Geoffroy Issues the Table of Reactivities

Date 1718

Geoffroy produced the first systematic treatment of chemical reactivities. He presented a table illustrating these relationships to the French Academy of Sciences, along with a law stating that highly reactive substances will displace less reactive ones in compounds.

Locale Paris, France

Key Figures

• Étienne-François Geoffroy (Geoffroy the Elder; 1672-1731), French chemist, physician, and pharmacist
• Sir Isaac Newton (1642-1727), English mathematician and physicist
• Torbern Olof Bergman (1735-1784), Swedish mineralogist
• Claude Louis Berthollet (1748-1822), French chemist

Summary of Event

Ancient Greek natural philosophers observed chemical changes and tried to explain them as functions of love or hatred between the elements. These anthropomorphic concepts satisfied alchemists for centuries, but in the Middle Ages such thinkers as Saint Albertus Magnus, who had observed that metals reacted differently with various substances, sought to understand these phenomena in terms of an affinitas (affinity) or specific force holding chemical bodies together in complex substances. During the Scientific Revolution of the seventeenth century, René Descartes developed a mechanical explanation of the universe, and chemists attempted to explain their observations in terms of moving particles rather than by such “occult forces” as attraction and repulsion.

In England, Sir Isaac Newton showed that the complicated motions of the heavenly bodies could be mathematically explained in terms of a precise gravitational force, though he publicly refrained from trying to explain the nature of this force. Nevertheless, Newton was an ardent alchemist who speculated that chemical substances were composed of particles possessing short-range attractive powers that varied in strength depending on the specific chemical species. Chemical reactions were therefore caused by varying attractions between these particles.

Newton’s analysis of long-range gravitational forces and short-range chemical forces fascinated Étienne-François Geoffroy, who had traveled to England in 1698. Geoffroy was elected a fellow of the Royal Society and thereafter closely followed the work of Newton and his disciples. In France, Geoffroy pursued his teaching and research in an anti-Newtonian academic environment at the Jardin du Roi and the Collège Royal (now the Collège de France). Cartesians, the followers of Descartes’s mechanical philosophy, disliked Newtonian ideas on attraction, which they saw as akin to the superstitious magical powers of ancient and medieval times. The modern mechanical worldview had no place for such forces, and the French Académie des Sciences (Academy of Sciences) went so far as to ban them from scientific discourse. Therefore, when Geoffroy began to think about ways in which he could systematize the growing experimental knowledge about chemical substances and their reactions, he expressed himself in terms of relationships (rapports) rather than affinities (affinités) or attractions.

In his research, Geoffroy performed experiments on acids, alkalis, and metals, and he also collected information on the experiments of others. Though other chemists had noticed that certain highly reactive substances could displace less reactive substances from compounds, Geoffroy was the first to organize the information on relative reactivities thus garnered into a table. In 1718, he delivered a ten-page paper, “Table des différens rapports observés en chymie entre différentes substances” (“table of the different relationships observed in chemistry between different substances”) to the Académie des Sciences. The basic idea of the paper involved a compound (AB) formed from two distinct substances (A and B) and the relationship between the compound and a third substance (C). Geoffroy argued that if C is capable of forming a stronger connection to A than is B, then C will displace B and form a new compound (AC). This general proposition was combined with a table indicating which substances formed stronger connections to which other substances, the Table of Reactivities.

Geoffroy’s general law proved less important than his sixteen-column table of specific chemical relationships, which had a great influence on eighteenth century chemists. He represented substances in his table by their alchemical symbols; for example, gold was a circle with a central dot, water was an apex-down triangle, and salt was a circle with a horizontal diameter. By populating his rows and columns with these symbols, Geoffroy made as clear as possible the relationships between various substances (the table’s popularity also stimulated a revived use of these symbols among chemists).

Across the top of the table, Geoffroy placed the symbols for specific acids, alkalis, and metals, and then, in the sixteen vertical columns beneath these elements and compounds, he placed a list of substances ordered by decreasing reactivity with the substance that headed the column. For example, the second column, which was headed by the symbol for what today’s chemists call hydrochloric acid, had directly beneath it the symbol for tin, which avidly reacts with this acid. Gold was at the column’s bottom position, since gold does not react at all with hydrochloric acid. Similarly, under the nitric acid column, the metals were ordered from the most to the least reactive as follows: iron, copper, lead, mercury, and silver. Geoffroy also schematized reactions between acids and alkalis, which helped chemists to understand the relative strengths of these importance substances.

