KOLBE, HERMANN

(b. Elliehausen, near Göttingen, Kingdom of Hanover, 27 September 1818; d. Leipzig, Germany, 25 November 1884)

chemistry. For the original article on Kolbe see DSB, vol. 7.

Kolbe was justly celebrated as one of the finest chemists of his generation, but he damaged his reputation by his obstinate retention of a theoretical viewpoint that both his contemporaries and his successors regarded as deficient and by his unfortunate polemics. Taking advantage of scholarship that has appeared subsequent to the original DSB article, the author of this postscript intends to provide a more nuanced assessment of Kolbe’s genuine and substantial contributions to the science of his day and to suggest a contextualized understanding of his furious public diatribes.

Evolution as Theorist . Kolbe’s life mission was to investigate the “rational constitutions” of organic molecules, and he was one of the greatest pioneers of this quest. According to Kolbe, experiment could be used as an inferential means to dissect schematically the formulas of organic substances, thus deducing the properties of the radicals that compose their molecules. His guide throughout was the dualistic electrochemical radical theory of Jöns Jacob Berzelius, which itself had been founded on the conviction that organic chemical theory must be based on analogies to inorganic chemistry. The evolution of Kolbe’s theory is most clearly exhibited in his Ausführliches Lehrbuch der organischen Chemie. This remarkable textbook was published in installments that were issued periodically between 1854 and 1878, and in reading it one can follow the twists and turns of Kolbe’s ideas, constantly being modified by new experiments and by the influence of the work of other scientists.

“Carbonic Acid” Theory . In the crucial decade of the 1850s Kolbe was in fact theoretically more flexible and more sensitive to the work of his self-declared “enemies” than has been appreciated. He accommodated increasingly to the ideas of the so-called type theorists, who emphasized the substitution of the hydrogen of organic molecules by chlorine and other atoms, and who deemphasized the relevance of inorganic chemistry for organic chemistry. Already in 1850 he had conceded that chlorine can substitute without dramatic change of properties of the substituted entity; in 1854 he agreed that oxygen could also substitute and began to develop a substitution-based theory much like that of the “typists.” After initial strong resistance, in 1856 he adopted Edward Fran-kland’s ideas of a “maximum saturation capacity” of radicals and atoms, which was the essence of what became known as valence theory. In 1857 he published a précis, and in 1860 a fully developed treatment, of a new “carbonic acid theory” that is well described in the original DSB article. What is not mentioned there is that Frank-land later plausibly asserted that the theory had been worked out in 1856 in private correspondence between Kolbe and himself, and that the 1857 article should have been published as a joint-authored paper. Kolbe conceded parts of Frankland’s claim but contested other parts, and the letters between them that would establish the truth of the matter have never been found.

Kolbe’s theory—or the Kolbe-Frankland theory— was parallel in many ways to the emerging theory of chemical structure, which was being developed about the same time by August Kekulé, Archibald Couper, and others, and it was similarly powerful in its ability to gaze inferentially into the interiors of invisibly small molecules. What Kolbe could not countenance in the rival structure theory was the notion that individual atoms could form directed bonds to other atoms; he was utterly convinced that atoms could not do this, and that even if they could, knowledge of such detail at the atomic-molecular level was beyond human ken. Kolbe’s molecules were formed of radicals or atomic groupings, combined (somehow) electrochemically and hierarchically, rather than “democratically,” as in structure theory. As similar as Kolbe’s and Kekulé’s theories were, they generated predictions that differed in the two cases. Unfortunately for Kolbe, the experimental tests resulted in repeated victories of structural principles over Kolbean ideas. By about 1870 virtually no one in the collegial community, not even his own students, adhered any longer to Kolbe’s “carbonic acid” radical theory or to his similar theory of the constitution of aromatic substances.

Contributions to Chemical Industry . During the 1860s, Kolbe’s good friend August Wilhelm Hofmann benefited from lucrative dye patents derived from his scientific work, and Kolbe, too, was sensitive to possible technological applications. In the fall of 1873 he developed a new and much less expensive way to make salicylic acid from phenol, using sodium hydroxide rather than sodium metal. A few weeks later he entered into partnership with Friedrich von Heyden, a student of his former student Rudolf Schmitt. Heyden provided the capital and most of the development work to take the process from the laboratory to industrial scale; he built a factory for this purpose in Radebeul, near Dresden. In the meantime, Kolbe engaged in aggressive market-oriented research and

development. He developed a tooth powder using salicylic acid and its methyl ester (synthetic oil of wintergreen), a mouthwash with a similar formulation, a foot powder, a bath salt product, and a tonic. He also championed two much larger potential applications of salicylic acid, as an antiseptic and a food preservative. Both had some success, though Joseph Lister’s preference for the antiseptic carbolic acid (phenol) as both stronger and less expensive proved difficult for Kolbe’s product to overcome, and there was significant market resistance to salicylic acid as a food preservative. But salicylic acid did become a widely used intermediate in a number of processes for perfumes, flavors, dyes, and pharmaceuticals—including, after Kolbe’s death, the most widely used manufactured pharmaceutical in history, aspirin. Salicylic acid made Kolbe a great deal of money, and proved to be a significant element in the rise of the German fine chemical industry in the late nineteenth century.

Professional Isolation . The conundrum that has puzzled all later observers is how Kolbe could hold so tenaciously to a theory that seemed to virtually all others so clearly past its prime, and hold to it, moreover, with an utter confidence that lent a tone of the holy fire of truth to his ferocious voice and pen. One key was his scientific education and the models of behavior after which he patterned himself. Kolbe’s earliest mentors were the superb chemists (and gentle personalities) Friedrich Wöhler and Robert Bunsen, but throughout his life his greatest heroes were Berzelius and Justus von Liebig. These two men were known for their occasionally caustic, sometimes even hyperbolic, critiques of the work of their contemporaries (in the case of the former in his annual Jahresberichte, and the latter in his journal Annalen der Chemie und Pharmacie). Moreover, in their middle age neither Berzelius nor Liebig stayed current with the latest research, and after about 1850 the outdated conservative views of Liebig in particular gave Kolbe the courage to continue the battle against what he considered the modish but utterly empty theory of chemical structure.

More broadly, this story must be placed in the larger context of the cultural history of the united German Empire after 1871, when Kolbe’s critiques began in earnest. In his classic work The Politics of Cultural Despair (1961), Fritz Stern first explored the development in late-nineteenth-century Germany of illiberal currents of thought that preceded the rise of national socialism. Kolbe displayed many of the characteristics of Stern’s protagonists: visceral political conservatism, fear and loathing of “modernity” in all its perceived manifestations, hyper-nationalism, anti-Semitism, and an abiding trust in authority and authoritarian political culture. For Kolbe, the theory of structure was false, meretricious, foreign (non-German) in its very essence, and it had been created and pursued especially by Frenchmen, liberals, Catholics, and Jews. Rightly or (more realistically) perversely, he associated structure theory with sensualism, materialism, liberalism, republicanism, and (possibly) irreligion. His beloved science of chemistry was being systematically destroyed by the structuralists (he thought), and he, at least, had the courage to speak up in its defense, even if he needed to do so alone. But his conduct destroyed much of his reputation, and in his last years his isolation from the peer community was nearly complete. The price of prejudice (or personality disorder?) is often high: in this case it was the self-inflicted demolition of a hitherto brilliant career.

SUPPLEMENTARY BIBLIOGRAPHY

Rocke, Alan J. The Quiet Revolution: Hermann Kolbe and the Science of Organic Chemistry. Berkeley: University of California Press, 1993. Cites additional articles by the author.

Alan J. Rocke