JULY,
1940
309
ARE THERE RULES in the HISTORICAL DEVELOPMENT of CHEMISTRY?' EDUARD FARBER Polyxor Chemical Company, New Haven, Connecticut
T
HE development of chemistry is connected with so many varied motives and reasons: religious, economic, personal, that it must seem as difficult to find rules in this development as it would be to iihd rules in the course of political events of history. Besides, for the progress in chemistry the observations of details are much more important than the development of general theories. How can we hope to find a rule for the fact that Louis Pasteur was attentive enough to see the diierences in crystal shape between the isomeric tartrates? In searching for rules in the historical development of chemistry, we cannot avoid the field of hypothesis. This might not seem especially objectionable in a science which is so justly proud of its solid fundament of facts. But, being theoretical as compared with actual experimental chemistry, the history of chemistry seems to shrink from becoming theoretical to the second degree by trying to develop theories. Such are the arguments which can he raised against the purpose of this essay. Let us now consider the reasons which might favor such an enterprise. (1) Theories or rules would facilitate a systematic arrangement of the historical facts. (2) This would constitute a great help in coordinating and grasping the historical events. No one can promise a rule or theory for the fact that Boyle's "Sceptical Chemist" had to appear in 1661. But some of the wntents of this hook can perhaps be made easier to understand and distinguish if we consider it in connection with a general development. (3) It is not to be expected that the rules which we may find will be generally accepted without discussion;
but i t is this disassion which is necessary to improve our h d i i g s and to lead to something better. (4) One object of scientific theories can scarcely be performed by the rules we may find for historical developments and that is the prediction of the immediate future. It would be very important if, by considering the rules of development, we could, if only in a very small way, achieve what political history has seemed unable to do: namely, to learn from the past for our future work. Haw difficult tEat would be can be proved from the history of catalysis. It might seem to us that a t least one important analogy to it had been developed long before the creation of this notion. I mean Albrecht von Haller's (1708-1772) discussions of "irritability," by which "a very slikht stimulus produces a movement altogether out of proportion to the original disturbance." But this physiological notion had no influence on the contemporary and following chemistry. As an experiment, I try to crystallize a number of rules. They do not form a system, because I do not pretend that they are complete or that the diierent rules are based on one another or are closely connected with one another. The six rules which I want to discuss briefly can be designated as follows: (1) Continuity.-The separation of matter or qualities into discontinuous, minute units is followed by a gradual approach to continuity. (2) Analogy and Rwersion.-New notions start from analogies, outgrow them to become self-evident, and are later often changed by a Copernican reversion. (3) Attributes and Substances.-Fundamental qualities are explained by fundamental substances (principles). They are modified by attributes which can ' Presented before the Division of History of Chemistry at the subsequently become new fundamental substances. ninety-eighthmeeting of the A. C. S., Boston. Mass., September (4) Isolation and Integration.-The development of 12, 1939.
the art of isolating produces the tendency to integration. (5) Particles and Shapes.-Models of matter develop from differences in the total shape of the otherwise uniform particles to specific arrangements of specifically different units. (6) Generalization.-One-sidedness in its tendency to generalization contributes to its own rectification. 1. CONTINUITY~ The tendency to approach a realization of continuity can be traced through the development of the atomic theory which destroyed the former meaning of the word atom just a t the time when it was first scientifically established in other respects. Further, i t can be found in the advance from the three or four primitive elements to the system of ninety-three elements with many times this amount of isotopes between. Another explanation of the trend to continuity could be found in the development of plastics in so far as here coherent films and threads are produced instead of the individual crystals which dominated chemistry more exclusively before the last few decades. If these developments were represented graphically their general form would be naturally the same, showing a very sudden rise in the last few decades. The same would be true of any other expression for the development of chemistry, for instance, of the number of chemists, publications, or patents in chemical fields. RULE
likationen doch wieder vergessen. Wie hatte man sonst in fast allen physikalischen Schriften lesen konnen, dass der Schall in bezug anf die Fortpflanzung, Reflexion und Brechung sich ganz wie das 1.icht verhalt? Wie hatte man diese Behauptung durch Experimente mit Schallspiegeln und Schalllinsen stiitzen konnen, die nur unter ganz hesonderen Umstanden gelingen, sonst aber illusorisch sind?" I t will he remembered that a hundred years ago Liebig predicted that organic chemistry would be merely a matter of routine and, as we may call it, of translation. That was a few years after the analogy of organic chemistry to notions developed in inorganic chemistry helped so much, for instance in Bunsen's work on the organic compounds of arsenic. Here we find one of the characteristic difficulties in trying to expose such rules. Bunsen published the work just mentioned in 1837, hut already in 1828 Berzelius pointed to the difficulties in attempting to find analogies between organic and inorganic nature.
