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ANTOINE EAVOISIER ^ K C O V S E R V A T I O N OF MATTER Delving deeper than the thumbnail sketches often found in chemistry textbooks into the way this seminal 18th-century French chemist designed and conducted his experiments reveals a scientist very recognizable to practicing chemists today Frederic L. Holmes, Yale University School of Medicine
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hroughout the year, historians of science have gathered in small groups in various parts of the world to mark the 200th anniversary of the death of Antoine Lavoisier (May 8, 1794). They have presented to one another the latest results of their studies of his scientific career. Despite more than a century of previous scholarship, these historians believe that much still needs to be learned about his life, his achievements, his scientific style, and his ability to transform chemistry as it was practiced when he entered the field. Although a few practicing chemists joined these gatherings, chemists in general have probably been little concerned with the current state of historical scholarship about Lavoisier. Almost all chemists know that Lavoisier was one of the greatest chemists of all time; some regard him as the founder of the modern field. Not surprisingly, what most of them know about Lavoisier derives from brief summaries of his life and work that they once encountered in the textbooks from which they first learned their chemistry. Like textbooks in other fields, those of chemistry typically include succinct descriptions of the early "heroic" figures from whom the science traces its descent. What these descriptions don't give—and what many practicing chemists might be fascinated to discover—is a sense of how much Lavoisier's investigative spirit and experimental style continue to pervade modern chemistry. The textbook sketches, which focus on Lavoisier's achievements, vary greatly in content, style, and quality. Some are short, pithy statements devoid of concrete detail. Others include summary descriptions of one or more of the specific experiments on which he built his theory of combustion, and some add a few details about his life. They are seldom longer than two or three paragraphs, and even these relatively short references to Lavoisier are often distributed through the text, 38
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dividing his work into parts that can be related directly to the topics in which modern chemistry is organized. A typical entry is the following passage taken from an introduction to a chapter on the conservation of mass and energy in the fourth edition of "Chemical Principles," by Richard E. Dickerson, Harry B. Gray, Marcetta Y. Darensbourg, and Donald J. Darensbourg, published in 1984: "The great French chemist Antoine Lavoisier (1743-1794) was the first to realize that mass was the fundamental quantity conserved during chemical reactions. The total mass of all products formed must be precisely the same as the total mass of all starting materials. With this principle Lavoisier demolished the long-accepted phlogiston theory of heat by showing that when a substance burns, it combines with another element, oxygen, rather than decomposing and giving off a mysterious universal substance called phlogiston. The principle of the conservation of mass is the cornerstone of all chemistry." This textbook characterization of one of Lavoisier's many achievements moves from his recognition of the conservation of mass in chemical reactions immediately to a statement of its permanent importance as the "cornerstone" of modern chemistry. The text then continues to discuss the conservation of mass and of energy as these concepts are understood today. The reader receives, therefore, a passing glimpse of Lavoisier as the "first" to recognize what has become a fundamental principle of the modern science. Historians often regard such encapsulated bits of history of science with ambivalence or even disdain. Textbook entries such as this seem to them drastically simplistic and serve to perpetuate a positivistic view of scientific advance no longer acceptable within historians' circles. Historians also charge that such textbook entries ignore all the changes in the understanding of Lavoisier and of his historical role that they believe their own work has brought about. Chemists who are aware of the recent historical literature
Lavoisier conducts an experiment in his laboratory to study human respiration in this drawing made by his wife, Marie Anne Pierrette Paulze, who depicted herself at the table at far right. argue, on the other hand, that one reason their own view of chemistry's history is different from that of historians is that historians of science write about issues—and in a language— that are interesting only to themselves. If historians have had so little impact on the historical images that chemists pass on in their textbooks, perhaps it is as much because the historians have failed to write about the aspects of their history that interest chemists as it is due to the chemists' inattention. In a book published in 1962 that has deeply influenced the subsequent development of the history of science, Thomas S. Kuhn asserted that a history of science concerned mainly to "determine by what man and at what point in time each contemporary scientific