FONTANA HISTORY OF CHEMISTRY

(Editor: Roy Porter)

THE FONTANA HISTORY OF
CHEMISTRY

William H. Brock

CONTENTS

COVER

TITLE PAGE

PREFACE TO THE FONTANA HISTORY OF SCIENCE

BIBLIOGRAPHICAL NOTE

INTRODUCTION

1 On the Nature of the Universe and the Hermetic Museum

Chinese Alchemy

Greek Alchemy

Arabic and Medieval Alchemy

Newton’s Alchemy

The Demise of Alchemy and its Literary Tradition

2 The Sceptical Chymist

Paracelsianism

Helmontianism

The Acid-Alkali Theory

A Sceptical Chemist

Boyle’s Physical Theory of Matter

The Vacuum Boylianum and its Aftermath

Newton’s Chemistry

The Phlogistonists

Conclusion

3 Elements of Chemistry

A Scientific Civil Servant

The Chemistry of Air

The Chemical Revolution

The Aftermath

Conclusion

4 A New System of Chemical Philosophy

Dalton’s ‘New System’

Dalton’s Life

The Atomic Theory

The Origins of Dalton’s Theory

Electrifying Dalton’s Theory

Chemical Reactivity

Prout’s Hypothesis

Volumetric Relations

Scepticism Towards Atomism

Conclusion

5 Instructions for the Analysis of Organic Bodies

Purity

The Basis of Chemistry

The Supply of Apparatus and Chemicals

Liebig, Organic Analysis and the Research School

Conclusion

6 Chemical Method

Classifying by Radicals

Classification by Types

7 On the Constitution and Metamorphoses of Chemical Compounds

The Establishment of Quantivalence

Kekulé and the Theory of Chemical Structure

The Triumph of Structural Theory

8 Chemistry Applied to Arts and Manufactures

The Alkali Industry

Dyestuffs and Colouring

9 Principles of Chemistry

Sorting the Elements

The Rare Earths

The Inert Gases

Manufacturing Elements

Mendeleev’s Principles

Conclusion

10 On the Dissociation of Substances Dissolved in Water

Proto-Physical Chemistry

Raoult and van’t Hoff

Electrochemistry from Faraday to Arrhenius

The Ionic Theory

The Reception of the Ionic Theory

11 How to Teach Chemistry

Frankland’s State-sponsored Chemistry

Armstrong’s Heuristic Method

Twentieth-century Developments in Teaching

The Laboratory

12 The Chemical News

Forming Chemical Societies

The Chemical Periodical

William Crookes, Chemical Editor

13 The Nature of the Chemical Bond

The Lewis Atom

Spreading the Electronic Theory

The Pauling Bond

14 Structure and Mechanism in Organic Chemistry

The Lapworth-Thiele-Robinson Tradition

The Michael-Flürscheim- Vorlãnder Tradition

The Electronic Theory of Organic Reactions

Organizing the Structure of Organic Chemistry

The Kinetics of Mechanisms

The Spread of Physical Organic Chemistry

Aromaticity

The Non-classical Ion Debate

Conclusion

15 The Renaissance of Inorganic Chemistry

Werner’s New Ideas

Sidgwick’s Electronic Interpretation of Co-ordination Chemistry

Australian Chemistry

Australian and Japanese Chemistry

Co-ordination Chemistry in Australia

Nyholm’s Renaissance

Conclusion

16 At the Sign of the Hexagon

Synthesis

Industrial Chemistry

Chemistry and the Environment

EPILOGUE

APPENDIX: HISTORY OF CHEMISTRY MUSEUMS AND COLLECTIONS

NOTES

BIBLIOGRAPHICAL ESSAY

INDEX

ACKNOWLEDGEMENTS

ABOUT THE AUTHOR

OTHER BOOKS BY

COPYRIGHT

ABOUT THE PUBLISHER

‘Chemical Industry, Upheld by Pure Science Sustains the Production of Man’s Necessities’, frontispiece to A. Cressy Morrison, Man in A Chemical World: the service of chemical industry (London & New York: Scribner’s, 1937) Reproduced courtesy of Scribner’s, Collier Macmillan, New York

PREFACE TO THE FONTANA HISTORY OF SCIENCE

Academic study of the history of science has advanced dramatically, in depth and sophistication, during the last generation. More people than ever are taking courses in the history of science at all levels, from the specialized degree to the introductory survey; and, with science playing an ever more crucial part in our lives, its history commands an influential place in the media and in the public eye.

Over the past two decades particularly, scholars have developed major new interpretations of science’s history. The great bulk of such work, however, has been published in detailed research monographs and learned periodicals, and has remained hard of access, hard to interpret. Pressures of specialization have meant that few survey works have been written that have synthesized detailed research and brought out wider significance.

It is to rectify this situation that the Fontana History of Science has been set up. Each of these wide-ranging volumes examines the history, from its roots to the present, of a particular field of science. Targeted at students and the general educated reader, their aim is to communicate, in simple and direct language intelligible to non-specialists, well-digested and vivid accounts of scientific theory and practice as viewed by the best modern scholarship. The most eminent scholars in the discipline, academics well-known for their skills as communicators, have been commissioned.

The volumes in this series survey the field and offer powerful overviews. They are intended to be interpretative, though not primarily polemical. They do not pretend to a timeless, definitive quality or suppress differences of viewpoint, but are meant to be books of and for their time; their authors offer their own interpretations of contested issues as part of a wider, unified story and a coherent outlook.

Carefully avoiding a dreary recitation of facts, each volume develops a sufficient framework of basic information to ensure that the beginner finds his or her feet and to enable student readers to use such books as their prime course-book. They rely upon chronology as an organizing framework, while stressing the importance of themes, and avoiding the narrowness of anachronistic ‘tunnel history’. They incorporate the best up-to-the-minute research, but within a larger framework of analysis and without the need for a clutter of footnotes – though an attractive feature of the volumes is their substantial bibliographical essays. Authors have been given space to amplify their arguments and to make the personalities and problems come alive. Each volume is self-contained, though authors have collaborated with each other and a certain degree of cross-referencing is indicated. Each volume covers the whole chronological span of the science in question. The prime focus is upon Western science, but other scientific traditions are discussed where relevant.

This series, it is hoped, will become the key synthesis of the history of science for the next generation, interpreting the history of science for scientists, historians and the general public living in a uniquely science-oriented epoch.

ROY PORTER

Series Editor

BIBLIOGRAPHICAL NOTE

So as not to encumber the book with footnotes, I have employed the simple device of indicating the source of a quotation by a superscript number. These sources will be found in the relevant notes section (often briefly) and more details are given in the bibliographical essay, which not only provides an up-to-date guide to the published literature, but is also my acknowledgement to the hundreds of historians whose work has guided me in writing this book. For historical convenience, trivial rather than systematic (IUPAC) names are used for inorganic compounds, viz. ‘alum’ rather than ‘aluminium potassium sulphate-12-water’. In the case of organic compounds, systematic names are used only for more complex compounds.

INTRODUCTION

That all plants immediately and substantially stem from the element water alone I have learnt from the following experiment. I took an earthern vessel in which I placed two hundred pounds of earth dried in an oven, and watered with rain water. I planted in it the stem of a willow tree weighing five pounds. Five years later it had developed a tree weighing one hundred and sixty-nine pounds and about three ounces. Nothing but rain (or distilled water) had been added. The large vessel was placed in earth and covered by an iron lid with a tin-surface that was pierced with many holes. I have not weighed the leaves that came off in the four autumn seasons. Finally I dried the earth in the vessel again and found the same two hundred pounds of it diminished by about two ounces. Hence one hundred and sixty-four pounds of wood, bark and roots had come up from water alone.

(JOAN-BAPTISTA VAN HELMONT, 1648)

Helmont’s arresting experiment and conclusion capture the essence of the problem of chemical change. How and why do water and air ‘become’ the material of a tree – or, if that sounds too biochemical, how and why do hydrogen and oxygen become water? How does brute matter assume an ordered and often symmetrical solid form in the non-living world? Helmont’s experiment also raises the issue of the balance between qualitative and quantitative reasoning in the history of chemistry. Helmont’s observations are impeccably quantitative and yet, because he ignored the possible role of air in the reaction he was studying, and since he knew nothing of the hidden variables of nutrients dissolved in the water or of the role of the sun in providing the energy of photosynthesis, his reasoning was to prove qualitatively fallacious.

Chemistry is best defined as the science that deals with the properties and reactions of different kinds of matter. Historically, it arose from a constellation of interests: the empirically based technologies of early metallurgists, brewers, dyers, tanners, calciners and pharmacists; the speculative Greek philosophers’ concern whether brute matter was invariant or transformable; the alchemists’ real or symbolic attempts to achieve the transmutation of base metals into gold; and the iatrochemists’ interest in the chemistry and pathology of animal and human functions. Partly because of the sheer complexity of chemical phenomena, the absence of criteria and standards of purity, and uncertainty over the definition and identification of elements (the building blocks of the chemical tree), but above all because of the lack of a concept of the gaseous state of matter, chemistry remained a rambling, puzzling and chaotic area of natural philosophy until the middle of the eighteenth century. The development of gas chemistry after 1740 gave the subject fresh empirical and conceptual foundations, which permitted explanations of reactions in terms of atoms and elements to be given.

Using inorganic, or mineral, chemistry as its paradigm, nineteenth-century chemists created organic chemistry, from which emerged the fruitful ideas of valency and structure; while the advent of the periodic law in the 1870s finally provided chemists with a comprehensive classificatory system of elements and a logical, non-historically based method for teaching the subject. By the 1880s, physics and chemistry were drawing closer together in the sub-discipline of physical chemistry. Finally, the discovery of the electron in 1897 enabled twentieth-century chemists to solve the fundamental problems of chemical affinity and reactivity, and to address the issue of reaction mechanisms – to the profit of the better understanding of synthetic pathways and the expansion of the chemical and pharmaceutical industries.

Returning to Helmont’s tree, an arboreal image and metaphor can be usefully deployed. The historical roots of chemistry were many, but produced no sturdy growth until the eighteenth century. In this healthy state, branching into the sub-disciplines of inorganic, organic and physical chemistry occurred during the nineteenth century, with further, more complex branching in the twentieth century as instrumental techniques of analysis became ever more sophisticated and powerful. Growth was, however, dependent upon social and environmental conditions that either nurtured or withered particular theories and experimental techniques.

Although conceived as a work of synthesis for the 1990s (there has been no extensive one-volume history of chemistry published since that of Aaron Ihde in 1964), The Fontana History of Chemistry draws extensively upon some of the themes and personalities treated in my own research as well as upon the post-war work of other historians of chemistry. Gone are the days of Kopp and Partington, when a history of chemistry could be allowed to unfold slowly in four magisterial and detailed volumes. My volume is designed to be neither a complete nor a detailed narrative; nor is it a work of reference like James R. Partington’s History of Chemistry, to which I, like all historians of chemistry, remain profoundly indebted. I am particularly conscious, for example, of ignoring developments such as photography (that most chemical of nineteenth-century arts), spectroscopy, Russian chemistry, or the emergence of ideas concerning atomic structure. In some cases, as with the omission of any emphasis on the role of Avogadro’s hypothesis in the nineteenth-century determination of atomic and molecular weights, the lacuna is justified historiographically; in other cases, as with my muted references to the roles of rhetoric and language in chemistry, it was a decision not to introduce a contemporary historiographic fashion in a book largely dedicated to a readership of chemists and science students.

In yet other cases, choices of subject matter, and therefore of omission, have stemmed from the decision to structure chapters around seminal texts, their writers and the schools of chemists associated with them. This principle of organization has been freely borrowed from Derek Gjertsen’s The Classics of Science (New York: Lilian Barber, 1984) and a book edited by Jack Meadows, The History of Scientific Development (Oxford: Phaidon, 1987), with which I was associated. To use a metaphor from organic chemistry, the book is arranged around textual types, each title standing symbolically for a paradigm, a theoretical, instrumental or organizational change or development that seems significant to the historian of chemistry. I have tried to lay equal emphasis upon the practical (analytical) nature of past chemistry as much as on its theoretical content, and, although it would have taken a volume in itself to analyse the development of industrial chemistry, I have tried to provide the reader with an inkling of the application of chemistry. Wherever possible I have stressed the significance of chemistry for the development of other areas of science, and I have noted some of the false steps and blind alleys of past chemistry as much as the developments that still remain part of the scientific record. Echoing Ihde’s incisive treatment, The Fontana History of Chemistry also provides a generous treatment of twentieth-century chemistry – albeit within the constraints of my chosen themes and typologies. I have tried wherever possible to illustrate the international nature of the chemical enterprise since the seventeenth century.

Helmont’s tree leads us both backwards and forwards in time – forwards to when evidence accrued that air (and gases) did participate in chemical change, and backwards to the ancient traditions of elements and of transmutation that Helmut had inherited. The book opens with the roots of chemistry and the social, economic and religious environments that promoted it before the time of Helmont. In particular, the opening chapter examines early chemical technologies and their rationalization by Greek philosophers in theories of elements or, more iconoclastically, in terms of corpuscules and atoms. The tree enters here again, for one of the perennial proofs for the existence of elements and for their number was the destructive distillation of wood by fire – an important phenomenon empirically (for it was the model for distillation techniques generally) and cognitively because it was the basis of the concepts of analysis and synthesis. Chemistry was, and is, concerned with the analysis of substances into their elements and the synthesis of substances from their elements or immediate principles.

The possibility of manipulating elementary matter into substances of commercial or – at the extreme – of spiritually uplifting value, such as silver and gold or an elixir of life, led to alchemy. The latter’s origin, as well as its formal connections with chemistry, are complex and even contentious. However, our contemporary demand for science to have empirical validation, as well as our respect for the technological manipulation of Nature’s resources for the benefit of humankind, can be traced back to the philosophical spirit of enquiry that underpinned alchemical investigations. And it goes without saying that alchemy provided early chemistry with much of its apparatus and manipulative techniques, as well as the idea of a formal symbolic language for practitioners of the art.

Each of the sciences, no doubt, has its own difficulties and peculiarities when it comes to presenting its historical development to a diverse audience of professional historians, scientists, students and laypersons; but chemistry, like mathematics, possesses a particularly intimidating obstacle in its language and symbolism, which potentially obscures what are usually quite simple theoretical ideas and experimental techniques. As William Crookes noted in 1865 when reviewing a book on stuttering that had been inappropriately sent to Chemical News for review:

Chemists do not usually stutter. It would be very awkward if they did, seeing that they have at times to get out such words as methylethylamylophenylium.

However, if (as Peter Morris has noted) the historian avoids chemical detail and language, the scientific story become exigious and almost trivial. For this reason, while the first twelve chapters should present little difficulty to a sophisticated general reader, I have not hesitated to use technical language in the five chapters that are devoted to twentieth-century chemistry. Because this is a history, and not a textbook, of chemistry, I have not defined and explained symbols, equations and technical vocabulary. These chapters will present little difficulty to readers who have a secondary or high-school foundation in chemistry (and will have the privilege of being critical of my treatment). At the same time, it is to be hoped that there is sufficient of a human interest story in the intellectual and experimental worlds of Pauling, Ingold, Nyholm, Woodward and the other giants of twentieth-century chemistry, to propel the non-chemical reader towards the final pages.

The history of chemistry has served and continues to serve many purposes: didactic and pedagogic, professional and defensive, patriotic and nationalistic, liberalizing and humanizing. As I write, especially in America, where words like ‘chemical’, ‘synthetic’ and ‘additive’ have unfortunately become associated with the pollution, poisoning and disasters caused by humans, the history of chemistry has come to be seen by leaders of chemical industry and educators as a possible way of revaluing chemical currency: that is, of demonstrating not only the ways in which chemistry plays a fundamental role in nature and our understanding of cosmic processes, but also how it is essential to the economy of twentieth-century societies. In other words, the history of chemistry not only informs us about our great chemical heritage, but justifies the future of chemistry itself. Such a justification echoes the liberal and moving words of the first major historian of chemistry, Hermann Kopp¹:

The alchemists of past centuries tried hard to make the elixir of life … These efforts were in vain; it is not in our power to obtain the experiences and views of the future by prolonging our lives forward in this direction. However, it is possible and in a certain way to prolong our lives backwards, by acquiring the experiences of those who existed before us and by learning to know their views as if we were their contemporaries. The means for doing this is also an elixir of life.

It is in this spirit that The Fontana History of Chemistry has been written.

1 On the Nature of the Universe and the Hermetic Museum

Maistryefull merveylous and Archimastrye Is the tincture of holy Alkimy;

A wonderful Science, secrete Philosophie,

A singular grace and gifte of th’Almightie:

Which never was found by labour of Mann,

But it by Teaching, or by Revalacion begann.

(THOMAS NORTON, The Ordinall of Alchemy, c. 1477)

In 1477, having succeeded after years of study in preparing both the Great Red Elixir and the Elixir of Life, only to have them stolen from him, Thomas Norton of Bristol composed the lively early English poem, The Ordinall of Alchemy. Here he expounded in an orderly fashion the procedures to be adopted in the alchemical process, just as an Ordinal lists chronologically the order of the Church’s liturgy for the year. Unfortunately, although the reader learns much of would-be alchemists’ mistakes, and of the ingredients and apparatus, of the subtle and gross works, and of the financial backing, workers and astrological signs needed to conduct the ‘Great Work’ successfully, the secret of transmutation remains tantalisingly obscure.

The historian Herbert Butterfield once dismissed historians of alchemy as ‘tinctured with the kind of lunacy they set out to describe’; for this reason, he thought, it was impossible to discover the actual state of things alchemical. Nineteenth-century chemists were less embarrassed by the subject. Justus von Liebig, for example, used the following notes to open his Giessen lecture course:

Distinction between today’s method of investigating nature from that in olden times. History of chemistry, especially alchemy …

Liebig’s presumption, still widespread, was that alchemy was the precursor of chemistry and that modern chemistry arose from a rather dubious, if colourful, past¹:

The most lively imagination is not capable of devising a thought which could have acted more powerfully and constantly on the minds and faculties of men, than that very idea of the Philosopher’s Stone. Without this idea, chemistry would not now stand in its present perfection …[for] in order to know that the Philosopher’s Stone did not really exist, it was indispensable that every substance accessible … should be observed and examined.

To most nineteenth-century chemists, and historians and novelists, alchemy had been a human aberration, and the task of the historian seemed to be to sift the wheat from the chaff and to discuss only those alchemical views (chiefly practical) that had contributed positively to the development of scientific chemistry. As one historiographer of the subject has put it²:

[the historian] merely split open the fruit to get the seeds, which were for him the only things of value. In the fruit as a whole, its shape, colour, and smell, he had no interest.

But what was alchemy? The familiar response is that it involved the pursuit of the transmutation of base metals such as lead into gold. In practice, the aims of the alchemist were often a good deal broader, and it is only because we take a false perspective in seeing chemistry as arising from alchemy that we normally narrowly focus on to alchemy’s concern with the transformation of metals. However, as Carl Jung pointed out in his study Psychology and Alchemy, there are similarities between the emblems, symbols and drawings used in European alchemy and the dreams of ordinary twentieth-century people. One does not have to believe in psychoanalysis or Jungism to see that the most obvious explanation for this is that alchemical activities were often concerned with a spiritual quest by humankind to make sense of the universe. It follows that alchemy could have taken different forms in different cultures at different times.

At the beginning of the twentieth century, after the elderly French chemist, Marcellin Berthelot, had made available French translations of a number of Greek alchemical texts, an American chemist, Arthur J. Hopkins (1864–1939), showed how they could be interpreted as practical procedures involving dyeing and a series of colour changes. He was able to show how Greek alchemists, influenced by Greek philosophy and the practical knowledge of dyers, metallurgists and pharmacists, had followed out three distinctive transmutation procedures, which involved either tincturing metals or alloys with gold (as described in the Leiden and Stockholm papyri), or chemically manipulating a ‘prime matter’ mixture of lead, tin, copper and iron through a series of black, white, yellow and purple stages (which Hopkins was able to replicate in the laboratory), or, as in the surviving fragments of Mary the Jewess, using sublimating sulphur to colour lead and copper.

While Hopkins’ explanation of alchemical procedures has formed the basis of all subsequent historical work on early alchemical texts, and while Jung’s psychological interpretation has stimulated interest in alchemical language and symbolism, it was the work of the historian of religion, Mircea Eliade (1907–86), who, following studies of contemporary metallurgical practices of primitive peoples in the 1920s, firmly placed alchemy in the context of anthropology and myth in Forgerons et Alchimistes (1956).

These three twentieth-century interpretations of alchemy, dyeing, psychological individuation and anthropology, together with the historical investigation of Chinese alchemy being undertaken by Joseph Needham and Nathan Sivin in the 1960s, stimulated the late Harry Sheppard to devise a broad definition of the nature of alchemy³:

Alchemy is a cosmic art by which parts of that cosmos – the mineral and animal parts – can be liberated from their temporal existence and attain states of perfection, gold in the case of minerals, and for humans, longevity, immortality, and finally redemption. Such transformations can be brought about on the one hand, by the use of a material substance such as ‘the philosopher’s stone’ or elixir, or, on the other hand, by revelatory knowledge or psychological enlightenment.

The merit of such a general definition is not only that it makes it clear that there were two kinds of alchemical activity, the exoteric or material and the esoteric or spiritual, which could be pursued separately or together, but that time was a significant element in alchemy’s practices and rituals. Both material and spiritual perfection take time to achieve or acquire, albeit the alchemist might discover methods whereby these temporal processes could be speeded up. As Ben Jonson’s Subtle says in The Alchemist, ‘The same we say of Lead and other Metals, which would be Gold, if they had the time.’ And in a final sense, the definition implies that, for the alchemist, the attainment of the goals of material, and/or spiritual, perfection will mean a release from time itself: materially through riches and the attainment of independence from worldly economic cares, and spiritually by the achievement of immortality.

The definition also helps us to understand the relationship between the alchemies of different cultures. Although some historians have looked for a singular, unique origin for alchemy, which then diffused geographically into other cultures, most historians now accept that alchemy arose in various (perhaps all?) early cultures. For example, all cultures that developed a metallurgy, whether in Siberia, Indonesia or Africa, appear to have developed mythologies that explained the presence of metals within the earth in terms of their generation and growth. Like embryos, metals grew in the womb of mother Nature. The work of the early metallurgical artisan had an obstetrical character, being accompanied by rituals that may well have had their parallel in those that accompanied childbirth. Such a model of universal origin need not rule out later linkages and influences. The idea of the elixir of life, for example, which is found prominently in Indian and Chinese alchemy, but not in Greek alchemy, was probably diffused to fourteenth-century Europe through Arabic alchemy. The biochemist and Sinologist, Joseph Needham, has called the belief and practice of using botanical, zoological, mineralogical and chemical knowledge to prepare drugs or elixirs ‘macrobiotics’, and has found considerable evidence that the Chinese were able to extract steroid preparations from urine.

Alongside macrobiotics, Needham has identified two other operational concepts found in alchemical practice throughout the world, aurifiction and aurifaction. Aurifiction, or gold-faking, which is the imitation of gold or other precious materials – whether as deliberate deception or not depending upon the circumstances (compare modern synthetic products) – is associated with technicians and artisans. Aurifaction, or gold-making, is ‘the belief that it is possible to make gold (or “a gold”, or an artificial “gold”) indistinguishable from or as good as (if not better than) natural gold, from other different substances’. This, Needham suggests, tended to be the conviction of natural philosophers rather than artisans. The former, coming from a different social class than the aurifictors, either knew nothing of the assaying tests for gold, or jewellery, or rejected their validity.

CHINESE ALCHEMY

Aurifactional alchemical ideas and practices were prevalent as early as the fourth century BC in China and were greatly influenced by the Taoist religion and philosophy devised by Lao Tzu (c. 600 BC) and embodied in his Tao Te Ching (The Way of Life). Like the later Stoics, Taoism conceived the universe in terms of opposites: the male, positive, hot and light principle, ‘Yang’; and the female, negative, cool and dark principle, ‘Yin’. The struggle between these two forces generated the five elements, water, fire, earth, wood and metal, from which all things were made:

Unlike later Greco-Egyptian alchemy, however, the Chinese were far less concerned with preparing gold from inferior metals than in preparing ‘elixirs’ that would bring the human body into a state of perfection and harmony with the universe so that immortality was achieved. In Taoist theory this required the adjustment of the proportions of Yin and Yang in the body. This could be achieved practically by preparing elixirs from substances rich in Yang, such as red-blooded cinnabar (mercuric sulphide), gold and its salts, or jade. This doctrine led to careful empirical studies of chemical reactions, from which followed such useful discoveries as gunpowder – a reaction between Yin-rich saltpetre and Yang-rich sulphur – fermentation industries and medicines that, according to Needham, must have been rich in sexual hormones. As in western alchemy, Taoist alchemy soon became surrounded by ritual and was more of an esoteric discipline than a practical laboratory art.

Belief in the transformation of blood-like cinnabar into gold dates from 133 BC when Li Shao-chun appealed to the Emperor Wu Ti to support his investigations:

Summon spirits and you will be able to change cinnabar powder into yellow gold. With this yellow gold you may make vessels to eat and drink out of. You will increase your span of life, you will be able to see the hsien of the P’eng-lai [home of the Immortals] that is in the midst of the sea. Then you may perform the sacrifices fang and shang and escape death.

From then on, many Chinese texts referred to the consumption of potable gold. This wai tan form of alchemy, which was systematized by Ko Hung in the fourth century AD, was not, however, the only form of Chinese alchemy.

The Chinese also developed nai tan, or physiological, alchemy, in which longevity and immortality were sought not from the drinking of an external elixir, but from an ‘inner elixir’ provided by the human body itself. In principle, this was obtained from the adept’s own body by physiological techniques involving respiratory, gymnastic and sexual exercises. With the ever-increasing evidence of poisoning from wai tan alchemy, nai tan became popular from the sixth century AD, causing a diminution of laboratory practice. On the other hand, nai tan seems to have encouraged experimentation with body fluids such as urine, whose ritualistic use may have led to the Chinese isolation of sex hormones.

As Needham has observed, medicine and alchemy were always intimately connected in Chinese alchemy, a connection that is also found in Arabic alchemy. Since Greek alchemy laid far more stress on metallurgical practices – though the preparation of pharmaceutical remedies was also important – it seems highly probable that Arabic writers and experimentalists were ‘deeply influenced by Chinese ideas and discoveries’.

There is some evidence that the Chinese knew how to prepare dilute nitric acid. Whether this was prepared from saltpetre – a salt that is formed naturally in midden heaps – or whether saltpetre followed the discovery of nitric acid’s ability to dissolve other substances, is not known. Scholars have speculated that gunpowder – a mixture of saltpetre, charcoal and sulphur – was first discovered during attempts to prepare an elixir of immortality. At first used in fireworks, gunpowder was adapted for military use in the tenth century. Its formula had spread to Islamic Asia by the thirteenth century and was to stun the Europeans the following century. Gunpowder and fireworks were probably the two most important chemical contributions of Chinese alchemy, and vividly display the power of chemistry to do harm and good.

As in the Latin west, most of later Chinese alchemy was little more than chicanery, and most of the stories of alchemists’ misdeeds that are found in western literature have their literary parallels in China. Although the Jesuit missions, which arrived in China in 1582, brought with them information on western astronomy and natural philosophy, it was not until 1855 that western chemical ideas and practices were published in Chinese. A major change began in 1865 when the Kiangnan arsenal was established in Shanghai to manufacture western machinery. Within this arsenal a school of foreign languages was set up. Among the European translators was John Fryer (1839–1928), who devoted his life to translating English science texts into Chinese and to editing a popular science magazine, Ko Chih Hui Phien (Chinese Scientific and Industrial Magazine).

GREEK ALCHEMY

Although it is possible to argue that modern chemistry did not emerge until the eighteenth century, it has to be admitted that applied, or technical, chemistry is timeless and has prehistoric roots. There is conclusive evidence that copper was smelted in the Chalcolithic and early Bronze Ages (2200 to 700 BC) in Britain and Europe. Archaeologists recognize the existence of cultures that studied, and utilized and exploited, chemical phenomena. Once fire was controlled, there followed inevitably cookery (gastronomy, according to one writer, was the first science), the metallurgical arts, and the making of pottery, paints and perfumes. There is good evidence for the practice of these chemical arts in the writings of the Egyptian and Babylonian civilizations. The seven basic metals gave their names to the days of the week. Gold, silver, iron, mercury, tin, copper and lead were all well known to ancient peoples because they either occur naturally in the free state or can easily be isolated from minerals that contain them. For the same reason, sulphur (brimstone) and carbon (charcoal) were widely known and used, as were the pigments, orpiment and stibnite (sulphides of arsenic and antimony), salt and alum (potassium aluminium sulphate), which was used as a mordant for vegetable dyes and as an astringent.

The methods of these early technologists were, of course, handed down orally and by example. Our historical records begin only about 3000 BC. With the aid of techniques derived ultimately from the kitchen, these artisans extracted medicines, perfumes and metals from plants, animals and minerals. Their goldsmiths constructed wonderful pieces of jewellery and their metallurgists worked familiarly with the common metals and their alloys, associating them freely with the planets. Jewellers were particularly interested in the different coloured effects of the various alloys that metallurgists prepared and in the staining of metallic surfaces by salts and dyes, or the staining of stones and minerals that imitated the colours of precious minerals. In fact, throughout the east we find an emphasis upon colour, and the establishment of what Needham describes as the industry of aurifiction. Clearly there existed a professional class of artisans, metallurgists and jewellers who specifically designed and made imitation jewellery from mock silver, gold or artificial stones. The Syrians and Egyptians appear to have developed a particular talent for this work, and written examples of their formulae or recipes have survived in handbooks that were compiled centuries later in about 200 BC. For example, to prepare a cheaper form of ‘asem’, an alloy of gold and silver:

Take soft tin in small pieces, purified four times; take four parts of it and three parts of pure white copper and one part of asem. Melt, and after casting, clean several times and make with it whatever you wish to. It will be asem of the first quality, which will deceive even the artisans.

Or, in the equivalent of nineteenth-century electroplating, to make a copper ring appear golden so that ‘neither the feel nor rubbing it on the touchstone will discover it’:

Grind gold and lead to a dust as fine as flour; two parts of lead for one of gold, mix them and incorporate them with gum, coat the ring with this mixture and heat. This is repeated several times until the object has taken the colour. It is difficult to discover because the rubbing power gives the mark of an object of gold and the heat [test] consumes the lead and not the gold.

In one sense this aurifictional technology can be described as simple empiricism. To say that, however, does not mean that its practitioners were devoid of ideas about the processes they worked, or that they had no model to underpin their understanding of what was happening. Given that these technologies were evidently closely bound up with magic, ritual and trade secrecy, this was equivalent to a theoretical underpinning. Although these artisans may not have had any sophisticated chemical theory to explain or guide their practices, that experience was undoubtedly bound up with ritualistic beliefs concerning the objects that were handled. We need only notice the more than obvious connection of the names of metals with the planets, and

TABLE 1.1 The ancient associations of metals and the heavens.

from them the names of the week (table 1.1), as well as beliefs that metals grew inside the earth, to conclude that myth and analogy played the equivalent role of chemical theory in these technologies. Moreover, it seems highly likely from later written records that metallurgists believed that, while metals grew normally at a slow pace within the earth, they could accelerate this process within the smithy, albeit an appropriate planetary god or goddess had to be propitiated by ritual purification for the rape of mother earth. It was this element of ritual, albeit in a Christianized form in the Latin west and a Taoist form in China, that was handed on to the science of alchemy.

