The Fontana History of Chemistry. William Brock J.

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