During the past decades, the historiography of nineteenth-century chemistry has become increasingly complex and at the same time more interesting. Rising on the sound “internalistic” foundations laid by Aaron J. Ihde’s The Development of Modern Chemistry (1964) and, of course, by James R. Partington’s A History of Chemistry (four volumes, 1961–1970), the edifice of more recent historiography depicts chemistry as an endeavor in close interaction with the cultural and intellectual currents of that time. Departing from the question of the disciplinary identity of chemistry during the nineteenth century and thus joining “the separate analyses of schools, disciplines, and traditions into an integrated analytical matrix,” Mary Jo Nye has with a sure hand sketched out the framework of this chemical edifice. As reflected in her book, new problems have moved to the forefront, among them the question of the disciplinary development of chemistry and its subdisci-plines, such as biochemistry, stereochemistry, and physical chemistry, as well as questions of the emergence of scientific schools and of science policy in general. Last but not least are the questions of the metaphysical background and of the internal discourses among chemists. In this context, two questions are of eminent importance: What is “chemical” in chemistry, that is, what distinguishes chemistry from its neighbor sciences? And how does chemistry arrange the objects of its scientific experiences?

CHEMICAL VERSUS PHYSICAL ATOMS

One may well say that it is the notion of units of matter showing certain measurable relations of their weight and possessing certain characteristics to explain the specificity of chemical reactions (that is, the notion of “chemical atomism”) that distinguished chemistry from its close relative, physics. This may sound a little strange, as we are used to seeing atoms as the same entities in all sciences. From the time of Democritus (ca. 410 b.c.) up to the first decades of the nineteenth century, atoms were considered to be little indivisible lumps of matter, which, when forming compounds, are attached to one another either by their respective shapes or by “affinities.”