For a science alchemy was. Theory controlled and exploited the empirical. Alchemy became a science when the masses of technical lore connected with dyeing and metallurgy became confronted by and amalgamated with Greek theories of matter and change. Greek philosophers with their strong sense of rationality and logic contributed a theory of matter that was able to order, classify and explain technological practice. The pre-Socratic philosophers of the sixth century BC had conjectured that the everyday substances of this material world were generated from some one primary matter. Both Plato (c 427–c 347 BC) and Aristotle (384–322 BC), teaching in the fourth century BC, had also written of this prime matter as a featureless, quality-less stuff, rather like potter’s clay, onto which the various qualities and properties of hotness, coldness, dryness and moistness could be impressed to form the four elements that Empedocles (d. c. 430 BC) had postulated in the fifth century BC. This quartet of elementary substances, in their turn, mixed together in various proportions to generate perceptible substances. Conversely, material substances could, at least in principle and often in practice, be analysed into these four components:

Although Aristotle seems not to have articulated a theory of cohesion, we may assume that the four elements were ‘bound together’ by the moist quality. Expressed in rectangular diagrammatic form, which became the basis for later geometrical talismans and symbols, each adjacent element can be seen to possess a common quality; hence all four of the elements are, in principle, interconvertible. Thus, by changing the form or forms (transformation) of bodies, Nature transmutes the underlying basic, or primary, matter into different substances. Despite pertinent criticisms by Theophrastus (371–286 BC), Aristotle’s pupil and successor at the Lyceum, that fire was different from other elements in being able to generate itself and in needing other matter to sustain it, the theory of the four elements was to remain the fundamental basis of theoretical chemistry until the eighteenth century.

For Aristotle there was a fundamental distinction between the physics of the heavens, which were eternal, perfect, unchanging and endowed with natural circular motion, and the sublunar sphere of the earth, which was subject to change and decay and where movement was either upwards or downwards from the centre of the universe. This sublunar region was composed from Empedocles’ four elements. Aristotle had rejected the atomic theory introduced in the fifth century BC by Democritus. The claim that the apparent differences between substances arose from differences in the shapes and sizes of uncuttable, homogeneous particles, while ingenious, seemed to Aristotle pure invention, whereas the four elements lay close to human sensory experience of solids and liquids and of wind and fire, or of hot and cold, wet and dry objects. How could atomism account for the wide variety of shapes and forms found in minerals in the absence of a formal cause? Moreover, to Aristotle, the postulation of a void meant that there was no explanation for motion, and without motion there could be no change. Atomism also failed to distinguish between physical and mathematical division – a problem that was overcome after Aristotle’s death by Epicurus (341–270 BC), who allowed that, although atoms were the unsplittable physical minima of matter, because an atom had definite size, it could be said to contain mathematically indivisible parts. Epicurus also explained the compounding of atoms together as they fell with equal speeds through the void as due to sudden ‘swerves’ or deviations. These unpredictable swerves are a reminder that atomism, as popularized in Epicurean philosophy, had more to do with the establishment of a moral and ethical philosophy than as an interpretation of the physics and chemistry of change. Swerving atoms allowed for human free will. Atomism for the Epicureans, as well as for its great poetic expositor, the Roman Lucretius in De rerum natura (c. 55 BC), was a way of ensuring human happiness by the eradication of anxieties and fears engendered by religions, superstitions and ignorance. Ironically, in the sixteenth century, atomism began to be used as a way of eliminating the superstitions and ignorance of Aristotelianism.

The other great post-Aristotelian system of philosophy, Stoicism, because it adopted and adapted considerable parts of Aristotelianism, was more influential. Founded by the Athenian, Zeno (342–270 BC), during the fourth century BC and refined and developed up to the time of Seneca in the first century AD, Stoicism retained Aristotle’s plenistic physics and argued for the indefinite divisibility of matter. Stoics laid stress on the analogy between macrocosm and microcosm, the heavens and the earth, and distinguished between inert matter and a more active form, the latter being called the pneuma, or vital spirit. Pneuma pervaded the whole cosmos and brought about generation as well as decay. Ordinary substances, as Empedocles and Aristotle had taught, were composed from the four elements, albeit hot and dry, fire and air were more active than passive wet and cold, water and earth. From this it was but a short step to interpreting air and fire as forms of pneuma, and pneuma as the glue or force that bound passive earth and water into cohesive substances. The concept was to have a profound effect on the interpretation of distillation.

Chemical compounds (an anachronism, of course) were mixtures of these four elements in varying proportions – albeit Aristotle’s and the Stoics’ views were rather more sophisticated than this bald statement suggests. The central theorem of alchemy, transmutation, could be seen in one of two ways, either as what we would call chemical change caused by the different proportions of elements and their rearrangement, or as a real transmutation in which the qualities of the elements are transformed. Alchemy allowed far more ‘transmutations’ than later chemistry was to allow, for it permitted the transmutation of lead or other common metals into gold or some other precious metal. A real transmutation of lead and gold was to be achieved by stripping lead of its qualities and replanting the basic matter that was left with the qualities and attributes of gold. Since lead was dense, soft and grey, while gold was dense, soft and yellow, only a change of colour seemed significant. However, although alchemy is usually taken to be the science of restricted metallic transmutations, it is worth emphasizing that it was really concerned with all chemical changes. In that very general sense, alchemy was the basis of chemistry.

One of the most important geographical areas for the creation of alchemy was Egypt during the Hellenistic period from about 300 BC to the first century AD. Egypt was then a melting pot for Greek philosophy, oriental and Christian religions, astrology, magic, Hermeticism and Gnosticism, as well as trade and technology. Hermeticism, which took its title from Hermes, the Greek form of the Egyptian deity, Thoth, the father of all book learning, was a blend of Egyptian religion, Babylonian astrology, Platonism and Stoicism. Its vast literature, the Hermetic books, supposedly written by Hermes Trismegistus, was probably compiled in Egypt during the second century BC. Gnosticism, on the other hand, was an ancient Babylonian religious movement, which stressed the dualism between light and darkness, good and evil. Gnosis was knowledge obtained only through inner illumination, and not through reason or faith. Humankind was assured of redemption only from this inner enlightenment. Gnosticism both competed with early Christianity and influenced the writing of the Gospels. As its texts show, however, Gnosticism was as much influenced by contemporary alchemy as it influenced alchemical language. For example, in the Gnostic creation story, chemical expressions referring to sublimation and distillation are found, as in the phrase ‘the light and the heavy, those which rise to the top and those which sink to the bottom’. The most important of the Gnostics, Theodotos, who lived in the second century AD, used metaphors of refining, filtering, purifying and mixing, which some historians think he may have drawn from the alchemical school of Mary the Jewess. When Gnostic language is met in alchemical texts of the period, such as the Dialogue of Kleopatra and the Philosophers, however, it is difficult to know whether the author is referring to the death and revivification of metals or to the death and regeneration of the human soul. Exoteric alchemy had become inextricably bound with esoteric alchemy.

Most historians have seen three distinctive threads leading towards the development of Hellenistic alchemy: the empirical technology and Greek theories of matter already referred to, and mysticism – an unsatisfactory word that refers to a rag-bag of magical, religious and seemingly irrational and unscientific practices. Undoubtedly this third ingredient left its mark on the young science, and it in turn has left its mark on ‘mysticism’ right up until the twentieth century. In Hellenistic Egypt, as in Confucian China, there was a distinctive tendency to turn aside from observation and experiment and the things of this world to seek solace in mystical and religious revelations. It was the absorption of this element into alchemy that splintered its adherents into groups with different purposes and which later helped to designate alchemy as a pseudo-science.

Recent studies have shown the considerable extent of pharmacological knowledge within the Arabic tradition. This tradition was to furnish the Latin west with large numbers of chemical substances and apparatus. It was clearly already well established in Greek alchemy, and it is to medicine that the historian must also look for another of alchemy’s foundation stones. For it was the Greek pharmacists who mixed, purified, heated and pulverized minerals and plants to make salves and tinctures. In Greek texts the word for a chemical reagent is, significantly, pharmakon.

The modern conspectus is, therefore, that practical alchemy was the bastard child of medicine and pharmacy, as well as of dyeing and metallurgy. By applying Aristotelian, Neoplatonic, Gnostic and Stoic ideas to the practices of doctors and artisans, Greek alchemists reinterpreted practice as transmutation. This point is especially clear in a seventh-century AD text by Stephanos of Alexandria, ‘On the great and sacred art, or the making of gold’, in which he attacked goldsmiths for practising aurifiction. If such craftsmen had been properly educated in philosophy, he commented, they would know that gold could be made by means of an actual transformation.

For one group of such-minded alchemical philosophers, astrology, magic and religious ritual grew at the expense of laboratory and workshop practice. Alchemical symbolism and allegory appealed strongly to the early Gnostics and Neoplatonists. The ‘death’ of metals, their ‘resurrection’ and ‘perfection’ as gold or purple dyes were symbolical of the death, resurrection and perfection of Christ and of what should, ideally, happen to the human soul. This esoteric alchemy is more the province of the psychologist and psychiatrist, as Jung claimed, or of the historian of religion and anthropology, than of the historian of chemistry. Nevertheless, as in the case of Isaac Newton, the historian of science must at all times be aware that, until the nineteenth century at least, most scientific activities were, fundamentally, religious ones. The historian of chemistry must not be surprised to find that even the most transparent of experimental texts may contain language that is allegorical and symbolical and which is capable of being read in a spiritual way.

Exoteric alchemists continued their experimental labours, discovered much that was useful then and later, and suffered the indignities of bad reputation stemming from less noble confidence tricksters. Another group became interested in theories of matter and promoted discussion of ideas of particles, atoms or minima naturalis. Finally, the artisans and technologists continued with their recipes, uninterested in theoretical abstractions.

The primitive notion that metals grew inside the earth had been supported by Aristotle in his treatise Meteorologica – the title referred to the physics of the earthly, as opposed to the celestial, sphere, and had nothing to do with weather forecasting. Less perfect metals, it was supposed, slowly grew to become more noble metals, like gold. Nature performed this cookery inside her womb over long periods of time – it was for this reason that, during the middle ages, mines were sometimes sealed so as to allow exhausted seams to recover, and for more metals to grow. If one interpreted the artisans’ aurifictions as aurifactions, then it appeared that they had successfully succeeded in repeating Nature’s process in the workshop in a short time. Perhaps further experimentation would bring to light other techniques for accelerating natural alchemical processes.

Although Aristotle had never meant by ‘prime matter’ a tangible stuff that could be separated from substances, this was certainly how later chemists came to think of it. Similarly the tactile qualities became substantialized (substantial forms) and frequently identified with the aerial or liquid products of distillation, or pneuma.

In gold-making, much use of analogy was made. Since there is a cycle of death and regrowth in Nature from the seed, its growth, decay and regeneration as seed once more, the alchemist can work by analogy. Lead is taken and ‘killed’ to remove its form and to produce the primary matter. The new substance is then grown on this compost. In the case of gold, its form is impressed by planting a seed of gold on the unformed matter. To grow this seed, warmth and moisture were requisite, and to perform the process, apparatus of various kinds – stills, furnaces, beakers and baths – was required, much of it already available from artisans or readily adapted from them.

A secret technical vocabulary was developed in order to maintain a closed shop and to conceal knowledge from the uninitiated, a language that through its long history became more and more picturesque and fanciful. In Michael Maier’s Atalanta fugiens (1618), we read that ‘The grey wolf devours the King, after which it is buried on a pyre, consuming the wolf and restoring the King to life.’ All becomes clear when it is realized that this refers to an extraction of gold from its alloys by skimming off lesser metal sulphides formed from a reaction with antimony sulphide and the roasting of the resultant gold – antimony alloy until only gold remains. As Lawrence Principe has noted, this incomprehension on our part is surely little different from today’s mystification when the preparative organic chemist issues the order, ‘dehydrohalogenate vicinal dihalides with amide ion to provide alkynes’. In other words, although alchemists undeniably practised deliberate obfuscation, much of our incomprehension stems from its being in a foreign language, much of whose vocabulary has been lost. On the other hand, we must recognize that obscurity also suited the rulers and nobility of Europe, who patronized alchemists in the hope of solving their monetary problems.

ARABIC AND MEDIEVAL ALCHEMY

Greeks alchemy spread geographically with Christianity and so passed to the Arabs, who were also party to the ideas and practices of Indian and Chinese technologists and alchemists. The story that alchemical texts were burned and alchemists expelled from Egypt by the decree of the Emperor Diocletian in 292 AD appears to be legendary. Alchemy does not seem to have reached the Latin west until the eleventh century, when the first translations from the Arabic began to appear. In Arabic alchemy (the word itself is, of course, Arabic), we meet for the first time the notion of the philosopher’s stone and potable gold or the elixir of life. Both these ideas are found in Chinese alchemy. Two alchemists who were much revered later in the Latin west were Jābir and Rhazes.

Over two thousand writings covering the fields of alchemy, astrology, numerology, medicine and mysticism were attributed to Jābir ibn Hayyān, a shadowy eighth-century figure. In 1942, the German scholar Paul Kraus showed that the entire Arabic Jābirian corpus was the compilation of a Muslim tenth-century religious sect, the Ism’iliya, or Brethren of Purity. No doubt, like Hippocrates, there was a historical Jābir, but the writings that survive and which formed the basis for the Latin writings attributed to Geber were written only in the tenth century. Until very recently, no Arabic originals for the Latin Geber were known and many historians suspected that they were western forgeries, or rather original compilations that exploited the name of the famous Arabic alchemist. William Newman has shown, however, that the Geberian Summa Perfectionis, arguably the most influential of Latin works on alchemy, was definitely based upon manuscripts of Jābirian translations already in circulation, and that it was the work of one Paulus de Tarento, of whom nothing is yet known.

The Jābirian corpus as well as the Latin Summa were important for introducing the sulphur – mercury theory of metallic composition. According to this idea, based upon Aristotle’s explanation in Meteorologica, metals were generated inside the earth by the admixture of a fiery, smoky principle, sulphur, to a watery principle, mercury. This also seems to have been a conflation with Stoic alchemical ideas that metals were held together by a spirit (mercury) and a soul (sulphur). The theory was to lend itself beautifully to symbolic interpretation as a chemical wedding and to lead to vivid conjugal images in later alchemical texts and illustrations. As critics in the Latin west like Albertus Magnus were to point out later, this did not explain satisfactorily how the substantial forms of different metals and minerals were produced. What is most interesting, therefore, is that the Summa clearly speaks of a particulate or corpuscular theory based upon Aristotle’s concession, despite his objection to atomism, that there were minima naturalia, or ‘molecules’ as we would say, which limit the analysis of all substances. The exhalation of the smaller particles of sulphur and mercury inside the earth led to a thickening and mixing together until a solid homogeneity resulted. Metals varied in weight (density or specific gravity) and form because of the differing degrees of packing of their constituent particles – implying that lighter metals had larger particles separated by larger spaces. Since the particles of noble metals such as gold were closely packed, the alchemists’ task, according to the author of the Summa, was to reduce the constituent particles of lighter, baser metals in size and to pack them closer together. Hence the emphasis upon the sublimation of mercury and its fixation in the practical procedures described by Geber. As in the original Jābirian writings, such changes to the density, malleability and colour of metals were ascribed to mercurial agents that were referred to as ‘medicines’, ‘elixirs’ or ‘tinctures’. Although these terms were also adopted in the west, it became even more common to refer to the agent as the ‘philosopher’s stone’ (lapidens philosophorum). References to a stone as the key to transmutation in fact go back to Greek alchemy and have been found in a Cairo manuscript attributed to Agathodaimon, as well as in the earliest known alchemical encyclopedia, the Cheirokmeta attributed to Zosimos (c. 300 AD).

Apart from its influence on alchemical practice, the Summa also contained an important defence of alchemy and, with it, of all forms of technology. Alchemy had always been too practical an art to be included in the curriculum of the medieval university; moreover, it had seemed theologically suspect insofar as it offered sinful humankind the divine power of creation. The Summa author, however, argued that people had the ability to improve on Nature because that was part of their nature and cited, among other things, farmers’ exploitation of grafting and alchemists’ ability to replicate (synthesize) certain chemicals found naturally. As Newman has suggested⁴:

During this innovative period, alchemical writers and their allies produced a literary corpus which was among the earliest in Latin to actively promote the doctrine that art can equal or outdo the products of nature, and that man can even change the order of the natural world by altering the species of those products. This technological dream, however premature, was to have a lasting effect on the direction taken by Western culture.

Exoteric alchemy, committed as it was to laboratory manipulation, in this way bequeathed a commitment to empiricism in science and emphasized the centrality of experiment.

Al-Razi (850–c. 923), or Rhazes, was a Persian physician and alchemist who practised in Baghdad and who compiled the extremely practical text, Secret of Secrets, which, despite its esoteric title and hint of great promises, was a straightforward manual of chemical practice. Rhazes classified substances into metals, vitriols, boraxes, salts and stones on the grounds of solubilities and tastes, and added sal ammoniac (ammonium chloride), prepared by distilling hair with salt and urine, to the alchemists’ repertory of substances. Sal ammoniac was soon found to be most useful in ‘colouring’ metals and in dissolving them.

A rationalist and systematist, Rhazes seems to have been among the first to have codified laboratory procedures into techniques of purification, separation, mixing and removal of water, or solidification. But although he and other Arabic authorities referred to ‘sharp waters’ obtained in the distillation of mixtures of vitriol, alum, salt, saltpetre and sal ammoniac, it is doubtful whether these were any more than acid salt solutions. On the other hand, it was undoubtedly by following the procedures laid down by Rhazes and by modifying still-heads that Europeans first prepared pure sulphuric, hydrochloric and nitric acids in the thirteenth century.

The Secret of Secrets was divided into sections on substances – a huge list and description of chemicals and minerals – apparatus and recipes. Among the apparatus described and used were beakers, flasks, phials, basins, crystallization dishes and glass vessels, jugs and casseroles, candle and naphtha lamps, braziers, furnaces (athanors), files, spatulas, hammers, ladles, shears, tongs, sand and water baths, hair and linen filters, alembics (stills), aludels, funnels, cucurbits (flasks), and pestles and mortars – indeed, the basic apparatus that was to be found in alchemical, pharmaceutical and metallurgical workshops until the end of the nineteenth century. Similarly, Rhazes’ techniques of distillation, sublimation, calcination and solution were to be the basis for chemical manipulation and chemical engineering from then onwards. We must be careful, however, not to take later European artists’ representations of alchemical workshops at face value.

A few of the techniques described by Rhazes deserve further comment. Calcination originally meant the reduction of any solid to the state of a fine powder, and often involved a change of composition brought about by means of strong heat from a furnace. Only later, say by the eighteenth century, did it come to mean specifically the reduction of a metal to its calx or oxide. There were many different kinds of furnace available and they varied in size according to the task in hand. Charcoal, wood and straw were used (coal was frowned upon because of the unpleasant fumes it produced). The temperature was raised blacksmith-fashion by means of bellows – hence the derogatory names of ‘puffers’ or ‘workers by fire’ that were applied to alchemists. Direct heat was often avoided in delicate reactions by the use of sand, dung or water baths, the latter (the bain-marie) being attributed to the third-century BC woman chemist known as Mary the Jewess. Needless to say, because heating was difficult to control, apparatus broke frequently. Even in the eighteenth century when Lavoisier found need to distil water continuously for a period of months, his tests were continually frustrated by breakages. By the same token, since temperature conditions would have been hard to control and replicate, the repetition of processes under identical conditions was difficult or impossible. However, whether alchemists were aware of this is doubtful.

Distillation, one of the most important procedures in practical chemistry, gave rise to a diversity of apparatus, all of which are the ancestors of today’s oil refineries. Already in 3000 BC there is archaeological evidence of extraction pots being used in the Mesopotamian region. These pots were used by herbalists and perfume makers. A double-rim trough was percolated with holes, the trough itself being filled with perfume-making flowers and herbs in water. When fired, the steam condensed in the lid and percolated back onto the plants below. In a variation of this, no holes were drilled and the distillate was collected directly in the trough around the rim, from where it was probably removed from time to time by means of a dry cloth. In the Mongolian or Chinese still, the distillate fell from a concave roof into a central catch-bowl from which a side-tube led to the outside. Modern experiments, using working glass models of these stills, have shown that⁵:

the preparation of strong spiritous liquor was, from a technological point of view, a rather simple matter and no civilisation had a distillation apparatus which gave it an advantage.

Even so, although the Chinese probably had distilled alcohol from wine by the fourth century AD, it was several centuries later before it was known in the west. Even earlier, in the second century of our era, the Chinese had discovered how to concentrate alcohol by a freezing process, whereby separation was achieved by freezing water and leaving concentrated alcohol behind.

The observation of distillation also provided a solution to the theoretical problem of what made solid materials cohere. The binding material could not be Aristotelian water since this patently could not be extracted from a heated stone. Distillation of other materials showed, however, that an ‘oily’ distillate commonly succeeded the ‘aqueous’ fraction that first boiled off at a lower temperature. It could be argued, therefore, that an ‘unctuous’, or fatty, moisture was the cohesive binder of solid bodies. This notion that ‘earths’ contained a fatty material was still to be found in Stahl’s theory of phlogiston in the eighteenth century.

An improvement on distillation techniques was apparently first made by Alexandrian alchemists in the first century AD – though, in the absence of recorded evidence, it is just as likely that these alchemists were merely adopting techniques and apparatus from craftsmen and pharmacists. This is particularly evident in the ‘kerotakis’, which took its name from the palette used by painters and artists. This wedge-shaped palette was fitted into an ambix (still-head) as a shelf to contain a substance that was to be reacted with a boiling liquid, which would condense, drip or sublime onto it. These alchemists made air cooling in the distillation process more efficient by separating the distillate off by a continuous process and raising the ambix well above the bikos or cucurbit vessel embedded in the furnace or sand bath. (In 1937 the word Ambix was adopted by the Society for the History of Alchemy and Early Chemistry as the title of the journal that ever since has played an important role in the history of chemistry.) In the Latin west the word alembic (from the Arabic form of ambix, ‘al-anbiq’) came to denote the complete distillation apparatus. By its means, rose waters, other perfumes and, most importantly, mineral acids and alcohol began to be prepared and explored in the thirteenth century.

Continuous distillations were also made possible in the ‘pelican’, so-called because of its arms, which bore resemblance to that bird’s wings. Such distillations were believed to be significant by alchemists, who were much influenced by Jābir’s reputed success at ‘projection’ (the preparation of gold) after 700 distillations. The more efficient cooling of a distillate outside the still-head appears to have been a European contribution developed in the twelfth century. Alchemists and technologists referred to these as water-cooled stills or ‘serpents’. This more efficient cooling of the distillate probably had something to do with the preparation of alcohol in the twelfth century, some centuries after the Chinese. This became an important solvent as well as beverage in pharmacy. By then chemical apparatus was becoming commonly made of glass. It should be noted that, although ‘alcohol’ is an Arabic word, it had first meant antimony sulphide, ‘kohl’. In the Latin west, alcohol was initially called ‘aqua vitae’ or ‘aqua ardens’ (the water that burns), and only in the sixteenth century was it renamed alcohol. It had also been named the ‘quintessence’, or fifth essence, by the fourteenth-century Spanish Franciscan preacher, John of Rupescissa, in an influential tract, De consideratione quintae essentiae. According to John, alcohol, the product of the distillation of wines, possessed great healing powers from the fact that it was the essence of the heavens. An even more powerful medicine was obtained when the sun, gold, was dissolved in it to produce ‘potable gold’. John’s advocation of the quintessence was extremely important since it encouraged pharmacists to try and extract other quintessences from herbs and minerals, and thus to usher in the age of iatrochemistry in the sixteenth century. Here was the parting of the ways of alchemy and chemistry.

The sixteenth century saw great improvements in chemical technology and the appearance of several printed books dealing with the subject. Such treatises mentioned very little chemical theory. They aimed not to advance knowledge, but to record a technological complex that, in Multhauf’s opinion, ‘although sophisticated, had been virtually static throughout the Christian era’. Generally speaking they discussed only apparatus and reagents, and provided recipes that used distillation methods. Many recipes, especially those for artists’ pigments and dyes, bear an astonishing resemblance to those found in the aurifictive papyri of the third century and therefore imply continuity in craftsmen’s recipes for making imitation jewellery, textile dyeing, inks, paints and cheap, but impressive, chemical ‘tricks’.

One such book was the Pirotechnia of Vannoccio Biringuccio (1480–1538), which was published in Italy in 1540. This gave a detailed survey of contemporary metallurgy, the manufacture of weapons and the use of water-power-driven machinery. For the first time there was an explicit stress upon the value of assaying as a guide to the scaling up of operations and the regular reporting of quantitative measurements in the various recipes. On alchemy, despite retaining the traditional view that metals grew inside the earth, Biringuccio provides a sceptical view based upon personal observation and experience⁶:

Now in having spoken and in speaking thus I have no thought of wishing to detract from or decrease the virtues of this art, if it has any, but I have only given my opinion, based on the facts of the matter. I could still discourse concerning the art of transmutation, or alchemy as it is called, yet neither through my own efforts nor those of others (although I have sought with great diligence) have I ever had the fortune to see anything worthy of being approved by good men, or that it was not necessary to abandon as imperfect for one cause or another even before it was half finished. For this reason I surely deserve to be excused, all the more because I know that I am drawn by more powerful reasons, or, perhaps by natural inclination, to follow the path of mining more willingly than alchemy, even though mining is a harder task, both physical and mental, is more expensive, and promises less at first sight and in words than does alchemy; and it has as its scope the observation of Nature’s powers rather than those of art – or indeed of seeing what really exists rather than what one thinks exists.

That is succinctly put: by the sixteenth century, the natural ores of metals, and their separations and transformations by heat, acids and distillations, had become more interesting and financially fruitful than time spent fruitlessly on speculative transmutations.

Alchemy had been transmuted into chemistry, as the change of name reflected. Here a digression into the origins of the word ‘chemistry’ seems appropriate. There is, in fact, no scholarly consensus over the origins of the Greek word ‘chemeia’ or ‘chymia’. One familiar suggestion has been a derivation of the Coptic word ‘Khem’, meaning the black land (Egypt), and etymological transfer to the blackening processes in dyeing, metallurgy and pharmacy. What is certain is that philosophers such as Plato and Aristotle had no word for chemistry, for the term ‘chymia’, meaning to fuse or cast a metal, dates only from about 300 AD. A Chinese origin from the word ‘Kim-Iya’, meaning ‘gold-making juice’, has not been authenticated, though Needham has plausibly suggested that the root ‘chem’ may be equivalent to the Chinese ‘chin’, as in the phrase for the art of transmutation, lien chin shu. The Cantonese pronunciation of this phrase would be, roughly, lin kem shut, i.e. with a hard ‘k’ sound. Needham concludes that we have the possibility that ‘the name for the Chinese “gold art”, crystallised in the syllable chin (kiem) spread over the length and breadth of the Old World, evoking first the Greek terms for chemistry and then, indirectly, the Arabic one’.

Whatever the etymology, the Latin and English words alchemia, alchemy and chemistry were derived from the Arabic name of the art, ‘al Kimiya’ or ‘alkymia’. According to the Oxford English Dictionary, the Arabic definite article, ‘al’, was dropped in the sixteenth century when scholars began to grasp the etymology of the Latin ‘alchimista’, the chemist or practitioner; but it is far more likely to have followed Paracelsus’ decision to refer to medical chemistry as ‘chymia’ or ‘iatrochemia’. The word ‘chymia’ was also used extensively by the humanist physician, Georg Agricola (1494–1555), whose study of the German mining industry, De re metallica, was published in 1556. Although he used Latin coinages such as ‘chymista’ and ‘chymicus’, it is clear from their context that he was still referring, however, to alchemy, alchemical techniques and alchemists, and that he was, in the tradition of humanism, attempting to purify the spelling of a classical root that had been barbarized by Arabic contamination.

Agricola’s simplifications were widely adopted, notably in the Latin dictionary compiled by the Swiss naturalist, Konrad Gesner (1516–65) in 1551, as well as in his De remediis secretis: liber physicus, medicus et partim etiam chymicus (Zurich, 1552). As Rocke has shown, the latter work on pharmaceutical chemistry was widely translated into English, French and Italian, and seems to have been the fountain for the words that became the basis of modern European vocabulary: chimique, chimico, chymiste, chimist, etc. Curiously, the German translation of Gesner continued to render ‘chymistae’ as ‘Alchemisten’. German texts only moved towards the form Chemie and Chemiker in the early 1600s.

By then, influenced by the practical textbook tradition instituted by Libavius, as well as by the iatrochemistry of Paracelsus (chapter 2), ‘alchymia’ or ‘alchemy’ were increasingly terms confined to esoteric religious practices, while ‘chymia’ or ‘chemistry’ were used to label the long tradition of pharmaceutical and technological empiricism.

NEWTON’S ALCHEMY

When the economist, John Maynard Keynes, bought some of Newton’s manuscripts in 1936 when Newton’s papers were unfortunately dispersed, he drew attention to the non-mathematical, ‘irrational’ side of Newton. Here was a famous scientist who had spent an equal part of his time, if not the major part, on a chronology of the scriptures, alchemy, occult medicine and biblical prophecies. For Keynes, Newton had been the last of the magicians. Historians have tended to ignore Newton’s alchemical and religious interests, or simply denied that they had anything to do with his work in mathematics, physics and astronomy. More recently, however, historians such as Robert Westfall and Betty Jo Dobbs, who have immersed themselves in the estimated one million words of Newton’s surviving alchemical manuscripts, have seen his interest in alchemy as integral to his approach to the natural world. They view Newton as deeply influenced by the Neoplatonic and Hermetic movements of his day, which, for Newton, promised to open a window on the structure of matter and the hidden powers and energies of Nature that elsewhere he tried to express and explain in the language of corpuscles, attractions and repulsions.

For example, the German scholar, Karin Figula, has been able to demonstrate that Newton was steeped in the work of Michael Sendivogius (1556–1636?), a Polish alchemist who worked at the Court of Emperor Rudolph II at Prague, where he successfully demonstrated an apparent transmutation in 1604. In his several writings, which were translated and circulated in Britain, Sendivogius wrote of a ‘secret food of life’ that vivified all the creatures and minerals of the world⁷:

Man, like all other animals, dies when deprived of air, and nothing will grow in the world without the force and virtue of the air, which penetrates, alters, and attracts to itself the multiplying nutriment.

As we shall see in the following chapter, this Stoic and Neoplatonic concept of a universal animating spirit, or pneuma, which bathed the cosmos, was to stimulate some interesting experimental work on combustion and respiration in the 1670s.

