George B. Kauffmanl CaliforniaState University. Fresno Fresno. CA 93740
Niels Bjerrum (1879-1 958): A Centennial Evaluation
The year 1979 marked a triple centennial in the history of Ikmish chemistry, being the hundredth anniversary of the birth of two of Denmark's most distinguished physical chemists, Siels Bjerrum (1879-1958) and Johannes Nicolaus 19471. as well as the hundredth nnniversnrv Hrensted 11879 . of ;he founding of t h e ' ~ e m i s kForening, ~ @ b e n h a v(n~ a n i & Chemical Societv). established in 1879. I t thus seems a fit occasion for an evaluation of the life and work of Niels Rjerrum. whom the American historian of chemistw Ralvh Ocsvcr has keferred to as the "dean of Danish phyiical ;hemi&" (I). Bjerrum is probably best known as the originator of the concept that strong electrolytes are almost completely dissociated into ions in solution. He pointed out that the thermodynamic "anomalies" of strong electrolytes can be explained by means of interionic forces, and he proposed the formation of what he called "ion pairs." He was the first chemist in Denmark toapply measurementsot'hydrogen ion concentratim to inorganic and physical chemistry studies, and he devised a well-knuwn extranolation method for the elimination of the diffusion poteniial. He was the first to study svstematicallv the theorv and sources of error in acid-base titrations, anb be determined the pH value a t the endpoint as well as dealine extensivelv with the deeree of hvdrolvsis in the titration of weak acids and weak bares. He was the first to enunciate the protonic concept of acids and bases associated with the names of J. N. Br$nsted and T. M. Lowry, and he undertook studies of the pH and fertility of soils. He completely altered our views on the constitution of ampholytes, es~eciallvamino acids, with his concept of zwitter ions, which broughthim unsought, but undying, fame in the field of leather chemistry. Bjerrum's contributions, however, were not limited to physical chemistry, for he applied classical mechanics and auantum theorv to the constitution and the outical and thermal properties of molecules, in which he laid the foundations for the field of chemical physics. In the area of inorganic chemistry, Bjerrum revolutionized coordination chemistry by his extensive use of physicochemical methods. He frequently used kinetic methods to elucidate mechanisms for the reactions which he studied. In his classic studies of the hydrates of chromium chloride, he.proved the existence of a hitherto unknown complex ion, ICr(Hz0)~C11~+, and succeeded in isolating compounds of this ion. 1n his doctoral dissertation on basic complexes of chromium, he discovered that these were of two twes-manifestlv basic and latentlv basic-and his work, which provided the fundamental conceDts for the mechanism of chrome tannine. aroused the inteiest of leather chemists. Basic solutions chromium salts contain hieh-molecular-weieht aemeeates. and conseauentlv " ~jerrum'sstudiesled him into the field of colloid chemistr;. In his studies of the function of the thiocyanate group as a ligand, he proved the existence of all six possible complexes of [Cr(H20)6-,(SCN),I3-" (n = 1 to 6 ) , isolated four of them, determined formation constants for the thiocyanate com~
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Part 11, dealing with Bjerrum's work, will appear in next month's issue. Presented before the Division of the History of Chemistry at the Second Chemical Congress of the North American Continent, Las Vegas, Nevada, August 25,1980.
Figure 1.
Niels Bjerrum.
