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Eighteenth-century Cultures Of Chemistry

Such was the program initiated by Etienne-François Geoffroy (Geoffroy the Elder; 1672–1731), who published a "Table des rapports" (table of affinities) in 1718. The substance at the head of a column is followed by all the substances that could combine with it in order of decreasing affinity—the degree of affinity being indicated by the place in the column. A substance C that displaces B from a combination AB to form AC will be located above B in the column because of its stronger affinity for A. Displacement reactions thus provided a qualitative measure of affinities and allowed predicting the outcome of reactions. Thus, chemistry came to be seen as a predictive and useful science in the eighteenth century.

It is important to stress that long before Lavoisier, chemistry had conquered the status of an autonomous academic discipline. A chemistry class had been established at the Paris Academy of Science in the late seventeenth century, whereas the physics class was only created in 1785. The chemistry class conducted systematic research programs in plant analysis and mineralogy. Not only were chemistry chairs established in a number of European universities, but also innumerable public and private courses of chemistry opened up with experimental demonstrations. They were attended by a variety of audiences: pharmacists, metallurgists, as well as gentlemen and "philosophes" who practiced chemistry as enlightened amateurs. Chemistry was promoted alongside Enlightenment values as a rational and useful knowledge that would be of benefit to economy and society. A key strategy for winning political support was the introduction of the distinction between "pure" and "applied" chemistry by Johan Gottschalk Wallerius (1709–1785), who took the chair of chemistry in Uppsala in 1753. This distinction asserted the dignity of pure chemistry while transforming the chronological priority of chemical arts into a logical dependence upon "pure" knowledge. Chemistry could thus be perceived as a legitimate academic discipline in university curricula and highly valued for its usefulness in various applications. At the same time in France, chemistry was celebrated in the context of the Encyclopédie as a model science based on empirical data rather than on a priori speculations, a science requiring craft and labor, cultivated by skilled "artists" working hard in their laboratories unlike those lazy philosophers who never took off the academic gown.

However, chemistry was more than a fashionable science. So decisive was the success of Lavoisier's revolution in the 1780s that most chemists and historians of science, according to Frederic Holmes, "viewed eighteenth-century chemistry as the stage on which the drama of the chemical revolution was performed" (Holmes, 1989, p. 3). They once described it as an obscure and inconsistent set of practical rules based on the erroneous phlogiston theory. This theory, shaped by Georg-Ernst Stahl in the early eighteenth century, explained a number of phenomena such as combustion, as well as properties such as metals or acids, by the action of an invisible principle or fire named phlogistan (from the Greek term for "burnt"). The canonical story thus culminated in Lavoisier's questioning the existence of phlogiston and its alleged presence in metals, in acids, in combustion and respiration, and consequently overthrowing the old paradigm.

When historians resist the temptation to read eighteenth-century chemistry backward, waiting for Lavoisier to arrive on the stage, they quickly realize that this standard picture was only one aspect among numerous diverse cultures of chemistry in the eighteenth century, many of which were extremely innovative. In workshops and firms, the invention of continuous processes led to what historians of industry described as "the chemical revolution." In more academic spaces, laboratory practices were also deeply changed by the study of salt solutions when wet analysis was added to the traditional fire analysis and color indicators were systematically applied to acids and alkalis. This change, especially visible in the research program conducted at the Paris Academy of Science on plant and mineral analysis, had a theoretical impact: chemists gave up the old concept of salt as a universal principle, in favor of the notion of middle salt—a substance resulting from the combination of volatile and nonvolatile salts or of alkali and acid. This redefinition subverted the traditional notion of principles as material entities as bearers of properties. Substances could present similar properties and belong to the same class despite their different constituent principles. The idea of interchangeability was reinforced by the displacement reactions that allowed the construction of affinity tables. Affinity tables favored the view that the behavior of a "mixt" (compound) depends less upon the nature of its constituent principles than on its relations with other substances. The relational identity of chemical substances minimized the importance of principles—whether they be three, four, or five—that chemists used to oppose to the mechanistic view of a "catholic matter." Moreover in a number of eighteenth-century chemistry courses—for instance in Hermann Boerhaave's (1668–1738) textbook and Guillaume-François Rouelle's (1703–1770) lectures—elements were often redefined as "agents" of chemical reactions rather than as constituent principles. Elements were consequently presented as "natural instruments" together with "artificial instruments" such as laboratory vessels, furnaces, and alembics. This pragmatic notion of elements accompanied their redefinition in operational terms as substances that could not be further decomposed by available analytic techniques.

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Science EncyclopediaScience & Philosophy: Categorical judgement to ChimaeraChemistry - Alchemy In The Scientific Revolution, Eighteenth-century Cultures Of Chemistry, From Phlogiston To Oxygen