Although Geoffroy’s table was popular and inspired other tables, it also provoked criticism on both experimental and theoretical grounds. For example, one critic pointed out that silver, which was very unreactive according to Geoffroy’s table, supplanted a very reactive substance in some reactions (in today’s terminology, when silver nitrate solution reacts with a solution of potassium sulfate, a precipitate of silver sulfate is formed). Some Cartesians criticized Geoffroy’s table, because they interpreted what he saw as a neutral term, “relationships” (rapports), to be equivalent to “affinities,” which they wished to exclude from their mechanical universe. Geoffroy responded that his relationships between chemical substances were due to structural features of the particles, for example, whether they were porous or pointed. Reactions could then be visualized in terms of the interlocking of these particles.

Geoffroy, like many eighteenth century chemists, exhibited both modern and old-fashioned ideas in grappling with chemical phenomena. He opposed alchemy, but his table contained a symbol for an “oily or sulfurous principle,” which, in 1720, he identified with phlogiston, a principle of combustibility that later proved to be nonexistent. Geoffroy’s table contained other errors, largely due to the imperfect state of chemical knowledge at the time, but it also contained important truths about reactivities and replacement reactions.

Significance

Despite his table’s imperfections and his limited understanding of the chemical principles behind it, Geoffroy was the first to construct an extensive arrangement of the observed reactive orders of a range of chemical reactions. At the time, chemists did not fully understand how temperature, concentration, and other factors affected reactivity. Nevertheless, what some chemists called “affinities” certainly played a role, and the increasing importance of affinity studies can be seen in the number of tables published. Between 1718 and 1750, only two tables appeared, but in the following decades the numbers accelerated: three in the 1750’s, four in the 1760’s, and five in the 1770’s.

As the number of such tables grew, the sophistication of each new table increased as well. When Torbern Olof Bergman published his very influential table of affinities in 1775, he included fifty-nine columns for a wide variety of chemical substances. He even had one table for reactions in solutions at room temperature and another table for the fusion reactions of dry substances at high temperatures. These two tables represented Bergman’s recognition that affinity relationships differed under wet and dry conditions. He also understood that to study all the possible relationships of the substances in his tables would require more than thirty thousand experiments.

By the end of the eighteenth century, chemists began to realize that tables of affinities were oversimplifications of the real complexities involved in chemical reactions. Nevertheless, great chemists such as Claude Louis Berthollet continued the tradition of chemical affinity, even though Berthollet’s work actually invalidated a major presupposition behind the belief in attractive chemical forces. In his Recherches sur les lois de l’affinité (1801; researches on the laws of affinity) and his Essai de statique chimique (1803; essay on chemical statics), Berthollet demonstrated that chemical reactions were influenced by the relative amounts of starting materials. Although he continued to believe that affinity was important in chemical reactions, his work foreshadowed the laws of mass action and chemical equilibria that were discovered later in the nineteenth century. It was not until the birth of physical chemistry at the end of the nineteenth century and the application of quantum mechanics to chemistry in the twentieth century that chemists finally understood what really happens when chemical substances selectively react with one another.

Bibliography

Bensaude-Vincent, Bernadette, and Isabelle Stengers. A History of Chemistry. Cambridge, Mass.: Harvard University Press, 1997. Chapter 2 examines the eighteenth century and the laboratory conditions and scientific institutions that served as the background of Geoffroy’s work in Paris. Index.

Brock, William H. The Chemical Tree: A History of Chemistry. New York: Norton, 2000. Brock discusses Geoffroy in his section on “Newton’s Chemistry” in chapter 2. Bibliographical essays on each of the chapters and an index.

Leicester, Henry M. The Historical Background of Chemistry. New York: John Wiley & Sons, 1956. Leicester deals with Geoffroy’s work on reactivities in chapter 12. References to primary and secondary sources at the ends of chapters. Name and subject indexes.

Partington, J. R. A History of Chemistry. Vol. 3. New York: Macmillan, 1962. Partington discusses Geoffroy’s life and work in chapter 2. References to primary and secondary sources in the footnotes. Name and subject indexes.

Thackray, Arnold. Atoms and Powers: An Essay on Newtonian Matter-Theory and the Development of Chemistry. Cambridge, Mass.: Harvard University Press, 1970. This thematic treatment of eighteenth century chemistry emphasizes the impact of Newton’s ideas on chemists. Geoffroy’s table forms an important part of this analysis. Select bibliography and index.