In a spurious work of Paracelsus, Von den natürlichen Dingen, it had been predicted that a new Elijah would appear in Europe some sixty years after the master’s death. A new age would be ushered in, in which God would finally reveal the secrets of Nature. This prophecy may explain why, as William Newman has suggested, early seventeenth-century Europe was peopled by several adepts like Sendivogius who claimed unusual powers and insights. Another, this time fictitious, adept was ‘Eirenaeus Philalethes’, whose copious writings were closely read by Newton. It is possible that Newton developed his interest in alchemy while a student at Cambridge in the 1660s under the tutelage of Isaac Barrow, who had an alchemical library. But it is equally likely that it was Robert Boyle’s interest in alchemy and in the origins of colours that stimulated Newton’s interest, as well as making him a convinced mechanical philosopher. Like Boyle, Newton was interested in alchemical reports of transmutations as providing circumstantial evidence for the corpuscular nature of matter. In addition, however, Newton was undoubtedly interested in alchemists’ Neoplatonic claims of secret (or hidden) virtues in the air and of attractions between heavenly and earthly matter, and in the possibility, claimed by many alchemical authorities, that metals grew in the earth by the same laws of growth as vegetables and animals. In April 1669 Newton bought a furnace as well as a copy of the compilation of alchemical tracts, Theatrum Chemicum. Among his many other book purchases was the Secrets Reveal’d of the mysterious Eirenaeus Philalethes, whom we now know to have been one of Boyle’s New England acquaintances, George Starkey. The book, which Newton heavily annotated, aimed to show that alchemy mirrored God’s labours during the creation and it referred to the operations of the Stoics’ animating spirit in Nature.

Starkey laid stress upon the properties of antimony, whose ability to crystallize in the pattern of a star following the reduction of stibnite by iron had first been published by the fictitious monk, ‘Basil Valentine’ in 1604 in The Triumphant Chariot of Antimony, one of the most important alchemical treatises ever published. Valentine, who was supposed to have lived in the early fifteenth century, was the invention of Johann Tholde, a salt boiler from Thuringia. The Triumphant Chariot was concerned with the preparation of antimony elixirs to cure various ailments, including venereal disease. In Secrets Reveal’d, Starkey referred to crystalline antimony (child of Saturn from its resemblance to lead) as a magnet on account of its pattern of rays emanating from, or towards, the centre. Newton appears to have spent much of his time in the laboratory in the 1670s investigating the ‘magnetic’ properties of the star, or regulus, of antimony, probably in the shared belief with Philalethes that it was indeed a Royal Seal, that is, God’s sign or signature of its unique ability to attract the world’s celestial and vivifying spirit.

Very possibly it was Newton’s interest in solving the impossibly difficult problem of how passive, inert corpuscles organized themselves into the living entities of the three kingdoms of Nature that drove him to explore the readily available printed texts and circulating manuscripts of alchemy, including, in particular, the works of Sendivogius and Starkey. As Professor Dobbs has expressed it⁸: ‘it was the secret of [the] spirit of life that Newton hoped to learn from alchemy’. Newton’s motive, which was probably shared by many other seventeenth-century figures, including Boyle, was quite respectable. Its purpose, ultimately, was theological. A deeper understanding of God could well come from an understanding of the ‘spirit’, be it light, warmth, or a universal ether, which animated all things.

THE DEMISE OF ALCHEMY AND ITS LITERARY TRADITION

Historians of science are the first to stress that any theory, however erroneous in later view, is better than none. Even so, many historians of science have expressed surprise that alchemy lasted so long, though we can easily underestimate the power of humankind’s fear of death and desire for immortality – or of human cupidity. To the extent that it undoubtedly stimulated empirical research, alchemy can be said to have made a positive contribution to the development of chemistry and to the justification of applying scientific knowledge to the relief of humankind’s estate. This is different, however, from saying that alchemy led to chemistry. The language of alchemy soon developed an arcane and secretive technical vocabulary designed to conceal information from the uninitiated. To a large degree this language is incomprehensible to us today, though it is apparent that the readers of Geoffrey Chaucer’s ‘Canon’s Yeoman’s Tale’ or the audiences of Ben Jonson’s The Alchemist were able to construe it sufficiently to laugh at it.

Warnings against alchemists’ unscrupulousness, which

TABLE 1.2 Chemicals listed in Chaucer’s ‘Canon’s Yeoman’s Tale.’

Alkali | Litharge
Alum | Oil of Tartar
Argol | Prepared Salt
Armenian bole | Quicklime
Arsenic | Quicksilver
Ashes | Ratsbane
Borax | Sal ammoniac
Brimstone | Saltpetre
Bull’s gall | Silver
Burnt bones | Urine
Chalk | Vitriol
Clay | Waters albificated
Dung | Waters rubificated
Egg White | Wort
Hair | Yeast
Iron scales |
Note that alcohol is not cited. |
Adapted from W. A. Campbell, ‘The Goldmakers’, Proceedings of the Royal Institution, 60 (1988) 163. |

are found in William Langland’s Piers Plowman, were developed amusingly by Chaucer in the Chanouns Yemannes Tale (c. 1387) in which he exposed some half-dozen ‘tricks’ used to delude the unwary. These included the use of crucibles containing gold in their base camouflaged by charcoal and wax; stirring a pot with a hollow charcoal rod containing a hidden gold charge; stacking the fire with a lump of charcoal containing a gold cavity sealed by wax; and palming a piece of gold concealed in a sleeve. Deception was made the more easy from the fact that only small quantities were needed to excite and delude an investor into parting with his or her money. These methods had hardly changed when Ben Jonson wrote his satirical masterpiece, The Alchemist, in 1610, except that by then the doctrine of multiplication – the claim that gold could be grown and expanded from a seed – had proved an extremely useful way of extracting gold coins from the avaricious.

As their expert use of alchemical language shows, both Chaucer and Jonson clearly knew a good deal about alchemy, as equally clearly did their readers and audiences (see Table 1.2). Chaucer had translated the thirteenth-century French allegorical romance, Roman de la Rose, which seems to have been influenced by alchemical doctrines, while Jonson based his character, Subtle, on the Elizabethan astrologer, Simon Forman, whose diary offers an extraordinary window into the mind of an early seventeenth-century occultist.

By Jonson’s day, the adulteration and counterfeiting of metal had become illegal. As early as 1317, soon after Dante had placed all alchemists into the Inferno, the Avignon Pope John XXII had ordered alchemists to leave France for coining false money, and a few years later the Dominicans threatened excommunication to any member of the Church who was caught practising the art. Nor were the Jesuits friendly towards alchemy, though there is evidence that it was the spiritual esoteric alchemy that chiefly worried them. Athanasius Kircher (1602–80), for example, defended alchemical experiments, published recipes for chemical medicines and upheld claims for palingenesis (the revival of plants from their ashes), as well as running a ‘pharmaceutical’ laboratory at the Jesuits’ College in Rome. In 1403, the activities of ‘gold-makers’ had evidently become sufficiently serious in England for a statute to be passed forbidding the multiplication of metals. The penalty was death and the confiscation of property. Legislation must have encouraged scepticism and the portrayal of the poverty-striken alchemist as a self-deluded ass or as a knowing and crafty charlatan who eked out a desperate existence by duping the innocent.

Legislation did not, however, mean that royalty and exchequers disbelieved in aurifaction; rather, they sought to control it to their own ends. In 1456 for example, Henry VI of England set up a commission to investigate

FIGURE 1.1 The preparation of the philosopher’s stone.

(After J. Read, Prelude to Chemistry; London: G. Bell, 1936, p. 132.)

the secret of the philosopher’s stone, but learned nothing useful. In Europe, Emperors and Princes regularly offered their patronage – and prisons – to self-proclaimed successful projectionists. The most famous and colourful of these patrons, who included James IV of Scotland, was Rudolf II of Bohemia, who, in his castle in Prague, surrounded himself with a large circle of artists, alchemists and occultists. Among them were the Englishmen John Dee and Edmund Kelly and the Court Physician, Michael Maier (1568–1622), whose Atalanta fugiens (1618) is noted for its curious combination of allegorical woodcuts and musical settings of verses describing the alchemical process. It was Maier, too, who translated Thomas Norton’s fascinating poem, The Ordinall of Alchemy, into Latin verse in 1618.

Such courts, like Alexandria in the second century BC, became melting pots for a growing gulf between exoteric and esoteric alchemy and the growing science of chemistry. Like Heinrich Khunrath (1560–1605), who ‘beheld in his fantasy the whole cosmos as a work of Supernal Alchemy, performed in the crucible of God’, the German shoemaker, Jacob Boehme (1575–1624), enshrined alchemical language and ideas into a theological system. By this time, too, alchemical symbolism had been further advanced by cults of the pansophists, that is by those groups who claimed that a complete understanding, or universal knowledge, could only be obtained through personal illumination. The Rosicrucian Order, founded in Germany at the beginning of the seventeenth century, soon encouraged the publication of a multitude of emblematic texts, all of which became grist to the mill of esoteric alchemy.

Given that by the sixteenth century, if not before, artisans and natural philosophers had sufficient technical knowledge to invalidate the claims of transmutationists, it may be wondered why belief survived. No doubt the divorce between the classes of educated natural philosophers and uneducated artisans (which Boyle tried to close) was partly responsible. There were also the accidents and uncertainties caused by the use of impure and heterogeneous materials that must have often seemingly ‘augmented’ working materials. As one historian has said, ‘fraudulent dexterity, false philosophy, public credulity and Royal rapacity’ all played a part. To these very human factors, however, must be added the fact that, for seventeenth-century natural philosophers, the corpuscular philosophy to which they were committed underwrote the concept of transmutation even more convincingly than the old four-element theory they rejected (chapter 2).

Nevertheless, despite the fact that the mechanical philosophy allowed, in principle, the transmutation of matter, by the mid eighteenth century it had become accepted by nearly all chemists and physicists that alchemy was a pseudo-science and that transmutation was technically impossible. Those few who claimed otherwise, such as James Price (1752–83), a Fellow of the Royal Society, who used his personal fortune in alchemical experiments, found themselves disgraced. Price committed suicide when challenged to repeat his transmutation claims before Sir Joseph Banks and other Fellows of the Society. By then, chemists had come to share Boerhaave’s disbelief in alchemy as expressed in his New Method of Chemistry (1724). Alchemy had become history, and they happily accepted Boerhaave’s allegory of the dying farmer who had told his sons that he had buried treasure in the fields surrounding their home. The sons worked so energetically that they achieved prosperity even though they failed totally to find what they had originally sought.

The absorption of the experimental findings of exoteric alchemy by chemistry left esoteric alchemy to those who continued to believe that there ‘was more to Heaven and earth’ than particles and forces. Incredible stories of transmutations continued to surface periodically during the eighteenth century. Indeed, legends concerning the ‘immortal’ adventurer, the Comte de Saint-Germain, continue into the twentieth century. In Germany, in particular, the Masonic order of Gold- und Rosenkreuz, which was patronized by King Frederick William II of Prussia, combined a mystical form of Christianity with practical work in alchemy based upon the study of collections of alchemical manuscripts. All of this increasingly ran against the rationalism and enlightenment of the age, and we know that at least one member, the naturalist, Georg Forster, left the movement a disillusioned man. Other alchemical echoes were to be heard in the speculative Naturphilosophie that swept through the German universities at the beginning of the nineteenth century and in the modified Paracelsianism of Samuel Hahnemann’s homeopathic system, which he launched in 1810.

Modern alchemical esotericism dates from 1850 when Mary Ann South, whose father had encouraged her interest in the history of religions and in mysticism, published A Suggestive Enquiry into the Hermetic Mystery. This argued that alchemical literature provided the mystic religious contemplative with a direct link to the secret knowledge of ancient mystery religions. After selling only a hundred copies of the book, father and daughter burned the remaining copies. Later, after she had married the Rev. A. T. Atwood, she claimed that the bonfire had taken place to prevent the teachings from falling into the wrong hands. Whatever one makes of this curious affair, her insight that alchemists had been really searching for spiritual enlightenment and not a material stone, supported by the translation of various alchemical texts into English, proved influential on Carl Jung when, in old age, Mrs Atwood republished her study in 1920. It also inspired Eugène Canseliet in France to devote his career to the symbolic interpretation of the statuary and frescoes of Christian churches and chateaux, as a result of the publication in 1928 of Le Mystère des Cathedrals by the mysterious adept ‘Fulcanelli’. The ability of the human mind to read anything into symbols has been mercilessly exposed by Umberto Eco in his novel, Foucault’s Pendulum (1988). In counterbalance, Patrick Harpur’s Mercurius (1990) paints a vividly sympathetic portrait of the esoteric mind.

Ironically, the growth of nineteenth-century chemistry encouraged a revival of alchemical speculation. Dalton’s reintroduction of atomism, the scepticism expressed towards the growing number of chemical elements (chapter 4), the discoveries of spectroscopists and the regularities of the periodic table (chapter 9), all suggested the possibility of transmutation. Although the possibility was given respectability by Rutherford’s and Soddy’s work on radioactivity at the beginning of the twentieth century and physically realized on an atomic scale in the 1930s, it had earlier led in the 1860s to ‘hyperchemistry’. We must not be surprised, therefore, to find gold transmutation stories occurring during even the most positivistic periods of Victorian science. During the 1860s, Chemical News (chapter 12) attributed the high price of bismuth on the metal market to a vogue for transmutation experiments. This was connected to a daring swindle perpetrated on the London stock-market by a Hungarian refugee, Nicholas Papaffy. Papaffy duped large numbers of investors into promoting a method for transforming bismuth and aluminium (then a new and expensive metal) into silver. This followed from a successful public demonstration at a bullion works in the classic tradition of Jonson’s Subtle. Needless to say, after trading offices were opened in Leadenhall Street, Papaffy decamped with an advance of £40 000 from the company. Nor was the American government less gullible. In 1897 an Irish – American metallurgist, Stephen Emmens, sold gold ingots to the US Assay Office that he claimed to have made from silver by his ‘Argentaurum Process’.

In France during the same period, hyperchemistry enjoyed the support of an Association Alchimique de France to which the Swedish playwright, August Strindberg, subscribed, and which influenced Madame Blavatsky’s ‘scientific’ writings for the theosophists and inspired the English composer, Cyril Scott (1879–1970), to compose the opera The Alchemist in 1925. The occult interest in alchemy has continued to the present day and has been given academic respectability since 1985 through the publication of the international scholarly review, Aries, a biannual devoted to the review of the history of esotericism, Hermeticism, theosophy, freemasonry, the Kabbalah and alchemy. Today, booksellers catalogue alchemy under ‘Occultism’ and not ‘History of Science’, while Ambix, the academic mouthpiece of the Society for the History of Alchemy and Chemistry (founded 1937) continues to receive occultist literature for review, as well as the occasional letter pressing its editor for ‘the secret of secrets’.

In 1980, at the phenomenal cost of $10 000, a bismuth sample was transmuted into one-billionth of a cent’s worth of gold by means of a particle accelerator at the Lawrence Laboratory of the University of California at Berkeley. The ‘value’ of the experiment is underlined in Frederick Soddy’s ironic remark some sixty years before⁹:

If man ever achieves this further control over Nature, it is quite certain that the last thing he would want to do would be to turn lead or mercury into gold – for the sake of gold. The energy that would be liberated, if the control of these sub-atomic processes were possible as in the control of ordinary chemical changes, such as combustion, would far exceed in importance and value the gold.

2 The Sceptical Chymist

I see not why we must needs believe that there are any primogeneal and simple bodies, of which, as of pre-existent elements, nature is obliged to compound all others. Nor do I see why we may not conceive that she may produce the bodies accounted mixt out of one another by variously altering and contriving their minute parts, without resolving the matter into any such simple and homogeneous substances as are pretended.

(ROBERT BOYLE, The Sceptical Chymist, 1661)

The phrase ‘The Scientific Revolution’ conjures up a rebellion against Greek authority in astronomy and dynamics, and physics in general. It reminds us of names like Copernicus, Kepler, Galileo, Harvey, Descartes, Bacon and Newton. Chemists’ names are missing. Indeed, a sixteenth- and seventeenth-century revolution in chemical understanding does not readily spring to mind. What was there to rebel against or to revolutionize? Was there a new chemical way of looking at substances in the seventeenth century that in any way paralleled the new physical way?

The historian’s reply has usually been a negative one, with the rider that chemistry developed much later than either astronomy or physics or anatomy and physiology; and that chemistry did not become a science until the eighteenth century. Its revolution was carried out by Lavoisier.

Whether or not this was the case, it can be agreed that chemistry presented the early natural philosopher with peculiarly difficult problems. The sheer complexity of most of the chemical materials with which chemists commonly worked can be seen, with hindsight, to have inevitably made generalizations extremely difficult. Chemists were considering with equal ardour the chemical components of the human and animal body, and of plants and minerals, the procedures of metallurgy, pottery, vinegar, acid and glass manufacture, as well as, in some quarters, abstractions like the philosopher’s stone and the elixir of life. There was no universally agreed chemical language, no convenient compartmentalization of substances into organic and inorganic, into solids, liquids and gases, or into acids, bases and salts; and no concept of purity. For example, when Wilhelm Homberg (1652–1715) ‘analysed’ ordinary sulphur in 1703, he obtained an acid salt, an earth, some fatty matter and some copper metal.

But perhaps the greatest stumbling block to the further development of chemistry was a case of insufficient analysis – there was a complete absence of a knowledge or concept of the gaseous state of matter. Chemistry remained a two-dimensional science, which studied, and only had equipment and apparatus to handle, solids and liquids.

This does not mean that chemistry lacked organization, for there were any number of grand theories that brought order and classification to this complicated subject. The problem with these organizational theories was not only their mutual inconsistency, but the fact that by the 1660s they looked old-fashioned and part of the pre-revolutionary landscape that astronomers and physicists had moved away from. To many natural philosophers, therefore, chemistry seemed tainted; it was an occult or pseudo-science that was beyond the pale of rational discourse.

This was where Boyle came in, for he devoted his life to bringing chemistry to the attention of natural philosophers as a subject worthy of their closest and honest attention. His intention was to ‘begat a good understanding betwixt the chymists and the mechanical philosophers’. In order to do this, he had to show, among other things, that the three or four traditional explanations of chemical phenomena lacked credibility and that a better explanation lay in the revived corpuscular philosophy.

PARACELSIANISM

Philippus Aureolus Theophrastus Bombast von Hohenheim (1493–1541), who rechristened himself Paracelsus in order to indicate his superiority to the second-century Roman medical writer, Celsus, was born near Zurich, then still nominally part of the Holy Roman empire and under Austrian domination. At the age of twenty-one, on the advice of his physician father, he visited the mines and metallurgical workshops in the Tyrol where he studied metallurgy and alchemy. After claiming a medical degree from Ferrara in Italy, Paracelsus became Medical Officer of Health at Basel, a position he was forced to leave in an undignified manner two years later after his abusive and bombastic manner had offended public opinion. Thereafter, he became a rolling stone, restlessly traversing the roads and countries of war-torn Europe, associating with physicians, alchemists, astrologers, apothecaries, miners, gypsies and the adepts of the occult.

It is easy to see why he offended. Not only did he lecture in German instead of Latin, an unorthodox behaviour for a physician, but he publicly burned the works of Galen and Avicenna to show his contempt for orthodox medical opinion – a ceremony that was to be repeated by Lavoisier and his wife 250 years later.

If your physicians only knew that their prince Galen … was sticking in Hell, from whence he has sent letters to me, they would make the sign of the cross upon themselves with a fox’s tail. In the same way your Avicenna sits in the vestible of the infernal portal.

Come then and listen, impostors who prevail only by the authority of your high positions! After my death, my disciples will burst forth and drag you to the light, and shall expose your dirty drugs, wherewith up to this time you have compassed the death of princes .… Woe for your necks on the day of judgement! I know that the monarchy will be mine. Mine too will be the honour and the glory. Not that I praise myself: Nature praises me.

Is this rhetoric or the ravings of a lunatic?

Not surprisingly, contemporary estimates of Paracelsus varied tremendously. An opinion that ‘he lived like a pig, looked like a drover, found his greatest enjoyment in the company of the most dissolute and lowest rabble, and throughout his glorious life he was generally drunk’, may be contrasted with his pupils’ expressions, ‘the noble and beloved monarch’, ‘the German Hermes’ and ‘our dear Preceptor and King of Arts’. What did this contradictory, bewildering figure do for chemistry? What did he teach?

Most of his writings were only published posthumously and there has always been controversy between historians who accept only the ‘rational’ writings as genuine and those who view his eclectic mixture of rationalism, empiricism, Neoplatonic occultism and mysticism as the genuine Paracelsus. Although he definitely subscribed to alchemy, i.e. to the doctrine of transmutation, ‘alchemy’ had a wider meaning for Paracelsus. It entailed carrying ‘to its end something that [had] not yet been completed’. It was any process in Nature in which substances worked or metamorphosed to a new end, and thus included cookery and the chemical arts as well as physiological processes such as digestion.

This widened sense of the word was to be reflected explicitly in what has been described as the first chemistry textbook, the Alchemia published by the Lutheran humanist, Andreas Libavius (1540–1616), in 1597, though, as we shall see, Libavius was contemptuous of Paracelsus. For Paracelsus, chemistry was the key subject for unveiling the secrets of a universe that had been created by a chemist and operated by chemical laws. The views of Aristotle and Galen were those of heathens and heretics and had to be replaced by an empiricism that was controlled by Christian and Neoplatonic insights. Paracelsus and his followers, such as Ostwald Croll in his ‘royal chemistry’, the Basilica Chymica (1609), often made much of the story of creation in Genesis, which they interpreted as a chemical allegory. Paracelsianism thereby came to share many of the attributes of esoteric alchemy in which ‘the art’ was essentially a personal religious avocation.

On the other hand, Paracelsus saw himself essentially as a medical reformer, as someone destined to refute age-old teachings and to base medical practice on what he claimed were more effective mineral medicines. He taught that the principal aim of medicine should be the preparation of arcana, most of which turn out to be chemical, inorganic remedies as opposed to the herbal, organic medicines derived from Greco-Roman medicine. The arcana would destroy and eliminate poisons produced by disease, which itself was due to the putrefaction of the ‘excrements’ produced in any ‘chemical’ process. Diseases were therefore specific, as the new pandemic of syphilis then sweeping Europe suggested, and were to be cured by specific arcana.

Paracelsus taught that macrocosm (the heavens) and microcosm (the earth and all its creatures) were linked together. The heavens contained both visible and invisible stars (astra) that descended to impregnate the matter of the microcosm, conferring on each body the specific form and properties that directed its growth and development. Like acted upon like. The task of the chemist was, by experiment and knowledge of macrocosmic – microcosmic correspondences (the doctrine of signatures), to determine an astral essence or specific virtue capable of treating a disease. To isolate the remedy, the alchemist-physician had to separate the pure essence from the impure, by fire and distillation. Here, Paracelsus owed much to the medieval technology of distillers and to the writings of John of Rupescissa in the fourteenth century. The latter had identified Aristotle’s fifth, heavenly element, the ether, as a quintessence that could be distilled from plants. Paracelsus and his followers were, however, rather more interested in the inorganic salts remaining after distillation than in the distillates themselves.

In this way Paracelsus initiated a new study he called ‘iatrochemistry’, which invoked chemistry to the aid of medicine. Whereas the Paracelsians were individualistic in their pantheistic interpretation of Nature, regarding chemical knowledge as incommunicable except between and through the inspiration proper to a magus, Libavius and the textbook writers who followed him argued that chemistry could be learned by all in the classroom, provided it was put into a methodical form. This construction of a pedagogical discipline involved the classification of laboratory techniques and operations and the establishment of a standardized language of chemical substances. Progress in chemistry, or in any science, would come only from a collective endeavour to combine the subjective, and possibly unreliable, contributions of individuals after subjecting them to peer review and measuring each one critically against past wisdom and experience.

Iatrochemical doctrines became extremely popular during the seventeenth century, and not unlinked with this was a rise in the social status of the apothecary. Both in Britain and on the Continent there was a compromise in which chemical remedies were adopted without commitment to the Paracelsian cosmology. Didactically acquired knowledge of iatrochemistry gave these medical practitioners (who in Britain were to become the general practitioners of the nineteenth and twentieth century) a base upon which they could branch out into their own medical practice and away from the control of university-educated physicians. The need for self-advertisement encouraged them to teach iatrochemical practice and to introduce inorganic remedies into the pharmacopoeia. They were therefore less secretive than the alchemists. Because they wanted to find and prepare useful medical remedies, they were keen to know how to recognize and prepare definite chemical substances with repeatable properties. In teaching their subject, what was wanted was a good textbook, which would provide clear and simple recipes for the preparation of their drugs, with clear unambiguous names for their substances and adequate instructions on the making and use of apparatus for the preparations. Theory could play second fiddle to practice.

Iatrochemistry became very much a French art and here the subject was helped in Paris by the existence of chemical instruction at the Jardin du Roi. Beginning with Jean Beguin’s Tyrocinium Chymicum in 1610, which plagiarized a good deal from Libavius’ Alchemia, each successive professor, Étienne de Clave, Christopher Glaser and Nicholas Lemery, composed a textbook for the instruction of the apothecary’s apprentices who flocked to their annual lectures. Many of these texts went into other languages, including Latin and English. By 1675, when Lemery published his Cours de Chimie, a textbook tradition had been firmly established as part of didactic chemistry and which considerably aided the establishment of chemistry as a discipline. Some historians of chemistry believe that this formulation of chemistry as a scholarly, didactic discipline, which began with Libavius well before the establishment of the mechanical philosophy, was far more significant than the latter for the creation of modern chemistry.

In chemical theory, Paracelsus introduced the doctrine of the tria prima, or the three principles. Medical substances, he said, were ultimately composed from the four Aristotelian elements, which formed the receptacles or matrices for the universal qualities of a trinity of primary bodies he called salt (body), sulphur (soul) and mercury (spirit).

The world is as God created it. He founded this primordial body on the trinity of mercury, sulphur and salt and these are the three substances of which the complete body consists. For they form everything that lies in the four elements, they bear them all the forces and faculties of perishable things.

The doctrine of the tria prima was clearly an extension of the Arabic sulphur – mercury theory of metals applied to all materials whether metallic, non-metallic, animal or vegetable, and given body by the addition of a third principle, salt.

This theory of composition, which essentially explained gross properties by hypothetical property-bearing constituents, rapidly replaced the old sulphur – mercury theory, though not the Aristotelian four elements. Paracelsus was happy to use Aristotle’s example of the analysis of wood by destructive distillation to justify the tria prima theory. Smoke was the volatile portion, mercury; the light and glow of the fire demonstrated the presence of sulphur; and the incombustible, non-volatile ash remaining was the salt. Water was included within the mercury principle, which explained the cohesion of bodies.

Van Helmont begged to differ and provided a simpler, and supposedly more empirical, alternative theory of composition.

HELMONTIANISM

Iatrochemistry came to fruition in the work of a Flemish nobleman, Joan-Baptista van Helmont (1577–1644). Present-day Belgium was then under Spanish control. In 1625, as a consequence of Helmont’s controversial advocation of ‘weapon salve’ treatment in which a weapon, and not a wound, was treated, he was denounced as a heretic by the Spanish Inquisition and spent the remainder of his life, like Galileo, under house arrest. As with Paracelsus, it was van Helmont’s posthumous writings that brought his name to fame and exerted a considerable influence upon seventeenth-century natural philosophers like Boyle and Newton. This influence was firmly established after 1648 with the posthumous publication of his Ortus Medicinae, which was issued in English in 1662 as Oriatricke or Physick Refined. Helmont, who claimed to have witnessed a successful transmutation of a base metal into gold, was a disciple of Paracelsus and an iatrochemist. However, like any good disciple, he modified, interpreted and disagreed with his master’s doctrines considerably.

After studying several areas of natural philosophy, he chose medicine and chemistry for his career, calling himself a ‘philosopher by fire’. He was strongly anti-Aristotelian, one facet of which was that he refused to accept the four-element theory. But neither was he able to accept Paracelsus’ tria prima. To simplify a rather complex philosophy, we can say that according to van Helmont there were two first beginnings of bodies: water and an active, organizing principle, or ‘ferment’, which moulded the various forms and properties of substances. This return to a unitary theory of matter was influenced by his interpretation of Genesis, for water, together with the heavens and the earth, had been formed on the first day.

In more detail, he imagined that there were two ultimate elements, air and water. Air was, however, purely a physical medium, which did not participate in transmutations, whereas water could be moulded into the rich variety of substances found on the earth. Van Helmont did not consider fire to be a material element, but a transforming agent. As for earth, from his experimental observations, he believed that this was created by the action of ferments upon water.

The first beginnings of bodies, and of corporeal causes, are two, and no more. They are surely the element water, from which bodies are fashioned, and the ferment.

As we have already seen in the introduction, the justification for this belief was an interesting, quantitative growth experiment with a young willow tree. Additional supporting evidence came from the fact that fish were nourished ‘solely’ by water, that seashells were found on dry land, and that solid bodies could be transformed into ‘savoury waters’, that is, into solution. In the latter case, Helmont took a weighed amount of sand, and fused it with excess alkali to form water-glass, which liquefied on standing in air. Here was a palpable demonstration of the reconversion of earth back into water. More remarkably, this ‘water’ could be reconverted back to ‘earth’ by treatment with acid, when the silica sand recovered was found to have the same weight as the starting material.

There are a number of interesting features about these experiments and Helmont’s reasoning. Their most important feature is not that Helmont misinterpreted his observations because he ignored the role of air, but that they were quantitative. The experiments were also controlled. In the willow tree experiment, Helmont covered the vessel so as to prevent dust contamination, which might have affected the result. Similarly, he dried the earth beforehand and used only distilled water. He clearly had thought about the experiment and possible objections that might be raised against his conclusions because of the way the experiment had been designed. All this was the hallmark of the experimental method that was to lead to the transformation of chemistry. In addition, it is noticeable that he implicitly assumed that matter was conserved in any changes it underwent. When metals were dissolved in acids they were not destroyed, but were recoverable weight for weight. Helmont also postulated the existence of an alcahest, or universal solvent, which had the property of turning things back into water. Much time and effort was spent by contemporary chemists, including Robert Boyle, in trying to identify this mysterious solvent.

There is a further item of interest to be found in Helmont’s writings. Since air could not be turned into water, he accepted it as a separate element. However, his keen interest was awakened by the ‘air-like’ substances that were frequently evolved during chemical reactions. Helmont identified these fuliginous effluvia as ‘gases’, from a Greek word for ‘chaos’ that Paracelsus had ascribed to air in another connection. Where did these uncontrollable, dangerous materials fit in Helmont’s ontology?

Gases were simply water, not air, for any matter carried into the atmosphere was turned into gas by the cold and ‘death’ of its ferments. A gas was chaos because it bore no form. A gas might also condense to a vapour and fall as rain under the influence of blas, a term that did not stay in chemical language, and which Helmont coined to refer to a kind of ‘gravitational’, astral influence or power that caused motion and change throughout the universe.

In a typical gas experiment, Helmont heated 62 lb (28 kg) of charcoal in air and was left with 1 lb (2.2 kg) of ash, the rest having disappeared as ‘spiritus sylvester’ or wild spirit. When charcoal was heated in a sealed vessel, combustion would either not occur, or would occur with violence as the spirit escaped from the exploding vessel. This disruptive experience led to Helmont’s definition of gas:

This spirit, hitherto unknown, which can neither be retained in vessels nor reduced to a visible body … I call by the new name gas.

Although Helmont implied by this a distinction between gas and air, and even between different gases, these were features to which commentators paid scant attention. The reason for this is that, in the absence of any suitable apparatus to collect and study such aerial emissions, it was impossible to distinguish between them chemically. Helmont himself had to be content with classifying gases from their obvious physical properties: for example, the wild and unrestrainable gas (spiritus sylvester) obtained from charcoal; gases from fermentations; vegetable juices; from the action of vinegar on the shells of certain sea creatures; intestinal putrefactions; from mines, mineral waters and from certain caverns like the Grotto del Cane near Naples, which allowed men to breathe but extinguished the life of a dog.

