CHEMISTRY

A mature discipline by the late eighteenth century, chemistry had thrown off the taint of both manual labor and alchemy; it featured a corps of practitioners, specialized journals, practical techniques and theoretical themes, and growing prestige; and it was thoroughly modernized by the revolutionary transformation that centered on the French chemist Antoine-Laurent Lavoisier (1743–1794). Led until the mid-nineteenth century by Jöns Jakob Berzelius (1779–1848) of Sweden, chemistry as a field of study and research increased in coherence and productivity. Chemical industry had engaged chemists throughout the century, but sustained and mutually reinforcing interactions of science and industry appeared only after midcentury. As World War I approached, reinterpretations issuing from physics as well as forces of fragmentation threatened the integrity of chemistry; but it resisted both reduction to physics and piecemeal assimilation to neighboring fields.

consolidation of a field

The chemical revolution replaced the phlogiston theory—that combustion and the formation of metallic "calces" (oxides) were losses of phlogiston—with the oxygen theory—that they were additions of oxygen; perfected a new nomenclature that designated compounds by composition; systematized pneumatic chemistry (which had revealed that air is plural and that airs could enter into chemical combination); explained, with the caloric theory of heat, changes in states of aggregation; accommodated the study of neutral salts, which had been dominant in prior practice; and established the "balance sheet method"—vital for pneumatic chemistry—that followed chemicals gravimetrically through reactions. Lavoisier's textbook, Traité élémentaire de chimie (1789; Elements of chemistry), epitomized these innovations.

Berzelius enlarged this synthesis with two further novelties: the chemical atomic theory, first articulated in England by John Dalton (1766–1844) and developed further by Berzelius; and the chemical effects of the electrical battery, devised in 1800 by the Italian Alessandro Volta (1745–1827). The atomic theory enhanced emergent notions of "stoichiometry" (the laws of chemical combination, especially definite and multiple proportions) and suggested that the law of definite proportions distinguishes compounds from mixtures. Berzelius undertook a vast project of chemical analysis that met new standards of precision. His goal: to distinguish compounds from mixtures and analyze all natural and artificial compounds. Both Berzelius and Humphry Davy (1778–1829) of England showed that the battery could decompose substances into electrically opposing constituents (e.g., salts into acids and bases). Berzelius reconceived inorganic chemistry by (1) according bases—formerly seen as passive substrates for coagulation of acids—positive properties, opposite to those of acids; and (2) anticipating that any compound, saline or not, consisted of paired, electrically opposing components. He thus characterized all compounds both quantitatively and qualitatively (by determining the constituents stoichiometrically and characterizing them electro-chemically). Berzelius revised Lavoisier's nomenclature to suit, replacing its French with Latin paradigms; and he devised the still-used symbols of composition (one- or two-letter abbreviations for the elements and superscripts—later changed to subscripts—for the numbers of atoms). The culmination of his work, comparable to Lavoisier's Traité, lay in his Essai sur la théorie des proportions chimiques (1819; Essay on the theory of chemical proportions) and his atomic weight tables of 1826.

This "electrochemical dualism" guided the next generation of chemists. Berzelius himself pursued it in mineralogy, a Swedish and German antecedent of academic chemistry, and in the nascent organic chemistry (of plant and animal substances). In mineralogy, Berzelius in 1814 showed that silica, traditionally thought a base, was an acid and that minerals were complex silicates; and his student Eilhard Mitscherlich (1794–1863) in 1818 discovered isomorphism, in which minerals preserve their crystal forms despite indefinite substitutions of some elements by chemically related ones. With minerals thus subjected to dualism, Berzelius boosted the subdiscipline of crystal chemistry. In organic chemistry, his work was informed by the claim of Lavoisier and his colleague Claude-Louis Berthollet (1748–1822) that organic compounds consist chiefly of carbon, hydrogen, oxygen, and nitrogen; by Lavoisier's belief that groupings of these elements (organic radicals) behaved like individual elements; and by Berzelius's own conclusion that organic matter occurred in mixtures of similar compounds. The task was therefore to separate distinct compounds from generic mixtures, analyze them, and interpret their composition dualistically. By 1814 Berzelius exemplified this approach, having performed among the first precise analyses of organic compounds. Thus conceived, organic chemistry dominated the discipline from the 1830s.

institutionalization: academics and industry

From 1800, chemistry was increasingly institutionalized academically. In Sweden, posts in governmental laboratories and mining and metallurgical enterprises were complemented with professorial positions, the first Swedish chair in chemistry appearing at Uppsala University in 1750. Berzelius, a medical graduate, held a post at the Karolinska (medical) Institute in Stockholm. In Britain, academics grew dominant after midcentury. In France, professorial posts appeared in institutions of applied science (schools or faculties of medicine, pharmacy, agriculture, mining, and engineering), where the distinction between pure and applied science encouraged teaching of theoretical chemistry and enhanced its social value. In Germany, institutionalization descended from pharmacy, especially the institute for chemical education and research-training founded in 1826, initially as a pharmacy school, by Justus von Liebig (1803–1873) at the University of Giessen and perpetuated by his students, notably August Wilhelm von Hofmann (1818–1892), in London and Berlin. It became the model for the proliferating German research institutes in natural sciences, the most prominent sites for chemical education and research-training in the nineteenth century. The laboratory and related resources commanded by German professors of chemistry fostered the growth and disciplinary identity of the field.

