In Search of El Dorado: John Dalton and the Origins of the Atomic Theory

Alan J. Rocke In Search of El Dorado: John Dalton and the Origins of the Atomic Theory THE HISTORIAN OF THE CHEMICAL ATOMIC THEORY EXPERIENCES AN embarrassment of riches—or just embarrassment—when he turns to the origin of the tale. He has a hero—the English Quaker and self-made natural philosopherJohn Dalton—as well as a birth date for the theory: Dalton’s September 6,1803, entry in his laboratory notebook. Beyond these apparently secure fixed points lurk historiographic monsters; and sometimes the bewildered historian is led to wonder how fixed even these apparently secure points are.1 Son of a Cumbrian weaver who lived near Kendal, John Dalton (1766-1844) was first a schoolteacher, but in 1793 was hired as a professor ofnatural philosophy at the dissent­ ing New College, Manchester. In 1800 he resigned his position (it was about to disappear, anyway, due to financial problems at the college), and thereafter earned his living in Manchester as a private lecturer and tutor. His most famous contribution was the atomic theoiy of matter. In what follows I review the diverse accounts of Dalton’s concep­ tual route to atoms, and attem pt to clear a pathway through the morass. W ith so many sharply differing stories, virtually all derived from Dalton himself, there is little likelihood of resolving all the anom­ alies. Nonetheless, there is reason to hope that one may make progress toward a probable picture ofhow Dalton arrived at his atomic theoiy. We social research Vol 72 : No 1 : Spring 2005 125 will see that his investigative pathway often appeared to move straight ahead, but Dalton was not always moving in the direction he thought he was. As an early Dalton obituarist proclaimed, “like Columbus, who missed an El Dorado, but found an America, he discovered something better.”2Thus, on one level this is a case study of a big mistake leading to a big breakthrough, parallel to Arthur Koestler’s famous depiction ofJohannes Kepler’s “sleepwalking” performance en route to the three laws of planetary motion. However, we will see that a close examina­ tion reveals many complications in this apparently simple plot line. The proper view is a more interesting one, comprising not only a kind of “thematic pluralism”written of by Gerald Holton, but also involving a multiplicity of circumstances and influences—both theoretical and empirical (Koestler, 1959; Holton, 1956: 340-51; 1986: 26). We should first be clear what the stakes are. A generation ago Henry Guerlac justly called Dalton’s contribution the first successful example of scientifically probing the world of the invisibly small, and he characterized this as the origin point of a “Molecular Revolution” as momentous as that of Newton (Guerlac, 1968: 70, 85). Indeed, Dalton’s work called forth a vigorous international research program that has a continuous histoiy from 1803 to the present—nanoscience long before the word became vogue. Almost from the start—we will examine the “almost” presently—that research program utterly transformed the science; moreover, it was atomistic theory that enabled chemistry, two generations after Dalton, to become the earliest example of a welldeveloped science-based theory acquiring the practical power to trans­ form the world of technology and commerce. Here is a brief discussion of how the theoiy works. Dalton knew (we use his data from the year 1810, but current definitions ofthe words “atom ” and “molecule”) that water consists of 87.5 percent oxygen and 12.5 percent hydrogen by weight; that is exactly seven times as much oxygen as hydrogen. If one assumes, with Dalton, that the invis­ ibly small water molecule consists of an atom of hydrogen united to an atom of oxygen, then every oxygen atom must weigh seven times as much as eveiy hydrogen atom, for under these circumstances it is obvi­ 126 social research ous that the weight ratio of the atoms must match the composition of the compound. But we notice that this procedure requires us to assume a formula for water. In contrast to Dalton, Humphry Davy and Jacob Berzelius assumed (in 1812 and 1814, respectively) that the formula for water was (as we would write today) H2O rather than Dalton’s HO. In...