In striking contrast to his French contemporary. René Descartes, who claimed that, apart from the existence of a human soul, life was a mechanistic process, Helmont refused to separate soul from matter itself. Matter became spiritualized and nature pantheistic. Such a spiritualization of matter proved especially attractive to various religious groups during the Puritan revolution in England. The writings of Paracelsus and Helmont circulated widely during the 1650s and 1660s, partly because they could be used as weapons in the power struggles between physicians and pharmacists, but also because religious ideology was in a state of flux. The Neoplatonic, unmechanical, vitalistic and almost anti-rational aspects of both Paracelsianism and Helmontianism appealed to many because they emphasized the significance of personal illumination against pure reason. This appealed to the Puritan conscience precisely because it could justify religious and political revolution for the sake of one’s ideals.

But along with the ideology went the ‘positive’ science of Helmont: gases, quantification and measurement, and iatrochemistry. Once the Commonwealth was achieved, the concept of personal illumination had to be played down (as Libavius had foreseen) in order to prevent anarchy. In the 1660s, therefore, Helmontianism came under attack. Whereas in the 1640s it had been argued by some that Oxford and Cambridge Universities ought to be reformed under Paracelsian and Helmontian lines, by the mid 1660s this was out of the question and the mechanical philosophy of Descartes, Boyle and Newton was to be triumphantly advocated by the new Royal Society. Nevertheless, echoes of Helmontianism remained in the works of Boyle and Newton.

THE ACID-ALKALI THEORY

This dualistic theory, based upon the old Empedoclean idea of a war of opposites, also stemmed directly from Helmont’s work. Helmont had explained digestion chemically as a fermentation process involving an acid under the control of a Paracelsian archeus or internal alchemist. At the same time, he was able to show that the human body secreted alkaline materials such as bile. One of his disciples, Franciscus Sylvius (1614–72), a Professor of Medicine at Leyden from 1658 until his death, and a leading exponent of iatrochemistry, extended Helmont’s digestion theory by arguing that it involved the fermentation of food, saliva, bile and pancreatic juices. For Sylvius, this was a ‘natural’ chemical process and involved no archeus, supernatural or astral mechanism of transformation. The pancreatic juices were a recent discovery of physiologists. By taste they were acidic, as was saliva; but bile was alkaline. Since it was well known that effervescence was produced when an acid and alkali reacted together, as when vinegar was poured onto chalk, Sylvius believed that digestion was a warfare, followed by neutralization, between acids and alkalis.

He did not hesitate to extend this conception of neutralization between two chemical opposites to other physiological processes. For example, by suggesting that blood contained an oily, volatile salt of bile (alkali), which reacted in the heart with blood containing acidic vital spirits, he explained how the vital animal heat was produced by effervescence. From this normal state of metabolism, pathological symptoms could be explained. All disease could be reduced to cases of super-acidity or super-alkalinity – a theory that was quickly exploited commercially by apothecaries and druggists and which is not unfamiliar from twentieth-century advertisements.

Sylvius’ theory was popularized by his Italian pupil, Otto Tachenius (1620–90), in the Hippocrates Chemicus (1666) – a title that advertised its iatrochemical approach explicitly. Amid its chemical explanations for human physiology lay a criticism that the greatest need in the 1660s was for a unifying theory of chemical classification and explanation to replace the tarnished hypotheses of the four elements and the three principles. Tachenius urged instead that physicians and chemists adopt a two-element theory that the properties and behaviour of substances lay in their acidity or alkalinity.

The fundamental problem with Tachenius’ suggestion was that there was no satisfactory definition of an acid or an alkali beyond a circular one that an acid effervesced with an alkali and vice versa.

A SCEPTICAL CHEMIST

Robert Boyle (1627–91), who was born in Ireland as the seventh son of the Earl of Cork, was educated at Eton and by means of a long continental tour from which he returned to England in 1644. In the 1650s he became associated with Samuel Hartlib and his circle of acquaintances, who sometimes referred to themselves as the ‘invisible college’. The Hartlibians were interested in exploiting chemistry both for its material usefulness in medicine and trade and for the better understanding of God and Nature. Since the group included the American alchemist George Starkey among its members, not surprisingly Boyle began to read extensively into the alchemical literature. Between 1655 and 1659 and from 1664 to 1668 Boyle lived in Oxford, where he became associated with the group of talented natural philosophers who were to form the Royal Society in 1661. Boyle was an extraordinarily devout man who, like Newton a generation later, wrote as much on theology as on natural philosophy. He paid for translations of the Bible into Malay, Turkish, Welsh and Irish, and left money in his will for the endowment of an annual series of sermons, to be preached in St Paul’s Cathedral, that would reconcile and demonstrate how science supported religion.

The generation before Boyle had seen a revival in the fortunes of the atomic theory of matter. Throughout the middle ages, as the text of Geber’s Summa perfectionis demonstrates, natural philosophers had been familiar with the Aristotelian doctrine of the minima naturalis, which they treated to all intents and purposes as ‘least chemical particles’. Lucretius’ poem, On the Nature of Things, had been rediscovered and printed in 1473. A century later, in 1575, Hero’s Pneumatica was published and disseminated an alternative non-Epicurean atomic theory in which the properties of bulk matter were explained by the presence of small vacua that were interspersed between the particles of a body. This theory, which allowed heat to be explained in terms of the agitation of particles, was exploited by, among others, Galileo, Bacon and Helmont in their search for an alternative to Aristotelianism. A century later, in 1660, the French philospher, Pierre Gassendi (1592–1655), advocated the Epicurean philosophy of atoms to replace Aristotelian physics. His work, Philosophiae Epicuri Syntagma, was a rambling summary of atomism, but its assertion of the vacuum provided an alternative to Descartes’ plenistic particle theory. Descartes’ three grades of matter, i.e. large terrestrial matter, more subtle or celestial matter that filled the interstices of the former, and still subtler particles that filled the final spaces, bore more than a passing resemblance to the elements of earth, air and fire, let alone Paracelsus’ principles of salt, mercury and sulphur. To those who have studied the matter, it is clear that Boyle was much indebted both to Gassendi and to his English disciple, Walter Charleton, whose Epicuro-Gassendo-Charletoniana (1654) had not only presented a coherent mechanical philosophy in terms of atoms or corpuscles, but placed it in an acceptable Christian context.

In 1661 Boyle published The Sceptical Chymist, a critique of peripatetic (Aristotelian), spagyric (Paracelsian and Helmontian) chemistry and the substantiation of physical and chemical properties into pre-existent substantive forms and qualities. Although designed as an argument in dialogue form between four interlocutors, Carneades (a sceptic), Themistius (an Aristotelian), Philoponus (a Paracelsian) and Eleutherius (neutral), Boyle’s rather verbose, digressive and rambling style makes it difficult for the modern reader to follow his argument. Much of the treatise becomes a monologue by Boyle’s spokesman, Carneades. Fortunately, there exists in manuscript an earlier, more straightforward, less literary, and hence more convincing, version of the essay, ‘Reflexions on the Experiments vulgarly alledged to evince the four Peripatetique Elements or the three Chymical Principles of Mixt Bodies’. Apart from one or two references to the later book, we shall follow the argument in this manuscript, which from internal evidence was written in 1658.

A typical defence of the four-element theory was to cite the familiar case of burning wood¹:

The experiment commonly alledged for the common opinion of the four elements, is, that if a green stick be burned in the naked fire, there will first fly away a smoake, which argued AIRE, then will boyle out at the ends a certain liquor, which is supposed WATER, the FIRE dissolves itself by its own light, and that incombustible part it leaves at last, is nothing but the element of EARTH.

Boyle, following Helmont quite closely, raised a number of objections to this interpretation. In the first place, although four ‘elementary’ products could be extracted from wood, from other substances it was possible to extract more or fewer.

Out of some bodies, four elements cannot be extracted, as Gold, out of which not so much as any one of them hath been hitherto. The like may be said of Silver, calcined Talke, and divers other fixed bodies, which to reduce into four heterogeneal substances, is a taske that has hitherto proved too hard for Vulcan. Other bodies there be, that can be reduced into more,… as the Bloud of men and other animals, which yield, when analyzed, flegme, spirit, oile, salt and earth.

Here Boyle seems to have stumbled upon a distinction between mineral and organic substances, but he did not develop this point. Instead, he objected to the assumption that the four products of wood were truly elements. A little further chemical manipulation suggested, indeed, that the products were complex.

As for the greene sticke, the fire dos not separate it into elements, but into mixed bodies, disguised into other shapes: the Flame seems to be but the sulphurous part of the body kindled; the water boyling out at the ends, is far from being elementary water, holding much of the salt and vertu of the concrete: and therefore the ebullient juice of several plants is by physitians found effectual against several distempers, in which simple water is altogether unavailable. The smoake is so far from being aire, that it is as yet a very mixt body, by distillation yielding an oile, which leaves an earthe behind it; that it abounds in salt, may appear by its aptness to fertilise land, and by its bitterness, and by its making the eyes water (which the smoake of common water will not doe) and beyond all dispute, by the pure salt that may be easily extracted from it, of which I lately made some, exceeding white, volatile and penetrant.

This criticism clearly shows how carefully Boyle had studied the products of the destructive distillation of wood – an experiment that used to be one of the introductory lessons in British secondary school chemistry syllabuses in the twentieth century.

Finally, Boyle turned his penetrating criticism to the method of fire analysis itself. Why was it, he asked, that if the conditions of fire analysis were slightly altered or a different method of analysis was used, the products of analysis were different? Thus, if a Guajacum log was burned in an open grate, ashes and soot resulted; but if it was distilled in a retort, ‘oile, spirit, vinegar, water and charcoale’ resulted. And whereas aqua fortis (concentrated nitric acid) separated silver and gold by dissolving the silver, fire would, on the contrary, fuse the two metals together. Moreover, the degree of fire (the temperature) could make the results of analysis vary enormously.

Thus lead with one degree of fire, will be turned into minium [lead oxide], and with another be vitrified, and in neither of these will suffer any separation of elements. And if it be lawful for an Aristotelian, to make ashes (which he mistakes for Earthe) passe for an element, why may not a Chymist upon the same principle, argue that glas is one of the elements of many bodies, because by only a further degree of fire, their ashes may be vitrified?

Boyle concluded, therefore, that fire analysis was totally unsuited to demonstrating that substances are all composed of the same number of elements. To do this was like affirming ‘that all words consist of the same letters’. Such a critique of the Aristotelian elements was by no means unique to Boyle. Indeed, there is considerable evidence that, apart from his own original experiments, he drew the main thrust of the critique from the writings of Gassendi, who had made similar points when reviving the atomic philosophy of Epicurus and Lucretius.

Once this is realized, the point of his objections to the three principles of Paracelsus becomes plain. Lying in the background to the ‘Reflexions’, and made explicit in The Sceptical Chymist, was a corpuscular philosophy. Boyle’s argument was that, even if there were three principles or elements inside a material, it did not necessarily follow that an analysis into these three parts was possible, or that they were the ultimate parts. Oddly enough, nineteenth-century organic chemists were to be faced by exactly the same problem: what guarantee was there that the products of a reaction told one anything about the original substance?

It is not altogether unquestionable that if three principles be separated from bodies, they were pre-existent in them; for, perhaps, when fire dos sever the parts of bodies, the igneous atoms doe variously associate themselves with the disjoined particles of the dissolved body, or else make severall combinations of the freed principles of the same body betwixt themselves, and by that union, or at least cohesion, there may result mixts of a new sort.

As Laurent discovered in the 1830s, such scepticism is valuable; but if taken too literally, it would prevent any use of reactions as evidence of composition.

Boyle therefore concluded of the Paracelsian principles that, until such time as someone analysed gold and similar substances into three consistent parts, ‘I will not deny it to be possible absolutely … yet must I suspend my belief, till either experience or competent testimony hath convinced me of it’.

There was one further card up Boyle’s sleeve; he was able to use the Helmontian theory of one element as an argument against the alternative three- and four-element theories. He appears at first to have had strong doubts concerning the truth of Helmont’s water hypothesis; but after experiments of his own he had to admit that it seemed plausible. In both the ‘Reflexions’ and The Sceptical Chymist, Helmont’s work appears in a favourable light. Nearly a third of the ‘Reflexions’ is devoted to a discussion of Helmont’s work. Some of Boyle’s own experiments seemed to support the water theory, though he remained agnostic on the question whether or not water was truly elementary. Indeed, in The Sceptical Chymist he argued that water itself was probably an agglomeration of particles.

Boyle’s experiments were very similar to those of Helmont:

I have not without some wonder in the analysis of bodies, marvelled how great a share of water goes to the making up of divers, whose disguise promises nothing neer so much. Some hard and solid woods yield more of water alone than all the other elements. The distillation of eels, though it yields some oile, and spirit, and volatile salt, besides the caput mortum, yet were all these so disproportionate to the water that came from them … that they seemed to have been nothing, but coagulated phlegme.

Boyle’s own astute version of the willow tree experiment, after verification with a squash or marrow seed left to grow in a pot for five months, involved growing mint in water alone, for, as he reasoned, if the plant drew its substance entirely from water, the presence of earth in which to grow the seed or shoot was irrelevant.

Helmont’s position, based upon a thorough experimental foundation, seemed on the face of things very attractive. But Boyle could find no evidence for the growth of metals or minerals from water; neither could he see how plant perfumes and nectars arose from water alone. There was no evidence that an alcahest existed and, in any case, the mechanical philosophy saw no ultimate physical difference between a solvent and a solute. Thus although Helmont’s experiments were a useful stick with which to beat the Aristotelian and Paracelsian theories of elements, Boyle was no partisan of Helmont’s alternative interpretation.

On the other hand, Helmont’s theory appealed to Boyle’s Biblical literalism, for the world, according to Genesis and Hebrew mythologies, had emerged ‘by the operation of the Spirit of God,… moving Himself as hatching females do … upon the face of the water’. This original water could never have been elementary, but must have consisted ‘of a great variety of seminal principles and rudiments, and of other corpuscles fit to be subdued and fashioned by them’. Possibly, then, common water had retained some of this original creative power.

Boyle’s advice on the whole question of the evidence for the existence of elements was to keep an open mind and a sceptical front.

The surest way is to learne by particular experiments what heterogeneous parts particular bodies do consist of, and by what wayes, either actual or potential fire, they may best and most conveniently be separated without fruitlessly contending to force bodies into more elements than Nature made them up of, or strip the severed principles so naked, as by making them exquisitely elementary, to make them laboriously uselesse.

There was irony in that final remark, for through his adherence to the corpuscular philosophy Boyle proceeded to make the concept of the element ‘laboriously uselesse’. Before pursuing this point, however, what sceptical mischief did Boyle wreak on the acid – alkali theory?

This theory was not discussed in either The Sceptical Chymist or its manuscript draft version. Instead, Boyle criticized Sylvius’ and Tachenius’ views in 1675 in Reflections upon the Hypothesis of Alcali and Acidium. Ten years previously, in his Experimental History of Colours (see chapter 5), Boyle had made an important contribution to acid – base chemistry with the development of indicators. He had found that a blue vegetable substance, syrup of violets, turned red with acids and green with alkalis. The test was applicable to all the known acids and could be used confidently to give a working definition of an acid: namely, that an acid was a substance that turned syrup of violets red. The test was also quantitative in a rough-and-ready way, since neutral points could be determined.

When Boyle came to consider the Sylvius – Tachenius theory in 1675, he was able to object to the vagueness of the terms ‘acid’ and ‘alkali’ as commonly used in the theory. Effervescence, he pointed out, was not a good test of acidity, since it was also the test for alkalinity; it also created difficulties with the metals, which effervesced when added to acids. Were metals alkalis? If zinc was reacted with the alkali called soda (sodium carbonate), it was dissolved. Was zinc, therefore, an acid?

Whereas in The Sceptical Chymist Boyle had only played the critic and not put forward any concrete proposal to replace the Aristotelian and Paracelsian theories, in the case of his criticism of the acid – alkali theory, he was able to offer an alternative, experimentally based classification of acidic, alkaline and neutral solutions, which could be used helpfully in chemical analysis. By building on this experimental work, succeeding chemists were able to develop the theory of salts, which proved one of the starting points for Lavoisier’s revision of chemical composition in the eighteenth century.

There was also a second important criticism of the acid – alkali theory. In its vague metaphorical talk of ‘strife’ between acidic and alkaline solutions, the theory possessed a decidedly unmechanical, indeed, anti-mechanical, air about it. To a corpuscular philosopher like Boyle, the theory was occult, in the seventeenth-century sense that it appealed to explanations that could not be reduced to the mechanical geometrical principles of size, shape and motion with which God had originally endowed them. Even so, it is doubtful whether Boyle subscribed fully to the reduction of chemical properties to geometrical qualities, as early eighteenth-century philosophers were to do. The most Boyle was prepared to argue was that chemical properties depended on the way the particles that composed one body were disposed to react with those of others.

He was, no doubt, acutely aware of the fact that, by abolishing Aristotelian formal causes, an explanation of the distinction between chemical species was lost. Gassendi’s solution, which Boyle followed, had been to introduce ‘seminal virtues’ or seeds, ‘which fit the corpuscles together … into little masses [which] shapes them uniformly’. Boyle’s experiments on variable crystalline shapes produced when the same acid was reacted with different metals enabled him to argue that each acid, alkali and metal had its own specific internal form or virtue, which could be modified in the presence of others. Here Boyle found the earlier idea of medieval minima and mixtion useful since, unlike physical atomism, it tried to explain combination by more than physical cohesion alone. As previously noted, another way forward, represented by Descartes, was to explain form geometrically by attributing chemical significance to the shapes of the ultimate physical particles. Descartes’ three elements came in three shapes, irregular, massive and solid, and long and thin. Although there was an obvious analogy with Paracelsian sulphur, salt and mercury, Norma Emerton has also noted the parallel with contemporary Dutch land drainage schemes in which a framework of sticks interleaved with branches was covered with stones to form a terra firma. For Descartes, therefore, composition (mixtion) and the new form was caused by simple entanglement.

BOYLE’S PHYSICAL THEORY OF MATTER

Boyle used to be dismissed by historians of chemistry as only a critic, but this is certainly not the tenor of his work as a whole. He was an extremely prolix, rambling and, by today’s standards, unmethodical writer who published some 42 volumes. He adopted a Baconian method towards his scientific activities, and this was often reflected in the apparently random method of composition, which never allowed him time to write a comprehensive treatise on chemistry. We know that his manuscripts were delivered to the printer in bits and pieces, always behind schedule, and full of addenda and ‘lost experiments’ from previous research projects. It is small wonder, then, that Peter Shaw, Boyle’s eighteenth-century editor, found it necessary to apologize to readers for the lack of system in Boyle’s collected works:

But as Mr Boyle never design’d to write a body of philosophy, only to bestow occasional essays on those subjects whereto his genius or inclination led him; ‘tis not to be expected that even the most exquisite arrangement should ever reduce them to a methodical and uniform system, though they afford abundant material for one.

Despite Shaw’s defensive remark, there was in fact a system in Boyle’s ‘ramblings’. Elsewhere Shaw himself identified it when he referred to Boyle as ‘the introducer, or at least, the great restorer, of the mechanical philosophy amongst us’. This claim that Boyle had restored the mechanical philosophy had first appeared in one of Richard Bentley’s Boyle lectures, or sermons, several years earlier.

The mechanical or corpuscular philosophy, though peradventure the oldest as well as the best in the World, had lain buried for many ages in contempt and oblivion, till it was happily restored and cultivated anew by some excellent wits of the present age. But it principally owes its re-establishment and lustre to Mr Boyle, that honourable person of ever blessed memory who hath not only shown its usefulness in physiology (i.e. physics) above the vulgar doctrines of real qualities and substantial forms, but likewise its great serviceableness to religion itself.

By the mid seventeenth century there was no longer any conceptual difficulty involved in the acceptance of minute particles, whether atomic or (less controversially) corpuscular, which, though invisible and untouchable, could be imagined to unite together to form tangible solids. No doubt the contemporary development of the compound microscope by Robert Hooke and others helped considerably in stimulating the imagination to accept a world of the infinitely small, just as the telescope had banished certain conceptual difficulties concerning the possibility of change in the heavens. If only Democritus had a microscope, Bacon said, ‘he would perhaps have leaped for joy, thinking a way was now discovered for discerning the atom’.

Boyle’s corpuscles were neither the atoms of Epicurus and Gassendi, nor the particles of Descartes and the Cartesians. They were at once more useful and more sophisticated than either of them. Boyle’s mechanical philosophy was built on the principles of matter and motion. The properties of bulk matter were explained by the size, shape and motion of corpuscles, and the interaction of chemical minima naturalia (molecules), the evidence for which lay in chemical phenomena. Like Bacon and his fellow members of the Royal Society, however, Boyle always claimed to dislike and distrust ‘systems’.

It has long seemed to me none of the least impediments of true natural philosophy, that men have been so forward to write systems of it, and have thought themselves obliged either to be altogether silent, or not write less than an entire body of physiology.

Yet, while he disagreed with Cartesian physics, he seems to have felt that Descartes’ picture of the world as an integrated system, or whole, was a fruitful one. He agreed that there were no isolated pieces in Nature; that every piece of matter in the universe was continually acted upon by diverse forces or powers. The world was a machine, ‘a self-moving engine’, ‘a great piece of clockwork’ comparable to ‘a rare clock such as may be seen at Strasbourg’, then the engineering marvel of Europe. God was the clock-maker, the universe was the clock.

All this sounds like a ‘system’, as indeed it was. What Boyle meant by opposing systems, as such, was that they were usually based upon an a priori, experimentally indefensible set of hypotheses. They had usually been assembled from hypotheses that were not verae causae (true causes), as Newton was to call the kind of hypothesis that ought to be acceptable in natural philosophy.

We can see now why Boyle could accept a mechanical, corpuscular system of philosophy. The corpuscular philosophy was a vera causa, which could explain a tremendous range of diverse phenomena, and which could be experimentally defended. At the same time, it avoided and did away with ‘inexplicable forms, real qualities, the four peripatetick elements … and the three chymical principles’. Hotness, coldness, colour and the many secondary qualities and forms of Aristotelian physics were swept aside and explained solely in terms of the arrangements, agglomerations and behaviour of chemical particles as they interacted. Boyle’s assertion of the corpuscular philosophy was like Galileo’s claim that the book of Nature was written in mathematical terms. Boyle’s book was ‘a well-contrived romance’ of which every part was ‘written in the stenography of God’s omnipotent hand’, i.e. in corpuscular, rather than geometrical, characters. By revealing its design, like Gassendi and Charleton earlier, Boyle reconciled what had formerly been perceived as an atheistical system with religion and, indeed, with the tenets of the Anglican church that had become the re-established Church of England following the Civil War.

Boyle demonstrated the usefulness of chemistry not merely to medicine and technology (where it had long been accepted) but also to the natural philosopher, who had long despised it as the dubious activity of alchemists and workers by fire. Boyle aimed to show natural philosophers that it was essential that they took note of chemical phenomena, for the mechanical philosophy could not be properly understood otherwise. It was true, he admitted, that the theories of ordinary spagyrical chemists were false and useless; nevertheless, their experimental findings deserved attention, for if they could be disentangled from false interpretations, much would be found that would illustrate and support the corpuscular theory of matter.

In this way, Boyle strove to ‘begat a good understanding betwixt the chymists and the mechanical philosophers’. Chemists recognized him as a fellow chemist, even though he was a natural philosopher; while the natural philosophers recognized him as a respectable chemist because he was also a member of their company. By advocating a mechanical philosophy, Boyle would raise the social and intellectual status of ‘workers by fire’, reduce their proneness to secrecy and mysterious language, and make them into natural philosophers. As he wrote in another essay of 1661²:

I hope it may conduce to the advancement of natural philosophy, if,… I be so happy, as, by any endeavours of mine, to possess both chymists and corpuscularians of the advantages, that may redound to each party by the confederacy I am mediating between them, and excite them both to enquire more into one another’s philosophy, by manifesting, that as many chymical experiments may be happily explicated by corpuscularian notions, so many of the corpuscularian notions may be commodiously either illustrated or confirmed by chymical experiments.

Boyle may be said to have united the proto-disciplines of chemistry and physics. But the partnership proved premature, for Boyle succumbed to the danger of not replacing the elements and principles of the chemists with a mechanical philosophy that was useful to the working chemist. This criticism can be most clearly made when discussing Boyle’s definition of the element in the sixth part of The Sceptical Chymist.

I now mean by elements, as those chymists that speak plainest do by their principles, certain primitive and simple, or perfectly unmingled bodies; which not being made of any other bodies, or of one another, are the ingredients of which all those called perfectly mixt bodies are immediately compounded, and into which they are ultimately resolved.

Leaving aside the fact that Boyle made no claim to be defining an element for the first time (as so many modern chemistry textbooks claim), in his next sentence he went on to deny that the concept served any useful function:

… now whether there be any one such body to be constantly met with in all, and each, of those that are said to be elemented bodies, is the thing I now question.

A modern analogy will make Boyle’s scepticism clear. If matter is composed ultimately of protons, neutrons and electrons, or, more simply still, of quarks, this, according to Boyle, should be the level of analysis and explanation for the chemist, not the so-called ‘elements’ that are deduced from chemical reactivity. To Boyle, materials such as gold, iron and copper were not elements, but aggregates of a common matter differentiated by the number, size, shape and structural pattern of their agglomerations. Although he clearly accepted that such entities had an independent existence as minima, he was unable to foresee the benefit of defining them pragmatically as chemical elements. For Boyle an ‘element’ had been irreversibly defined by the ancients and by his contemporaries as an omnipresent substance.

The seventeenth-century corpuscular, physical philosophy was all very well. It might explain chemical reactions, but it did not predict them, nor did it differentiate between simple and complex substances, the elementary and the compound. Nor, at this stage, did it align the supposed particles with weight and the chemical balance. Hence, although corpuscularianism was not overtly denied by later chemists, who were often content to accept it as an explanation of the physical character of matter, in chemical practice it was ignored. Chemists still needed the concept of an element and blithely returned to the four elements or to some other elementary concept. One thing had changed, however, as a result of Boyle’s criticisms. It was no longer possible to argue seriously that all of the possible elements, however many a chemist might postulate, were ubiquitously present in a particular material. Boyle’s scepticism suggested the possibility that some substances might contain less than the total number of elements; this made it possible for later chemists to be pragmatic about elements and to increase their number slowly and stealthily throughout the eighteenth century.

This more pragmatic view is seen clearly in Nicholas Lemery’s Cours de chymie (1675; English trans. 1686)³:

The word Principle in Chymistry must not be understood in too nice a sense: for the substances which are so-called, are Principles in respect to us, and as we can advance no further in the division of bodies; but we well know that they may be still further divided in abundance of other parts which may more justly claim, in propriety of speech, the name of Principles: wherefore such substances are to be understood as Chymical Principles, as are separated and divided, so far as we are capable of doing it by our imperfect powers.

This comes pretty close to Lavoisier’s operational definition of an element (Chapter 3).

It would be wrong to leave the impression that Boyle was a modern physical chemist, or, rather, chemical physicist. As a corpuscularian, Boyle had no difficulty in accepting the plausibility of transmutation of metals; indeed, a particle theory made ‘the alchymists’ hopes of turning other materials into gold less wild’. We know that Boyle took stories of magical events and of successful transmutations extremely seriously. In 1689 Boyle helped to secure the repeal of Henry IV’s Act against the multiplication of silver and gold, on the grounds that it was inhibiting possibly useful metallurgical researches. Throughout his life he investigated alchemists’ claims, albeit privately and cautiously and even secretly since, as recent research has shown, he clearly identified transmutation with the intervention of supernatural forces.

THE VACUUM BOYLIANUM AND ITS AFTERMATH

Boyle’s other principal contribution to natural philosophy was his investigation of the air, made possible by the invention of the air pump. The vacuum pump was first developed in Germany by Otto von Guericke, who demonstrated at Magdeburg in the 1650s how air could be pumped laboriously out of a copper globe to leave a vacuum. He then found that the atmosphere exerted a tremendous compressing force upon the globe. This was demonstrated theatrically in the famous Magdeburg experiment, which involved sixteen horses in trying to tear two evacuated hemispheres apart. Details of Guericke’s pumping system, which were published in 1657, rapidly awakened interest throughout Europe; for if a vacuum really was formed, this was prima facie evidence for the fallibility of Aristotelian physics and evidence in favour of the corpuscular philosophy.

Assisted by a young and talented laboratory assistant, Robert Hooke, Boyle built his own air pump in 1658 and began to investigate the nature of combustion and respiration with its aid. Some forty-three of his experimental findings, most of which he had had carefully witnessed by reputable friends and colleagues, were published in 1660 in New Experiments Physico-Mechanical touching the Spring of the Air and its Effects. Boyle’s law, linking pressure (the spring) and volume of the air, was developed from an experimental investigation provoked by a controversy after the book’s publication. For many years subsequently the British referred to the vacuum affectionately as the ‘vacuum Boylianum’.

Experiments with birds, mice and candles slowly led Boyle to conclude that air acted as a transporting agent to remove impurities from the lungs to the external air. (Incidentally, Boyle’s observation that insects do not die in a vacuum was confirmed in the twentieth century by Willis Whitney at the General Electric Company.) Like Helmont, Boyle never conceived of the air as a chemical entity; rather, it was a peculiar elastic fluid in which floated various reactive particles responsible for the phenomena of respiration, the rusting of iron, deliquescence and the greening of copper. On the other hand, Boyle clearly perceived that something in the air was consumed or absorbed during respiration and combustion, but he remained suitably cautious about its identification. His followers, including Hooke, who, as Curator of Experiments for the Royal Society, soon carved out an independent career for himself, were more confident.

During the English Civil War, Oxford was a Royalist stronghold. King Charles’ physician, William Harvey, who had demonstrated the circulation of the blood in 1628, was Warden of Wadham College, where he stimulated the development of co-operative investigations of physiology. The arrival of Boyle in Oxford in the 1650s further encouraged an interest in chemical questions among this community of undergraduates and Royalist exiles from London, including Richard Lower, John Mayow, John Wallis, John Wilkins and Christopher Wren. In 1659 Boyle hired an Alsatian immigrant, Peter Stahl, to teach chemistry publicly in Oxford. Those who were particularly interested in solving some of Harvey’s unanswered puzzles, including what happened to blood in the lungs or what was the origin of the blood’s warmth, took Stahl’s courses in the hope of finding chemical solutions. Among Boyle’s assistants at this time were Hooke and Mayow.

In the Micrographia (1665), a pioneering treatise on microscopy and many other subjects, Hooke developed a theory of combustion that owed something to the two-element acid-alkali theory of Sylvius, and even more to a widely known contemporary meteorological theory that was based upon a gunpowder analogy. According to this ‘nitro-aerial’ theory, thunder and lightning were likened to the explosion and flashing of gunpowder, whose active ingredients were known to be sulphur and nitre. By analogy, therefore, a violent storm was explained as a reaction between sulphureous and nitrous particles in the air. Since it was also known that nitre lowered the temperature of water and fertilized crops, it could be argued that the nitrous particles of air were probably responsible for snow and hail and for the vitality of vegetables. Such ideas can be traced back to Paracelsus and to alchemical writers such as Michael Sendivogius.

Hooke laid out his version of this theory in the form of a dozen propositions. He assumed that air was a ‘universal dissolvent’ of sulphureous bodies because it contained a substance ‘that is like, if not the very same, with that which is fixt in saltpetre’. During the solution process a great deal of warmth and fire was produced; at the same time, the dissolved sulphureous matter was ‘turn’d into the air, and made to fly up and down with it’.