plexes of Au(1) and Au(III), and proved the existence of thiocyanogen in aqueous solution. In short, Niels Bjerrum was notpnly one of the most creative and innovative chemists of his time hut also one of the most versatile. Life
Niels Janniksen Bjerrum was born in Copenhagen, Denmark on March 11,1879, the eldest of eight children of the well-known ophthalmologist and university professor Jannik Petersen Bierrum (1851-1920) and his wife Anna Katrine 1.orentine kijerrum (nee Johansen) (185619.41) ( I I1 j. Hoth his varenrs' ramilies were orircinallv farmers from Schleswig. andhis father's family could be traeed back eight t o Peder Nielsen Bierrum, born on October 12, 1635. Bierrum's father's younger sister Kirstine Bjerrum Meyer was a physicist whose field of interest was close to physical chemistry. She edited Oersted's works and wrote a-treatise on the history of the concept of temperature. Living in the Bjerrum house from 1880 to 1885, she was like a second mother to young Niels and undoubtedly aroused his interest in science. Bjer~m described his childhood home as "a gathering place for a erouD. of ~oliticallv and relieiouslv liberal Dersons in. terested in natural science, whose conversations influenced the listening children" (5). He remembered it with deep gratitude, &d to its early influence he ascribed his outlook on life-his democratic ways, his aversion to arbitrariness, and his critical but respectful attitude toward Christianity. Bjerrum's parents moved several times in central Copenhagen, but in 1891 they acquired a seashore villa residence in the suburb of Hellerup. Every year from age eleven to twenty-three, Bjerrum spent summer vacations a t his maternal grandparents' home a t Volume 57, Number 11, November 1980 1 779
Figure 2. Professor Jannik Bjerrum with his wifeandeight children in thegarden in front of their house in Helierup in 1900. Niels. the eldest son, is at the right of the back row. (Photo courtesy of Professor Jannik Bjerrum. Copenhagen).
Kolding in Jutland, where on Kolding Fjord he developed his lifelong love for sailing and the sea. Throughout his life he spent !is summer holidays sailing, often with his maternal uncle Age, only one year his senior. In 1926 he became part owner of the 14-ton Bermuda cutter "Chita" along with his friend Niels Bohr (1885-1962). In 1934 Bohr gave up sailing after his eldest son Christian was swept overboard and drowned off the Swedish coast. Further traeedv was avoided when Ole Chiewitz, a friend and classmate i f ~Bbhr's,forcibly restrained Bohr from divine overboard to save his son. Bierrum continued sailing well& his seventies, and it wasnot until this time that he reluctantlv consented to own a boat with a motor. From the age of five, Bjerrum attended the Bondensens skole (rural school), and from the age of nine, the Borgerdydskole (school of civic virtue). From the age of twelve to eighteen (1891-1897) he attended the Metropolitanskole (a Copenhagen cathedral school, affiliated with the Church of Our Ladv). ".. where he develooed a lasting friendshio with several of his classmates,.especially with Johannes Nicolaus Brdnsted (1879-1947), his keen but friendly rival in physical chemistry (12). Bjerrum found mathematics and natural science easv. but he exoerienced ereat difficultv with languages, inci;;ding ~ a n i s composit&n, h and his high grades on
Figure 3. Nieis Bjerrurn, his wife Ellen. son Jannik. and infant daughter Badil, 1912. (Photo courtesy of ProfessorJannik Bjerrurn. Copenhagen.) 780 1 Journal of Chemical Education
his university entrance examination pleasantly surprised his language teachers. Bjermm had already studied chemistry as a schoolboy; his aunt Kirstine Meyer had given him a copy of Wilhelm Ostwald's "Lehrhuch der allgemeinen Chemie," and he had also studied Ostwald's "Elektrochemie: Ihre Geschichte und Lehre" (1896). However, he had not decided whether he wanted to major in chemistry or physics at the University of Copenhagen. In order to make up his mind, following his graduation in 1897 he worked on chemical preparations in Prof. Emil Koefoed's laboratory at the Farmaceutisk Laereanstalt (Pharmaceutical Institute). That autumn he decided to become a chemist. and after a conversation with Prof. Sophus Mads ~drgensen(1837-1914) (13,14), on February 1,1898 he began a four-year course leadine to a master's degree in chemistry, which hk was awarded in ianuary 1902. His examiner, Prof. Jdrgensen, almost failed Bjerrum because in his thesis "En kritisk-historisk fremstilling af fumar- og maleinsyreisomerien" (A