fact, law, and theory was discovered or invented" presented a false view of the historical process. Perhaps—as he wrote in his now famous 'The Structure of Scientific Revolutions"—"science does not develop by the accumulation of individual discoveries and inventions." Even those historians who did not accept Kuhn's own account of science as developing through alternating periods of "normal" and "revolutionary" science came to share the broader claim that the history of science should not seek to pick out of the past those achievements that collectively constitute the sciences of today. That approach came to be disparaged as "presentism," or Whiggism. Since the 1960s, historians of science have generally maintained that they must immerse themselves in the contexts of the historical periods in which they work, distancing themselves from the connections between the science of a past era and its counterpart in the present day. Within their own discipline, historians of science have thrived by following this precept. They have learned to see much of value in earlier science, even in those laws, facts, or theories discarded by later scientists. They have learned, for example, not to see the phlogiston theory simply as a "wrong" theory of combustion that required a Lavoisier to overthrow it, but as a powerful organizing idea in the qual-
itative chemistry of the mid-18th century. Until it was overtaken by new problems and investigative standards with which it could not cope, phlogiston effectively guided experimental chemists in their research. By detaching themselves from "presentism," however, historians have also, to a large degree, detached themselves from the very aspects of an older history of science that made it interesting to practicing scientists. Chemists may be prepared to accept that phlogiston was an effective theory in its time, if historians are prepared to show how the theory functioned in ways that chemists can relate to their own laboratory experience. Textbook references such as the one quoted earlier suggest, however, that chemists are not prepared to give up the view that a central function of their history must be to recall how and when the laws, principles, and theories by which they live today were first discovered or invented. Is there an impasse here, a gulf between chemists and historians of chemistry that cannot be bridged? Or is there a sense in which both are right? Is it possible to develop a history of chemistry in which both past and present find room for expression? I would like to explore these possibilities, using the textbook attribution of the conservation of mass to Lavoisier as an illustrative example. Chemistry textbooks that credit Lavoisier with having been "the first chemist to realize the importance of the principle of the conservation of mass" sometimes substantiate that generalization by quoting all or part of the following passage translated from 'Traité élémentaire de chimie," the textbook in which Lavoisier presented a synthesis of his chemical system in 1789: "For nothing is created, either in the operations of art, or in those of nature, and one can state as a principle that in every operation there is an equal quantity of material before and after the operation; that the quality and the quantity of the [simple] principles are the same, and that there are nothing but changes, modifications. SEPTEMBER 12,1994 C&EN 3 9
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"It is on this principle that the whole art of making experiments is founded. One must suppose in every case a true equality or equation between the principles of the bodies one examines, and those which one obtains through the analysis." With a few changes in terminology to modernize the language, Lavoisier's declaration provides so impeccable a statement of what present-day chemists mean by the conservation of matter that its repeated appearance in textbooks written two centuries later seems, at first, unproblematic. Why then did one of the leading Lavoisier Some of Lavoisier's laboratory scholars, Henry Guerlac, equipment, displayed at the Museum of write in 1962 that the beTechnology of the Conservatory of Arts lief that Lavoisier had & Measurements in Paris, include ushered in the "age of (clockwise from above) an ice calorimeter, a fermentation apparatus, quantitative chemistry," and an apparatus designed for largeenunciated "for the first scale combustion experiments in oil. time the principle of the Conservation of Mass in sic idea of causality. It is not surprising, if the principle is chemical reactions," and "inaugurated the use of the balbased on such a fundamental conception, that statements of ance," was only a "cliché of histories of chemistry"—a clithe principle can be found among writers concerned with ché that was, according to Guerlac, "to say the least . . . a ideas about matter ever since antiquity. gross oversimplification?" Meyerson also emphasized, however, that a principle of Guerlac argued that "the so-called Conservation Law . . . the conservation of matter is rather vague, because it does had long been a working principle of chemists and had not specify what properties of matter—for example, whethbeen clearly enunciated at least as early as the first decades er weight, volume, or mass—remain constant. Only in the of the seventeenth century." In 1992, William H. Brock, the