The Fontana History of Chemistry. William Brock J.
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