast to the dwindling reputation of the old master Berzelius, there was the growing reputation acquired at the time by Liebig as a result of his fundamental studies in organic chemistry. On the other hand, however, the time was not yet ripe for a rational concept of catalytic phenomena because the concept of the rate of chemical reaction was not yet available. By far the most frequently performed chemical processes in those days were those between salts, and as is well-known they proceed at such a fast rate that even today the time required has defied measurement. The few slow-rate processes were consequently not regarded as really typical (since, of course, all events, chemical ones too, require time) but rather as inconvenient anomalies which impeded the instantaneous formation of the desired substances without perceptible cause. Accordingly we find that the oldest scientific examination of a catalytic process - the admirable study by Clément and Désormes in 1806 of the formation of sulphuric acid under the action of the oxides of nitrogen which, surprisingly, Berzelius overlooked - accounts only uncertainly for the promotion of sulphurous acid oxidation by stating that the oxygen would be supplied to the oxidizable substance by the oxides of nitrogen in a more convenient or suitable form
The development of a rational view of the nature of catalysis was thus absolutely dependent on the creation of the concept of the rate of chemical reaction. The concept was formulated (after an inadequate attempt by Berthollet) by the German amateur scientist Wilhelmy and by a remarkable chance (or is it the intrinsic logic of historical evolution?) the first paper to submit a proper concept of the rate of chemical reaction also constitutes the first quantitative study of a process proceeding under catalytic action.
The reaction in question was the inversion of cane sugar. The name originates from a prior study by Biot and Persoz who used the polarimeter designed by the former and established that the solution of cane sugar which rotates the polarization plane of light to the right, rotates it to the left on the addition of a dilute acid. It was found chemically that cane sugar absorbs the elements of water and changes into a mixture of two different sugars, one being weakly dextrorotatory and the other strongly laevorotatory, hence the resultant is a rotation to the left. At the same time these workers observed that the process is not completed instantaneously but requires a period of time varying with the nature and concentration of the added acid as well as with the temperature; Biot who, as a physicist, was more readily inclined than all the chemists of his day (Wilhelmy too was a physicist) to regard the observed phenomenon as a systematic transient process, also pointed out the importance of a more thorough investigation of these phenomena. However, only Wilhelmy was sufficiently interested to undertake not only the necessary experiments, but in particular also the fundamental task of formulating concepts.
The ratio of the amount of substance (cane sugar in this case) converted in a given time to the time required for the process he conceived and defined as a new concept, the rate of chemical reaction, recognizing its appropriate mathematical definition at once to be the differential quotient of the amount of substance with respect to time. Since this parameter should be the same in any portion of a reacting solution, i.e. independent of the absolute amount of substance, the amount of substance must be related to a unit, e.g. volume, in other words it can most easily be conceived as a concentration.
Wilhelmy then demonstrated that on the simplest assumption that the amount of sugar (in the sense just defined) converted under the given conditions in each clement of time is proportional to the amount remaining unchanged, there is a large measure of agreement between the observed changes in rotation and those calculated on the basis of this assumption, and thus he discovered the general law for the time dependence of the (simplest) chemical processes. It has subsequently proved to be the fundamental law of chemical kinetics.
The influence of the acid proved to be (approximately) proportional to its concentration, besides being dependent on its chemical nature. That statement is a further general law, i.e. one of catalytic effect; yet in his paper Wilhelmy did not use or mention that concept at all but left the chemical aspect of the matter unsaid.
Nowadays, however, we recognize that simultaneously with the typical case of a chemical reaction a typical case of catalytic effect had been studied which constitutes a limiting case. For, with pure water the inversion of cane sugar scarcely proceeds and subsequently it required very thorough, difficult studies before this effect and its order of magnitude were established.
Initially Wilhelmy's paper had no repercussions whatsoever in Science. On the one hand there was an increasing number of cases of catalytic actions which, with a greater or lesser degree of accuracy, chemists were familiar with; on the other hand there was a growing knowledge of slow-rate chemical processes and the laws governing them. Neither line of development, however, had any effect on the other. Whereas in studies spanning practically the whole of his life, Schönbein, for example, discovered the most variegated and surprising cases of catalysis and notified them to his reluctantly listening colleagues (who in those days had devoted all their energies to the problems of producing and classifying organic compounds), expressly pointing out the inability of contemporary science to comprehend them, he still held that those processes are initiated solely by the catalysts. He was totally lacking the idea of the chemical rate and therefore the concept of chemical acceleration as well, hence his contribution to the knowledge of catalysis was restricted to collating a profusion of material highly interesting owing to its unexpectedness. And yet a number of chemical reactions, from which the concept of chemical rate and the laws of chemical kinetics were developed even in more complex cases, were of catalytic nature without particular attention being paid to that fact. The conditions were hence such that sooner or later both lines of research had necessarily to combine and it was my personal good fortune that I was able to apply the finishing touch.