post-Newtonian world could mass be viewed as the fundaauthor of a new general history of chemistry, took a similar mental property conserved, and because mass is more abposition: "The balance pan had always been the principal stract, there is still a tendency to think, especially in chemistool of assayers and pharmacists, while the conservation of try, of weight as the operative property conserved. mass and matter had always been implicit in chemists' rejection of alchemical transmutation and their commitment These ambiguities are conspicuously illustrated in the deto chemistry as the art of analysis and synthesis." Are the scriptions of Lavoisier's role in current chemical textbooks. chemists who continue to portray Lavoisier in their textStatements such as Lavoisier "was the first to realize" or to books as the originator of this "cornerstone" of modern "realize the importance of" the principle leave it undeterchemistry simply perpetuating a myth whose lack of validmined whether he discovered it through his quantitative ity historians have long since exposed? experiments or assumed it as an a priori foundation for his well-known balance-sheet experiments. Similarly, textbook A historical answer to this question must first consider attributions of the recognition of the conservation of mass to some ambiguities in the definition and status of the princiLavoisier overlook the fact that Lavoisier's oft-quoted stateple of the conservation of matter, even as it is understood in ment refers only to "the quantity of material" and to "the modern chemistry. At the beginning of this century, the principles" (by which he meant something like the "chemiFrench philosopher Emile Meyerson pointed out the inaccucal elements") as unchanged in chemical operations. racy of the common assumption that this conservation principle was grounded in empirical evidence. Not only in These considerations suggest that the question of whethLavoisier's time, but even a century later, Meyerson noted, er it is historically accurate to credit Lavoisier with "recog"the certainty with which the principle of the conservation nition" of the conservation of mass cannot be adjudicated of matter appears invested exceeds the certainty permitted merely by relating his well-known statement to the prior by the experiments which are supposed to serve as its baand subsequent history of chemistry. The meaning and the sis." Meyerson argued that the principle was never an emsignificance of his generalization are inseparable from his pirical generalization but an a priori inference from the baexperimental practice. To understand his position—and his 40
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role in the formulation of this chemical "cornerstone"—it is necessary to follow Lavoisier into the laboratory in which he devised, and demonstrated the power of, a new mode of chemical investigation. Just as historians have shown that Lavoisier was not the first to state the principle of conservation of matter, so have they found that he did not initiate quantitative measurement in chemical operations. The balance had long been a part of the essential instrumentation of a chemical laboratory. Several landmark discoveries were made through weight measurements before Lavoisier took up the problem of combustion in 1772. It was by such methods that the Scottish physician and chemist Joseph Black established, in 1756, the existence of a new species of air (which he named "fixed air," now known as carbon dioxide) that could be released from mild alkalies. In 1772, Guyton de Morveau, a lawyer in Dijon, France, who also pursued an active career in chemistry, demonstrated conclusively through quantitative experiments that all metals gain weight when calcined. These qualifications do not, however, diminish either the importance or the novelty of the quantitative methods that Lavoisier introduced into chemical investigation. Prior to 1772, balance measurements were of limited scope and importance in laboratory practice. The Swedish historian Anders Lundgren pointed out in 1990 that pharmacists regularly weighed out the ingredients of their preparations, but they required only approximate measurements. Assayers determined with precision the quantities of precious metals contained in ores but did not need to extend their measurements to other substances. During the 18th century, chemists made great progress in the identification of acids, bases, and neutral salts, relying on qualitative procedures such as Apparatus designed by Lavoisier in 1773 (at left) for experiments to confirm that an "elastic fluid" (a gas) is released from a metal ore when the ore is heated is clearly only a slight modification of equipment in use at the time, such as that described by the English chemist Stephen Hales in "Vegetable Staticks," published in 1727 (at right). Lavoisier placed a sample of a lead ore called minium along with powdered charcoal on a pedestal inside a bell jar inverted in a water bath. After raising the water level inside the jar by suction through a siphon, he focused the Sun's rays on the sample through a large magnifying lens. He attempted to quantify the amount of gas produced from measurement of the change in height of the water column but was unsatisfied with the precision of his result. The drawing is Lavoisier's own, published in "Opuscules physiques et chymiques."