Critical-Historical Survey of the Isomerism of Fumaric and Maleic Acids) he had not confined his criticism to the history hut had mistakenly extended it to the chemistry. Immediately upon receipt of his master's degree Bjerrum became assistant a t the University Chemical Laboratow under Emil Petersen (1856-1907). who had recently sucieeded the famous thermochemist ~"iiusThomsen (1826-1909) (15). As soon as he had become an assistant, Rjerrum began work un duublr salts oimercuric halides ior a orize c(m~oetition. hut after carrying out some experimental work, he realized that he could not complete the work within the allotted time. and he withdrew from the competition (86). Receiving little research encouragement from his professors, Bjerrum, upon the urging of Prof. Martin Knudsen (1871-1949), the physicist and hydrographer, undertook a study of the accuracy of chloride determinations in seawater, which led to his first publications (16). However, Bjerrum was interested in chemistry not oceanography, and although Prof. Jdrgensen, who was Alfred Werner's principal scientific adversary, had taken no ~ersonalinterest in Bierrum during his student davs., Jdrgensen's monumental work on coordination compounds influenced Bierrum in his choice of a oroblem for his first mature reseaich. Impressed by a number of striking parallels between green chromic chloride and the cobalt-ammines. he emharked on a study cnf chrwnium compounds, particul&ly thestaceof chromium(II1) rhlori(1e inaqueous sulution. that resulted in the publication of seven during the next eight years (17-20). His 122-page paper "Studier over Kromiklorid" (Studies on Chromic Chloride) (18) was awarded the Royal Danish Society of Sciences and Letters' coveted silver medal, and his 170-page dissertation "Studier over basiske Kromiforbindelser" (Studies on Basic Chromic Compounds) (21) earned him his doctorate under Jdrgensen in 1908 and was later abridged and translated into German (. 1 9 ~. ) . To further his knowledge of physical chemistry, during the summer of 1905 Bierrum worked for three months under Robert Luther (186a1945) in Ostwald's laboratory in Leipzig where he made the acquaintance of such ohvsical chemists as \lax Harlenstein ~187~-194'2,. Hans v o ~ a l h a n(l877-IB47,. Carl Drucker (187W!), and Carl Benedicks ,lA~Tr-l9;jdl.One result of' Hjerrum's trip abroad was the publicntiun of his article on a rheoretical and experimental itudv ofthe redurtion (tf the overall liquid-liquid junrtion potential by use oia hridge ufconrentrated potassium chl(,ridesolution (221 In thespring of 1907 Hjerrum married Kllen Drcyer, the beautiful and vivaciousdaughter of Consul Peter Dreyer, a wine merchant from h n d e r s . This haoov marriaee r ~ w l t e din f Jannik, the oldest chiid (h.1909). now one of the world's leading authorities on stahilitv constants of complex ions, has continued his father's work. His three daughters-Bodil (Mrs. Hans-Bdrge Krogh), Marianne (Mrs. Erik Stolpe), and Kirstine (Mrs. Erik Juhl,
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deceased in 1962)-all married professional men. In May-June 1907, Bjerrum visited Alfred Werner (1866-1919) in Zurich, and the founder of cwrdination chemistry recognized that his own interpretation of the nmstitution of an isomer oi Recoura's salt, [Cr(H~O)sCIIS04, was incorrect, while Hjerrum's was correct 117a. 23). Niels Rjerrum had his heart set on an academic career. The llniversity of Copenhagen had two professorships in chemistry, both ot' which were filled by young men; in Septemher 1907 the organic chemist Einar Hiilmann (1873-1946) had succeeded Emil Petersen, and in January 1908 the inorganic chemist Julius Pewrsen (1865-1931 I had succeeded .Jarpensen. Howevc.r, in May 1908 a third chair was estahlishrd, and hoth Bjerrum and his friend Hrsnsted applied for the position. The faculty decided that the twocandidatesshould compete bv each deliverinr: - five lectures-three on a subject of their own choice and two on an assigned topic. The competition was postponed until November to allow Bjerrum time to defend his doctoral dissertation, which he did successfully on November 6, 1908. Bjerrum, for whom public speaking was an effort, chose the topic "Om Elektrolyters Farve og Bygning" (On the Color and Structure of Electrolytes), while Br6nsted, an elegant and fluent lecturer, chose to speak on "De luftformige Stoffers Ligevaegtsforhold" (The Equilibrium of Gaseous Substances). The competition began on November 13 and concluded on December 5. Brdnsted, Bjerrum's senior by onlv seventeen davs. was