Initially I had merely been endeavouring to find a quantitative measure for the concept of chemical affinity, a concept every bit as important as it was imprecise in those days, and following (unwittingly at the time) a train of ideas enunciated by Cato Guldberg I had envisaged both static or equilibrium methods as well as dynamic methods for this purpose, based on the measurement of rates of reaction. From the literature of organic chemistry, of which I had to keep track in the exercise of my teaching duties, I remembered several cases in which for preparative purposes esters had been broken down into acid and alcohol by the action of strong acids, e.g. hydrochloric or sulphuric acid in concentrated form. To be able to use aqueous solutions I resorted to those esters which are quite readily soluble in water, and I can still recall the joyous excitement with which for the first time I followed the rapid rise in the acid titre in an aqueous solution of common acetic ester to which hydrochloric acid had been added. Methyl acetate proved even more suitable owing to its greater solubility and faster reaction rate, and so one of my first studies in chemical dynamics, in 1883, dealt right away with a catalytic process, i.e. the catalytic saponification of this particular ester under the action of various acids.
This is not the place to describe the development of the affinity problem, especially the measurement of the "strength" of acids, which were then the actual object of my studies. It need only be mentioned that the sought-for relation between the static and dynamic methods proved real, and the "strength" was acknowledged to be a common property of the particular acids independent of the nature of the special reaction. Soon afterwards I studied the inversion of sugar in the light of these considerations and immediately found that this classical reaction, too, was determined quantitatively by the same property of the acids, as was of course to be expected from the previous results.
These studies showed up incontrovertibly the close relation between the strength of the acids and their catalytic action, and I searched for other acid catalyses with a view to studying this relation further on as impartial material as possible. Certain oxidation and reduction processes which, in contrast to salt formation and salt decomposition processes, proceed in finite, sometimes conveniently measurable times, seemed the most appropriate. The oxidation of hydrogen iodide by bromic acid recommended itself in that it was easily measured and it was the first to be carried out. It was then found that in contrast to the previously studied catalyses, here the reagents themselves interact at a measurable rate even before another substance has been added. In modern parlance the reaction is accelerated by the presence of hydrogen ions and these are already present in the reagents2; in those days, however, there could be no question of that because the study was conducted in 1887, immediately before the free-ion theory had been created and announced to the world. Inevitably, therefore, I was compelled to the view that the nature of catalysis is not be sought in the inducement of a reaction, but in its acceleration and the relevant publication of 1888 contains explicitly the corresponding mathematical arguments which were perhaps already implicitly embodied in the 1883 paper on methyl acetate.
I would be breaking my obligation to be frank - an obligation which for the historian in particular with regard to his own papers must have the force of the most inviolable law-were I to omit the observation that even at that time I was not particularly impressed at all by this advance. Physical chemistry had just entered on the stupendously fecund years, the way for which l had been paved by Van 't Hoff's theory of osmotic pressure and by Arrhenius' theory of free ions and electrolytic dissociation. Everywhere the traditional chemical theories were being remoulded in accordance with the new concepts, and new ideas and concepts had become such a commonplace for me and my few colleagues that little trouble was taken to single out each detail appropriately. It was not until somewhat later when I personally turned to energetics and thus freed myself from hypothetical ideas from which no direct, experimentally verifiable conclusions can be derived, that I also felt the need to put an end to the stagnation in which the study of catalytic phenomena had ended up as a result of such ideas. I recalled the naive drawings which a prominent worker at that time had published in order to "visualize" the catalytic effect of pounded glass on the combination of the constituents of detonating gas with moderate heating; the drawings showed how the sharp edges of the glass splinters cut the gas molecules into atoms which were then able to combine freely. And there was more of that sort of thing such as the late Lémery with his spikes and hooks on the atoms. I therefore took the opportunity offered to me by many reports, etc. to combat those injurious hypotheses and draw attention to the incomparably greater effectiveness of the simple definition of catalysis based on measurable facts which states that catalysis is a chemical acceleration brought about by the presence of substances which do not appear in the reaction product. A few general conclusions, a deanship programme and a widely read paper which I gave in 1901 at the Hamburg Natural Scientists' Convention completed this side of the task. Its necessity emerged quite clearly at that meeting, for in the chemical literature of those days it is not uncommon to encounter the comment "that the name catalysis is not an explanation of these processes", and that comment was to be taken as a reason for rejecting the concept in question. As though Berzelius had not already pointed out how a premature and overhasty attempt at elucidation without proper experimental evidence must have a damaging effect on how the issue develops ; as though the half-century that had elapsed in the meantime had not afforded continuous proof of the absolute correctness of Berzelius' warning by its barrenness in this sector with its later glut of fruits!