precipitation reactions, the recognition of crystalline forms, and a cycle of analysis and synthesis in which the identification resulted from reproducing the original substance by recombining the components previously separated from it. From the beginning of his scientific career, Lavoisier displayed a strong interest in quantitative measurements and instruments, especially in the barometer and the hydrometer. Some historians have argued that he was inspired by the methods of experimental physics and aspired to introduce similar methods into chemistry. The experimental methods that most broadly transformed chemistry, however, were ones he devised mainly in response to the particular problems that he encountered after he took up, in 1772, the general problem of how "airs," or "elastic fluids," are fixed in and released from solid and liquid bodies. Initially, he adapted to his purposes apparatus and methods already available in the chemical repertoire, but as the questions he took up pressed him to seek more reliable and more decisive quantitative results, he gradually developed new and more complicated forms of apparatus and forged the distinctive experimental style that later commentators have called his balance-sheet method. Several historians have pointed out that what distinguished Lavoisier's work from that of his predecessors was not his use of the balance, but its systematic use, and especially its extension to what would later be called gaseous reactions. Because the problems he took up centered on the fixation and release of what he called elastic fluids, however, Lavoisier's quantitative experiments from the beginning were more complicated than is implied in the phrase "use of the balance." He did rely on the balance to determine the weights of solids or fluids and was concerned from an early stage to improve the precision of that instrument. To determine the quantities of elastic fluids released or absorbed, however, he measured volumes rather than weights. The basic apparatus for such measurements, the pneumatic trough, had been invented during the 1720s by the avid English advocate of Newtonian quantitative experimentation, Stephen Hales, and was coming into increasing use by the 1770s in chemical laboratories. For Lavoisier, however, the measured volume was not an end in itself but a basis for calculating the weight of an air gained or lost. To produce chemical changes in closed spaces on a scale large enough so that the volume changes yielded accurate weights of the airs in question presented Lavoisier with daunting technical problems. In solving them, he was led gradually to design apparatus and to combine components in ways that diverged further and further from the standard equipment of an 18th-century chemical laboratory. Moreover, to make the conversions from volume to weight, he needed to know the densities of the respective airs, another exceedingly difficult technical problem in his time. These basic strategies first emerged in 1773, as Lavoisier pursued the earliest phase of what he saw in advance would be a prolonged study of the various operations—including combustions, calcinations, fermentation, "vegetation," and respiration—that absorb or SEPTEMBER 12, 1994 C&EN 4 1
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release an air. His methods evolved over time, however. Beginning with the basic proofs that metals and combustibles absorb an unspecified portion of the atmosphere in calcinations and burning and that the reduction of metallic calces releases an air, he moved on to more complex problems. His early experiments required reliable results; his later ones demanded increasingly exact results. His early experiments were performed with modified forms of wellknown chemical apparatus; his later ones, with equipment increasingly designed specifically for the particular requirements of his experimental problems. The emergence of an experimental style rooted in methods devised by his predecessors, but quickly acquiring distinctive features, can be followed with special clarity in the successive experiments Lavoisier performed in 1773 to confirm his conjecture of "the existence of an elastic fluid fixed in metallic calces." Having shown already that lead gains weight and absorbs air in calcination, he wished to demonstrate that an elastic fluid is disengaged in the reduction of minium (a lead ore regarded as a form of the metallic calx). Lavoisier reported several of these experiments in 1774 in a treatise entitled "Opuscules physiques et chymiques." He also mentioned there that he had made various other attempts "of which a great number were unsuccessful, the details of which" he would spare the reader. The laboratory notebook in which Lavoisier recorded these experiments still survives, affording historians an opportunity they have not yet exploited to show step-by-step how Lavoisier moved toward the approach he had reached by the time he presented his results in public. In the meantime, even from the two experimental procedures that he did describe in print, we can attain a good overview of two formative stages in the development of his quantitative style. In the first experiment, Lavoisier placed 2 gros (about 7.6 g) of minium mixed with 12 grains of powdered charcoal on a pedestal inside a bell jar inverted over a water bath. He raised
