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A Tale of Two Chemists

Seymour Mauskopf

A World on Fire: A Heretic, an Aristocrat, and the Race to Discover Oxygen. Joe Jackson. xiv + 414 pp. Viking, 2005. $27.95.

Lavoisier in the Year One: The Birth of a New Science in an Age of Revolution. Madison Smartt Bell. xiv + 214 pp. Atlas Books/W. W. Norton and Company, 2005. $22.95.

The story of the chemical revolution that took place at the end of the 18th century is one of the most compelling in the history of science. Nearly 60 years ago, this narrative was given particular dramatic force by James Bryant Conant in a case study titled The Overthrow of the Phlogiston Theory. In 1962, Conant's formulation achieved iconic status in Thomas S. Kuhn's seminal work, The Structure of Scientific Revolutions. Kuhn, like Conant, shaped his account as a duel between two heroic scientific protagonists, Joseph Priestley and Antoine Laurent Lavoisier.

On Bastille Day in 1791...Click to Enlarge Image

The drama was heightened by the fact that Priestley, the apostle of the phlogiston theory, had discovered a gas that promoted combustion and respiration far better than ordinary air. He had named it dephlogisticated air (more on this later). This same gas, about which Lavoisier had learned from Priestley, became the centerpiece of Lavoisier's new antiphlogistic theory and was given a new name by him: le principe oxygine ("acid maker"). The fact that we still call the gas oxygen and find dephlogisticated air an obsolete and mystifying name shows clearly who was the victor in this intellectual battle.

The two books under review here deal with this central episode of the chemical revolution—and with much more. A World on Fire, by Joe Jackson, elaborates on both of Conant's heroic figures, providing additional irony and piquancy by considering their full biographies. Priestley, the scientifically conservative phlogistonist, was a flaming radical in virtually all of his other activities and writings. In contrast, Lavoisier, the revolutionary scientist, was very much a member of the social and political French establishment of the ancien régime. The violence and harassment that Priestley suffered for his political and religious views, particularly for his support of the French Revolution, drove him from England to America. At the moment Priestley was leaving for the New World, Lavoisier was already imprisoned, and during the Reign of Terror he would forfeit his life for his prior social and political associations and activities. Madison Smartt Bell's Lavoisier in the Year One focuses on Lavoisier but parallels A World on Fire in providing accounts of both his scientific and his extrascientific pursuits, culminating in his death by guillotine on May 8, 1794. (The "year one" of the title refers to the first year of the new revolutionary calendar, the interval between September 22, 1792, and September 21, 1793.)

Neither of these books is written by a professional historian of science. Indeed, both authors are, among other things, novelists. In light of this, let me compliment them at the outset for having really worked at writing serious historical studies. Each has developed deep knowledge of and quite exceptional rapport with the social, cultural and political milieus of the times and places in which their subjects lived. In the case of Jackson, this is no mean feat, because he is concerned with three countries (England, France and the new United States of America). For social and political context, Bell relies on the magisterial writings of Lavoisier biographer Jean-Pierre Poirier and, to a degree, on the equally excellent study of Lavoisier by Arthur Donovan.

Both Jackson and Bell are at their best in detailing the activities of Priestley and Lavoisier that, strictly speaking, lay outside of their science. As it happens, I was reading these accounts of Priestley's travails just as the British government was, in the weeks after the London underground bombing, instituting draconian measures against anyone expressing support of Islamic-based terrorism. What struck me with shattering force was how similar Priestley's situation in the early 1790s was to that of those accused or suspected of supporting terrorism today. He was both a political and a religious radical, and the British establishment treated him like one.

Lavoisier's life also emerges as being highly pertinent today in terms of his political and social activities, because he was in many respects the first major scientist to deploy his expertise—and more important, his prestige—in the service of the state. He was, in a phrase, the first modern government scientist. Through my own work, I am most familiar with his role as the leader of the French gunpowder service, but that was only one of a multitude of things he did for his country. Some were done through his position in the Académie des Sciences; others arose from his work as a fermier général, a collector of state taxes. As is well known, there was a reciprocity, even a synergy, between Lavoisier the tax collector and economist, and Lavoisier the quantitative "book-keeper" of chemical reactions. He brought rectitude and rigor to France's economic activity—perhaps too much at times, and this came to haunt him during the revolution. It didn't help that as a power broker in the Académie des Sciences, Lavoisier had also slighted the scientific pretensions of future revolutionary leaders such as Jean-Paul Marat. Marat—and others—remembered.