It is appropriate here to examine in terms of catalysis the relation of Berzelius' definition as given above to that found here. The outcome of this examination can be predicted right away: Berzelius had in fact done practically everything possible in keeping with the viewpoints of his age to characterize the essential nature of these processes.
Since he had no concept for the difference between slow-rate and fast-rate chemical processes, he denoted states with the intrinsic capacity (the necessary excess of free energy) to change into other states by the symbolic term "dormant affinities". By stating that a re-arrangement takes place in the sense of a greater electrochemical neutralization he points out, however, that a state of higher equilibrium or lower free energy is attained, i.e. the process cannot occur in conflict with the second law of thermodynamics (a not infrequent, implicit assumption of the contemporary critics of that concept). Only the statement that the catalysts acted by their mere presence and not by their affinity can be criticized. In contrast none of the profounder theories of catalysis allowing for causal circumstances, some of which have recently been advanced and others revived, has prospered better than Clement and Désormes' theory of intermediate reactions. This is based precisely on the participation of the catalyst in the reactions actually occurring, in the sum of which, however, the catalyst is not directly involved, although the partial reactions contain the catalyst as a major chemical component of the process. I have already stressed that there is no decisive reason to assume that all catalyses can be attributed to such intermediate reactions; yet it must be conceded that no other equally effective principle has hitherto been found in the theory of catalysis.
In sum, therefore, it may be stated that Berzelius' definition had almost attained the acme of perfection possible in his day but the most important concept for a successful mastery in theoretical terms of the overall phenomenon was still lacking. Presumably this is the main reason why, in the struggle for survival, Liebig's much less perfect but explicit definition (although giving rise to a false opinion) had provisionally been victorious. At that time, when a scientific treatment of catalysis was still impracticable, the advantages of Berzelius' definition could not be shown to full effect, and it was only after the necessary conditions had been created that the methodical tact of the great Swedish scientist became brilliantly apparent.
Conversely, in view of these facts, I need waste no words in stating that individual scientists who were apparently of the opinion that all that is required to become a historian of chemistry is an acquaintance with old chemical books and texts refused to recognize in the remoulded concept of catalysis a repetition of Berzelius' or Liebig's definition. The distinction between the old and the new formulations consisting in the incorporation of the concept of the rate of chemical reactions is so great that it immediately asserted itself in the objective development of catalysis.
Although neither Berzelius' good definition nor Liebig's bad definition promoted in any way the development of this scientifically interesting and technically highly important field, the new definition had that effect at once.
At first, of course, this effect was felt in the rather restricted sphere within which the new concept had arisen. For me personally the advent of this field of study came after I had completed extremely urgent tidying-up and construction work which had been necessitated by the introduction of the above-mentioned new, fundamental ideas into general chemistry at a period of my life when, after ten years' assiduous and unstinting work at these tasks I was experiencing profound exhaustion for the first time. I remember how, shortly before, Lothar Meyer had urgently warned against overworking since he himself had experienced its malicious consequences. (Not withstanding every sympathy of his fine, pleasing nature with the sudden development of the scientific field to which he had devoted his main life's work, he could not suppress a certain uneasy feeling that the direction of this development was totally outside the path which he had regarded as the most promising and therefore the most likely.) At the time I answered him with the rashness and enthusiasm of youth that it was more important to center universal interest on the whole matter as quickly as possible than to keep a single individual in a fit state for later work by sparing one's person. For even if I were worn out after a few years, so many young, fresh workers would have taken over from me in the meantime that the loss of my personal contribution would be replaced many times over, while conversely these selfsame workers, more valuable because of their greater energy, would be lacking because they would not have been attracted to the new field by a burning interest of the day.
I have to confess that at the time the actual significance of such exhaustion brought about by keenly assiduous work was not very clear to me, so that I made that self-sacrifice with a certain amount of awareness, of course, yet without precise foreknowledge of its consequences. Nevertheless, I believe that even had I been better aware of the future in store for me, I would not have acted very differently since the logic of the consideration just mentioned is clearly not affected.