MITSCHERLICH, FEBRUARY 22, 182S5 "Die hisher hefolgte Weis, die Produkte der organischen Natur ganz wie diejenigen der unorganischen aufzustellen und zu behandeln, istdie vornehrnlichste Ursache der Unordnung in der Pflanzenchemie und der Schwierigkrit, die Details derselben klar aufzufassen und im Gedachtnids zu behalten . . ." And about forty years later KekulC explained how he had to abandon the explanation of aromatic substances RULE 2. ANALOGY AND REVERSION by analogies with fatty substances.= This shows an important general feature of all these The first discovery of an analogy is an event of great bearing. Generally i t becomes a matter of simple trans- rules. They do not describe .&e movement of the lation once the code for it is found. Just then, when the whole of chemi'stry a t one time and the tendencies in all formerly surprising discovery is turned into a matter of fields of this vast science. The chemistry of one group routine and seems to he too evident for further proof, of substances could he in the first phase, that of disthe time comes when exceptions and deceptions are covering analogies, while others may already have found and a total reversion is prepared. Such funda- reached the stage where reversion, begins. We can exmentally different thmgs as light and matter are first emplify this in the development bf the chemistry of connected by analogies. Newton w s i t q a "Spirit of fats. This group of substances was united under the Wine has a refractive Power in a middle degree between notion that one common principle exists in all of them, those of Water and oily Substances, and accordingly the principle which makes them fatty. After Chevreul seems to be composed of both, united by Fermentation; crystallized the different kinds of fatty acids and the Water, by means of some saline Spirits with which demonstrated their individualities, the old notion of the 'tis impregnated, dissolving the Oil, and volatizing it fatty principle was overcome; This revolution turned by the Action. And as Light congregated by a Burning- out to be a reversion. The old substantial principle glass acts most upon snlphureous Bodies, to burn them had.to he abandoned; instead, a new one was found, into Fire and Flame; so, since all Action is mutual, not a substance, but a principle of structure. sulphurs ought to act most upon Light." RULE 3. AITRIBUTES AND SUBSTANCES It was Newton, too, who considered colors and sounds as analogous. E. Mach criticizes how physicists This shows that some developments can be considered in the early nineteenth century tried to develop this under several of our rules a t the same time. For infurtherE4"Obgleich nun Fresnel die Wichtigkeit der stance, we see in this example a similar use of substanDimension der Wellenlangen vollkommen klar gestellt tial principles as in many other fields. They develop hatte, so war dies wenige Dezennien nach seinen Pnh- from an original simplicity, which makes them startling and evident in one, to more complicated methods of ' F~RBER. "Der Stetigkeitsgedanke," Osiris, 3, 47-68 (1937). explanation. Sulfur once was an alchemistical element. -a "Opticks." 4th ed., London, 1730 (reprinted by G. Bell & Sons, Ltd., London, 1931) p. 275. Ges. Schriften, von E. voN MmscEI~R~rcn, hg. von A. M i t s ' MACH,"Prinkipien der physikalischen Optik," 1. A. Barth, cherlich, E. S . Mittlec u. Sohn, Berlin. 1896, s. 82 sep. Leipzig, 1929, p. 380.
BERZELIUS TO
Ann., 137, 129 (188fi).