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the water level inside the jar by suction through a siphon and covered the water with a thin layer of oil to prevent the "air" released in the process from being absorbed by the water. He marked the water level with a strip of paper and then focused the rays of the Sun on the minium through a large magnifying lens for several hours. When the reduction was complete and the vessel had cooled, he again observed the water level and estimated that "about 14 cu in of elastic fluid" had been disengaged. The volume of the lead recovered being about Vn cu in, he concluded that "the volume of the elastic fluid disengaged equaled 448 times the volume of the lead reduced." A comparison of Lavoisier's apparatus with an illustration taken from "Vegetable Staticks," published in 1727, in which Hales had published a series of "chymio-static experiments" showing that great quantities of "air" can be disengaged from many substances, reveals immediately that Lavoisier had adopted for his experiments one of the forms of pneumatic troughs that Hales had invented. The only procedural novelty that Lavoisier added was the layer of oil. That was because he expected the air evolved to be similar to "fixed air," which Black had found to be extremely soluble in water. In reporting the quantity of air released as the number of times the volume of the lead in which it had previously been "fixed," Lavoisier also followed the precedent of Hales, who had frequently represented the volume of the air produced in his experiments as so many times the "bulk" of the material that had contained it. Nor was Lavoisier's use of the burning glass to reduce the minium novel: It had already been applied to the calcination of antimony in 1705 by Wilhelm Homberg, one of the most prominent chemists in the early French Academy of Sciences, and by several contemporary members of the academy, in-
77MS elaborate, multipart apparatus, designed and used by Lavoisier in 1773, enabled him to repeat his experiments on the combustion of minium using a much larger sample of the ore. He heated the sample in a retort in a furnace (at far left) and captured the air released in another form of a Hales pneumatic trough (center). The vessel was so large, however, that he needed a vacuum pump to raise the water level. (This two-part apparatus is shown in the right portion of the figure.) With this equipment, Lavoisier determined much more accurately the weights of the various products of his experiment, but he still puzzled over an apparent "loss of weight that I observed/'
Lavoisier designed and used the equipment shown above right and in detail above and belowrightfor fermentation experiments; this setup is displayed at the Museum of Technology of the Conservatory of Arts & Measurements in Paris. eluding Lavoisier, during the previous autumn to study the combustion of diamonds. In this formative experiment of his incipient research program, therefore, Lavoisier exclusively employed methods and procedures well known when he entered the field and with them managed to obtain an important new result. He was, however, dissatisfied with that result. "Although this first experiment was decisive enough," he wrote afterward, "it nevertheless left me with some anxiety." He had been able to use only a small quantity of minium, because of the narrow focus of the burning glass, but had been forced to put it in a large bell jar, so that the jar would not become hot enough to crack. Consequently, he was able to disengage only a few cubic inches of the air into the relatively large volume of air already contained in the jar, and "the least change of temperature would cause sensible errors." To overcome these limitations, Lavoisier designed a far more complicated apparatus, each component of which was a modification of standard chemical equipment. Heating the minium in a retort in a furnace enabled him to work with a much larger quantity, 6 oz, or 24 times the amount used in the first experiment. Because the apparatus had to be both airtight and heated very hot, however, none of the commonly available retorts he tried proved satisfactory. Glass ones cracked, and clay ones leaked. Finally, he had a craftsman make one for him consisting of three pieces of iron soldered together. To capture the air, he connected the retort through carefully luted tubes into another form of a Hales pneumatic trough. This was a combination that Guillaume-François Rouelle, a popular French teacher of chemistry during the previous decades, whose lectures Lavoisier had once followed, had long since introduced into laboratory practice. To handle the volumes with which he intended to work, however, Lavoisier had to enlarge the scale of the pneumatic vessel, which made it too difficult to draw the water level up by suction with his mouth, and he had to add a third element, a vacuum pump, to do the job. Lavoisier realistically assessed the degree of his own originality in the design of his apparatus, when he wrote that he had had
"recourse to an apparatus, the idea for which comes originally from M. Hales, which has since been improved by the late M. Rouelle, and to which I have myself made several changes and additions relative to the circumstances." With this experimental design, Lavoisier was able to obtain 560 cu in of air, a volume he could measure with considerable accuracy. This was, he wrote, "equal to 747 times the volume of lead which served to form it." If he had stopped there, Lavoisier would have achieved no more than a more accurate version of his first experiment. "Reflecting" on the result, however, he cast it in another form. Having weighed the minium before the experiment and the lead found in the retort afterward, he determined that the "loss of weight had been 6 gros 6 grains," about 23 g. If one assumed that the density of the air released was equal to that of the atmosphere, then the volume found would weigh only 3 gros 41 grains. If the air released was the same as that released in actions of acids on chalk, then, as he had estimated from experiments he had previously performed on that process, its density was about 0.575 grain per cu in, and the weight would be 4 gros 34 grains. Even then, "there still remained a deficit of 1 gros 44 grains." That was no minor error, as it amounted to more than one quarter of the weight lost by the lead. Lavoisier looked for possible sources of this "loss of weight that I observed." Having noticed a few drops of water in the receiver after each experiment of this type, he "suspected" that the minium might have contained some water that separated during the reduction. When he carried out an experiment to check this possibility, however, he could account for only 24 grains of the deficit. The only other cause for the missing SEPTEMBER 12,1994 C&EN 43