At all events Lothar Meyer's warning went unheeded and the consequences which he had predicted came about a few years later. The worst manifestations of exhaustion were successfully cured by a long period of rest but it was immediately apparent to me that I had lost once and for all my former capacity for carrying out experimental work until physically tired. It thus came about that although towards the end of the 1890's my colleagues and pupils had begun on a wide scale to investigate catalytic phenomena, I myself was almost unable to take an active, personal part in the experimental work involved. A few years later, for reasons which I shall not disclose here, I had to renounce altogether my university professorship. In the interim the suggestions which I had made before then bore rich fruit and of my former colleagues I would single out G. Bredig as having made a manifold, successful contribution to the new field. At the same time biology, too, gave closer attention to the problem of catalysis, which is, of course, one of the organism's main agencies for an enormous variety of purposes, and again the kinetic definition proved superior to all other attempted generalizations, some of which were more figurative than objective.
The point of these considerations is that in fact the situations to which reference has been made were conducive to a favourable evolution of science. It would be idle to speculate how they might, perhaps, have been otherwise; in contrast it is important that we have been able to convince ourselves that the present state is healthy and requires no special intervention or guidance whatsoever. The only debatable point might be whether the speed of the evolution is fully consistent with the importance of the subject; for all that, however, we know from catalysis how easily the intervention of a specific catalyst in the form, say, of a new universal conception, or else of a young research worker gifted with unusual creative powers, can increase the speed to a multiple.
At any rate, faced with this situation, I felt obliged to describe its antecedents and to say a further few words about my personal circumstances. The unusual distinction to which I am indebted for the opportunity to speak here has also generated a certain degree of objective interest in the conditions which nurtured the studies considered worthy of such a distinction, and in the consequences ensuing for the workers themselves. When I consider the flourishing state of the field in question I can find no justification for the regrets or reproaches which from time to time have been addressed to me for abandoning this work. Only yesterday in Kocher's report on his fundamental studies of the functions of the thyroid gland and its accessory organs we heard an account of the effect of the secretions from this "chemical apparatus" on man, its carrier, which are an excellent example of how catalysts function in the organism. The old contrasts of the classical "temperaments", reducible to the contrast between the slow and the quick, appear in this connection to be a result of the quantitative proportion of two opposing catalysts. Since the proof for the importance of the new field is forthcoming in so unsought-for and at the same time in so fundamental a manner, there cannot be any shadow of doubt about the flourishing future of such concepts. Turning to the personal side I should like to comment as follows.
The most general and positive result of the study of the brain in recent decennia has been the doctrine of the localization of the separate functions. It might well be argued that this proof was really superfluous for it conflicts with the first principles of logic to assume the existence of a multiplicity of intellectual functions without attributing to them correspondingly distinct multiplicity in their organ. Nevertheless, the experimental proof is so much more convincing than such a general consideration that great weight attaches to it in any case. Furthermore it proves the individual relation whereas the general consideration has to stop short at the details.
In the light of this theory we now understand how certain parts of the brain are so worn out by excessive strain that subsequently they only function much less perfectly than before. The individual organs follow the same pattern as the whole organism, i.e. they have their period of growth, of stationary, maximum activity and then of aging decline. In specific circumstances the period of aging decline can set in earlier in a particular organ than in the organism as a whole which, in a certain general or theoretical sense, is left a cripple or invalid. I have repeatedly stressed in the past that this selfsame, extremely heavy strain imposed by research most readily produces this type of partial invalid and in respect of certain functions which I could once perform perfectly, I must count myself such an invalid.
It is not without painful emotions that I make such an avowal although these emotions are much less painful if the realisation is one's own than if conveyed by another person. And there is a comforting side to this acknowledgement, namely that although individual fields have been exhausted, other fields have been left untouched to a proportionately greater extent precisely on account of the one-sidedness of the former activity which caused the damage. In other words, when such a contingency arises the afflicted person has to look for activities which he would earlier have liked to pursue but could not, owing to the inexorable demands of the day, and it is highly probable that he will find fields in which he will be able to perform work which not only occupies his time and affords him a need-felt satisfaction but possibly is of almost equal value to his achievements in what is now an exhausted specialist field.
To illustrate with a practical example the form that such a change-over can take, I would like to mention that the general or philosophical side of my speciality and also the general problems of Science as a whole interested me from the very beginning. When, in about 1880, I prepared the first draft schemes for systematizing the then still completely chaotic subject of general chemistry, I knew of no better way to aid myself than by attempting simultaneously to formulate a universal system for all sciences. After the specifically chemical scope had been exhausted to the point where it yielded only a slow and meagre harvest I reverted, instinctively at first but then consciously, to the field where in fact I had already carried out quite considerable preliminary work, although that had only been published occasionally and in passing. Hence it was only necessary to make my subsidiary work my main work in order first subjectively to eliminate the cheerless feeling of being an invalid, and second objectively to derive from what remained to me as much useful work as possible in the prevailing circumstances. I would like to outline below a part of this work which is closely related to the special problem forming the main theme of this paper3.