In the first half of the century, heavy chemical industry—especially production of "soda" (sodium carbonate) from sea salt by the Leblanc process, the lead-chamber process to produce sulfuric acid and its improvement by the Gay-Lussac tower, and the use of chlorine products in bleaching—involved inventors, entrepreneurs, and chemists, but no characteristic patterns dominated their relations.

controversies: atomism and organic composition

Disagreements persisted about the atomic theory and organic composition. Though distinct, in their resolution these questions were linked. Most chemists, seeing atoms as hypothetical, insisted on empirical "equivalent weights," eschewed determining the supposed actual weights and formulas, and relied on conventions. The diversity of these conventions, however, hindered communication and obscured or distorted relationships among substances. In inorganic chemistry, theoretical commitments and experimental anomalies hindered the reform of atomic weights and formulas; but problems in organic chemistry fostered it. Dualism was undermined by the discovery of substitution—in which electronegative chlorine, for example, could replace electropositive hydrogen with little change in properties—and by other evidence that organic radicals were mutable. Berzelius insisted that inorganic chemistry remain the template for organic; younger chemists demanded the reverse. Charles-Frédéric Gerhardt (1816–1856) and Auguste Laurent (1807–1853) of France

portrayed the diverse reactions of organic compounds as substitutions of atoms by radicals in simple, inorganic types, and they founded this "type" theory on reforms of atomic weights and formulas. Their successors, especially Alexander Williamson (1824–1904) of Britain, Hofmann, and Friedrich August Kekule von Stradonitz (1829–1896) of Germany, proposed a new, structural theory of organic chemistry, relying on the reforms of Gerhardt and Laurent and exploiting the newly conceived property of valence to interpret chemical combination. To foster consensus on atomic weights, structural chemists called the first international chemical congress, at Karlsruhe, in 1860. The persuasive analysis of atomic weights presented there by the Italian Stanislao Cannizzaro (1826–1910) encouraged gradual agreement. Organic chemistry now flourished. Jacobus Henricus van't Hoff (1852–1911) of Holland and Joseph-Achille Le Bel (1847–1930) of France pioneered the analysis of the spatial arrangements of atoms in compounds, and others synthesized many new substances.

Chemistry also spawned additional subdisciplines. Biochemistry (initially, "physiological chemistry"), emerging from both chemistry and physiology, was lodged in German physiology institutes. Physical chemistry, emergent from disparate strands, focused on solutions, thermodynamics, electrochemistry, and spectroscopy. Two of its leaders, Wilhelm Ostwald (1853–1932) and van't Hoff, founded its first journal, Zeitschrift für physikalische Chemie (1887;Journal of physical chemistry). The field flourished in Germany and after 1900 in the United States. Inorganic chemistry, long overshadowed by organic, reemerged following the creation (in 1869) by the Russian chemist Dmitri Mendeleyev (1834–1907) of the periodic table, itself resting on the post-Karlsruhe consensus; and coordination chemistry, created in the 1890s largely by Alfred Werner (1866–1919) of Germany.

From the 1850s, artificial dyestuffs and their control and synthesis by structural organic chemists transformed both chemical industry and academic chemistry. Firms proliferated in Britain and France, but from about 1870, German firms, benefiting from the expertise of academic chemists and new patterns of interaction with them, grew dominant. They created industrial research laboratories staffed by academically trained chemists; and they diversified into fine chemicals, pharmaceuticals, and agricultural chemicals. Their near monopolies often lasted until the end of World War II.

relations with physics and other fields

Physics had long interacted episodically with chemistry, but the advent of physical chemistry announced increasing intrusions. The discovery of the electron in 1897 by the English physicist Joseph John Thomson (1856–1940) and the demonstration by the New Zealand-born British physicist Ernest Rutherford (1871–1937) that atomic mass is concentrated in the nucleus led to new theories of valence on the part of the American academic physical chemists Gilbert N. Lewis (1875–1946) and Irving Langmuir (1881–1957), who found in the electron pair the basis of the chemical bond. Physicists' studies of atomic structure now distinguished the elements by atomic number, representing the positive charge on the nucleus, rather than by atomic weight, and permitted the accommodation of isotopes into the periodic table. After World War I, quantum mechanics transformed interpretations of chemical bonds and molecular structure. So profound have been the influence of physics and of the proliferating chemical subdisciplines, interdisciplinary interactions, and practical applications of chemistry, that some analysts regard the field as having lost its core identity in the twentieth century; others hold that the theoretically driven questions and the persistent importance of laboratory techniques, departmental structures, and teaching commitments of the professoriate have preserved the integrity of the field.

See alsoEducation; Science and Technology.

bibliography

Bensaude-Vincent, Bernadette, and Isabelle Stengers. A History of Chemistry. Translated by Deborah van Dam. Cambridge, Mass., and London, 1996.

Knight, David, and Helge Kragh. The Making of the Chemist: The Social History of Chemistry in Europe, 1789–1914. Cambridge, U.K., 1998.

Levere, Trevor H. Transforming Matter: A History of Chemistry from Alchemy to the Buckyball. Baltimore, Md., 2001.

Melhado, Evan M., and Tore Frängsmyr, eds. Enlightenment Science in the Romantic Era: The Chemistry of Berzelius and Its Cultural Setting. New York, 1992. Reprint, New York, 2003.

Travis, Anthony S. The Rainbow Makers: The Origins of the Synthetic Dyestuffs Industry in Western Europe. Bethlehem, Pa., 1993.

Evan M. Melhado