SPECIAL REPORT to be only to demonstrate that an elastic fluid exists in a metallic calx by showing that a large quantity is released from a calx when it is reduced. That he followed Hales' example, not only in the design of the experiment but also in presenting the volumes as the relevant quantities, suggests a person who did not yet know that weight comparisons would become his fundamental criterion for interpreting compositions and processes. In the second experiment, he first reported volumes as in the first one, and then he shifted to weights. That he made no comment on the reason for this shift suggests that he made the transition within Beginning in 1773, Lavoisier conducted a lengthy study of the various operations—including respiration, shown here—that absorb or release an "air." Drawing is by Madame Lavoisier. the local context of this particular experimental problem, without fully grasping the broader implications it weight that he could think of was that "the elastic fluid diswould eventually come to have. engaged from minium is more dense than that released" in acid-alkali neutralizations. To clarify that possibility, he reLavoisier's description of the experiment gives no intimaalized, he would have to embark on a major research tion that he intended initially to balance the weight of the project, requiring special apparatus, to "determine the relareduction products with the weight of the initial ore to sustive densities of the different elastic fluids that are disentain an argument that the ore was composed of the lead and gaged from bodies." the elastic fluid released. When it turned out that they were far from equal, he assumed that the "deficit" could be elimThe methods and the reasoning with which Lavoisier reinated if he could find another product that he had oversponded to the problems encountered in this series of exlooked or correct the value he had used to calculate one of periments display, in nascent form, characteristics that he the weights. He never entertained the possibility that the continued to develop and consolidate through the remainquantity of matter after the operation was really unequal to der of his experimental career. A close consideration of their that before the operation. That is to be expected, if, as histonature can, therefore, reveal much about the foundation of rians assert, the "conservation of matter" had long been an the quantitative methods through which he eventually implicit assumption in chemical operations. transformed the practice of chemistry. This interpretation can only be suggestive, because any Historians have looked far and wide for the sources of account of scientific investigation based on the scientist's Lavoisier's balance-sheet method. Underlying their search has published reports is indirect. Scientists typically reconstruct been an assumption that, because chemistry was predomiwhat they have done in light of what they have learned nantly qualitative before he entered the field, he must have during the process. Yet, it is unlikely that Lavoisier would brought his quantitative method to his chemical investigaretrospectively have portrayed his experimental pathway as tions from somewhere else—whether that be experimental more improvised than it actually was. A full reconstruction physics, commercial account ledgers, or some other external of his experimental pathway during these crucial months of domain. In doing so, they have generally overlooked the more 1773, such as can be done with Lavoisier's surviving labostraightforward possibility that the source of his methods was ratory notebooks, will, I suspect, reinforce this view of a the very domain in which Lavoisier developed these methods; young scientist gradually acquiring, as he proceeded, the that is, that they were the product of his day-by-day experielements of the scientific style that so distinguished the maence as he attacked the problem he had chosen for his reture scientist he later became. search agenda, the fixation and release of airs. He may not have brought to these problems the foreknowledge that deterWhy should a fine-structured reconstruction of this early mining the weights of the substances that enter and leave phase of Lavoisier's experimental pathway concern anyone such processes, in keeping with a principle that they must equal except specialist historians of science? Why should the inone another, would become his steady guide to the solution of choate beginnings of his research program interest modern these problems. He may instead have come only gradually to research chemists, who may want to know only what realize that the solutions he found for particular problems could Lavoisier contributed to the permanent structure of their be generalized into a widely applicable method. field? More is involved here than obtaining further details about a certain stage in Lavoisier's scientific career. The The pattern visible in the experiments previously described great scientists of the past are popularly regarded as geniussupports such an interpretation. His initial objective appeared 44