chosen unanimouslv, largely on his ipeking ability, &d'~jerrum,to whom all chance of academic advancement seemed blocked, was deeply disappointed. The blow was somewhat softened by the official statement of December 17: "Both competitors were unusually capable and promising young scientists . . . so that we would not have hesitated to recommend either one of them if there were only one applicant" ( 5 ) . Bjerrum's depression soon lifted, and the followingsix years which elapsed before he obtained a professorship were filled with work and travel. In May 1909, a t the Seventh International Congress of Applied Chemistry held in London, in a Dauer entitled "A New Form for the Electrolytic Dissociation ?heoryM (241, he proposed the revolutionary hypothesii that strung electrolytes are completely d~ssociakdin aqueoussolution. fourteen vears hefore Debve and Huckel's classic work. In the'summer of 1910 Bjerrum worked for a month in Paris with the eminent French physical chemist Jean Perrin (1870-1942) determining the value of Avogadro's number from the Brownian movement of rubber latex particles in a viscous glycerin-water mixture (25). A grant from the Carlsbere Foundation (26) and a small salarv from Walther Nernst (18~i4-19.lllenabled Rjerrum, his wif&and infant son to wend the vear of 1911 iree of teaching- and administrative duties a t ~ e & s t ' sinstitute in Berlin. With Nernst, Bierrum determined the heat capacities of gases a t high temperatures by the so-called explosion method (27), which led him to apply quantum theory to the interpretation of infrared spectra (28). With these papers Bjermm became the pioneer of a new science on the physics-chemistry interface, a discipline to be called "chemical physics" ahout a decade later (29). Although he was well aware of the significance of the quantum theory (30), as developed by his friend and fellow Dane Niels Bohr, for atomic-molecular problems in general, Bjermm made no further contributions to quantum theory because he felt that he was going too far afield from his first loves-physical and inorganic chemistry. In 1912 Bjerrum was promoted to docent at the university and a member of the faculty. On August 1,1914, the first day of World War I, in which Denmark remained neutral, he was appointed Professor of Chemistry a t the poorly equipped Kongelige Veterinaer- og Landhohdjskole (Royal Veterinary and Agricultural College) in Copenhagen, a position left vacant by the death of OdinT. Christensen (1851-1914). In that same year his German monograph on the theory and sources of error in alkalimetric and acidimetric titrations (31) ap-
of Professor Jannik Bjerrum, Copenhagen.)
peared. Many persons considered Bjerrum overqualified for his new position and considered as wasteful his teaching of a heteroeeneous flock of first-year veterinary and agriculture students who were not used ;o studying. However, Hjerrum believed good teachina to be as important as good research, and he was a painstaking teacher,-especially i n elementary courses (32). His text on inorganic chemistry (1916), which went through six editions, includes a comprehensi\,e but elementary introduction to physical chemistry (03) Thc third edition the~ Brmsted definitions of acids and ~ (1992). , ~ ,, in which ~ ~ ~ ~ bases appeared in a textbook for the first time, has been translated into German. Russian. and Enelish (33). and no less an authority than Frederick George ~ ' b n n a nconsidered it the finest introduction to modern chemistry. Bjerrum always maintained that he had obtained some of his best scientific ideas from his teaching, and his years a t the Royal Veterinary and Agricultural College were extremely fruitful ones. After leaving the domain of chemical physics, he returned to coordination chemistry and physical chemistry, with valuable contributions to the chemistry of acids and bases, electrolytes, soil, proteins (he proposed the concept of zwitter ions in 1923). and chromium complexes. He attracted research workers not only from Denmark hut also from abroad. Among his collaborators who became professors may he listed E. A. Guggenheim (England); Vaino Sihvonen (Finland); Ludwig Ebert (34) and Erich Manegold (35) (Germany); Lazlo Zechmeister (36) (Hungary); Erling Schreiner (Norway); Edward Jo6zefowicz (37) (Poland); and Hans L. J. Backstram, Cyrill Brosset, Erik Larsson (381, and Lennart Smith (Sweden). ~
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Figure 5. Niels Bjerrum on his 77th birthday. March 11. 1956. (Photo courtesy of Professor Jaonik Bjerrum, Copenhagen.)
