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.
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.
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