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es who came to their chosen tasks with unique insights to which ordinary mortals have no access or whose whole ca reers consisted of the systematic working out of a farsighted vision. If some of them turn out instead to have had to feel their way into the unknown, learning what they were doing as they did it, knowing in advance just enough to take the next step, then the gulf between them and more ordinary research scientists of the present becomes less im mense. The achievements of historic figures are no less im pressive, but their day-to-day experiences are less foreign to those who read or write about them today. This is not the place to trace the further development of Lavoisier's quantitative methods as he pursued his experi mental program over the next two decades. I have elsewhere described in great detail the later stages of his investigative pathway, during which he applied the balance-sheet method and his growing repertoire of apparatus and methods to in creasingly difficult problems. It will suffice to mention here that, throughout his scientific life, when he measured the quantities of materials before and after a chemical operation, they seldom came out to be equal. Lavoisier consistently re sponded to these discrepancies in the same way he did dur ing his early experiments: He tried to identify sources of error in his experiments to account for them. Only occasionally did he allude to the underlying principle justifying his pragmatic approach. Lavoisier never tried to prove that matter is con served in chemical changes. That was so axiomatic to him that it would have seemed completely illogical to think otherwise. Are the chemical textbooks wrong, then, to state that Lavoisier was the first to realize that mass was the funda mental quantity conserved during chemical reactions? Put so starkly, such phrases are clearly misleading; but with rel atively modest modifications, they can be made to fit with what we know historically about Lavoisier and his times. Lavoisier was neither the first to express a principle of con servation of matter nor to apply it in practice. He was the first, however, to show that by using such a principle to guide his experimental practice he could arrive at results powerful enough to transform his field. The most cogent phrase in his general statement of the principle, quoted pre viously, was that "It is on this principle that the whole art of making experiments is founded." That claim was not lit erally true, even when he made it in 1789; but by making it the principle on which his own art of making experiments was founded, he had ensured that it would become more and more true of the chemistry of the future. I mentioned earlier the disparity between the outlook of historians of science, who focus on past science within its own temporal context, and that of scientific textbooks, which con tinue to fix on those past achievements that remain in the structure of science today. I would argue that both approach es are valid within their own contexts. History is distorted if detailed accounts of past scientific eras eliminate the ideas and investigations that were significant in their own time but did not survive. It is also distorted if those ideas are treated as "mistakes" because they did not withstand scrutiny in the light of later knowledge. There are, however, achievements of the past that are of enduring value in science. Such achieve ments are no longer regarded as discoveries of timeless truths, but many of them will last as long as science is practiced in the general manner that is familiar today. It seems to me fully appropriate that today's scientists take a special interest in the
origins of such lasting parts of the structure of their current science and that science textbooks devote to such topics the very limited space they can spare for history. That is not to say that the brief accounts one finds in cur rent textbooks are satisfactory as they stand. William B. Jensen, a professor of chemistry at the University of Cincin nati, who has involved himself more deeply than most chemists in the history of his field, has rightly taken chem ists to task for almost totally ignoring the existing historical literature when they themselves write on historical subjects. This neglect is obvious among authors of chemical text books. Even a modicum of attention would protect them from the blatant factual errors that occur frequently in their brief accounts. Were they to look more deeply into what historians have written about the episodes they wish to summarize, they would not find all of the issues that cur rently concern historians relevant to their own interests. They would find, however, that moderate adjustments in the canonical stories they repeat through successive editions and generations of textbooks could make them historically accurate while still preserving those features of the past that they believe relevant for today's students of science. •
Frederic L. Holmes is a profes sor and chairman of the section on the history of medicine at Yale University School of Med icine. After receiving a bache lor's degree in quantitative biol ogy from Massachusetts Insti tute of Technology, Holmes earned a doctorate in the histo ry of science from Harvard Uni versity and began an academic career that took him to ΜΓΓ, Yale University, the University of Western Ontario, and back to Yale, where he assumed his present position in 1979. Holmes studies what he calls the fine structure of scientific in vestigation, examining the day-to-day activity of great scientists to try to uncover how they work and what leads to their discover ies. Among the scientists he has studied are Lavoisier, the 19thcentury French physiologist Claude Bernard, and the early 20thcentury German and British biochemist Hans Krebs. Holmes served as vice president and then president of the History of Science Society from 1979 to 1983. One of his most recent awards is this year's Dexter Award for outstanding achievement given by the American Chemical Society's Division of the History of Chemis try. He is the author of six booh, including "Lavoisier and the Chemistry of Life: An Exploration of Scientific Creativity" (Univer sity of Wisconsin Press, 1985).
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