Volume 57, Number 11. November 1980 / 781
In 1931 Bjerrum was offered the ~rofessorshipin inorganic chemistry at the University of copenhagen, where h e had unsuccessfully sought a professorship 23 years earlier, but he declined the position, preferring instead to remain a t the Royal Veterinary and Agricultural College, whose chemistry lahoratorv he had done so much to develoo. In 1931 he also became a-member of the board of trustees of the Carlsherg Foundation (26). a nosition which he occupied until 1956: from 1937 to1%6 hk served as Chairman of the ~ a r l s h e r g Lahoratorv. He was also a hoard member of a number of firms connected with the chemical industry such as the (larkberg Brewery (Chairman from 19R:Ii and the Danish Sugar Manut'arturers (Chairman from 1941). He served as Dirertor of the Royal Veterinary and Agricultural College from 1939 to 1946, uhirh included the difficult lustrum of German occupation. All these administrative activities naturally r ~ d u r e dhis rime available for research, hut after he retired at the age of seventy in 1949, he resumed his former pace of research. Works from this oeriod included regearch on the structure of ice (1950195g (39) (Bjerrum always maintained t h s t until we understand the ~ r o ~ e r t i of e sice. we can have no hooe of understanding those of water), a monograph on the caieium ortho~hoephates(1958) ( 4 0 ) . which continued work that he had done-more than two decades earlier (1936) (411, and his last pnpw "The Electrical Contact Potential and the Individual Activity of Single Inns" (42). On the morning of September 25, 1958, Bierrum worked in the Chemistrs 1)eoartment library as usial. That afternoon he suffereda stioke, and he died peacefully on Septemher 30,1958. Thus ended the life of the man whom E. A. Guggenheim has called "without any comparison the most versatile physical chemist of his generation" (8b). Niels Bjerrum possessed an insatiable curiosity not only for science but also for evervthine . around him. He was extremelv tolerant except when it came to tyranny, arbitrariness, bypocrisy, pomp, deceit, and loose thinking. An active member of the International Union of Pure and Applied Chemistry's inorganic nomenclature committee. he was instrumental in gett[ng German scientists admitted into the IUPAC, which had been founded after the end of World War I. He became a member of the Royal Danish Academy of Science and Letters in 1916 and served as its treasurer (1927-1931). He was co-founder of the Danish Fysisk Forening (Physical Society) and was an honorary or corresponding member of twenty-one learned societies. He was awarded honorary doctorates-from the Universitat Gljttingen (19491, Danmarks Teknisk H6jskole (1954), and the University of Turku (Swedish, Abo) (1955). In 1928 the Selskahet for Naturlaerens Udbredelse, Kdbenhavn awarded him its Oersted Medal. simultaneouslv with Br6nsted.
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(91 Christiansen,J.A,Kemisk MoonrdsbladogNordlak HondalsblodforKemis*lndndfn, 40.13 (1959):FYsisk lidrskrilb, 57.24 (1959). (10) Gustsvson. K. H.. J. Soc Leath. Trades' Chemlals.43, 72 (1959): J . Amer. Loath. Chemiafa Assoe.. 54,104 (19591. (11) Hicbert, E. N., "Niela J a n n i k n Bjemm: in Gillhpie, C. C. (Edilar), ' n i a i o n ~ of Scientific Biography: Chsrlea S&hner'%Sons., NsluYork, 1970, Vol. 2, p. 169. 112) Bell, R. P., J. Cham. Soc., 1950.408. 1131 ,.., Worn-, ...........