Soon it had to be split into diierent kinds of modified sulfur until each of these modifications claimed its recognition as distinct elements. The whole development of radioactive substances can be understood under this general rule. Originally some of them were substances invented in order to explain the cause of alpha and beta activities and the simplification of radiation graphs. Uranium X,and Uranium Xz bear a certain historical analogy to the different kinds of mercury which centuries before designated some hidden qualities in matter.
phenomena" are often responsible for new discoveries. From remote comers discoveries are made which extend or try to extend over the whole field of chemistry. It is not by developing general thoughts that general theories are found in chemistry, but from concentrating upon hitherto neglected and perhaps unimportant details that new systems of theories develop sometimes. The tendency to explain everything from one point of view which makes use of analogies according to our Rule 2 and in some respects is a development as outlined in Rule 4, has sometimes, not only the result of overthrowing existing theories, but often to correct its RULE 4. ISOLATION AND INTEGRATION inherent one-sidedness just by attempting to extend it Obviously this rule has some fundamental connection over the entire field, and this not only in chemistry but with the first one, inasmuch as isolation and integration in other sciences, too. This points to one peculiarity common to these six can be considered from the point of view of discontinuity and continuity. In a very general manner it can rules. They are not confined to chemistry; they are be said that the isolation of chemical substances leads not specific enough. It may be one of the propositions to a completing of their system and therefore the "in- of the further development to go deeper into specializategration" of chemical substances in science as well as tions, but a t the present time it may be an advantage in technic. There the integration consists in assembling to restrict the attempt to find rules to such generalities. large quantities of these isolated units of substance re- It serves as a connection to the history of other sciences. sulting sometimes in new problems and discoveries. and it grows out of the unity of them all. Our Rule 2, This integration of large quantities has for instance led for instance, can explain a certain generality of simulto the discovery of new compounds made from acety- taneous events in the development of physics as well lene, as by-products in the manufacture of acetic acid. as zoology or mineralogy: The difference between Cuvier's theory of incomparable types and Geoffroy RULE 5. PARTICLES AND SHAPES Saint-Hilaire's "unity of plan" or theory of analogs in In 1773 T. Bergman developed a theory to explain zoology about 1830 corresponds to a similar controversy the nature of the calkspar. The whole rhomboeder is between Berthollet and Proust mainly between 1801 and not only the form of the large crystals as we see them 1806. Comparative anatomys was created nearly a t the but also the form of the smallest particles of which this same time that comparative chemistry found relations mineral is built. Wollaston, on the contrary, considered between inorganic and organic substances and developed the structural elements of crystals as mathematical the notion of homologous series of substan~es.~ This is the only rule we can find up to now which points surrounded by forces of attraction and repulsion (1813). Already a t that time the theory seemed to be connects the place of the scientific event with the time abandoned which tried to explain chemical and physical a t which it took place. It would be very difficult to qualities of substances by the shape of their molecules. try to explain, for instance, why Avogadro's theory had This theory is closely related to the notion of signatures to wait until Cannizzaro revived it:.. We may learn which served to explain the physiologipl action of from such events the necessity for repeated proclamaleaves and fruits from plants according to their re- tions of new findings which Avogadro had neglected or of a concerted effort in collaboration which was achieved semblance to organs of the human body. But as I pointedout before this does not mean that in a t the conference of 1860. But we cannot hope to find a general rule for the every respect such notions had to be condemned as obsolete and that recurring to them should be considered reactions which the knowledge oi the present stage of as a medieval trend in chemistry, proof of which is the chemistry a t any time provoked in contemporaneous rBle which the shape of molecules plays in modern ex- scientists. planations of lubricating oils. OWEN,"Lectures . . . ," Longmans, Brown. Green, and Longmans, London, 1843, "On the archetype and homologies of RULE 6. GENERALIZATION the vertebrate skeleton," printed for the author by R. and J. E. As Whewell explained in his famous book,? "residual Taylor, 1848.
7
Wmwm,~, ''History of the inductive sciences." London.
183747.
SCHIEL, Ann., 43, 107 (1842); Dmas, Compl. rand., 15, 935 (1842); GE~nanDr, "Prkisde chimie Organique," Fortin, Masson et Cle, Paris, 1845, Vol. 2, p. 489.