The nitro-aerial theory received its fullest development in the writings of the Cornish Cartesian physician, John Mayow (1641–79) in Five Medico-Physical Treatises published in 1674. How much of his work was mere summary of the ideas of Boyle, Hooke and the Oxford physician, Richard Lower, has been the subject of dispute. Even if his work was syncretic, it was of very considerable interest and influence. Mayow used the theory to explain a very wide range of phenomena, including respiration, the heat and flames of combustion, calcination, deliquescence, animal heat, the scarlet colour of arterial blood and, once more, meteorological events. He showed that, when a candle burned in an inverted cupping glass submerged in water, it consumed the nitrous part of the air, which thereupon lost its elasticity, causing the water to rise. The same thing happened when a mouse replaced the candle.

Hence it is manifest that air is deprived of its elastic force by the breathing of animals very much in the same way as by the burning of flame.

Calcination involved the mechanical addition of nitro-aerial particles to a metal, which, as he knew from some of Boyle’s findings, brought about an increase of weight – an explanation also propagated by Mayow’s obscure French contemporary, Jean Rey. This explanation seemed confirmed by the fact that antimony produced the same calx when it was heated in air as when it was dissolved in nitric acid and heated.

Early historians of chemistry liked to find a close resemblance between Mayow’s explanation and the later oxygen theory of calcination. But it is only the transference properties that are similar. Quite apart from different theoretical entities being used in the two theories, we must note that Mayow’s theory was a mechanical, not chemical, theory of combustion. A more serious historiographical point is that Mayow’s theory essentially marked a return to a dualistic world of principles and occult powers. Sulphur and nitre now replaced the tria prima of Paracelsus.

Nitro-aerial spirit and sulphur are engaged in perpetual hostilities with each other, and indeed from their mutual struggles they meet, and from their diverse states when they succomb by turns, all changes of things seem to arise.

Neither Boyle nor Hooke appears to have referred to Mayow’s work in their writings. In any case, Boyle was sceptical of the ‘plenty and quality of the nitre in the air’.

For I have not found that those that build so much upon this volatile nitre, have made out by any competent experiment, that there is such a volatile nitre abounding in the air. For having often dealt with saltpetre in the fire, I do not find it easy to be raised by a gentle heat; and when by a stronger fire we distil it in closed vessels, it is plain, that what the chemists call the spirit of nitre (nitric oxide), has quite differing properties from crude nitre, and from those that are ascribed to the volatile nitre of the air; these spirits being so far from being refreshing to the nature of animals that they are exceeding corrosive.

Despite the speculative character of the nitro-aerial theory, there is much to admire concerning Mayow’s experimental ingenuity. Although he did not develop the pneumatic trough, he devised a method for capturing the ‘wild spirits’ that Helmont had found so elusive by arranging for pieces of iron to be lowered into nitric acid inside the inverted cupping glass. As we can see, however, the results were inevitably baffling to Mayow, for although the water level in the cup eventually rose (as the nitro-aerial theory predicted), it was initially depressed. (Insoluble hydrogen would have been the first product of this displacement reaction; secondary reactions would have then produced soluble nitrogen dioxide.)

NEWTON’S CHEMISTRY

Newton’s interest in chemistry was life-long and reputedly aroused when, as a schoolboy at Grantham Grammar School, he lodged with an apothecary. He wrote only one overtly chemical paper, but important and influential chemical statements are to be found in the Principia Mathematica (1687) and the Opticks (1704). As mentioned in Chapter 1, there also exist in manuscript thousands of pages of chemical and alchemical notes, much of them identifiable as transcriptions from contemporary printed or manuscript works. Newton seems to have been interested in both exoteric and esoteric alchemy, that is, his interest extended beyond the empirical and experimental information that might be gleaned from alchemical texts to the ‘mysteries’ and secrets that were imparted in metaphor and allegory.

Newton was principally influenced by Helmont and Boyle; he also found the nitro-aerial theory attractive as a sustaining principle reminiscent of Helmont’s blas.

I suspect, moreover, that it is chiefly from the comets that spirit comes, which is indeed the smallest but the most subtle and useful part of the air, and so much required to sustain the life of all things with us.

And in the Principia Newton more than hinted that all matter took its origin in water.

The vapours which arise from the sun, the fixed stars, and the tails of comets, may meet at last with, and fall into, the atmospheres of the planets by their gravity, and there be condensed and turned into water and humid spirits; and from thence, by a slow heat, pass gradually into the form of salts, and sulphurs, and tinctures, and mud, and clay, and sand, and stones, and coral, and other terrestrial substances.

Nature was a perpetual worker; all things, he wrote in the Opticks, grow out of, and return by putrefaction into, water.

Nevertheless, Newton subscribed wholeheartedly to Boyle’s corpuscular philosophy, to which he added the mechanisms of attraction and repulsion to explain not merely the gravitational phenomena of bulk planetary matter, but also the chemical likes (affinities) and dislikes (repulsions) that individual substances displayed towards one another. Such inherent powers of matter, which Newton attributed to a subtle ether that bathed the universe, replaced the astral influences of Paracelsus and the blas of Helmont as the causes of motion and change. Newton made this the subject of his only published chemical paper, ‘De natura acidorium’, written in 1692 but not published until 1710, as well as the ‘Queries’ 31 and 32 of the 1717 edition of the Opticks. In these writings Newton suggested that there were exceedingly strong attractive powers between the particles of bodies, which extended, however, only a short distance from them and varied in strength from one chemical species to another. This hypothesis of short-range force led him to speculate about what eighteenth-century chemists called ‘elective affinities’ and the reason why, for example, metals replaced one another in acid solutions. He gave the replacement order of six common metals in nitric acid.

The investigation of chemical affinity became one of the absorbing problems of chemistry. In 1718, Étienne Geoffroy (1672–1731) produced the first table of affinities, and more elaborate ones were produced by Torbern Bergman (1735–84) and others from the 1750s onwards. As the Newtonian world picture grew in prestige, chemists and natural philosophers also began to interpret these tables in terms of short-range attractions. In 1785 Buffon even identified the laws of affinity with gravitational attraction; but all attempts to satisfy what has been described as the ‘Newtonian dream’ to mathematize (i.e. quantify) affinity ended in failure. It was left to Claude Berthollet to point out in 1803 that other factors, such as mass (concentration), temperature and pressure, also decided whether or not a particular reaction was possible.

Newton’s ether, the active principle of chemical change, was exploited by large numbers of eighteenth-century chemists, including the important Dutch teacher, Hermann Boerhaave (1668–1738). The latter’s Elementa Chemiae (1732), which appeared in English in 1741, assimilated ether to fire. Fire, said Boerhaave, consisted of subtle, immutable bodies that were capable of insinuating themselves into the pores of bodies; it was ‘the great changer of all things in the universe, while itself remaining unchanged’. Like his German contemporary Georg Stahl, whose work he ignored, Boerhaave treated fire, together with the other three Aristotelian elements, as one of the four ‘physical instruments’ available to chemists. Because of the connections that were established between the Scottish universities and the University of Leiden, where Boerhaave taught, Boerhaave came to have considerable influence on the teaching of chemistry to medical students in Scotland by William Cullen (1710–90) and his pupil, Joseph Black (1728–99).

Cullen, for example, explained chemical attraction as due to the self-repulsive character of the particles of etherial fire and to the relative densities of ether within two attracting bodies compared with the density of ether in the external environment. The solid and liquid states similarly depended upon the relative quantities of ether and ordinary matter within a substance – a model that was to have important consequences for the conceptualization of gases. This identification of ether and fire, or heat, stimulated Cullen’s pupil, Joseph Black, to the study of calorimetry, the establishment of the concepts of specific heat capacity and latent heat, and the exploration of the qualitative difference between air and a ‘fixed air’ (carbon dioxide), whose presence in magnesia alba (basic magnesium carbonate) he had deduced in 1766.

Newton was also the inspiration behind the experimentally deft attempts made by Stephen Hales (1677–1761) to discover the mechanism of plant growth through an investigation of the movement of sap. It was while making these investigations in the 1720s that he discovered that plants and minerals contained, or held within their pores, large quantities of air. In his Vegetable Staticks published in 1727, Hales devoted over a third of the book to a demonstration of this finding, which he proved by heating solids and liquids in a gun barrel and collecting the ejected air over water in a vessel suspended from a beam. This discovery that air could be ‘fixed’ was the beginning of pneumatic chemistry, and a key factor in the eighteenth-century ‘chemical revolution’.

THE PHLOGISTONISTS

By rejecting the claim that the ultimate elements could ever be identified by fire analysis alone, and by arguing that whatever was released by fire were not elements but classes of substances, Boyle failed to be helpful to the practical chemist. The result was that practical chemists went back to the elements. But with one difference. They now began to separate physical from chemical theories of matter and to accept that, to all intents and purposes, substances that could not be further refined by fire or some other method of analytical separation were effectively chemical elements. This did not preclude the possibility that these ‘elements’ were composed from smaller physical units of matter, but this was a possibility that the investigative chemists could ignore. Such a pragmatic attitude was to reach its final form in Lavoisier’s definition of the element in 1789. We find a good example of this attitude in the theory of elements advocated by Georg Stahl (1660–1734), which is customarily referred to as the phlogiston theory. This in turn had been developed from the writings of Becher.

The severe economic problems of the several small and scattered states and principalities that made up the Holy Roman Empire had encouraged rulers to surround themselves with advisors and experts. As we have seen, this was one of the reasons why alchemists were often to be found at European courts, as were ‘projectors’ and inventors of various kinds. With the growth of government and civil service, the Germanies developed a tradition of cameralism (economics), which strove to make their countries self-sufficient through the strict control of the domestic economy and the efficient exploitation of raw materials and industry. It was the problems connected with mining and with glass, textile, ceramic, beer and wine manufacturing that encouraged the German states to take chemistry seriously. By the beginning of the eighteenth century, chemistry was to be found in many German universities in both the contexts of medicine and cameralism.

Johann Becher (1635–82?) was an early cameralist. With the backing of the Austrian emperor, Leopold I, he founded a technical school in Vienna in 1676 for the encouragement of trade and manufacture. Some years later he moved to the Netherlands to try to launch a scheme for recovering gold from silver by means of sea sand, and he is reputed to have died in London after investigating Cornish mining techniques. Becher wrote of himself in his most important book, Physica Subterranea (1667), that he was⁴:

… One to whom neither a gorgious home, nor security of occupation, nor fame, nor health appeals to me; for me rather my chemicals amid the smoke, soot and flame of coals blown by bellows. Stronger than Hercules, I work forever in an Augean stable, blind almost from the furnace glare, my breathing (sic) affected by the vapour of mercury. I am another Mithridates saturated with poison. Deprived of the esteem and company of others, a beggar in things material, in things of the mind I am Croesus. Yet among all these evils I seem to live so happily that I would die rather than change places with a Persian king.

Despite its title ‘Subterranean physics’, Becher’s treatise was concerned with the age-old problem of the chemical growth of economically important minerals. A deeply religious work, it was vitalistic and Paracelsian in tone. For Becher, Nature, created by God the chemist, was a perpetual cycle of change and exchange, to which the mercantile economy was an analogy. He could not agree with Helmont’s reduction of the elements to water, claiming that this was a misreading of Genesis; for the Bible had said nothing about the creation of minerals. Since these had clearly developed after the organic world, he supposed that they had been generated from earth and water. Although he rejected Paracelsus’ tria prima, he argued that there were three forms of earth, which, for our convenience, can be symbolized as El, E2 and E3:

terra fluida (E1), or mercurious earth, which contributed fluidity, subtility, volatility and metallicity to substances;

terra pinguis (E2), or fatty earth (the ancient unctuous moisture of the alchemists), which produced oily, sulphureous and combustible properties; and

terra lapidea (E3) or vitreous earth, which was the principle of fusibility.

Air was not a part of mineral creation. Becher implied that the terra pinguis was an essential feature of combustibility, but, unlike Stahl later, he did not notice its participation in reversible reactions. He treated fire solely as an instrument, or agent, of change. Minerals grew from seeds of earth and water in varying proportions under the guidance of a formative principle. Because he had a unified view of Nature, he also referred at length to the more complex compositions of the vegetable and animal kingdoms, where both fire and air were incorporated. However, in re-editing the Physica in 1703, Stahl concentrated solely on the mineral theory.

Stahl, a Professor of Medicine at the newly opened University of Halle, was a Lutheran pietist and a vitalist who kept his chemistry separate from his medicine and vehemently denounced the claims of iatrochemistry. Like Becher, he worked in the cameralist tradition, his first publication, the Zymotechnia Fundamentalis (1697), being concerned with the preparation of fermented beers, wines and bread. It was to help improve the smelting of ores that he first turned to Becher’s treatise.

Like Boyle and Newton, he believed that matter was composed of particles arranged hierarchically in groups or clumps to form ‘mixts’ or compounds. There were four basic types of corpuscle, Becher’s three ‘earths’ and water. In 1718 Stahl redesignated Becher’s terra pinguis (E2) as ‘phlogiston’. If we symbolize water by W, then the four elements, whose existence we can only deduce from experiment, combine together by affinity or the cohesion of water to form secondary (chemical) principles. These substances, like gold and silver and many calces (earths) are extremely stable and cannot be simplified. They are in practice the simplest entities with which the chemist can work, and were to become the elements of modern chemistry. Further combinations among these secondary principles produced mixts such as the metals and salts:

E1 + E2 + E3 + W → secondary principles (e.g. gold) → mixts (e.g. metals) → higher mixts, etc. (e.g. salts)

Moreover, following Boyle, the ultimate four elements are not necessarily omnipresent; but for the secondary principles and mixts to be visible, the particles of the elements and secondary principles have to aggregate among themselves. Echoing Helmont, Stahl believed that ‘gas’ was a release of water vapour from a decomposing mixt.

Stahl, who appears to have had a good working knowledge of the practice of metallurgy, saw an analogy between organic combustion and the calcination of metals. Whereas contemporary metallurgists used charcoal in smelting to provide heat and to ‘protect’ the metal from burning, Stahl supposed that all flammable bodies contained the second earth, phlogiston, which was ejected and lost to the atmosphere during combustion:

In the particular case of metals, X is the calx (oxide).

Stahl was astute enough to see that the reaction was reversed when a calx was heated with charcoal, and interpreted this as due to the transfer of fresh phlogiston from the charcoal:

X + phlogiston → metal [reduction]

Another brilliant explanation was the combustion of sulphur, and its recovery (synthesis) after treatment with salt of tartar (potassium carbonate):

burn

sulphur → universal acid + phlogiston

universal acid + salt of tartar → vitriolated tartar

vitriolated tartar + charcoal → sulphur

This cyclic transaction confirmed Stahl’s belief that sulphur was a mixt containing phlogiston and the principle of acidity, which, following Becher, he called the ‘universal acid’ since he assumed that it was present in all acids. The universal acid itself was a mixt composed from the vitriolic earth and water.

Such transfers as occurred with metals, sulphur and acids were not possible with organic substances, that is, with materials extracted from animals and vegetables, and this made the study of mineral, or inorganic, chemistry all the more interesting. A metal could be made to undergo a series of chemical transformations and be restored completely weight for weight; but an organic material such as a potato would be totally destroyed by chemical manipulation and no amount of added charcoal would ever restore it. Stahl, still unaware of the significance of air in chemical change, had drawn a definite line between inorganic and organic chemistry. In the case of the latter, it appeared that an appeal to the supernumerary properties of a vital soul or organizing principle was still necessary. This was not needed in mineral chemistry, and Stahl rejected Becher’s belief that minerals grew beneath the ground.

Stahl’s phlogistic principle readily explained the known facts of combustion. Combustion obviously ceased because a limited amount of air could only absorb a limited amount of phlogiston. When the air became saturated, or ‘phlogisticated air’, combustion ceased. Equally, combustion might cease simply because substances only contained a limited amount of phlogiston. Obviously, however, phlogiston could not remain permanently in the atmosphere otherwise respiration and combustion would be impossible. Unlike Becher, Stahl assumed that phlogiston was absorbed by plants (as Helmont’s willow tree experiment, and the properties of wood charcoal, demonstrated), which were then eaten by animals. There was a phlogiston cycle in Nature and phlogiston was the link between the three kingdoms of Nature. It was this cycle that was transformed into photosynthesis at the end of the eighteenth century.

To the modern mind the principal snag, indeed absurdity, of the phlogiston theory is that metals and other combustibles gain in weight when burned in air. But according to the phlogiston theory something is lost. Why, then, was there not a corresponding reduction in weight? Stahl himself noticed without comment that, in the reduction of lead oxide (i.e. during the addition of phlogiston), the lead formed weighed a sixth less than the original calx. Possibly this was an exception to the rule, for if Stahl’s paradigm was organic distillation, organic substances do appear to lose weight when they are burned and if the gaseous products of combustion are ignored.

In any case, Stahl’s phlogiston was a principle of far more than mere combustion; it did duty to explain acidity and alkalinity, the colours and odours of plants, and chemical reactivity and composition. Weight change was a physical phenomenon and, while it might be indicative of chemical change, it clearly did not assume a fundamental role in Stahl’s conception of chemistry. Finally, we should note that eighteenth-century chemists were by no means unanimous that metals increased in weight during calcination. Improvements in heating technology had actually made it more difficult to demonstrate. Because experiments were frequently made with powerful burning lenses, which produced temperatures well in excess of the sublimation or vaporization points of oxides, we can well understand why chemists frequently reported losses in weight.

In reality, what seems to us today to be an acute problem with the credibility of the phlogiston theory only became problematical when the gaseous state of matter began to be explored in the 1760s. It was then that phlogiston began to take on bizarre and inconsistent guises: as an incorporeal, etherial fire; as a substance with negative weight; as the lightest known substance, which buoyed up heavier substances; or as one of the newly discovered factitious airs, inflammable air (hydrogen). Boyle’s sceptical and investigative tradition then came into its own again when Lavoisier dismissed Stahl’s theory of composition, and phlogiston in particular, as a ‘veritable Proteus’.

CONCLUSION

It is clear that the kind of chemistry inherited from the seventeenth century was changed in at least six ways by the chemists of Lavoisier’s generation: air had to be adopted as a chemically interactive species; the elemental status of air had to be abolished and exchanged for the concept of the gaseous state; the balance had to be used to take account of gases; the weight increases of substances burned in air had to be experimentally established; a working, practical definition of elements had to be established; and a revised theory of composition had to be adopted, together with a more satisfactory and less-confusing terminology and nomenclature that reflected compositional ideas. The thrust of these revisions was accomplished by Lavoisier and has usually been referred to as the chemical revolution. Does this mean, therefore, that we have to accept that there was no mood for change in the seventeenth century comparable to the revolutionary accomplishments of astronomers, physicists, anatomists and physiologists?

Seventeenth-century chemical practice encompassed four distinctive fields of endeavour. Alchemy, though intellectually moribund, still attracted attention both as a religious exercise and because, in principle, it would have given support to the new corpuscular philosophy. Practical alchemists even at this late stage of its development could still stumble upon important empirical discoveries. In 1675, for example, Hennig Brand, while exploring the golden colour of urine, caused excitement with his discovery of phosphorus. Among medically oriented chemists, iatrochemistry had received its impetus from the writings of Paracelsus, Helmont and the exponents of the acid-alkali theory. The iatrochemists were an important group because they considered their calling worth teaching. In France, in particular, chemistry came to acquire a public following that was reflected in the production of large numbers of textbooks and instruction manuals. The iatrochemists thereby helped to establish chemistry’s respectability and ensured that it would become an important part of the medical and pharmaceutical curriculum. In effect, they began the first phase of the long chemical revolution. A third chemical constituency was that of the chemical technologists, who, in a small but significant way, continued to provide data from their observations and experiments, and who encouraged the cameralistic interest in chemistry.

Finally, there was the critical, but experimentally fruitful, work of Boyle, who did not hesitate to draw upon the work of the other three fields as evidence for the mechanical-corpuscular philosophy. In his hands chemistry became a respectable science. The ‘occult’ forms and qualities of Aristotle were replaced by geometrical arrangements and (in the hands of Newton) forces of attraction and repulsion; the secrecy of the alchemists and that of the technologists was abandoned, and an attempt was made to reform the chaotic and imprecise language of chemistry. While none of these reforms resulted in chemistry as we know it, it would be churlish to deny that chemistry changed during the seventeenth century and shared in the momentum of the general Scientific Revolution.

Nevertheless, the pragmatic element remained undefined and the subject remained the two-dimensional study of solids and liquids and ignored the gaseous state until the time of Hales. Until the role of gases was established and understood, there was a technical frontier that hindered further innovation. That was why late-eighteenth-century chemical progress has always seemed so much more impressive and why, fairly or unfairly, Lavoisier’s synthesis of constitutional ideas and experiment appears as impressive as the work of Newton in physics the century before.

3 Elements of Chemistry

Doubtless a vigorous error vigorously pursued has kept the embryos of truth a-breathing: the quest for gold being at the same time a questioning of substances, the body of chemistry is prepared for its soul, and Lavoisier is born.

(GEORGE ELIOT, Middlemarch, 1872)

‘Chemistry is a French science; it was founded by Lavoisier of immortal fame.’ So wrote Adolph Wurtz in the historical ‘Discours préliminaire’ of his Dictionnaire de chimie pure et appliquée (1869). Needless to say, at a time of intense European nationalism and rivalry, in science as much as in politics, such a claim proved instantly controversial. In fact, as early as 1794, Georg Lichtenberg (1742–99) had argued that the anti-phlogistic chemistry was bringing nothing new to Germany. ‘France’, he claimed, ‘is not the country from which we Germans are accustomed to expect lasting scientific principles.’ As far as Lichtenberg was concerned, whatever might be of value in Lavoisier’s new system of chemistry was really of German origin. Thorpe’s riposte to Wurtz seventy years later was that ‘chemistry is an English science, its founder was Cavendish of immortal memory’ – thus invoking an earlier controversy over which European nation’s chemists had first synthesized water. Raoul Jagnaux’s Histoire de chimie (1896) presented the history of chemistry almost entirely as a French affair, with Lavoisier, once again, as its founder. This led twentieth-century German historians to write histories that emphasized that the origins of modern chemistry lay in the chemical contributions of Stahl and, before him, of Paracelsus.

Today we can smile at such nationalistic obsessions and agree that, even though Lavoisier could never have achieved what he did without the prior and contemporary investigations and interpretations of British, Scandinavian and German chemists and pharmacists, there is an essential grain of truth in Wurtz’s statement. For Lavoisier restructured chemistry from fundamental principles, provided it with a new language and fresh goals. To put this another way, a modern chemist, on looking at a chemical treatise published before Lavoisier’s time, would find it largely incomprehensible; but everything written by Lavoisier himself, or composed a few years after his death, would cause a modern reader little difficulty. Lavoisier modernized chemistry, and the benchmark of this was the publication of his Traité élémentaire de chimie in 1789. On the other hand, historians have come to recognize the continuities between Lavoisier’s work and that of his predecessors. Lavoisier’s deliberate decision to break with the past and to put chemistry on a new footing inevitably meant that he was cavalier with history and that he paid scant attention to his predecessors – thus indirectly providing a source of his own mythology as the father of chemistry.

A SCIENTIFIC CIVIL SERVANT

Antoine-Laurent Lavoisier was born in Paris on 27 August 1743, the son of a lawyer who held the important position of solicitor to the Parisian Parlement, the chief court of France. His wealthy mother, who also came from a legal family, died when Lavoisier was only five. Not surprisingly, therefore, Lavoisier’s education was geared to his expected entry into the legal profession. This meant that he attended, as a day pupil, the best school in Paris, the Collège des Quatres Nations, which was known popularly as the Collège Mazarin. The building still survives and now houses the Institut de France, of which the French Academy of Sciences is a part. The Collège Mazarin was renowned for the excellence of both its classical and scientific teaching. Lavoisier spent nine years at the Collège, graduating with a baccalaureate in law in 1763. This legal training was to help him greatly in the daily pursuit of his career and can be discerned in the precision of his scientific arguments; but his spare time was always to be devoted entirely to scientific pursuits.

One of the close friends of the Lavoisier family was a cantankerous bachelor geologist named Jean-Étienne Guettard (1715–86). Aware of young Lavoisier’s scientific bent, Guettard advised him, while still at the Collège Mazarin, to join a popular chemistry course being given by Guillaume-François Rouelle (1703–70) in the lecture rooms of the Jardin du Roi. Rouelle was following in the tradition established in the seventeenth century of giving public lectures in chemistry aimed at students of pharmacy and medicine. Among his innovations was a new theory of salts, which abandoned both the Paracelsian view that they were variations of a salt principle, and Stahl’s view that they were combinations of water and one or more earths. Instead, Rouelle classified salts according to their crystalline shapes and according to the acids and bases from which they were prepared. Rouelle was also responsible for propagating the phlogiston theory among French chemists by incorporating it into his broader view, adopted from Boerhaave and Stahl, that the four traditional elements could function both as chemical elements and as physical instruments. Thus, fire or phlogiston served a double function as a component of matter and as an instrument capable of altering the physical states of matter. This was different from Stahl, who allowed air and fire only instrumental functions. Air, water and earth could similarly serve as instruments of pressure and solution, and for the construction of vessels, as well as entering into the composition of substances. Rouelle, therefore, accepted Hales’ proof that air could act chemically; like the other three elements, it could exist either ‘fixed’ or ‘free’.

Rouelle’s pupil, G. F. Venel, was one of the few French chemists to pursue Hales’ work before the 1760s. He argued that natural mineral waters were chemical combinations of water and air, and that seltzer water could be reproduced by dissolving soda (sodium carbonate) and hydrochloric acid in water. He also advocated that the reactions of air had to be subsumed ‘under the laws of affinity’. In this way, air came to occupy one of the columns of the many dozens of different affinity tables that were published during the middle of the eighteenth century.

Lavoisier’s earliest knowledge of contemporary ideas concerning the elements, acidity, air and combustion was probably derived from Rouelle’s lectures, which he attended in 1762, as well as from Macquer’s Élémens de chymie théorique (1749) and Venel’s article on ‘chemistry’ in the third volume of the great French Encyclopédie (1753). Between them, Rouelle, Macquer and Venel turned their backs on Boyle’s seventeenth-century physical programme of attempting to reduce chemistry to ‘local motion, rest, bigness, shape, order, situation and contexture of material substances’. Instead, inspired by Newton, they intended to fuse the corpuscular tradition with the more pragmatic chemical explanations of Stahl. They also introduced Lavoisier to the quantitative analysis of minerals.

During the 1750s and 1760s the French government became aware that industry was ‘pushed much further in England than it is in France’. Wondering whether Britain’s increasing wealth and prosperity from trade and manufacture came because ‘the English are not hindered by regulations and inspections’, the French commissioned a series of reports on their country’s industries and natural resources. This interest had several effects: there was a sudden wave of translations of, chiefly, German and Scandinavian technical works on mining, metallurgy and mineral analysis; with these works, part and parcel, came an awareness of the phlogistic theory of chemical composition; moreover, chemists who had trained in pharmacy and medicine, like Macquer, began to find their services in demand for the solution of industrial problems. Guettard had long cherished an ambition to map the whole of France’s mineral possessions and geological formations, and the government readily gave approval in 1763. Needing an assistant who could identify minerals, Guettard persuaded Lavoisier to join him on his geological survey, which lasted until 1766.

In their travels through the French countryside, Lavoisier paid particular attention to water supplies and to their chemical contents. One mineral that particularly interested him was gypsum, popularly known as ‘plaster of Paris’ because it was used for plastering the walls of Parisian houses. Why, Lavoisier wondered, did the gypsum have to be heated before it could be applied as a plaster? Since water could be driven from the plaster by further heating, it seemed that the water could be ‘fixed’ into the composition of this and other minerals – a phenomenon that Rouelle had already termed ‘water of crystallization’. He then showed that it was the loss of some of the fixed water that explained the transformation of gypsum into plaster by heating. Lavoisier was to find the idea of ‘fixation’ significant.

Although Guettard’s geological map of France was never published and Lavoisier’s geological work remained largely unknown to his contemporaries, the work on gypsum was presented to the Academy of Sciences in February 1765, when Lavoisier was twenty-two. With a clear, ambitious eye on being elected to the Academy, the year before he had entered the Academy’s competition for an economical way of lighting Parisian streets. (This was some forty years before coal gas began to be used for this purpose.) Although his involved, meticulous study of the illuminating powers of candles and oil and pieces of lighting apparatus did not win him first prize when the adjudication was made in 1766, his report was judged the best theoretical treatment. King Louis XV ordered that the young man should be given a special medal.

Thus by 1766, this ambitious man had succeeded in bringing his name before the small world of Parisian intellectuals. In the same year, two years before he reached his legal majority of 25, Lavoisier’s father made a large inheritance over to him. To further his complete financial independence, in 1768 Lavoisier purchased a share in the Ferme Générale, a private finance company that the government employed to collect taxes on tobacco, salt and imported goods in exchange for paying the State a fixed sum of money each year. Members received a salary plus expenses, together with a ten per cent interest on the sum they had invested in the company. Such a tax system was clearly open to abuse; consequently, the fermiers were universally disliked and were to reap the dire consequences of their membership of the company during the French Revolution. All the evidence suggests that Lavoisier’s motives in joining the company were purely financial and that, as political events moved later, he strove actively to rid the system of corruption and fraud. Unfortunately, Lavoisier’s later suggestion that the fermiers should beat the smugglers by building a wall around Paris for customs surveillance was to lead to hostility towards him, as may be gathered from the punning aphorism ‘Le mur murent Paris fait Paris murmurant’ (The wall enclosing Paris made Paris mutter).

In 1771, at the age of twenty-eight, Lavoisier further cemented his membership of the Ferme Générale by marrying the fourteen-year-old daughter of a fellow member of the company, Marie-Anne Pierrette Paultze (1758–1836). Despite their difference of age and their childlessness, their marriage was an extremely happy one. Marie-Anne became her husband’s secretary and personal assistant. She learned English (which Lavoisier never learned to read) and translated papers by Priestley and Cavendish for him, as well as an Essay on Phlogiston by the Irish chemist, Richard Kirwan. The latter was then subjected to a critical anti-phlogistic commentary by Lavoisier and his friends, which actually led to Kirwan’s conversion. She also took lessons from the great artist, Louis David, in order to be able to engrave the extensive illustrations of chemical apparatus that appeared in Lavoisier’s Elements. David, in turn, portrayed the Lavoisiers together.

Madame Lavoisier was also hostess at weekly gatherings of Lavoisier’s scientific friends – a role she continued after his execution. It was through such continuing social activities in her widowhood that she met the American physicist, Benjamin Thompson (1753–1814), better known as Count Rumford, whose experiments on the heat produced during the boring of cannon had led him to question the validity of Lavoisier’s caloric theory of heat. After rejecting the suits of Charles Blagden and Pierre du Pont (whose son, Irénée, was to found the huge American chemical company), widow Lavoisier married Rumford in 1805; but they soon proved incompatible and quickly separated. Madame Lavoisier is a good example of how, before the time when they enjoyed opportunities to engage in higher education and in independent scientific research, women played a discrete, but essential, role in the development of science. At a time when the well-off could afford domestic servants, wives and sisters had abundant leisure to help their scientifically inclined fathers, husbands and brothers in their researches.

