(b.Magdeburg, Germany, 15 July 1871; d. Berlin, Germany, 3 September 1942).
Bodenstein was the son of Franz Julius Bodenstein, a brewery owner, and Elise Meissner, the daughter of August Christian Meissner, a district court judge. His father’s business awakened an interest in chemistry, which he soon began to study in a sort of alchemical workshop erected in the cellar of the private house attached to the brewery. Second, the roof of the brewery tempted him to practice mountain-climbing techniques, which he later put to use on the glaciers forming the roof of the Swiss Alps. In short, he became a chemist and an Alpinist. At age seventeen Bodenstein entered the University of Heidelberg. After six semesters he began his doctoral work under Victor Meyer. At first the subject, the thermal decomposition of hydrogen iodide, did not appeal to him; he would have preferred preparing organic compounds and colorful substances. He ably conducted the experiments involved, which required great technical skill (including glassblowing) and interpreted the results in accord with the very “new” kinetic theory of gases. Everything seemed to agree perfectly. Even though the interpretation has subsequently been altered, his work stands as a milestone in the study of reaction kinetics.
Bodenstein was awarded the doctorate summa cum laude in 1893. For the next two years he continued his training under Liebermann at BerlinCharlottenburg and under Nernst at Göttingen. He also spent one year in the army, serving in a cavalry regiment. In 1896 he returned to Heidelberg and married Marie Nebel. Bodenstein’s chief scientific interest was still reaction kinetics, and in 1899 he published his Habilitationsschrift, “Über die Gasreaktionen in der chemischen Kinetik,” a work that brought him to the attention of the scientific world.
From 1900 to 1906 Bodenstein worked with Ostwald’s group of researchers at Leipzig, where he investigated the kinetics of catalytic processes. He was the first to suggest that in heterogeneous catalysis it is not the concentration of the substance in the reaction vessel that is decisive, but rather the concentration at the surface of the catalyst. And as early as 1906 he applied the method later named for Langmuir and Hinshelwood to the heterogeneous dissociation of antimony hydride. In the same year Nernst summoned Bodenstein to Berlin as extraordinary professor and department head at the institute of which he became director many years later at the end of his career. While at Berlin he studied catalysis in flowing systems, as well as the kinetics of gas reactions (hydrogen bromide dissociation). A notable result from this period was the designation of diffusion and reaction as possible steps determining the velocity. The dimensionless quotient obtained by multiplying the velocity of flow with the pipe length and dividing by the diffusion constant is today known as the Bodenstein number.
In l908 Bodenstein accepted a professorship at the Technische Hochschule in Hannover. There, during a balloon flight that took place on an exceptionally stormy day and ended with a dramatic landing, he met Walter Dux; on the way back to Hannover they worked out a plan for the experiments on the photochemical chlorine hydrogen reaction that later became famous. The dissociation of hydrogen bromide had been shown to be far more complicated than the simple proportionality relationships that held for hydrogen iodide. The study of the photochemical chlorine hydrogen reaction resulted in a further surprise: the velocity was found to be proportional to the square of the chlorine concentration and inversely proportional with the oxygen concentration. Through the concept of a chain reaction Bodenstein explained this law and, simultaneously, the fact that the photochemical yield exceeded the Einstein law of equivalents by a factor of l04. This accomplishment was the start of a long struggle to determine the nature of the chain propagators involved, their formation and deformation. Finally, more than a decade after Bodenstein’s work with Dux, the question was settled by postulating the existence of the “atomic” chain originally proposed by Nernst.
By that time Bodenstein had returned to the University of Berlin, where he had become Nernst’s successor as head of the Institute of Physical Chemistry in 1923. Although reluctant to leave Hannover, he could not refuse a call to a university with a physics faculty that included Planck, Einstein, von Laue, and Nernst. In the succeeding years Bodenstein was awarded many honors: membership in the Prussian Academy of Sciences, an honorary doctorate from the Technische Hochschule in Hannover, an honorary doctorate of science from Princeton University, and honorary membership in the Chemical Society (London) und in other academies and chemical and physical-chemical societies, in Germany and abroad.
Until the end of his life Bodenstein was occupied with “Abschlussarbeiten am Chlorknallgas.” He originally believed he had been particularly fortunate to begin his research on kinetic reactions with the obviously “simple” case of hydrogen iodide. But the more scientists studied chain reactions, the more they found that even very simpleseeming gross reaction equations can result from complicated chain mechanisms, and they were no longer sure whether hydrogen iodide formation is really a reaction between hydrogen and iodine molecules. A remark that Bodenstein made late in his life may be interpreted as indicating that he had come to believe it necessary to revise his original views: “I would like to investigate hydrogen iodide once again with the aid of modern techniques.” He did not live to do so. It was only in 1967 that this reaction, too, was shown by John H. Sullivan to take place through the intermediary of halogen atoms,
Bodenstein always regarded his work on “Chlorknallgas” as his most important scientific achievement. We must agree with him when we consider everything that has emerged from the research he and his school devoted to that reaction: the concept of the chain reaction, the explanation of why the law of equivalents is violated in photochemical reactions, the computation of rate equations from a reaction mechanism scheme, the theoretical calculation of the chain length, the idea of explosions produced by chain branching, the explanation of the sensitivity of a chain reaction to impurities and wall influences and the quantitative control of these disturbances, the importance of the threefold collision for kinetics, the determination of the absolute values of the velocity constants of all individual reactions in the formation of hydrogen chloride and of phosgene, and the explanation of the inhibition of reactions during strong drying as resulting from the introduction of impurities that break the chains. The knowledge gained in studying the chlorine hydrogen reaction has been applied to many other chain reactions.
Bodenstein died following a brief illness. He was engaged in research until the end of his life, not only guiding the work of students but also conducting experiments himself.
The obituary notice by M. von Laue, in, Jahrbuch der Preussischen Akademie der Wissenschaften for 1946- 1949, 127–139, includes a bibliography of about 200 papers by Bodenstein. Among them are “Gasreaktionen in der chemischen Kinetik,” in Zeitschrift fur physikalische Chemie, 29 (1899), p1. I. 167–158, pts, 2–3, 295–333; “Photochemische Kinetik des Chlorknallases” ibid., 85 (1913). 297–397: “Abschlussarbeiten am Chlorknallgas,” pt. 1 in Sitzungsberichte der Preussischen Akademie der Wissenschaften zu Berlin, Phys.-math. Abu, 1936, 2–18; and pts. 2–3 in Zeitschrift für physikalische Chemie, B48 (1941), 239–288, and “100 Jahre Photochemie des Chlorknallgases,” in Berichte der Deutschen chemischen Gesellschaft75A (1942), 119–125.