Priestley and Lavoisier, then, make for vividly contrasting studies of scientists who lived fully active lives outside the laboratory during these turbulent times. The nonscientific aspects of the lives and careers of the two men are dealt with quite brilliantly by both Bell and Jackson. Indeed, it probably helps that they are novelists; historical writing (at its best) can be riveting, and there is probably no better way to master the craft of dramatic narration than by writing novels.

However, the handling of the scientific activities of Priestley and Lavoisier is less successful and betrays, in my opinion, the authors' lack of a fully professional viewpoint, which is not unexpected, given that they are not historians of science. Jackson's book is the more egregious in this regard. My principal criticism has to be couched carefully, because I realize that many readers may well sympathize with Jackson's and Bell's perspective more than mine. What I find troubling is the evaluation of the phlogiston theory, the theory espoused by Priestley and shattered by Lavoisier, as bad science, as patently erroneous science that would naturally be repudiated by anyone who paid attention to his or her senses. Here is Jackson's narrative on Priestley's naming of "dephlogisticated air":

Yet in the midst of his greatest triumph, he made his greatest mistake. . . .

. . . Despite the existence of his senses, he was still tangled up in phlogiston: he claimed his discovery was air somehow stripped of that flammable, mythical fluid. He'd broken through in the lab, but not in his mind.

Oxygen was not yet oxygen. Joseph stuttered in the worst way he ever had, and called his new find "dephlogisticated air."

Perhaps the principal lesson Kuhn taught was the need for the historian of science to empathize with scientific theories and practices—with what he called "paradigms"—of earlier ages. The corollary of such empathy is the realization that scientific change is not an unambiguous or simple move from error to truth. Indeed, as Bell realizes, the phlogiston theory was a powerful means of providing order and guidance for research in many domains of chemical investigation. It took Lavoisier himself several years to move from adherence to phlogiston to his new oxygen-based chemistry. Without denying the power—and yes, superiority—of Lavoisian chemistry, a true historian of science would be interested in evaluating the scientific functions, and virtues, of the phlogiston theory, even though it was overthrown.

In his discussion of the scientific changes taking place in 18th-century chemistry, Bell is actually much more evenhanded and well informed historically than is Jackson. I was therefore quite stunned to see him miss the theoretical point of Priestley's "dephlogisticated air." The name came from a rather straightforward application of phlogiston theory, in which the chemical process of combustion was viewed as the release by a combustible substance of its flammable material (phlogiston) into the ambient air, as can be "seen" when a log in a fireplace shoots off flame and leaves a small pile of ash. As new gases were revealed, some, such as "fixed air" (CO2), were found to be far less supportive of combustion (and respiration) than ordinary air; others, like the new gas that Priestley had discovered, were found to be far more so.

In accord with this understanding of the nature of combustion, Priestley gave a quite lucid and logical interpretation of the new gases. Their ability to support combustion and respiration was more-or-less inversely proportional to the amount of phlogiston they contained. Gases such as CO2 were already saturated with phlogiston and could not absorb any more from the combustible material. However, the new gas Priestley had discovered allowed combustion to take place with great alacrity; therefore it must be practically devoid of phlogiston—"dephlogisticated air."

This was the core proposition of Priestley's phlogistic interpretation. Hence my amazement when I read Bell's misunderstanding of Priestley's theory:

Theory was not his strongest suit, and he failed to consider that a loss of phlogiston should not have made the new gas more hospitable to combustion than atmospheric air, though he had noticed that it was.

The move to a new chemistry involved, first, the reversal of that core proposition about the nature of combustion: the demonstration that something was, in fact, absorbed from the air by the burning substance. This Lavoisier showed quantitatively in his famous pedestal experiments with sulfur and phosphorus in 1772. Second, the nature of the "something" had to be identified. This, too, was Lavoisier's achievement, but it only became possible once Priestley had identified the gas that vigorously supported combustion and told Lavoisier about it. Third—and most fundamentally—it was necessary to reconceptualize the chemical natures of the different gases. There existed no fundamental "pure air" that produced other types of gases through absorption of phlogiston, as Priestley had surmised. Rather, gases came in different chemical species, and one of these was the gas that so vigorously supported combustion and became united with the combustible. This, too, was Lavoisier's accomplishment, but, as one could guess, it was hardly just the result of a new observation.

To me, the most interesting aspect of the history of science is the study of the laborious processes by which facts and theories that seem clear and natural to us were hammered out by earlier scientists. To assume that they should have known better and have recognized the new theory as "obvious" completely misses what is most intellectually fascinating about the development of the sciences.

But, as I have also suggested, the history of science is more than the study of scientific change; it is also the study of human beings. This important aspect is dealt with in quite extraordinary fashion by the authors of these studies of Priestley and Lavoisier. Both books make for exciting reading.

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