As a rich and talented man, Lavoisier was an obvious candidate for election to the prestigious Academy of Sciences. Unlike the Royal Society, whose Fellows have always been non-salaried, the French Academy of Sciences was composed of eighteen working ‘academicians’ or pensionnaires. As civil servants, they were paid by the French government (until 1793, by the Crown) to advise the State and to report on any official questions put to them as a body. There were also a dozen honorary members drawn from the nobility and clergy, a dozen working, but unpaid, ‘associates’ (associée) and, to complete the pecking order, a further dozen unpaid assistants (élèves or adjoints). The Academy also made room for its retired pensioners and for foreign honorary associates.

Because of its tight restriction on the number of salaried members, and of members generally, election to the Academy was a prestigious event in the career of a French scientist. This accolade was in contrast to Britain’s Royal Society, which allowed relatively easy access to its fellowship by those with wealth or social status as well as those with scientific talent; consequently, its fellowship lacked prestige. Indeed, until its election procedures were reformed in 1847, fellowship of the Royal Society was not necessarily the mark of scientific distinction that it is today.

The three working grades of the Académie, together with its aristocratic honorary membership, clearly reflected the rigid hierarchical structure of eighteenth-century French society. In practice, the pensioners were allocated between the six sciences of mathematics, astronomy, mechanics, chemistry, botany and anatomy (or medicine). Biology and physics were added under Lavoisier’s directorship of the Académie in 1785. Like the Nobel prizes today, such a distribution frequently prevented the election of a deserving candidate because the most appropriate scientific section was full. There was also a tendency to elect or to promote on grounds of seniority rather than merit. Because membership was restricted, vacancies often led to intense lobbying for positions, factionalism, ill-feeling and sometimes (as with Lavoisier’s election as an associé in 1772) to the bending of rules. The repeated failure of the revolutionary, Jean-Paul Marat, who fancied himself an expert chemist, to gain admission in the 1780s, led him and others to oppose the Academy. Its close association with Royal patronage and its reflection of the ‘corrupt’ hierarchical structure of the ancien régime in any case made it inevitable that it would be suppressed by the revolutionary government in August 1793.

Although, as was to be expected for one so brash and young, Lavoisier failed on his first attempt to join the Academy in 1766, by a modest bending of the rules to create an extra vacancy for him, he was successfully admitted to the lowest rank of assistant chemist in 1768. His chief sponsor described him as ‘a young man of excellent repute, high intellect and clear mind whose considerable fortune permits him to devote himself wholly to science’. Any fears that his membership of the tax company would interfere with his role as academician were probably repressed by the thought that he would be able to entertain on a lavish scale!

Much of Lavoisier’s fortune was probably spent on the best scientific apparatus that money could buy. Some of his apparatus was unique and so complex that his followers were forced to simplify his experimental procedures and demonstrations in order to verify their validity. It should not be thought from this that Lavoisier threw money away on instruments unnecessarily. For example, when measuring the quantity of oxygen liberated from lead calx in 1774, he found that traditional glass retorts were unusable because the lead attacked the glass; clay retorts gave similarly erroneous readings because of their porosity; hence for precise volumetric measurements Lavoisier was forced to design and have made an airtight iron retort. Expense was justified, then, because of the new standard of precision that Lavoisier demanded in chemistry. In the Traité he recognized that economies and simplifications would be possible, ‘but this ought by no means to be attempted at the expense of application, or much less of accuracy’.

Lavoisier was to be a loyal servant of the Academy, by helping to prepare its official reports on a whole range of subjects including – to select from one biographer’s pagelong list – the water supply of Paris, prisons, hypnotism, food adulteration, the Montgolfier hydrogen balloon, bleaching, ceramics, the manufacture of gunpowder, the storage of fresh water on ships, dyeing, inks, the rusting of iron, the manufacture of glass and the respiration of insects. It has been pointed out that, without an ethic of service, such as was entailed in a centralized Royalist state, a privileged citizen such as Lavoisier would have had no incentive to involve himself in such a ‘dirty’ subject as chemistry.

THE CHEMISTRY OF AIR

The problem of the Parisian water supply came to Lavoisier’s attention during the year of his election to the Academy when the purity of water brought to Paris by an open canal was questioned. The test for the potability of water involved evaporating it to dryness in order to determine its solid content. But the use of this technique reminded academicians, including Lavoisier, of the long tradition in the history of chemistry that water could be transmuted into earth. Obviously, if this were the case, the determination of the solid content ‘dissolved’ in water would reveal nothing about its purity.

As we have seen, the transmutation of water into earth had been a basic principle of Aristotle’s theory of the four elements, and a crucial, experimental, factor in van Helmont’s decision that water was the unique element and basis of all things. Although by the 1760s most chemists could no longer credit that such an apparently simple pure substance as water could be transmuted into an incredibly large number of complicated solid materials, it was seriously argued by a German chemist, Johann Eller, in 1746 that water could be changed into both earth and air by the action of fire or phlogiston. For Eller this was evidence that there were only two elements, fire and water. The active element of fire acted on passive water to produce all other substances.

It seems clear from the design of Lavoisier’s experiment on the distillaton of water, which he began in October 1768, that he suspected that the earth described in Eller’s experiment (which he probably read about in Venel’s article on ‘water’ in the fifth volume of the Encyclopédie in 1755) was really derived from the glass of the apparatus by a leaching effect. By weighing the apparatus before and afterwards, and also weighing the water before and after heating continuously for three months, Lavoisier showed that the weight of ‘earth’ formed was more or less equal to the weight loss of the apparatus. Intriguingly, Lavoisier did not clinch his quantitative argument by analysing the materials in the sediment and showing that they were identical to those in glass. Moreover, since the correlation of weights was not exact, some room for doubt remained until two decades later when Lavoisier showed that water was composed of hydrogen and oxygen.

Enough had been done, however, to convince Lavoisier that Eller’s contention that water could be transmuted into earth was nonsense. This was reported to the Academy in 1770. He also surmised, under the influence of Venel’s views on the chemical dissolution of air in liquids and solids, that there was a more plausible explanation of water’s apparent change into vapour or air when heated – namely, that heat, when combined with water and other fluids, might expand their parts into an aerial condition. Conversely, when air was stripped of its heat it lost its voluminous free aerial state and collapsed into, or was ‘fixed’ into, a solid or liquid condition, just as Stephen Hales had found in the 1720s when analysing the air content of minerals and vegetables.

Lavoisier recorded these ideas in an unpublished essay on the nature of air in 1772. Here was the basis for a theory of gases – though at this juncture Lavoisier knew nothing at all of the work of Priestley and others on pneumatic chemistry. He was also, not surprisingly, still interpreting his model of the gaseous state in terms of phlogiston. When air was fixed¹:

… there had to be a simultaneous release of phlogiston or the matter of fire; likewise when we want to release fixed air, we can succeed only by providing the quantity of fire matter, of phlogiston, necessary for the existence of the gaseous state [l’état de fluide en vapeurs].

Lavoisier was now clear that there were three distinct states of matter²:

All bodies in nature present themselves to us in three different states. Some are solid like stones, earth, salts, and metals. Others are fluid like water, mercury, spirits of wine; and others finally are in a third state which I shall call the state of expansion or of vapours, such as water when one heats it above the boiling point. The same body can pass successively through each of these states, and in order to make this phenomenon occur it is necessary only to combine it with a greater or lesser quantity of the matter of fire.

Moreover, it followed from the fact that metals disengaged ‘air’ when they were calcined, that metals contained fixed air:

Apparatus for the preparation, collection and study of gases was a necessary factor in the chemical revolution. It was not until 1727 that Stephen Hales hit upon a way to isolate the ‘air’ produced from a heated solid. In order to estimate as accurately as possible the amount of ‘air’ produced and to remove any impurities from it, Hales ‘washed’ his airs by passing them through water before collecting them in a suspended vessel by the downward displacement of water.

Hales, like John Mayow in the seventeenth century, still thought in terms of a unique air element, but Joseph Black’s demonstration that ‘fixed air’ (carbon dioxide) was different from ordinary air encouraged Henry Cavendish, Joseph Priestley and others to develop Hales’ apparatus to study different varieties of air – or gases, as Lavoisier was to call them. An incentive here was the invention of soda water by Priestley, which encouraged interest in the potentially health-giving properties of artificial mineral waters generally. In 1765, while investigating spa waters, the English doctor, William Brownrigg, invented a simple shelf with a central hole to support a receiving flask or gas holder. This creation of the ‘pneumatic trough’ enabled gas samples to be transferred from one container to another and for gases to join solids and liquids on the chemical balance sheet.

Joseph Priestley (1733–1804) is surely one of the most engaging figures in the history of science. The son of a Yorkshire Congregational weaver and cloth-dresser, Priestley was trained for the Nonconformist ministry at a Dissenting academy in Daventry. Like most Nonconformist academies of the period, this taught a wider curriculum than the universities that included the sciences. After serving a string of ministries, where his theological views became increasingly Unitarian, and a teaching post at the famous Warrington Academy, in 1773 Priestley became the librarian and household tutor of William Petty, the second Earl of Shelburne who, while Secretary of State in Chatham’s cabinet, had opposed George III’s aggressive policy towards American colonists. Already the author of innumerable educational works, in 1767 Priestley had published a History and Present State of Electricity, which launched him upon a part-time career in science. While minister of a Presbyterian congregation at Leeds, and living next door to a brewery, Priestley had begun investigating the preparation and properties of airs. Under Shelburne’s patronage, Priestley had the necessary leisure to prepare some five volumes containing detailed accounts of these experiments on airs, as well as a number of theological works. There was a connection here in that Priestley was attempting to explore the relationship between matter and spirit.

In 1780, retaining a life annuity from Shelburne, Priestley returned to the ministry at Birmingham’s New Meeting. Here he found convivial philosophical and scientific company in the Lunar Society composed of rising industrialists and intellectuals such as Mathew Boulton, James Watt, Josiah Wedgwood and Erasmus Darwin. Although its members were united in their support for the American War of Independence and for the initial stages of the French Revolution, it was Priestley the preacher-orator who was publicly identified with radical criticism of English politics and the discrimination against Dissenters. In 1791 a ‘Church and King’ mob destroyed Priestley’s home and chapel, forcing him to flee to London. Although he was eventually compensated for the loss of his property, in 1794 he decided to emigrate and to join two of his sons in America.

Here he was warmly welcomed in Philadelphia, where he was offered the Chair of Chemistry at the University of Pennsylvania. Instead, Priestley moved to Northumberland, in rural Pennsylvania, where he hoped to found an academy for the sons and daughters of political refugees who would join him there. It did not work out and Priestley spent his declining years cut off by distance from European, and even American, intelligence, and fighting a rearguard action against Lavoisier’s chemistry in his fascinating Considerations on the Doctrine of Phlogiston (1796). Although outmanoeuvred by Lavoisier, Priestley lived on in two ways. His young executor, Thomas Cooper (1759–1839), a fellow refugee from English politics, acquired sufficient up-to-date knowledge of chemistry from studying in Priestley’s library and laboratory to become one of America’s leading chemical educators. A century after Priestley’s discovery of oxygen, in August 1874, a national meeting of chemists, gathered at his home in Northumberland (now a Priestley Museum), decided to create the American Chemical Society.

It was Cavendish who began the collection of water-soluble gases over mercury, but Priestley who brought their study and manipulation to perfection. Curiously, believing that chemistry, like physics, required expensive and complicated instruments, Lavoisier only rarely used the pneumatic trough; instead, he developed an expensive and sophisticated gasometer. A good third of Lavoisier’s Elements of Chemistry was devoted to chemical apparatus. Until the appearance of Michael Faraday’s Chemical Manipulation in 1827, Lavoisier’s descriptions remained the bible of instrumentation and chemical manipulative techniques.

In the spring of 1772, Lavoisier read an essay on phlogiston by a Dijon lawyer and part-time chemist, Louis-Bernard Guyton de Morveau (hereafter Guyton) (1737–1816). In a brilliantly designed experimental investigation, Guyton showed that all his tested metals increased in weight when they were roasted in air; and since he still believed that their combustibility was caused by a loss of phlogiston, he saved the phenomena by supposing that phlogiston was so light a substance that it ‘buoyed’ up the bodies that contained it. Its loss during decomposition therefore caused an increase of weight. Most academicians, including Lavoisier, thought Guyton’s explanation absurd. Following his previous reflections on the role of air, Lavoisier speculated immediately that a more likely explanation was that, somehow, air was being ‘fixed’ during the combustion and that this air was the cause of the increase in weight. It followed that ‘fixed air’ should be released when calces were decomposed – just as Hales’ earlier experiments in Vegetable Staticks had suggested.

One final Encyclopédie article seems to have influenced Lavoisier decisively at this juncture. This was an essay on ‘expansibility’ published in the sixth volume in 1756 by another pupil of Rouelle’s, the philosopher and civil servant, Jacques Turgot. Like Lavoisier, Turgot combined a career of public service with spare-time research in chemistry. But he never published his reflections (or if he did so, he did it anonymously), and we only know of his interesting thoughts from his private correspondence. Turgot arrived independently at the same solution as Lavoisier, namely that Guyton’s experiments could be explained as due to the fixing of air. He had actually learned of Guyton’s work before Lavoisier in August 1771. In a private letter to Condorcet, Turgot noted³:

The air, a ponderable substance which constantly enters into the state of a vapour or expansive fluid according to the degree of heat contained, but which is also capable of uniting with all the other principles of bodies and forming in that state part of the constitution of different compounds … this air combines or separates in different chemical reactions because of a greater or lesser affinity that it has for the principles to which it was attached or with those that one presents to it.

Given that Lavoisier was party to the same intellectual influences as Turgot, it was not surprising that they should have reached the same conclusions. Whether Lavoisier was aware or not of Turgot’s thoughts, he took pains constantly to preserve priority of the idea that it was air that was fixed in calcination, rather than liberated, as he had first thought earlier in 1772. If air was an expanded fluid combined with phlogiston, as Turgot’s Encyclopédie article had suggested, then the phlogiston released during combustion (the process of ‘fixing air’) would explain the heat and light generated during the reaction. It followed that heat and light came from the air, not the metal as the Stahlians had always maintained:

Lavoisier was able to verify this in October 1772 by using a large burning lens belonging to the Academy. When litharge (an oxide of lead) was roasted with charcoal, an enormous volume of ‘air’ was, indeed, liberated. In order to investigate this phenomenon more closely, and in order to ensure priority after finding that sulphur and phosphorus also gained in weight when burned in air, Lavoisier deposited a sealed account of his findings in the archives of the Academy, which he allowed to be opened in May 1773⁴:

What is observed in the combustion of sulphur and phosphorus, may take place also with all bodies which acquire weight by combustion and calcination, and I am persuaded that the augmentation of the metallic calces is owing to the same cause. Experiment has completely confirmed my conjectures: I have carried out a reduction of litharge in a closed vessel, with the apparatus of Hales, and I have observed that there is disengaged at the moment of passage from the calx to the metal, a considerable quantity of air, and that this air forms a volume a thousand times as great as the quantity of litharge employed. This discovery seems to me one of the most interesting that has been made since Stahl and as it is difficult in conversation with friends not to drop a hint of something that would set them on the right track, I thought I ought to make the present deposition into the hand of the Secretary of the Academy until I make my experiments public.

In committing himself to the hypothesis that ordinary air was responsible for combustion and for the increased weight of burning bodies, Lavoisier demonstrated that he was ignorant of most contemporary chemical work on the many different kinds of airs that can be produced in chemical reactions. In Scotland, a decade earlier in 1756, Joseph Black had succeeded in demonstrating that what we call ‘carbonates’ (e.g. magnesium carbonate) contained a fixed air (carbon dioxide) that was fundamentally different in its properties from ordinary atmospheric air. Unlike ordinary air, for example, it turned lime water milky and it would not support combustion. Black’s work did not achieve much publicity or publication in France until March 1773. A few years later, Henry Cavendish studied the properties of a light inflammable air (hydrogen), which he prepared by adding dilute sulphuric acid to iron. These experiments were to stimulate the astonishing industry of Priestley who, between 1770 and 1800, prepared and differentiated some twenty new ‘airs’. These included (in our terminology) the oxides of sulphur and nitrogen, carbon monoxide, hydrogen chloride and oxygen. The fact that most of these were ‘acid’ airs was to be, for Lavoisier, an intriguing phenomenon.

Hence, although largely unknown to Lavoisier in 1772, there was already considerable evidence that atmospheric air was a complex body and that it would be by no means sufficient to claim that air alone was responsible for combustion. Lavoisier seems to have been aware of his chemical ignorance. He wrote in his laboratory notebook on 20 February 1773:

I have felt bound to look upon all that has been done before me as merely suggestive. I have proposed to repeat it all with new safeguards, in order to link our knowledge of the air that goes into combination or is liberated from substances, with other acquired knowledge, and to form a theory.

And, with the firm and confident intention of bringing about, in his own prescient words, ‘a revolution of physics and chemistry’, he spent the whole of 1773 studying the history of chemistry – reading everything that chemists had ever said about air or airs since the seventeenth century and repeating their experiments ‘with new safeguards’. His results were summarized in Opuscules physiques et chimiques published in January 1774.

Ironically, far from clarifying his ideas, his new-found familiarity with the work of pneumatic chemists now led him to suppose that carbon dioxide, ‘fixed air’, in the atmosphere was responsible for the burning of metals and the increase of their weight. This was not unreasonable, and the explanation for Lavoisier’s misconception will be clear. Most calces (that is, oxides) can only be reduced to the metal by burning them with the reducing agent, charcoal (C), when the gas carbon dioxide is produced:

calx + C → metal + fixed air

It was easy to suppose, therefore, that the same fixed air was responsible for combustion:

metal + fixed air → calx

As he noted plaintively in a notebook⁵:

I have sometimes created an objection against my own system of metallic reduction which consists of the following: lime [CaO] according to me is a calcareous earth deprived of air; the metallic calces, on the contrary, are metals saturated with air. However, both produce a similar effect on alkalies, they render them caustic.

Obviously, Lavoisier needed to distinguish between air and fixed air, carbon dioxide. It should be noted how this reasoning was based upon the complementarity of analysis and synthesis. If two simple substances could be combined together to form a compound, then, in principle, it ought to be possible to decompose the compound back into the same components. Lavoisier was to find a perfect example of this in the red calx of mercury, a substance that caused him to revise his original hypothesis significantly.

Two things caused Lavoisier to change his mind. First, his attention was drawn by Pierre Bayen, a Parisian pharmacist, to the fact that, when heated, the calx of mercury (HgO), a remedy used in the treatment of venereal disease, decomposed directly into the metal mercury without the addition of charcoal. No fixed air was evolved. As Bayen pointed out, this observation made it difficult to see how the phlogiston theory could be right. Here was a calx regenerating the metal without the aid of phlogiston in the form of charcoal! Secondly, the mercury calx had also come to the attention of Priestley because of a contemporary uncertainty whether the red calx produced by heating nitrated mercury was the same as that produced when mercury was heated in air. In August 1774 he heated the calx in an enclosed vessel and collected a new ‘dephlogisticated air’, which he found, after some months of confusing it with nitrous oxide, supported combustion far better than ordinary air did. Unknown to Priestley the Swedish apothecary, Scheele, had already isolated what he called ‘fire air’ from a variety of oxides and carbonates in the years 1771–2. But Scheele, working in isolation even in Sweden, did not help to shape Lavoisier’s views in the same way that Bayen and Priestley did. These experiments were reported directly to Lavoisier by Priestley when he was on a visit to Paris during October 1774, but he also published an account of the new air at the end of the same year.

Bayen’s and Priestley’s observations, together with his own experiments with mercuric oxide, caused Lavoisier to revise his hypothesis of 1774. In April 1775, Lavoisier read a paper to the Academy of Sciences ‘on the principle which combines with metals during calcination and increases their weight’ in which, still more confused, he identified the principle of combustion with ‘pure air’ and not any particular constituent of the air. This new hypothesis, which was published in May, was seen by Priestley. The latter, realizing that Lavoisier had not quite grasped that the ‘dephlogisticated air’ generated from the calx of mercury was a constituent part of ordinary air, gently put him right in another book he published at the end of 1775. This, together with further experiments of his own, finally led Lavoisier to the oxygen theory of combustion. In revising the so-called ‘Easter Memoir’ for publication in 1778, and in an essay published the year before, he wrote as follows:

The principle which unites with metals during calcination, which increases their weight and which is a constituent part of the calx is: nothing else than the healthiest and purest part of air, which after entering into combination with a metal, [can be] set free again; and emerge in an eminently respirable condition, more suited than atmospheric air to support ignition and combustion.

Because this ‘eminently respirable air’ burned carbon to form the weak acid, carbon dioxide, while non-metals generally formed acidic oxides, Lavoisier called the new substance oxygen, meaning ‘acid former’⁶:

… the purest air, eminently respirable air, is the principle constituting acidity; this principle is common to all acids.

The etymology, for those who no longer read Greek, is still obvious in the German word for oxygen, Sauerstoff. By this Lavoisier did not mean that all substances containing oxygen were acids, otherwise he would have been hard pressed to explain the basic reactions of metallic oxides. Oxygen was only a potentially acidifying principle; for its actualization, a non-metal had also to be present. Although soon destined to be overthrown as a model of acidity, this was the first chemical theory of acidity; it suggested a general way of preparing acids (by the oxidation of non-metals with nitric acid) and, in terms of ‘degrees of oxidation’, it provided for the time a very reasonable explanation of the different reactivities of acids.

By 1779 half of Lavoisier’s revolution was over. Oxygen gas was a ponderable element containing heat (or caloric, as Lavoisier called it to avoid the word phlogiston), which kept it in a gaseous state. On reacting with metals and non-metals, the heat was released and the oxygen element affixed to the substance, causing it to increase in weight. Metals formed basic oxides, non-metals formed acids (acid anhydrides). In respiration, oxygen burned the carbon in foodstuffs to form the carbon dioxide exhaled in breath, while the heat released was the source of an animal’s internal warmth. (Lavoisier and the mathematician, Pierre Simon Laplace, demonstrated this quantitatively with a guinea pig in 1783 – the origin of the expression ‘to be a guinea pig’.) Respiration was a slow form of combustion. The non-respirable part of air, mofette or azote, later called nitrogen, was exhaled unaltered.

At first glance, in this new theory, phlogiston seems to be transferred from a combustible, such as a metal, to oxygen gas. In reality, although Lavoisier waited some years before articulating the new theory in detail, there were major differences between caloric and phlogiston. Caloric was absorbed or emitted during most chemical reactions, not just those of oxidation and reduction; like Boerhaave’s etherial ‘fiery vigour’, it was present in all substances, whereas phlogiston was usually supposed absent from incombustibles; when added to a substance, caloric caused expansion or a change of state from solid to liquid, or liquid to gas; above all, caloric could be measured thermometrically, whereas phlogiston could not.

Nevertheless, Lavoisier did not challenge the old theory until 1785.

The principal reason why Lavoisier was unable to suggest in 1777 that chemists would be better off by abandoning the theory of phlogiston was that only this theory could explain why an inflammable air (in fact hydrogen) was evolved when a metal was treated with an acid, but no air was evolved when the basic oxide of the same metal was used. If the metal contained phlogiston, the explanation, as Cavendish suggested, was simple:

Lavoisier’s gas theory gave no hint why these two reactions behaved differently. Similarly, his belief that all non-metals burned to form an acid oxide appeared to be weakened by the case of hydrogen, which seemed to produce no identifiable product. If this seems odd, it must be borne in mind that moisture is so ubiquitous in chemical reactions that it must have been easy to ignore and overlook its presence.

It was Priestley who first noticed the presence of water when air and ‘inflammable air’ (hydrogen) were sparked together by means of an electrostatic machine. He described this observation to Cavendish in 1781, who repeated the experiment and reported it to the Royal Society in 1784:

By the experiments … it appeared that when inflammable air and common air are exploded in a proper proportion, almost all of the inflammable air, and near one-fifth of the common air, lose their elasticity and are condensed into dew. It appears that this dew is plain water.

Cavendish told Priestley verbally about his findings. Priestley then told his Birmingham friend James Watt, the instrument maker, who independently of Cavendish arrived at the conclusion that water must be a compound body of ‘pure air and phlogiston’. Watt made no statement to this effect until after Lavoisier announced his own experiments and conclusions, which themselves were triggered by references to Cavendish’s experiments that were made by Cavendish’s secretary, Charles Blagden, during a visit to Paris in 1783. Watt then claimed priority, but found himself forestalled by the prior appearance of Cavendish’s paper.

Much ink and rhetoric was to be spilled over rival claims – Cavendish or Watt in England, or Lavoisier in France. In fact, it was only Lavoisier who interpreted water as a compound of hydrogen and oxygen; Watt agreed, albeit within the conceptual framework of the phlogiston theory, while Cavendish instead viewed water as the product of the elimination of phlogiston from hydrogen and oxygen:

In other words, for Cavendish this was not a synthesis of water at all; instead, as a phlogistonist, he preferred to see inflammable air as water saturated with phlogiston and oxygen as water deprived of this substance. When placed together the product was water, which remained for him a simple substance. As we shall see, it was this same experiment of Cavendish’s that led him to record that nitrous acid was also produced – owing to the combination of oxygen with nitrogen – but that a small bubble of uncondensed air remained (chapter 9).

For Lavoisier, however, Cavendish’s work was evidence that water was not an element. Assisted by the mathematical physicist, Simon Laplace (1749–1827), he quickly showed that water could be synthesized by burning inflammable air and oxygen together in a closed vessel; and with the help of another assistant, Jean-Baptiste Meusnier, he showed that steam could be decomposed by passing it over red-hot iron. Priestley was never convinced by this analysis, arguing that the hydrogen could have come from the iron, not the water. The matter was settled (though never for Priestley) in 1789 when two Dutch chemists, Adriaan van Troostwijk (1752–1837) and Jan Deiman (1743–1808), synthesized water from its elements with an electric spark. The same electric machine could be used to decompose water into its constituents. Once current electricity became available with the voltaic cell in 1800, this same experiment was to usher in the age of electrochemistry. Given Lavoisier’s commitment to oxygen as an acid former, it is not surprising that he should have been so quick off the mark if Cavendish’s work provided him with an essential clue; in fact Lavoisier’s notebooks show that after 1781 he had repeatedly burned hydrogen in search of an acidic product.

Whatever the merits of the claim that Lavoisier was the first to grasp that water was a compound of hydrogen (meaning ‘water producer’) and oxygen, the important point was that he could now explain why metals dissolved in acids to produce hydrogen. This, he asserted, came not from the metal (as the phlogistonists claimed, some even identifying phlogiston with inflammable air), but from the water in which the acid oxide was dissolved:

Although it was left to Davy and others to develop the point, the understanding of water also helped lead to a hydrogen theory of acidity.

THE CHEMICAL REVOLUTION

Lavoisier was now in a position to bring about a revolution in chemistry by ridding it of phlogiston and by introducing a new theory of composition. His first move in this direction was made in 1785 in an essay attacking the concept of phlogiston. Since all chemical phenomena were explicable without its aid, it seemed highly improbable that the substance existed. He concluded:

All these reflections confirm what I have advanced, what I set out to prove [in 1773] and what I am going to repeat again. Chemists have made phlogiston a vague principle, which is not strictly defined and which consequently fits all the explanations demanded of it. Sometimes it has weight, sometimes it has not; sometimes it is free fire, sometimes it is fire combined with an earth; sometimes it passes through the pores of vessels, sometimes they are impenetrable to it. It explains at once causticity and non-causticity, transparency and opacity, colour and the absence of colours. It is a veritable Proteus that changes its form every instant!

By collaborating with younger assistants, whom he gradually converted to his way of interpreting combustion, acidity, respiration and other chemical phenomena, and by twice-weekly soirées at his home for visiting scientists where demonstrations and discussions could be held, Lavoisier gradually won over a devoted group of anti-phlogistonists. Finding that editorial control of the monthly Journal de physique had been seized by a phlogistonist, Lavoisier and his young disciple, Pierre Adet (1763–1834), founded their own journal, the Annales de Chimie in April 1789. The editorial board soon included most converts to the new system: Guyton, Berthollet, Fourcroy, G. Monge, A. Seguin and N. L. Vauquelin. This is still a leading chemical periodical. While Director of the Academy of Sciences from 1785, Lavoisier was also able to alter its structure so that the chemistry section consisted only of anti-phlogistonists.

It is significant that Lavoisier’s new theory was one of acidity as much as combustion. Stahlian chemists had not foreseen that there were many types of ‘airs’ or gases, but, as Priestley’s career shows, they actually had little difficulty in conceptualizing them within a phlogistic framework. The appearance of gases also led to a modification in the phlogistic theory of acidity. According to Stahl, vitriolic acid (sulphuric acid) was the universal acid – ‘universal’ in the sense of being the acid principle present in all substances that displayed acidic properties. However, with the discovery of fixed air, several chemists, led by Bergman in Sweden, had decided that this, not vitriol, was the true universal acid. Such a view was argued vociferously by the Italian, Marsilio Landriani, during the 1770s and 1780s. Landriani claimed to have found evidence that fixed air was a component of all three mineral acids as well as the growing number of vegetable acids such as formic, acetic, tartaric and saccharic acids. It was really this theory of acidity that Lavoisier had to challenge in the 1780s.

Lavoisier’s method was to challenge the theory as displayed in the French translation undertaken by his wife of Richard Kirwan’s Essay on Phlogiston and the Constitution of Acids. He was able to convince Kirwan that the acidity of fixed air was sufficiently explained by the fact that it contained oxygen. The irony here was that Lavoisier’s new theory retained in effect the Stahlian notion of a universal acid principle in the form of oxygen. In practice, the explanation of properties by principles was not to last much longer after the advent of Dalton’s atomism and the evidence that not all acids contained oxygen.

The demonstration by Hales that fixed air formed part of the composition of many solids and liquids had also given rise to speculations that this air was vital to vegetable and animal metabolisms. For example, in 1764, an Irish physician, David Macbride, concluded that ‘this air, extensively united with every part of our body’, served to prevent putrefaction, a prime example of which was the disease called scurvy. The recognized value of fresh vegetables in inhibiting scurvy, he suggested, was due to their fermentative powers. The fixed air that they produced during digestion served to prevent putrefaction inside the body.

It was this suggestion that inspired Priestley to investigate the effects of airs on living organisms – a programme of research that was to form the basis of Davy’s earliest research some time later. Initially, in 1772, Priestley concluded that fixed air was fatal to vegetable life, but this was probably due to the fact that he used impure carbon dioxide from a brewery, or that he was using it in excess. Others, including Priestley’s Mancunian friend, Thomas Henry, found the opposite, that flowers thrived in fixed air. It was while repeating these findings that Priestley discovered that, in the presence of sunlight (but not otherwise), plants growing in water, such as sprigs of mint, gave off dephlogisticated air. This had already been anticipated in 1779 by Jan Ingenhousz (1730–99) who, together with Jean Senebier (1742–1809) in Geneva, laid the foundations of a theory of photosynthesis in plants.

Three particularly important converts to the new chemistry were Guyton (whose work had earlier catalysed Lavoisier’s interest in combustion), Claude-Louis Berthollet (1748–1822) and Antoine Fourcroy (1755–1809). Berthollet’s conversion to Lavoisier’s views seems to have arisen because of his own perturbation at the weight changes involved in calcination, to which Guyton had drawn attention. In his Observations sur l’air (1776), Berthollet explained acidity and weight changes in combustion by means of fixed air, and otherwise incorporated Lavoisier’s work on oxygen into the phlogiston framework. It was the analysis of water, together with increasing personal contact with Lavoisier in the Academy, where they found themselves drawing up joint referees’ reports, that converted Berthollet to Lavoisier’s position by 1785. In fact, Berthollet always had certain reservations. In particular, he never accepted the oxygen theory of acidity, and his investigation of chlorine (first prepared by Scheele in 1774 and assumed by Lavoisier to be oxygenated muriatic acid) seemed to confirm his doubts. In later life he also firmly rejected the notion that chemical properties could be explained in terms of property-bearing principles.

