The World Inside

Michael D. Gordin reviews Image and Reality, Alan J. Rocke’s book on the changing 19th-century understanding of molecular structure.

Alan J. Rocke. Image and Reality: Kekulé, Kopp, and the Scientific Imagination. Chicago: University of Chicago Press, 2010. 416 pp. $45 cloth, $45 e-book.

The birth of structure theory in organic chemistry is one of the great intellectual dramas in the history of science. Here we find personal rivalries, wild dreams, and passionate arguments as chemists stripped down the electrochemical dualist theory, which split organic molecules into positively charged and negatively charged halves, and replaced it with a framework of valences and structures that endures to the present. And yet it is a history that is all too little known, even to organic chemists themselves, remaining the purview of a few scholars whose findings are mostly locked away in specialist journals. I believe Alan J. Rocke’s Image and Reality—the first volume in the University of Chicago Press series “Synthesis,” cosponsored by the Chemical Heritage Foundation—will change that.

The World Inside - August Kekulé

Sausage formula from August Kekulé

Sausage formula from August Kekulé’s Lehrbuch der organischen Chemie.

Science History Institute

Rocke has produced a striking reinterpretation of the development of structure theory centered on the work of August Kekulé. Image and Reality not only synthesizes three decades of Rocke’s own scholarship—principally published in Chemical Atomism in the Nineteenth Century (1984), The Quiet Revolution (1993), and Nationalizing Science (2001)—but also moves far beyond it. The author shows in detail how chemists in the middle decades of the 19th century, primarily in the Germanophone world, moved from a principled resistance to speculations on the internal composition of molecules to a stunningly successful and highly visual understanding of the microworld. This dramatic transformation was the result of experimental and theoretical developments over a period of decades. By 1865, when Kekulé proposed his cyclohexatriene structure for the puzzling benzene (C6H6), this strange proposition was accepted almost without objection. Twenty years earlier, even claiming that one might differentiate individual bonds in a molecule was heresy to the positivist philosophy dominant among chemists, which eschewed such “metaphysical” fantasies.

Rocke explains this amazing change by focusing on science as both a public and a private activity. Image and Reality provides an impressive analysis of the public dimensions of science, especially its collaborative nature, drawn primarily from three very different kinds of sources: published research articles, correspondence, and textbooks. Rocke presents the major (and hotly contested) findings in the publications of the day to show how chemists used these papers to hone an increasingly complicated picture of the organic world. But articles tell only a fraction of the story, for much of the thinking that went into a single-authored paper emerged from extensive correspondence among the growing chemical community. The back-and-forth of debate sparkles in these lively exchanges. And, finally, Rocke joins those historians of science who take textbooks seriously as scientific sources: they are not fossilized knowledge; instead the best of that time contain “almost as many new ideas as were to be found in the journal literature of that day,” and they were the primary means by which the younger generation learned what chemistry was (p. 93). Each of these sources takes us through a different kind of “public science,” and the reader is treated to a detailed yet accessible tour of great chemical minds: Kekulé, Emil Erlenmeyer, Hermann Kopp, Hermann Kolbe, Aleksandr Butlerov, and more.

But Rocke also wants to understand the private dimensions of chemistry. When historians discuss “private science,” they are usually referring to laboratory notebooks and other traces of scientific work in production. Rocke focuses instead on the most private aspects of science—what happens in the mind during moments of scientific cognition—and he has a theory as to what that is: “My sense is that human minds work far more visually, and less purely linguistically, than we realize” (p. xii). The most illuminating exploration of this theme is Rocke’s elegant analysis of Kekulé’s famous dream while on a London bus of a snake eating its tail, a vision that he claimed (decades later) led him to the hexagonal structure of benzene. This account has remained rather suspect for over a century, and Rocke is at his best when he teases out the nuances of this narrative and provides reasonable arguments for why we should take seriously Kekulé’s efforts to verbally report chemical thinking that takes place primarily in images.

Historians have been loath to enter the confines of the mind, and for some pretty good reasons. We do not after all have direct access to the thoughts of dead chemists (or even of living ones). We only know what they have chosen to record (really the subset of that which has survived), and documents “rarely mention such mental details” (p. 328). Yet even these details are not transparent records of thoughts; each was written with a specific audience in mind. Rocke is rigorous and clear in his defense of at least trying to plumb deeper into the mind, but I suspect resistance to his approach will continue. We seem faced with a fitting analog to the plight of Rocke’s chemists early in his book: historians are stuck with a firm methodological conviction that risks blinding them to how things really are.