The Fontana History of Chemistry. William Brock J.

(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