Fourcroy was Lavoisier’s principal interpreter to the younger generation. His ten-volume Système des connaissances chimiques (1800) codified and organized chemistry for the next fifty years around the concepts of elements, acids, bases and salts. Fourcroy saw this structure not only as ‘consolidating the pneumatic doctrine’ but as affording ‘incalculable advantage(s)’ for learning and understanding chemistry (see Table 3.1).

While still a phlogistonist, Guyton was much exercised by the inconsistent nomenclature of chemists and pharmacists. Unlike botany and zoology, whose terminology had been revised and made more precise earlier in the century by the

TABLE 3.1 The contents of Fourcroy’s Système des connaissances chimiques (1800) arranged by classes of substances.

Class | Volume
1. Undecomposed or simple bodies | 1
2. Burned bodies; oxides or acids | 2
3. Salifiable bases; earths and alkalis | 2
4. Salts | 3, 4
5. Metals and metal salts containing an excess of acid (although belonging to class 1, these were dealt with separately because of their number and importance) | 5, 6
6. Minerals | 6
7. Vegetable compounds | 7, 8
8. Animal compounds | 9, 10

Swede, Karl Linnaeus, chemical language remained crude and confusing. In 1782 Guyton made a series of proposals for the systematization of chemical language.

Alchemical and chemical texts written before the end of the eighteenth century can be difficult to read because of the absence of any common chemical language. Greek, Hebrew, Arabic and Latin words are found, there was widespread use of analogy in naming chemicals or in referring to chemical processes, and the same substance might receive a different name according to the place from which it was derived (for example, Aquila coelestis for ammonia; ‘father and mother’ for sulphur and mercury; ‘gestation’ as a metaphor for reaction; ‘butter of antimony’ for deliquescent antimony chloride; and ‘Spanish green’ for copper acetate). Names might also be based upon smell, taste, consistency, crystalline form, colour, properties or uses. Although several of these names have lingered on as ‘trivial’ names (which have even had to be reintroduced in organic chemistry in the twentieth century because systematic names are too long to speak), Lavoisier and his colleagues in 1797 decided to systematize nomenclature by basing it solely upon what was known of a substance’s composition. Since the theory of composition chosen was the oxygen system, Lavoisier’s suggestions were initially resisted by phlogistonists; adoption of the new nomenclature involved a commitment to the new chemistry.

Following the inspiration of Linnaeus, Guyton suggested in 1782 that chemical language should be based upon three principles: substances should have one fixed name; names ought to reflect composition when known (and if unknown, they should be non-committal); and names should generally be chosen from Greek and Latin roots and be euphonious with the French language. In 1787, Guyton, together with Lavoisier, Berthollet and Fourcroy, published the 300-page Méthode de nomenclature chimique, which appeared in English and German translations a year later. One-third of this book consisted of a dictionary, which enabled the reader to identify the new name of a substance from its older one. For example, ‘oil of vitriol’ became ‘sulphuric acid’ and its salts ‘sulphates’ instead of ‘vitriols’; ‘flowers of zinc’ became ‘zinc oxide’.

Perhaps the most significant assumption in the nomenclature was that substances that could not be decomposed were simple (i.e. elements), and that their names should form the basis of the entire nomenclature. Thus the elements oxygen and sulphur would combine to form either sulphurous or sulphuric acids depending on the quantity of oxygen combined. These acids when combined with metallic oxides would form the two groups of salts, sulphites and sulphates. In the case of what later became called hydrochloric acid, Lavoisier assumed that he was dealing with an oxide of an unknown element, murium. Because of some confusion over the differences between hypochlorous and hydrochloric acids, in Lavoisier’s nomenclature hydrochloric acid became muriatic acid and the future chlorine was ‘oxygenated muriatic acid’. The issue of whether the latter contained oxygen at all was to be the subject of fierce debate between Davy, Gay-Lussac and Berzelius during the three decades following Lavoisier’s death.

The French system also included suggestions by Hassenfratz and Adet for ways in which chemicals could be symbolized by geometrical patterns: elements were straight lines at various inclinations, metals were circles, alkalis were triangles. However, such symbols were inconvenient for printers and never became widely established; a more convenient system was to be devised by Berzelius a quarter of a century later.

During the eighteenth century some chemists had turned their minds to quantification and the possible role of mathematics in chemistry. On the whole, most chemists agreed with Macquer that chemistry was insufficiently advanced to be treated mathematically. Although he believed, correctly as it turned out, that the weight of bodies bore some relationship to chemical properties and reactions, the emphasis on affinity suggested that the project was hopeless. Nevertheless, Lavoisier, inspired by the writings of the philosopher, Condillac, believed fervently that algebra was the language to which scientific statements should aspire⁷:

We think only through the medium of words. Languages are true analytical methods. Algebra, which is adapted to its purpose in every species of expression, in the most simple, most exact, and best manner possible, is at the same time a language and an analytical method. The art of reasoning is nothing more than a language well arranged.

In a paper on the composition of water published in 1785, Lavoisier stressed that his work was based upon repeated measuring and weighing experiments ‘without which neither physics nor chemistry can any longer admit anything whatever’. Again, in another essay analysing the way metals dissolve in acids, Lavoisier used the Hassenfratz – Adet symbols:

In order to show at a glance the results of what happens in the solution of metals, I have constituted formulae of a kind that could at first be taken for algebraic formulae, but which do not have the same object and which do not derive from the same principles; we are still very far from being able to obtain mathematical precision in chemistry and therefore I beg you to consider the formulae that I am going to give you only as simple annotations, the object of which is to ease the workings of the mind.

The important point here was that Lavoisier used symbols to denote both constitution and quantity. Although he did not use an equals sign, he had effectively hit upon the idea of a chemical equation. As we shall see, once Berzelius’ symbols became firmly established in the 1830s, chemists began almost immediately to use equations to represent chemical reactions.

While producing the Méthode de nomenclature chimique with Lavoisier and the others, Guyton was converted to the new chemistry. Because the new language was also the vehicle of anti-phlogiston chemistry, it aroused much opposition. Nevertheless, through translation, it rapidly became and still remains the international language of chemistry.

TABLE 3.2 Lavoisier’s ‘elements’ or ‘simple substances’.

Lavoisier’s final piece of propaganda for the new chemistry was a textbook published in 1789 called Traité élémentaire de chimie (An Elementary Treatise on Chemistry). Together with Fourcroy’s larger text (published in 1801), this became a model for chemical instruction for several decades. In it Lavoisier defined the chemical element pragmatically and operationally as any substance that could not be analysed by chemical means. Such a definition was already a commonplace in mineralogical chemistry and metallurgy, where the analytical definition of simple substances had become the basis of mineralogical classification in the hands of J. H. Pott, A. F. Cronstedt and T. Bergman. It was for this reason that Lavoisier’s list of 33 basic substances bore some resemblance to the headings of the columns in traditional affinity tables. Lavoisier’s list included substances such as barytes, magnesia and silica, which later proved to be compound bodies.

After discussing the oxygen theory in part I of the Traité, he discussed their preparation and properties, their oxides and then their salts formed from acidic and basic oxides in part II. Caloric disengaged from oxygen explained the heat and light of combustion. It has been said that the elements formed the bricks while his new views on calcination and combustion formed the blueprint. The Traité itself formed a dualistic compositional edifice. Whenever an acidic earth and metal oxide (or earth) combined, they produced a salt, the oxygen they shared constituting a bond of union between them. As was appropriate for an elementary text, part III, a good third of the book, was devoted to chemical instrumentation and to the art of practical chemistry.

Lavoisier’s table of elements did not include the alkalis, soda and potash, even though these had not been decomposed. Why were they excluded from his pragmatic definition of simple substances? Two reasons have been suggested. In the first place, he was prepared to violate his criterion because of the chemical analogy between these two alkalis and ‘ammonia’, which Berthollet had decomposed into azote (nitrogen) and hydrogen in 1785. Lavoisier was so confident that soda and potash would be similarly decomposed into nitrogen and other unknown principles, that he withheld them from the table of simple substances. On the other hand, although confident that muriatic acid was also compound, because the evidence was not so strong as for the alkalis, he included it in the list of elements. While we may admire Lavoisier’s prescience – Davy was to decompose soda and potash in 1808 – this was a disturbing violation of his own pragmatism. What guarantee did the chemist have that any of Lavoisier’s simple substances were really simple? As we shall see, Lavoisier’s operational approach caused a century of uncertainty and helped to revive the fortunes of the ancient idea of primary matter.

A second explanation is more subtle. Lavoisier’s simple substances were arranged into four groups (see table 3.2). Three of the groups contained the six non-metals and seventeen metals then known, both of which were readily oxidizable and acidifiable, together with the group of five simple ‘earths’. The remaining group was light, caloric, oxygen, azote (nitrogen) and hydrogen. At first glance these elements appear to have nothing in common, but the heading Lavoisier gave them, ‘simple substances belonging to all the kingdoms of nature, which may be considered the elements of bodies’, provides the clue. Lavoisier probably saw these five elements as ‘principles’ that conveyed fundamental generic properties. Light was evidently a fundamental principle of vegetable chemistry; caloric was a principle of heat and expansibility; oxygen was the principle of acidity; hydrogen was the principle of water that played a fundamental role in all three kingdoms of Nature; and nitrogen was a principle of alkalinity. If the 1789 list of elements is compared with a preliminary list he published in 1787, it is found that azote was moved from its original position among the non-metals. It is not unlikely that this change was connected with the decomposition of ammonia and Lavoisier’s decision that soda and potash were compounds of ‘alcaligne’, a nitrogenous principle of alkalinity.

If this interpretation is correct, it illustrates again the role of continuity in Lavoisier’s revolutionary chemistry. Although we cannot now know if this was the position Lavoisier held – a position that was in any case subject to refutation and modification within a few years – it is intriguing to notice that organic chemists (beginning with Liebig) came to see certain elements, namely hydrogen, oxygen, carbon and nitrogen, as the ‘universal’ or ‘typical’ elements of mineral, animal and vegetable chemistry. It was on the basis of this that Gerhardt and Hofmann were to build a ‘type theory’ or organic classification and from which Mendeleev was to learn to classify a greatly extended list of elements in 1869.

By the mid 1790s the anti-phlogistonian camp had triumphed and only a few prominent chemists, such as Joseph Priestley, continued as significant critics. Unfortunately, by then the French Revolution had put paid to the possibility that Lavoisier would apply his insights to fresh fields of chemistry.

THE AFTERMATH

Although opposition to Lavoisier’s chemistry remained strong in Germany for a decade or more, largely for patriotic reasons, and although Cavendish and Priestley never converted, the speed of its uptake is impressive. Much depended, of course, on key teachers. In Germany, Sigismund Hermstadt (1760–1832) translated the Traité in 1792, and in the same year Christoph Girtanner (1760–1800) published a survey of Lavoisier’s chemistry. At Edinburgh the French-born Joseph Black, who had always taught that phlogiston was a principle of levity, lectured on the new chemistry while not necessarily committing himself to it until 1790. His successor, Thomas Charles Hope (1766–1844), ensured that large audiences of medical students learned the new theory after 1787. Scottish opposition seems to have been largely confined to geology, where James Hutton found phlogiston more accommodating to his theory that it was solar light and his need for a plutonic ignitor in the absence of oxygen deep inside the earth; and animal physiology, where, despite Lavoisier’s view of animal heat as the natural exothermic product of burning food inside the body, Adair Crawford developed a complex mechanism involving air, heat, blood, phlogiston and the specific heat capacity of blood.

Despite Lavoisier’s continued research after 1789 – for example, he began some promising work on the analysis of organic substances – he found his official activities as an academician and fermier taking up more and more of his time as the Revolution, which broke out in that year, created more and more technical and administrative problems.

When Lavoisier was born, France was still a monarchy and power lay firmly in the hands of the Crown and aristocracy together with the Roman Catholic church. These two powerful and sometimes corrupt groups, or Estates, which were virtually exempt from taxation, were the landlords of the majority Third Estate of peasant farmers, merchants, teachers and bankers from whom France’s wealth was derived. Agricultural depression, a rise in population and a succession of expensive wars (including France’s intervention in the American War of Independence in 1778) led France towards bankruptcy in the 1780s. The only solution to this seemed to be to introduce a more equitable system of taxation, which, in turn, involved the reformation of political structure, including the reduction of King Louis XVI’s despotic powers.

On 14 July 1789 revolution broke out with the storming of the Bastille prison in Paris. In fear of their lives, Crown and aristocracy renounced their privileges, while a National Assembly composed of the Third Estate drew up the Declaration of the Rights of Man. National unity was short-lived, however, as the more radical Jacobins manoeuvred for political power and the downfall of the monarchy. War with Austria and Prussia was to prove the excuse for the King’s execution on 21 January 1793. In the period of terror and anarchy that followed, Lavoisier was to lose his life. For, despite his undoubted support for the initial phase of the Revolution and his hard work within the Academy in improving the quality of gunpowder or in devising the metric system in 1790, his services to France and his international reputation were, in the words of one historian, ‘as dust in the balance when weighed against his profession as a Fermier-Géneral’. On 24 November 1793 Lavoisier and his fellow shareholders (including his father-in-law) were arrested and charged, ludicrously, with having mixed water and other ‘harmful’ ingredients in tobacco, charging excessive rates of interest and withholding money owed to the Treasury.

Although later investigations by historians have revealed the worthlessness of these charges, they were more than sufficient in the aptly named ‘Age of Terror’ to ensure the death penalty. Even so, there is some evidence that Lavoisier, alone of the fermiers, might have escaped but for the evidence that he corresponded with France’s political enemies abroad. The fact that his correspondence was scientific did not, in the eyes of his enemies, rule out the possibility that Lavoisier was engaged in counter-revolutionary activities with overseas friends.

Lavoisier was guillotined on 8 May 1794. The mathematician Lagrange commented, ‘It required only a moment to sever his head, and probably one hundred years will not suffice to produce another like it.’ Following the centenary of the French Revolution in the 1890s, a public statue was erected to commemorate Lavoisier. Some years later it was discovered that the sculptor had copied the face of the philosopher, Condorcet, the Secretary of the Academy of Sciences during Lavoisier’s last years. Lack of money prevented alterations being made and, in any case, the French argued pragmatically that all men in wigs looked alike anyway. The statue was melted down during the Second World War and has never been replaced. Lavoisier’s real memorial is chemistry itself.

CONCLUSION

A rational reconstruction of what seem to have been the essential features of the ‘chemical revolution’ would draw attention to six necessary and sufficient conditions. First, it was necessary to accept that the element, air, did participate in chemical reactions. This was first firmly established by Hales in 1727 and accepted in France by Rouelle and Venel. Although Hales tried to explain the fixation of air by solids by appealing to the attractions and repulsions of Newtonian particle theory, there was no satisfactory explanation for its change of state. Secondly, it was necessary to abandon the belief that air was elementary. This was essentially the contribution of the British school of pneumatic chemists. Beginning in 1754 with Black, who showed that the ‘fixed air’ released from magnesia alba had different properties from ordinary air, and continuing through Rutherford, Cavendish and Priestley, it was found possible to prepare and study some twenty or more ‘factitious airs’ that were different from ordinary air in properties and density. Their preparation and study were made possible by the development of apparatus by Hales for washing air, the pneumatic trough, thus extending the traditional ‘alchemical’ apparatus of furnaces and still-heads that had hitherto largely sufficed in chemical investigations. Whether factitious airs were merely modifications of air depending upon the amounts of phlogiston they contained, or distinct chemical species in an aerial condition, or the expanded particles of solid and liquid substances, was decided by Lavoisier’s development of a model of the gaseous state.

The concept of a gas was a necessary third condition for the reconstruction of chemistry. By imaging the aerial state as due to the expansion of solids and liquids by heat, or caloric, Lavoisier brought chemistry closer to physics and made possible the later adoption of the kinetic theory of heat and the development of chemical thermodynamics. The balance pan had always been the principal tool of assayers and pharmacists, while the conservation of mass and matter had always been implicit in chemists’ rejection of alchemical transmutation and their commitment to chemistry as the art of analysis and synthesis. With the conceptualization of a whole new dimension of gaseous-state chemistry, however, it was necessary that chemical analysis and book-keeping should always account for the aerial state. Here was a fourth necessary condition that raised problems for phlogistonists when Guyton demonstrated conclusively in 1771 that metals increased in weight when they were calcined in air. Many historians, like Henry Guerlac, saw this as the ‘crucial’ condition for effecting a chemical revolution and the event that set Lavoisier on his path to glory.

Largely for pedagogic reasons, generations of historians, chemistry teachers and philosophers of science have interpreted the chemical revolution as hinging upon rival interpretations of combustion – phlogiston theory versus oxygen theory. More recently, those historians who have seen Lavoisier’s chemistry as literally an anti-phlogistic chemistry have had a wider agenda than combustion in mind. In particular, it now seems clear that the interpretations of acidity was a major issue for Lavoisier and the phlogistonists. Indeed, it could be argued that, once Lavoisier had the concept of a gas, it was the issue of acidity, not combustion, that led him to oxygen – as its very name implies. The transformation of ideas of acidity, therefore, formed a fifth factor in the production of a new chemistry.

Finally, and not least, the sixth necessary condition was a new theory of chemical composition and organization of matter in which acids and bases were composed from oxygen and elements operationally defined as the substances that chemists had not succeeded in analysing into simpler bodies. Oxygen formed the glue or bond of dualistic union between acid and base to form salts, which then compounded in unknown ways to form minerals. To make this more articulate and to avoid confusion with the unnecessary thought patterns of phlogiston chemistry, a new language was required – one that reflected composition and instantly told a reader what a substance was compounded from. After 1787 chemists, in effect, spoke French, and this underlined the new chemistry as a French achievement.

Although he pretended at the beginning of the Traité that it had been his intent to reform the language of chemistry that had forced the reform of chemistry itself, it was clearly because he had done the latter that a new language of composition was needed. As historians have stressed, the new nomenclature was Lavoisier’s theoretical system. He justified its adoption in terms of Condillac’s empirical philosophy that a well constructed language based upon precise observation and rationally constructed in the algebraic way of equal balances of known and unknown would serve as a tool of analysis and synthesis.

Observation itself involved chemical apparatus – not merely the balance, but an array of eudiometers, gasometers, combustion globes and ice calorimeters, which would enable precise quantitative data to be assembled. In this way chemical science would approach the model of the experimental physicists that Lavoisier clearly admired and with whose advocates he frequently collaborated.

This last point has led some historians to question whether Lavoisier was a chemist at all and whether the chemical revolution was instead the result of a brief and useful invasion of chemistry by French physicists. Others, while admitting the influence of experimental physics on Lavoisier’s approach, continue to stress Lavoisier’s participation in a long French tradition of investigative analysis of acids and salts to which he added a gaseous dimension. Even Lavoisier’s choice of apparatus, though imbued with a care and precision lacking in his predecessors’ work, was hallmarked by the investigative procedures of a long line of analytical and pharmaceutical chemistry. All historians agree, however, that until about 1772, when events triggered a definite programme of pneumatic and acid research in his mind, Lavoisier’s research was pretty random and dull, as if he were casting around for a subject (‘une belle carrière d’expériences à faire’) that would make him famous. Seizing the opportunity, the right moment, is often the mark of greatness in science. Priestley and Scheele believed that science progressed through the immediate communication of raw discoveries and ‘ingenious simplicity’. Lavoisier’s way, to Priestley’s annoyance, was to work within a system and to theorize in a new language that legislated phlogiston out of existence.

Like Darwin’s Origin of Species, Lavoisier’s Traité was a hastily written abstract or prolegomena to a much larger work he intended to write that would have included a discussion of affinity, and animal and vegetable chemistry. Like Darwin’s book, it was all the more readable and influential for being short and introductory. If more information was required, Fourcroy’s encyclopedic text and its many English and German imitations soon provided reference and instruction. But this was not the end of the chemical revolution. To complete it, Lavoisier’s elements had to be reunited with the older corpuscular traditions of Boyle and Newton. This was to be the contribution of John Dalton.

4 A New System of Chemical Philosophy

Atoms are round bits of wood invented by Mr Dalton.

(H. E. ROSCOE, 1887)

Before Dalton came on the scene, chemistry can hardly be described as an exact science. A wealth of empirical facts had been established and many theories had been erected that bound them together, not the least impressive of which were Lavoisier’s new dualistic views of chemical composition and his explanations of combustion and acidity. Most of eighteenth-century chemical activity had been qualitative. Despite the Newtonian dream of quantifying the forces of attraction between chemical substances and the compilation of elaborate tables of chemical affinity, no powerful quantitative generalizations had emerged. Although these empirically derived affinity relations often allowed the course of a particular chemical reaction to be predicted, it was not possible to say, or to calculate, how much of each ingredient was needed to perform a reaction successfully and most economically. Dalton’s chemical atomic theory, and the laws of chemical combination that were explained by it, were to make such calculations and estimates possible – to the benefit of efficient analysis, synthesis and chemical manufacture.

As a consequence of the power of the corpuscular philosophy, by the end of the seventeenth century it had become a regulative principle, or self-evident truth, that all matter was ultimately composed of microscopic ‘solid, hard, impenetrable, moveable’ particles. As we saw in the second chapter, however, such ultimate descriptions of Nature were of little use to practical chemists, who preferred to adopt a number of empirically derived elementary substances as the basic ‘stuffs’ of chemical investigation. Lavoisier’s famous definition of the element in 1789 made it clear that speculations concerning the ultimate particles or atoms of matter were a waste of time; chemistry was to be based on experimental knowledge¹:

All that can be said upon the number and nature of elements [i.e. in an Aristotelian or Paracelsian sense] is, in my opinion, confined to discussions entirely of a metaphysical nature. It is an unsolvable problem capable of an infinity of solutions none of which probably accord with Nature. I shall be content, therefore, in saying that if by the term elements we mean to express those simple and indivisible atoms of which matter is composed, it seems extremely probable we know nothing at all about them; however, if instead we apply the term elements or principles of bodies, to express our idea of the last point which analysis is capable of reaching, we must admit as elements, all the substances into which we are capable, by any means, to reduce bodies during decomposition. Not that we can be certain that these substances we consider as simple may not be compounded of two, or even a greater number of principles; but, since these principles cannot be separated, or rather since we have not hitherto discovered the means of separating them, they act with regard to us as simple substances, and we ought never to suppose them compounded until experiment and observation has proved them to be so.

For the same reason, although Dalton believed in physical atoms, most of his interpreters were content with a theory of chemical atoms – the ‘minima’ of the experimentally defined elements. Whether these chemical atoms were themselves composed from homogeneous or heterogeneous physical atoms was to go beyond the evidence of pure stoichiometry.

Stoichiometry was a subject invented by the German chemist Jeremias Richter (1762–1807), who had studied mathematics with the great philosopher, Immanuel Kant, at the University of Königsberg, and for whom he wrote a doctoral thesis on the use of mathematics in chemistry. This was, in practice, nothing grander than an account of the determination of specific gravities, from which Richter calculated the supposed weights of phlogiston in substances. Just as Kepler had searched for mathematical relations and harmony in astronomical data gathered by Tycho Brahe, so Richter spent his spare time as a chemical analyst in the Berlin porcelain works searching for arithmetical relations in chemistry. As Partington noted sardonically, Richter spent his entire life finding ‘regularities among the combining proportions where nature had not provided any’.

The exception was his discovery in 1792, while investigating double decompositions, that, because neutral products were formed, the reactants must ‘have amongst themselves a certain fixed ratio of mass’.

If, e.g., the components of two neutral compounds are A – a, a and B – b, b, then the mass ratios of the new neutral compounds produced by double decomposition are unchangeably A – a:b and B – b:a.

This law of neutrality was a special case of what came to be known as the law of reciprocal proportions. Richter referred to the study of these ratios as ‘stoichiometry’ and went on to examine how a fixed weight of an acid was neutralized by different weights of various bases. This investigation led him to claim, erroneously, that combining proportions formed arithmetical and geometrical series. It was Ernst Fischer, a Berlin physicist, who, when translating Berthollet’s Recherches sur la lois de l’affinité into German in 1802, pointed out that Richter’s results could be tabulated to show equivalent weights of a series of acids and bases. If 1000 parts of sulphuric acid was taken as a standard and the base equivalents needed for neutralization arranged in one column, and the amounts of other acids needed to neutralize these bases in another, then an analyst could gather at a glance how much of a particular base would neutralize a particular acid:

Thus, 672 equivalents of ammonia neutralized 427 of fluoric, 577 of carbonic and 712 of muriatic acids. Analysts now had a definite method of controlling the accuracy of their work and of calculating beforehand the composition of salts under investigation.

Dalton’s atomic theory was to provide a rational explanation for these regularities. There has been some debate as to whether Dalton was directly influenced by Richter. He certainly knew of Richter’s investigations, but probably not until after he had derived his own explanation from other sources.

DALTON’S ‘NEW SYSTEM’

What was ‘new’ in John Dalton’s A New System of Chemical Philosophy? The obvious reply seems to be the introduction of chemical atomism – the idea that each of Lavoisier’s undecompounded bodies was composed from a myriad of homogeneous atoms, each element’s atom differing slightly in mass. The surprising thing, however, is that only one chapter of barely five pages in the 916-page treatise was devoted to the epoch-making theme. These five pages, together with four explanatory plates, appeared at the end of the first part of the New System, which was published in Manchester in 1808 and dedicated to the professors and students of the Universities of Edinburgh and Glasgow, who had heard Dalton lecture on ‘Heat and the Chemical Elements’ in 1807, and to the members of Manchester’s Literary and Philosophical Society, who had ‘uniformly promoted’ Dalton’s researches. A second, continuously paginated, part of the New System, dedicated to Humphry Davy and William Henry, was published in 1810. Astonishingly, the third part, labelled as a second volume, did not appear until 1827. Even then the design was incomplete and a promised final part concerned with ‘complex compounds’ was never published.

Dalton’s apparent dilatoriness is easily explained by the fact that he earned his living as a private elementary teacher, which left him little time for the exacting experimental work and evidence upon which he based the New System. For it was a ‘new’ approach that he was taking, familiar though his scheme has become. Dalton recognized his innovation as being a ‘doctrine of heat and general principles of chemical synthesis’. A theory of mixed gases, which he developed in 1802, led him in 1803 to ‘new views’ on heat as a factor in the way elements (or, rather, atoms) combined together, a process he referred to as ‘chemical synthesis’. The fact that chemical compounds, or compound atoms (molecules), might be binary, ternary, quaternary, and so on up to a maximum of twelve atoms, gave Dalton a structure for his text: a detailed experimental examination of heat and the gaseous state, a theory of atomism and combination, which included the measure of atomic mass as a relative atomic weight, followed by a detailed account of the properties of the known elements, their binary combinations, ternary combinations and so on. Thus, although the exegesis of the atomic theory was limited to five pages, the whole of the New System was, in fact, imbued with a new stoichiometric approach to chemistry – that elements compounded together in fixed proportions by weight because of attractions and repulsions between the tiny particles of heat and elementary forms that made up laboratory chemicals. Inevitably, because Dalton was a slow worker and unable to spare time from teaching for research and writing, it was left largely to others, notably Thomas Thomson and Jacob Berzelius, to exploit the full consequences of Dalton’s insight.

DALTON’S LIFE

John Dalton (1766–1844) was born at Eaglesfield in Cumbria, the son of a weaver, and, like most contemporary members of the Society of Friends, was a man of some learning. The highly efficient Quaker network of schooling and informal education ensured that Dalton received a good schooling; he himself began to teach village schoolchildren when he reached the age of twelve. In his teens he mastered sufficient geometry to be able to study Newton’s Principia. At the age of fifteen, Dalton and his brother moved to Kendall, in the English Lake District, where they acquired their own school, which offered Greek, Latin, French and mathematics. At Kendall, Dalton was befriended by the blind Quaker scholar, John Gough, who further encouraged Dalton’s mathematical abilities and knowledge of Newtonian natural philosophy, including the work of Boyle and Boerhaave. The constant stimulation of rapidly changing weather conditions among the mountains and lakes of Westmorland and Cumberland (present-day Cumbria) interested him in meteorology. The records he kept over a five-year period were published in Meteorological Essays in 1793. In the same year, on Gough’s recommendation, Dalton moved to Manchester as tutor in mathematics and natural philosophy at New College, a Dissenting academy that had begun its distinguished life elsewhere as the Warrington Academy. Here Priestley had taught between 1761 and 1767.

Although Manchester New College moved to York in 1803, Dalton, finding Manchester congenial, spent the remainder of his life there as a private teacher and industrial consultant. Not only was there an abundance of paid work in Manchester for private tutors because of a rising industrial middle class (Dalton’s most famous pupil was a brewer’s son, the physicist James Prescott Joule), but the presence of the Literary and Philosophical Society, whose Secretary Dalton became in 1800 and President from 1817 until his death, proved a congenial venue for the presentation and articulation of his scientific work. Dalton read his first scientific paper, on self-diagnosed colour blindness (long after known as Daltonism) to the Society in 1794. He went on reading papers and reports to the Society up to his death. From about 1815 onwards, however, Dalton failed more and more to keep pace with the chemical literature. In 1839 he suffered the ignominy of having a paper of his on phosphates and arsenates rejected by the Royal Society on the grounds that a superior account of these salts had already been published by Thomas Graham.

Despite such failings, Dalton retained the respect of the chemical and scientific communities. Together with two other Dissenters from Anglicanism, Michael Faraday and Robert Brown, the botanist, and despite the angry opposition of Oxford High Churchmen, Dalton was awarded an honorary degree by Oxford University in 1832. A year later the government awarded him a Civil List pension for life, and in 1834 Edinburgh University gave him another honorary degree. His final accolade was a public funeral in Manchester. Even if we grant that some of these honours served a secondary purpose of drawing attention to scientists and their contribution to culture in Victorian Britain, we are bound to ask: What did Dalton do to merit such public honours?

THE ATOMIC THEORY

The straightforward answer is that Dalton rendered intelligible the many hundreds of quantitative analyses of substances that were recorded in the chemical literature and that he provided a model for the long-standing assumption made by chemists that compounds were formed from the combination of constant amounts of their constituents. He regarded chemical reactions as the reshuffling of atoms into new clusters (or molecules), these atoms and compound atoms being pictured in a homely way as little solid balls surrounded by a variable atmosphere of heat.

This statement, however, tells us little about Dalton’s originality; after all, the atomic theory of matter had existed for a good two-thousand years before Dalton’s birth. In Ireland, at the end of the eighteenth century, William Higgins (1762–1825) had used atomism in his A Comparative View of the Phlogiston and Antiphlogiston Theories (1789) to refute the phlogistic views of his countryman, Richard Kirwan. Higgins later claimed that Dalton had stolen his ideas – an inherently implausible notion that, nevertheless, has been supported by several historians in the past. In fact, Dalton’s originality lay in solving the problem of what philosophers of science have called transduction; he derived a way of calculating the relative weights of the ultimate particles of matter from observations and measurements that were feasible in the laboratory. Although atomic particles could never be individually weighed or seen or touched, Dalton provided a ‘calculus of chemical measurement’ that for the first time in history married the theory of atoms with tangible reality. He had transduced what had hitherto been a theoretical entity by building a bridge between experimental data and hypothetical atoms.

