AUGUST, 1951
NIELS BJERRUM RALPH E. OESPER University of Cincinnati, Cincinnati, Ohio
COPENHAGEN, which in a chemical historical sense is synonomous with Denmark, has long been the home of famous chemists. Since the days of Oersted its specialty has been men who work in the borderland between physics and chemistry. The present dean of Danish physical chemists is Niels Bjerrum, whose name and accomplishments are known the world over. Born on March 11, 1879, a t Copenhagen, he studied a t the TJniversity of Copenhagen, where he took his doctorate in 1908 under S. M. Jorgensen. His teaching has been in two institutions, his alma mater and the Royal Veterinary and Agricultural College of Copenhagen, where he was professor of chemistry from 1914 until his retirement in 1949. His 70th birthday was honored by the issuing of a volume of "Selected Papers,'" which gives a cross section of his many and varied publications. The divisions of this book: History of Chemistry; Chemical Physics; Physical Chemistry; Inorganic Chemistry, indicate the main lines of his interests. Bjerrum's historical articles are "reviews of the development of chemistry seen with the eyes of one of our outstanding chemists." Though few in number, they are valuable because of his keen insight. His work in chemical physics came fairly early (1911-14). These papers dealt with the relations of thermodynamic data t o other values which could he secured spectroscopically. He used both classical mechanics and the quantum theory in these papers which are concerned with the constitution and the optical and thermal properties of molecules. Physical chemistry makes up the bulk of his puhlications. The idea of complete dissociation of strong electrolytes was advanced in 1909 and developed in subsequent papers, where interionic forces, activity coefficients, and studies of ionic distribution coefficients ' See review, J.
CHEM.EDUC.,26, 626 (1949).
were given due consideration, especially with respect to reaction velocities. Brownian movements in viscous liquids, the application of hydrogen ion concentrations, the elimination of the diusion potential, etc., are typical examples of the matters that engaged his active and fertile mind. Equally important is his work on the theory of acid-base titrations, the source and rlimination of errors in such procedures, ampholytes (dissociation constants of amino acids) and so forth. He was keenly interested in the application of the theory of acidity to soil science, i.e., the discovery of the factors which determine the pH of the soil. The relation between molecular constitution and the first and second dissociation constant of dibasic acids, electrometric measurements with the hydrogen electrode in acid-base mixtures with salts, are still other fields that have engaged his attention. The work in inorganic chemistry deals primarily with chromium complex compounds. Typically, he approached the numerous problems they presented by physicochemical methods. Colloids, the preparation of collodion membranes with reproducible permeabilities, complex gold salts, and thiocyanogen complexes have also profitted from his able studies. Professor Bjerrum's "Laerebog i uorganisk Kemi" has gone through five Danish editions and been translated into German, Russian, and English. From 1903 t o 1948 he published about 90 papers. I n 1939 he was visiting lecturer a t Brown University. He holds honorary memberships in the chemical societies of Holland, England, Belgium, Switzerland, and Sweden, and is a member of the academies in Denmark, Sweden, Norway, Vienna, and New York. He is a member of the board of the Carlsberg Foundation, the Rask-Oersted Foundation, and the scientific committee of the Solvay Institute for Chemistry. The Oersted medal was awarded to him in 1928.