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(14) Kauffman, G. B., J. CHEM. EDUC., 36,521 (1959); Chvmio, 6,180 (1960). (15) Bjerrum, N.; Tids. Indwlri, LO, 65 (1909): Bar., 42.4971 (1910). (16) Bjerrum, N., Forsl#big Meddolelse fro d d donske hydrograliske Lobomforium, 2, 11 (19031: 3.19 (1903): Meddrlelsar fro Kommlasionm far Houundsraddzer Setin'
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Acknowledgment The author gratefully acknowledges the assistance of Prof. Jannik Bjerrum, Dr. K. H. Gustavson, the late Prof. E. A. Guggenheim, and Det Kongelige Danske Videnskabernes Selskab (The Royal Danish Society of Science and Letters). He is also indebted to the late Lydik Siegumfeldt Jacobsen for assistance in translation and to the California State University, Fresno for a sabbatical leave of absence. Literature Cited (1) Oespex, R. E., J. CHEM. EDUC., 28,433 (1951). "Dmk biografmklihIr~r:RhUltLF~~lag,Cc~, (2) Vribel,S.."N.J.Bjen-:in 1934. Vol. 3. p p 183-185. (3) For a lit of Bjerrum's 80 publications fmm 1908 to 1935 see Veibl. 5. (Editor). "Kemien i Dsnmark, Vol. 2: Dansk Kernisk Bibliwafi 1m1935: Nyt Nordisk Forlag. Arnold Busek. Copenhagen. 1943. pp. 61-67, (4) Uomack,A..NoluihisIoririk Tidende, 22.58 (1956). (5) Jenaen,A. T., Ouamigt ouer Def Kg1 Donska VidenskabemoaSelskoba Virkaomhod. 1958-53.99. (6) Jensen. A. T.. DenKongdigo V o f d n o e r ag LondboWjakole Ar?sktiff. 1959.91. 17) Partington, J. R., Nature. 183.290 (1959). (8)Guz~enheim,E. A., (a) Tmw. Forodw Soc. M,unpaginated, unindexedfmntiapis. (1959): (h) R o c . Chem. Soc., 1960,104.
782 1 Journal of Chemical Education
Figure 6. Niels Bjerrum receiving an honorary doctorate, University of Abo (Turkul. Finland. 1955. (Photo couriesy of Professor Jannik Bjerrum. Copenha-
Prior, Copenhagen, 1998. (22) Bjerrum, N.. Z phwik. Chem., 53,428 (1905): sre a h 2.Eldfrochsm., 17.58.389
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d s u l o h w i k Ges. 16.640.737 11914). (29) Umy. H: c:, il Chcm. P&., 1 , l (19331: (30) Bjerrum, N., Fyaisk Tids., 14.49 (1915): NoIurew Verden, 3,529 (1919). (311 Rjerrum, N., "Die Theorie der alkslimetrischen und azidimekischen Titriarungen: Ferdinand Enke, Stuttpsrt, 1914. (321 Bjerrum. N.. "Vejledning ti1 indledende 0 v e b r i Den kgl. Veterinaer- og Landbohflskoles kemiske Lsbaratorium," Copenhagen, 1916. (33) Bjorrum. N., "Laerebog i uorganisk Kemi for Elever pas Den kgl. Veferinaer- og hdboMjskole," hdboMjskolem kemiske isboratoriun, Copenhagen. 19161917; "Laerehog i uorganisk Kcmi: 2nd Ed., 1920; 3rd Ed., 1932; 4th Ed.,l93?; 5th Ed., 194s; 6th Ed., 195s; "Xurm lrhrbueh der anorganischen Chemie," transl. by L. Ehert, Ju!iusSpringer, Berlin. 1933;"~ralk:ku~neorg~~i~h~~kdKhi~ii... I. Kavlrnovskii (Edilol). Mmow, 1935; "lnowanic Chemistry: frsnsl. by R. P. Bell. Heinomenn. London, 193612ndEd., 1948. (341 Bjerrum. N., and Ebert, L.. Kgl. Danske Vidanskob. Selsbob, Molh-lys. Medz., 6 (9). 1,1915,
(37) Bierrum. N.,andJ6mfff;ez.E., 2. physik. Chsm., 135.194 (1932). (38) Bjerrum, N., and Larsson, E., Z. physib. Chem., 121,358 (1927). (39) Bjerrum, N., Fysisb Tida.. 48,71(1950);Kgl. Donske Vidonskab. Selskob. Moth.-fy. Medd., 27 (1). l(1951); Chem. ond lad.. 1952,364: Science, 115,385 (1952). (40) Bjermm,N.,Kgl.Dambe Videnskob. %&hob, Moth-ha. M d d , 31 (7),1(1958);tmal. intoEngl by M. H. Rand as"Caleium Orthophoe~hates:AERE-nans.841,United Kingdom Atomic E n c w Research Establishment, Harwell, Rerkshke, Engl..
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