Dalton’s calculus involved four basic, but reasonable, assumptions. First, it was supposed that all matter was composed of solid and indivisible atoms. Unlike Newton’s and Priestley’s particles, Dalton’s atoms contained no inner spaces. They were completely incompressible. On the other hand, recognizing the plausibility of Lavoisier’s caloric model of changes of phase, Dalton supposed that atoms were surrounded by an atmosphere of heat, the quantity of which differed according to the solid, liquid or gaseous phase of the aggregate of atoms. A gas, for example, possessed a larger atmosphere of heat than the same matter in the solid state. Secondly, Dalton assumed, as generations of analysts before him had done, that substances (and hence their atoms) were indestructible and preserved their identities in all chemical reactions. If this law of conservation of mass and of the elements was not assumed, of course, transmutation would be possible and chemists would return to the dark days of alchemy. Thirdly, in view of Lavoisier’s operational definition of elements, Dalton assumed that there were as many different kinds of atoms as there were elements. Unlike Boyle and Newton, for Dalton there was not one primary, homogeneous ‘stuff’; rather, particles of hydrogen differed from particles of oxygen and all the particles that had so far been defined as elementary.

In these three assumptions Dalton moved away completely from the tradition of eighteenth-century matter theory, which had emphasized the identity of matter and of all material substances. In so doing. Dalton intimately bound his kind of atomism to the question of how elements were to be defined. In a final assumption, he proposed to do something that neither Lavoisier nor Higgins had thought of doing, namely to rid metaphysical atomism of its intangibleness by fixing a determinable property to it, that of relative atomic weight. To perform this transductive trick, Dalton had to make a number of simple assumptions about how atoms would combine to form compound atoms, the process he termed chemical synthesis. In the simplest possible case, ‘when only one combination of two bodies can be obtained, it must be presumed to be a binary one, unless some cause appear to the contrary’. In other words, although substances A and B might combine to form A₂B₂, it is simpler to assume that they will usually form just AB. Similarly, if ‘two combinations are observed, they must be presumed to be a binary and a ternary’:

A + 2B = AB₂ or 2A + B = A₂B

Dalton made similar rules for cases of three and four compounds of the same elements, and pointed out that the rules of synthesis also applied to the combination of compounds:

CD + DE = CD₂E etc.

These assumptions of simplicity of composition, which, as we shall see, had a theoretical justification, have long since been replaced by different criteria. Although they led to many erroneous results, the assumptions proved fruitful since they allowed relative atomic weights to be calculated. Two examples, both given by Dalton, will suffice.

Hydrogen and oxygen were known to form water. Before 1815, when hydrogen peroxide was discovered, this was the only known compound of these two gases. Dalton quite properly assumed, therefore, that they formed a binary compound; in present-day symbols:

H + O = HO

From Humboldt and Gay-Lussac’s analyses of water, it was known that 87.4 parts by weight of oxygen combined with 12.6 parts of hydrogen to form water. This ratio, H : O :: 12.6 : 87.4, must also be the ratio of the individual weights of hydrogen and oxygen atoms that make up the binary atom of water. Since hydrogen is the lightest substance known, it made sense to’ adopt it as a standard and to compare all heavier chemical objects with it. If the hydrogen atom is defined as having a weight of 1, the relative atomic weight of an atom of oxygen will be roughly 7. (Dalton always rounded calculations up or down to the nearest whole number.) Similarly, Dalton assumed ammonia to be a binary compound of azote (nitrogen) and hydrogen. From Berthollet’s analysis he calculated the relative atomic weight of nitrogen to be 5 or, after further experiments in 1810, 6.

TABLE 4.1 Some of Dalton’s relative weights.

Dalton was well aware of the arbitrary nature of his rules of simplicity. In the second part of the New System in 1810 he allowed the possibility that water could be a ternary compound, in which case oxygen would be 14 times heavier than hydrogen; or, if two atoms of oxygen were combined with one of hydrogen, oxygen’s atomic weight would be 3.5. This uncertainty was to plague chemists for another fifty years.

From the beginning, Dalton symbolized his atoms²:

… by a small circle, with some distinctive mark; and the combinations consist in the juxta-position of two or more of these.

The synthesis of water and ammonia were represented as:

Such symbols referred to the atom and were therefore conceptually very different from alchemical symbols or those of Hassenfratz and Adet, which only had a hazy or qualitative meaning. Earlier symbols had been a shorthand; Dalton’s circles conveyed a theoretical meaning as well as being a convenient abbreviation.

Dalton was never to become reconciled to the symbols introduced by Berzelius, even though he himself used alphabetical abbreviations within circles for elements such as iron, sulphur, copper and lead. In 1837, soon after the British Association for the Advancement of Science had persuaded British chemists to adopt Berzelius’ symbols, Dalton wrote a testimonial for Thomas Graham’s application for the Chair of Chemistry at University College London.

Berzelius’s symbols are horrifying: a young student in chemistry might as soon learn Hebrew as make himself acquainted with them. They appear like a chaos of atoms. Why not put them together in some sort of order?…[They] equally perplex the adepts of science, discourage the learner, as well as to cloud the beauty and simplicity of the Atomic Theory.

Clearly Dalton felt strongly about his innovation and was prepared to criticize a professorial candidate with one hand while supporting him with another. Indeed, Dalton suffered the first of his two strokes in April 1837 after angrily discussing symbols with a visitor.

Dalton’s symbols did not survive, mainly one suspects because they were an additional printing expense, but both they, as well as Berzelius’ simplification, encouraged people to acquire a faith in the reality of chemical atoms and enabled chemists to visualize relatively complex chemical reactions. As in mathematics, chemistry could advance only to a certain degree without an adequate symbolism for its deeper study. Between them, Lavoisier and Dalton completed a revolution in the language of chemistry.

Dalton’s hieroglyphs also reveal that he had a three-dimensional geometrical model of combination in mind. When three or more particles combined, he conceived that like particles stationed themselves as far apart as possible. This conception offers not only an important clue concerning the origins of Dalton’s atomic theory, but an explanation of his opposition to the notion derived from the volumetric combination of gases that equal volumes contained equal numbers of particles.

THE ORIGINS OF DALTON’S THEORY

How did Dalton come to think of weighing atoms? There have been many different attempts by chemists and historians to explain this. Dalton supplied three, mutually inconsistent, accounts of his voyage of discovery. Reconstruction has been made difficult by the fact that most of Dalton’s surviving papers were destroyed during the Second World War, and, but for the fact that Henry Roscoe and Arthur Harden quoted from them in a historical study published in 1896, historians would have been hard-pressed for evidence. Although the debate over influences remains unresolved, all historians agree that Dalton must have come to his ‘new views’ through the study of the physical properties of gases, which in turn depended upon his youthful interest in meteorology. For, once air had been shown to be heterogeneous, and not a homogeneous element, the question arose whether oxygen, nitrogen, carbon dioxide and water vapour were chemically combined in air (perhaps a compound actually dissolved in the water vapour?) or merely mixed together. The fact that atmospheric air appeared to be homogeneous and that its gaseous components were not stratified according to their specific gravities (itself an indication that chemists like Priestley were prepared to think in terms of the specific weights of gas particles long before Dalton) made most late-eighteenth-century chemists believe that atmospheric gases were chemically combined.

Dalton thought differently. His long study of Newton’s Principia had made him familiar with Newton’s demonstration that Boyle’s law relating pressure and volume could be derived from a model in which homogeneous air particles were self-repulsive with a power inversely proportional to the distance. As a result of his meteorological studies, Dalton had become convinced by 1793 that water vapour could not possibly be chemically combined in air; instead, it was diffused among the other aerial particles and so freely available for precipitation or condensation as rain or dew. But if water was not chemically combined, why should the other constituents of air be?

If Newton’s model of the self-repulsion of air particles was translated into a model of self-repulsive constituents of air, what would be the consequences? Provided particles of one kind did not repel particles of a different gas, as Dalton showed, each gas or vapour would behave as if in a vacuum. The net effect would be a homogeneous mixture as the different gas particles repelled their own kinds. As to the cause of their self-repulsion, Lavoisier’s model of a gas supplied a satisfactory candidate: caloric. By imagining that the particles of oxygen, nitrogen, carbon dioxide and water vapour were surrounded by atmospheres of heat, Dalton arrived at a theory of mixed gases and, incidentally, a law of partial pressures that proved essential in quantitative work in gas analysis and barometry.

Dalton’s ‘New theory of the constitution of mixed aeriform fluids and particularly of the atmosphere’ was published in Nicholson’s Journal in 1801. It proved controversial, but this was no bad thing for Dalton’s British and European reputation. Most chemists who believed in the chemical theory of air wondered how it was that caloric atmospheres in different particles did not repel one another. Why suppose that there were ‘as many distinct kinds of repulsive powers, as of gases … and that heat was not the repulsive power in any one case’?

Dalton’s ingenious reply to this difficulty was published in full in the second part of the New System and was premised on differences of size of gaseous particles, the size being a function of both the atom’s volume and the radius of its atmosphere of heat. Using diagrams that look like the later magnetic force diagrams popularized by Faraday, Dalton showed visually that ‘no equilibrium can be established by particles of different sizes pressing against each other’. It followed that different particles would ‘ignore’ one another even when surrounded by the repulsive imponderable of heat. Such a static model remained the only satisfactory explanation of gaseous diffusion, partial pressures and atmospheric homogeneity until it was replaced in the 1850s by the kinetic theory of gases.

As historians of chemistry have shown, this second model of mixed gases, which was dependent on the sizes of atoms, was first developed by Dalton in September 1804, a full year after he had developed the first list of particle weights. The question of size offers a clue to his thinking during the previous year.

One of Dalton’s few supporters for the first theory of mixed gases was his Mancunian friend, William Henry (1774–1836), the owner of a chemical works for the manufacture of the pharmaceutical, milk of magnesia, used in the treatment of digestive complaints. Henry had at first opposed Dalton, only to be converted when he found that ‘water takes up the same volume of condensed gas as of a gas under ordinary pressure’. Henry’s law that the solubility of a gas at a given temperature depended upon pressure, which he discovered in 1803, was powerful evidence that solution was a purely mechanical effect. If chemical affinity was not involved, it seemed equally unlikely to be involved in the atmosphere. Moreover, as Henry found, a mixture of gases dissolved in water was ‘retained in its place by an atmosphere of no other gas but its own kind’.

Henry’s experiments were intriguing. Why, Dalton wondered, did different gases have different solubilities in water? Why were light and elementary gases such as hydrogen and oxygen least soluble, whereas heavier compound gases such as carbon dioxide were very soluble? If his first theory of mixed gases was correct, why should gases have different solubilities? Was solubility proportional to density and complexity? At this stage Dalton clearly thought solubilities were a function of the sizes of particles³:

I am nearly persuaded that the circumstance depends upon the weight and number of the ultimate particles of the several gases: those whose particles are lightest and single being least absorbable, and others more according as they increase in weight and complexity.

One can see how this line of reasoning would lead automatically to ‘an inquiry into the relative weights of the ultimate particles of bodies … a subject as far as I know, entirely new’. It is important to realize, however, that Dalton really needed to know the weights of particles only because he wanted an estimate of their sizes from the simple relationship, density = weight/volume.

As we have seen, at the end of 1803 Dalton estimated the weights of gas atoms using known chemical analyses and the rule of simplicity. From these he derived a number of atomic volumes and radii, but was unable to find any simple or regular correlation with solubility. Even so, as late as 1810 in the New System he continued to record atomic sizes alongside atomic weights.

It was evidently not until 1804 that Dalton realized that relative atomic weights were a useful explanation of the law of constant composition and that the simple rules of chemical synthesis from which he had derived them explained and predicted that, when elements combined to form more than one compound, the weights of one element that combined with a fixed weight of the other were bound to be small whole numbers. For example if

then the weights of A combined with weight B are in the simple ratio of 1:2. Dalton drew attention to the fact that this was the ratio of hydrogen to carbon in methane (CH₄) and ethane (C₂H₄), and that in the difficult and complicated cases of the oxides of nitrogen the ratio of oxygen to nitrogen was 1 : 2 and 1:3.

There were a large number of cases of this ‘law of multiple proportions’ that had been reported in the literature as a result of the dispute between Proust and Berthollet. When Berthollet accompanied Napoleon’s expedition to Egypt in 1798, he was surprised to find huge deposits of soda by the shores of salt lakes. Mineralogical analysis showed that the soda arose from a reaction between salt and limestone in the lake bottom, in complete contradiction to the usual laboratory reaction in which soda [sodium carbonate] and calcium chloride reacted to form salt and limestone [calcium carbonate]. He concluded that the enormous concentration of salt in the lakes had forced the reversal of the usual reaction. In other words, the action of mass (concentration) could overcome the usual play of elective affinities between substances. In modern terms, Berthollet had stumbled upon an equilibrium reaction:

CaCl₂ + Na₂CO₃ CaCO₃ + 2NaCl

It was this awareness of the role of mass in reactions that caused Berthollet during the next few years to challenge the usual implicit presumption of chemists that substances combined together in fixed proportions, or that constant saturation proportions always characterized chemical union. Instead, Berthollet proposed that compounds combined together in variable and indefinite proportions, and he pointed to solutions and alloys, and what would today be defined as mixtures, as empirical evidence for his claim.

This radical reconceptualization of composition was immediately challenged by a fellow Frenchman, Joseph-Louis Proust (1754–1826), who worked as an analyst in Spain. In a long series of meticulous analyses and friendly challenges to Berthollet, Proust argued that there was overwhelming evidence that regular compounds were formed from their constituents in fixed and definite proportions. There might well be more than one compound of the same two substances, but their proportions were regular.

Although neither contender gained a definite victory (for Berthollet was perfectly correct in his position over some of the difficult substances like glasses that he examined), by 1810, and in the light of Dalton’s theory, it was seen that the laws of definite and multiple proportions offered a securer foundation for quantitative chemistry. For the time being Berthollet’s views, which were eventually to illuminate physical chemistry and the theory of semiconductors, served only to confuse and handicap the development of analytical chemistry, which was so beguilingly explained by Dalton’s theory.

In 1808 William Hyde Wollaston and Thomas Thomson provided further convincing experimental examples of multiple proportions when they showed that there was a 2 : 1 ratio of CO₂ in the bicarbonate and carbonate of potassium (viz. KHCO₃ or K₂O.2CO₂.H₂O and K₂CO₃ or K₂O.CO₂), and, for the same amount of acid in the normal and acid oxalates of potash and strontia, there was double the amount of base in the acid oxalates.

It was in the context of this experimental work with oxalates that Thomson recommended Dalton’s chemical atomism, having already briefly referred to it in the third edition of his important textbook, System of Chemistry, in 1807. Thomson’s initial account was based directly on conversations Thomson had had with Dalton in Manchester in 1804. Soon afterwards Dalton had read an account of his first list of atomic weights in a paper read to the Manchester Literary and Philosophical Society in October 1803 (published with differences in 1805). Thomson was also directly responsible for inviting Dalton to Scotland in 1807 to lecture on his views on air, heat and chemical synthesis to audiences at the Universities of Edinburgh and Glasgow. It was these lectures that led to the New System.

Although Dalton’s brilliant insight was developed by others, it is worth emphasizing that he retained other imaginative insights that remained undeveloped for decades. In particular, it is clear from surviving remnants that Dalton built models of atoms and compounds in order to illustrate his theory. This model-building followed directly from his first thoughts on mixed gases in 1803⁴:

When an element A has an affinity for another B, I see no mechanical reason why it should not take as many atoms of B as are presented to it, and can possibly come into contact with it (which may probably be 12 in general) except so far as the repulsion of the atoms of B among themselves are more than a match for the attraction of an atom of A. Now this repulsion begins with 2 atoms of B to 1 of A, in which case the 2 atoms of B are diametrically opposed; it increases with 3 atoms of B to 1 of A, in which case the atoms of B are only 120° asunder; with 4 atoms of B it is still greater as the distance is then only 90°; and so on in proportion to the number of atoms. It is evident then from these positions, that, as far as powers of attraction and repulsion are concerned (and we know of no other in chemistry) binary compounds must first be formed in the ordinary course of things, then ternary, and so on, till the repulsion of the atoms of B (or A, whichever happens to be on the surface of the other), refuse to admit any more.

This statement shows that Dalton’s apparently intuitive appeal to a principle of simplicity in chemical synthesis was backed up by a geometrical force model – a model that, in a radically different setting, was to be used by ligand-field theorists a century and a half later. But it was entirely speculative, and, although it gave ‘order’ to Dalton’s symbols, it was not a path that the empirically minded Berzelius was to follow in his own symbolic language.

ELECTRIFYING DALTON’S THEORY

Dalton presented his theory within the context of ideas concerning heat at a time when the chemical world had become excited by the news of galvanic or current electricity. In 1800 the Italian physicist, Alessandro Volta (1774–1827), described his ‘voltaic pile’ or battery in a paper published by the Royal Society. This simple machine made from a ‘pile’ or ‘battery’ of alternating zinc and silver discs gave chemists a powerful new analytical tool. As Davy said later, its use caused great excitement and it acted as ‘an alarm-bell to experimenters in every part of Europe’. Almost immediately it was found that the battery would decompose water into its elements. While there was nothing extraordinary about this further confirmation of Lavoisier’s chemistry, the puzzling fact was that hydrogen and oxygen were ejected from the water at different poles – the hydrogen at what Volta designated as the negative pole, and the oxygen at the positive pole. Two chemists who particularly concerned themselves with this galvanic phenomenon (the term ‘electrolysis’ was not coined by Faraday until 1832) were Davy and Berzelius.

Humphry Davy (1778–1829) was born at Penzance in Cornwall and educated locally. Intending to qualify as a doctor, he was apprenticed to a surgeon in 1795 and began to read Lavoisier’s Elements of Chemistry in French in his spare time. Though ignorant and completely self-taught, like Priestley before him, Davy began to repeat, correct and devise new experiments. Apart from this growing interest in chemistry, he wrote poetry (for this was the era of Romanticism when young men poured forth their individual feelings in verse), he admired the rich Cornish scenery and he fished. Through a friendship with Gregory Watt, the tubercular son of James Watt, Davy came to the attention of Thomas Beddoes, a pupil of Joseph Black and a former lecturer in chemistry at the University of Oxford, who had resigned from ‘that place’ because of his support for the French Revolution and his suspiciously radical politics. In 1798 Beddoes, convinced that the many gases that Priestley had discovered might prove beneficial in the treatment of tuberculosis (TB) and other urban diseases, founded a subscription-based Pneumatic Institute in Bristol. He persuaded Davy, whom he recognized as a man of talent, to join him as a research assistant. Davy probably still expected to qualify as a doctor, perhaps by saving sufficient money to enter Edinburgh University as a result of this experience. In the event, he became a chemist.

Davy’s risky and foolhardy experiments at Bristol, in which he narrowly escaped suffocation on several occasions, brought him fame and notoriety in 1800 when he published his results in Researches, Chemical and Philosophical; Chiefly Concerning Nitrous Oxide … and its Respiration. None of his inhalations demonstrated chemotherapeutic benefits – though his results with nitrous oxide (laughing gas) were to be the cause of regular student ‘saturnalia’ in chemical laboratories throughout the nineteenth century. Not until 1846 was the gas used as an anaesthetic. This inhalation research, and some further essays published in 1799, which included an attack on Lavoisier’s notion of caloric and the substitution of light for caloric in gaseous oxygen (phosoxygen), brought Davy’s name to the attention of another patron, Benjamin Thompson, who had also denied that heat was an imponderable fluid.

Count Rumford, as he is better known, had founded the Royal Institution in London in 1799 as a venue for publicizing ways in which science could help to improve the quality of life of the deserving poor and for the rising middle classes. By 1801 Rumford needed a new Professor of Chemistry. Davy’s appointment coincided with the wave of contemporary interest in electrolytic phenomena and, although he lectured, dazzlingly, on many other subjects at the Royal Institution, it was his research on electrochemistry that captured the public’s imagination and ensured the middle-class success of the Institution.

By building bigger and more powerful batteries, and by using fused electrolytes rather than electrolytes in solution, Davy confirmed Lavoisier’s hunch that soda and potash were not elementary by isolating sodium and potassium in 1807. In the next few years he demonstrated that Lavoisier’s alkaline earths were also compounds and prepared calcium, strontium and barium electrolytically. Later still, Davy argued convincingly against the view that muriatic acid contained oxygen, and for the opinion that oxymuriatic acid, which he renamed chlorine, was an undecompounded elementary body – a point supported by his isolation of its conjoiner, iodine, in 1813.

This succession of corrections to Lavoisier’s chemistry has led some historians to feel that Davy set out systematically to destroy French chemistry. Indeed, by 1815 he had critically and effectively questioned most of the assumptions of the antiphlogistic chemistry – that acidity was due to oxygen, that properties were due to ‘principles’ rather than arrangement, that heat was an imponderable fluid rather than a motion of particles, and that Lavoisier’s elements were truly elementary. Although Davy was often bold in his speculations and use of analogical reasoning, in stripping Lavoisier’s system to its empirical essentials he did not replace it with any grand system of his own, except to suggest that chemical affinity was, in the final analysis, an electrical phenomenon.

In the early 1800s there were two different opinions on the cause of electrolysis. According to the ‘contact theory’ advocated by Volta, electricity arose from the mere contact of different metals; an imposed liquid merely acted as a conductor. Since this theory did not easily account for the fact that the conducting liquid was always decomposed, the alternative ‘chemical theory’ argued that it was the chemical decomposition that produced the electric current. Davy found fault with both theories and as so often in the history of science, he drew a compromise: the contact theory explained the ‘power of action’ of, say, zinc becoming positively charged when placed in contact with copper; this power then disturbed the chemical equilibrium of substances dissolved in water, leading to a ‘permanent action’ of the voltaic pile. As to the cause of the initial ‘power of action’, Davy was in no doubt that it was chemical affinity⁵:

Is not what has been called chemical affinity merely the union or coalescence of particles in naturally opposite states. And are not chemical attractions of particles and electrical attractions of masses owing to one property and governed by one simple law?

If Davy was the first chemist to link chemical reactivity with electrolytic phenomena, it was the Swede, Berzelius, who created an electrical theory of chemistry. Davy had concluded from his long and accurate work on electrolysis that, in general, combustible bodies and bases tended to be released at the negative pole, while oxygen and oxidized bodies were evolved at the positive pole⁶:

It will be a general expression of the facts in common philosophical language, to say, that hydrogen, the alkaline substances, the metals, and certain metallic oxides, are attracted by negatively metallic surfaces [i.e. electrodes]; and repelled by positively electrified metallic surfaces; and contrariwise, that oxygen and acid substances are attracted by positively electrified metallic surfaces, and repelled by negatively electrified metallic surfaces; and these attractive and repulsive forces are sufficiently energetic to destroy or suspend the usual operation of elective affinity.

Berzelius, with his patron-collaborator, William Hisinger, had reached the same conclusion independently in 1804, but only developed the important and influential electrochemical theory, which was to leave a permanent mark on chemistry, in 1810 after he had learned of Dalton’s atomic theory. Jöns Jacob Berzelius (1779–1848), after being brought up by his stepfather, studied medicine at the University of Uppsala. Here he read Fourcroy’s Philosophie chimique (1792) and became convinced of Lavoisier’s new system. A competent reader and writer of English, French and German, and alert to the latest developments outside Sweden, his graduation thesis in 1802 was on the medical applications of galvanism. This brought him to the attention of Hisinger, a wealthy mine owner, who invited Berzelius to use the facilities of his home laboratory in Stockholm. Together they not only drew important conclusions about electrolysis, but discovered a new element, ‘ceria’, in 1803, which later turned out to be the parent of several ‘rare-earth’ elements (see chapter 9).

By 1807 Berzelius had become independent of Hisinger’s patronage when he was elected to a Chair of Chemistry and Pharmacy at the Carolian Medico-Chirurgical Institute in Stockholm. His light lecturing duties allowed him plenty of time to research in the Institute’s modest laboratory. Elected a member of the Swedish Academy of Sciences in 1808, in 1818 he became one of its joint secretaries. The appointment included a grace-and-favour house in which he built a simple laboratory adjacent to the kitchen. Here he took occasional pupils, such as Mitscherlich and Wöhler.

Berzelius first learned of Dalton when planning his own influential textbook, Larbok i kemien, the first volume of which was published in 1808. Somehow Berzelius had acquired a copy of Richter’s writings on stoichiometry (he remarked on how unusual this was) and so learned of the law of reciprocal proportions and of the idea of equivalents. He saw immediately how useful these generalizations were for analytical chemistry. An avid follower of British chemical investigations, Berzelius learned of Dalton’s theory when he read a reference to it in Wollaston’s report on multiple proportions in Nicholson’s Journal. Because of the European wars, which made scientific communication difficult, he was unable to obtain a copy of Dalton’s New System (from Dalton himself) until 1812. Nevertheless, just from Wollaston’s brief account he saw immediately that a corpuscular interpretation of these analytical regularities was ‘the greatest step which chemistry had made towards its completion as a science’.

His own analytical results more than confirmed that, whenever substances combined together in different proportions, they were always, as Dalton had already concluded, in the proportions A + B, A + 2B, 2A + 3B, A + 4B, etc. Berzelius reconciled this regularity with Berthollet’s views on the influence of mass in chemical reactions. He agreed that Berthollet was right in supposing that substances could combine together in varying proportions; but these proportions were never continuously variable, as Berthollet had argued against Proust, but fixed according to Dalton’s corpuscular ratios.

Berzelius’ teaching duties included the training of pharmacists. He was, therefore, conscious of the fact that the Swedish Pharmacopoeia had not been revised since the days of phlogiston chemistry and that by 1810 its language had become embarrassingly out of date. In 1811, in an attempt to persuade the government to make a sensible decision on its pharmaceutical nomenclature, Berzelius devised a new Latin classification of substances, which exploited the electrochemical phenomena that he and Davy had studied, and firmly founded the organization of ponderable matter on the dualistic system that lay at the basis of Lavoisier’s antiphlogistic nomenclature.

Ponderable bodies were divided into two classes, ‘electropositive’ and ‘electronegative’ according to whether during electrolysis they were deposited or evolved around the positive or negative pole. Since these definitions reversed

FIGURE 4.1 Berzelius’ classification of substances. (Based on C. A. Russell, Annals of Science, 19 (1963): 124.)

the convention that Davy had already introduced, Berzelius was soon obliged to conform to the definition that electropositive substances were attracted to the negative pole. It was because of the theoretical implications of galvanic language that Faraday, in 1832, introduced the valueneutral nomenclature of electrodes, cathodes, anodes and so on. Berzelius’ electropositive and electronegative substances then became anions and cations respectively.

Oxygen, according to Berzelius, was unique in its extreme electronegativity. Other, less electronegative substances, like sulphur, could be positive towards oxygen and negative towards metals. On combination, a small residual contact charge was left, which allowed further combination to occur to form salts and complex salts. Thus, electropositive metals might form electropositive (basic) oxides (as electrolysis demonstrated), which would combine with electronegative acidic oxides to form neutral salts. The latter, however, might still have a residual charge that allowed them to hydrate and to form complex salts:

The scheme allowed the elements to be arranged in an electrochemical series from oxygen to potassium, based upon the electrolytic behaviour of elements and their oxides. Because salts were defined as combinations of oxides, Berzelius had to insist for a long time that chlorine and iodine were oxides of unknown elements, and that ammonia was similarly an oxide of ‘ammonia’. It was not until the 1820s that Berzelius finally capitulated and agreed that chlorine, iodine and bromine (which he placed in the special category of forming electronegative ‘haloid’ salts) were elements and that ammonia was a compound of nitrogen and hydrogen only.

It was this electrochemical system which was to have far-reaching analogical implications for the classification of organic substances. It also allowed Berzelius in 1813 to introduce a rational symbolism based upon the Latin names of the elements. Compounds were denoted by a plus sign between the constituents, as in copper oxide, Cu + O, the electropositive element being written first. Later, Berzelius dispensed with the plus sign and set the two elements side by side as in algebra. Different numbers of elements were then indicated by superscripts, e.g. S²O3, a molecule of ‘hyposulphuric acid’. These joined symbols, which were criticized initially for being potentially confusing with algebraic symbolism, only began to be used in the 1830s. It was Liebig who, in 1834, introduced the subscript convention we still use today, though French chemists went on using superscripts well into the twentieth century. Because of the importance of oxygen in Berzelius’ system, he abbreviated it to a dot over its electropositive congener, i.e. Cu = Cu + O. In 1827 he extended this to sulphur, which was indicated by a comma, i.e. copper sulphide, Cú.

In a further ‘simplification’, which in practice wrought havoc in the classification of organic compounds and in communication between chemists, Berzelius in 1827 introduced ‘barred’ or underlined symbols to indicate two atoms of an element. (Since the bar was one-third up the stem of the symbol it involved printers making a special type, thereby losing one advantage over Dalton’s symbols; hence the use of underlined symbols in some texts.) The symbols for water and potash alum thus became, respectively:

Although Berzelius introduced symbols as a memory aid to chemical proportions, they were initially adopted by few chemists. Berzelius himself virtually ignored his own suggestions until 1827, when he published the organic chemistry section of his textbook, which appeared in German and French translations soon afterwards. Indeed, the development of organic chemistry was undoubtedly the key factor into pushing chemists into symbolic representations. Following the determination of a group of younger British chemists to introduce Continental organic research into Britain, Edward Turner employed Berzelius’ symbols in the fourth edition of his Elements of Chemistry in 1834. From then on, together with chemical equations, whose use in Britain was pioneered by Thomas Graham, symbols became an indispensable part of chemical communication.

TABLE 4.2 The development of the chemical equation.

As we have seen, Dalton angrily rejected Berzelius’ symbols mainly on the grounds that they did not indicate structure but were merely synoptic. Nor was he at all pleased with the way Berzelius had taken over his creation and transformed it electrochemically. On his part, Berzelius, after struggling for years to obtain a copy of Dalton’s New System, expressed deep disappointment with the book when he eventually read it in 1812⁷:

I have been able to skim through the book in haste, but I will not conceal that I was surprised to see how the author has disappointed my hopes. Incorrect even in the mathematical part (e.g. in determining the maximum density of water), in the chemical part he allows himself lapses from the truth at which we have the right to be astonished.

Berzelius’ extensive account of his interpretation of Dalton’s theory was published in English in Thomas Thomson’s monthly Annals of Philosophy in 1813. These articles were criticized by Dalton on at least five grounds. Whereas Dalton could see no good reason geometrically why atoms had to be spherical or all the same size, these were cardinal assumptions of Berzelius, who put them to good use in 1819 when he explained the isomorphism of crystals that Mitscherlich had discovered when studying with him in Stockholm. (Isomorphism refers to the fact that a family of salts containing different metals tend to have similar or identical crystal shapes.) Again, unlike Dalton, Berzelius refused to allow combinations of the type 2A + 2B or 2A + 3B on the grounds that, logically, nothing would prevent such ‘atoms’ from being divided. Dalton disagreed, since self-repulsions could be appealed to. Only after a lifetime’s analysis, in 1831, did Berzelius accept that occasionally two atoms of an element could combine with two or more other atoms. Before then this had led Berzelius to assume that all metallic oxides had the form MO. In the cases of the alkali metals and of silver, which are actually M₂

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