The part to which I am referring concerns the general issue of the types of scientific discoveries that are actually known and possible. The general assumption of coherence of the world, which as we know forms the basis of all science, provides the means to survey such types. Whether that coherence obtains universally is a question that need not be answered here since only those parts where the coherence has actually been found become part of Science.
The existence of this coherence, and thus the most general problem of Science, can be expressed as the general function equation
F(a,b,c,d...) = 0
Increasing specialization of the general equation yields the types of scientific discoveries being sought.
We know to start with that in theory at least each object is related to every other but that, owing to the presence of the threshold, i.e. the limited acuity of our sensory perceptions (even of such that are sharpened by instruments), the practical proof of existing relations is rather narrowly restricted. It thus follows that whereas in principle the above equation should relate to the whole Universe; for Science the general equation breaks down into a large number of partial equations, each applicable only to a finite number of objects a,b,c... It might be mentioned in passing that there is no need at all for these objects to be of the more specific character of magnitudes; it is sufficient for them to be objects, i.e. distinguishable one from another.
Here arises the first task, which is to become familiar with the objects a,b,c... that are interrelated. The botanist, for example, studying the plants of a particular area establishes such a relation. This problem fills the deficit in the class of descriptive sciences in the stricter sense. Each group so related gives an appropriate concept, the characteristics, symbols or attributes of which are none other than the objects a,b,c...
Apart from this task, the simplest, there is also the complementary task of proving that the function F is closed, in other words that no objects other than a,b,c and d are contained in the relation concerned. These relations are especially important in that they define the natural invariants, i.e. the objects which remain within the scope of the term in all circumstances. The chief such case is that of energy where it has been acknowledged that the sum total of this magnitude cannot be modified by any process whatsoever.
Where the objects a,b,c, etc. are not simple but themselves contain many symbols (that is to say, that they are compound or complex concepts), further investigation can be made into special relations between these attributes of the concepts. The chief case arises where the objects are measurable in that a number can be assigned to them which establishes their value, i.e. quite definite relations to objects of the same kind. There, in each definite case of the function F(a, b,c ...), definite values belong to its terms and to determine this quantitative relation is the corresponding scientific task. An example is the gas equation pv - RT = 0, which defines the behaviour of an ideal gas as a function of the various pressures, volumes, amounts and temperatures.
The problem of determining such a relation is generally solved by selecting two of the parameters which are variable and varying them while maintaining all others constant. This is done with all the terms a,b,c, etc. in pairs until sufficient single equations have been obtained to formulate the overall equation.
The number of single equations necessary is invariably less than that of the possible binary combinations. After the necessary number of single equations has been found, it is therefore always possible to form further pairs of relations (and, of course, ternary and higher if the number of independent variables is greater) the form and content of which is also defined by the single equations that have been established, without the need for special experimental study of them. This is termed the deductive process. Plainly it is not consistent with the traditional definition of deduction but is in fact the only process known to, and used by, science to derive unknown from known relations.
Faced with this general consideration it will immediately be realized on inquiry into the particular position occupied within this general scheme by the scientific field of catalysis that it is in the first stages of its development. At present the main task is still essentially to discover and scientifically to establish the various cases of catalysis. For the moment it is still scarcely possible to summarize these cases systematically or decide which types of reaction are catalysed, and the relation between the chemical nature of the catalyst and that of the reagents. For catalysis based on intermediate reactions, however, it is possible to state that the substances must be related in a way favourable to the occurrence of such possible intermediate reactions which proceed collectively at a much faster rate than the immediate or main reaction. It will hence be abundantly clear again that a special problem of chemical kinetics is involved in the special case of these catalyses and that until a way has been found whereby a rate of chemical reaction can generally be calculated in advance as a function of the chemical nature of the reagents and perhaps of the special form of the reaction equation, the catalysis problem cannot satisfactorily be answered.
Consequently, even in this personal special case, the great unity of all science stands out decisively as a general regulative principle.
* The lecture was extemporized from brief notes and was afterwards reconstituted from the notes so that the reasoning, but not the wording, is reproduced. - Translated from Annalen der Naturphilosophie, Vol. 9.
From Nobel Lectures, Chemistry 1901-1921, Elsevier Publishing Company, Amsterdam, 1966