Radicals, Reactions, Realism - Philosophy of Chemistry - page 183

“Hitherto, the definitely recognized units in chemistry have been: atoms,
molecules, ions, and electrons. And now, in addition to these four, chemistry,
it seems, has to take into account a fifth entity - free radicals.” 19
Hence, nothing went wrong as far as Gomberg was concerned - except that he
had not found a free radical.

12.4 What Is This Thing Called Radical?

In what sense can a radical be called a substance or a material carrier of
chemical change? Obviously, radicals do not fit into imaginable general schemes
of chemical stuff. At least they do not in every respect that might be considered
typical for usual manifest material. Joachim Schummer, for example, discusses an
“experimental stuff hierarchy” (Schummer 2008 , 13). According to this classical
hierarchy, chemical work starts with heterogeneous mixtures and proceeds analyti-
cally 20 to chemical elements via homogeneous mixtures and pure compounds.
Gomberg

s radical surely is a compound and not an element. Whether or not
“it” - in the solid state - was heterogeneous or homogeneous, however, was
not possible to decide for Gomberg. Because its chemical identity had been not
yet discovered, the purification of the obtained material, be it solid or dissolved, had
to be performed by trial and error. 21 Hence, an assignment of Gomberg

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s stuff

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according to classical substance systems hardly seems possible.
In order to find the epistemological place of the concept of radical in Gomberg s

days it is useful to apply different theoretical approaches from chemistry and the
heritage of the historically oriented philosophy of science. The over-arching
approach we shall refer to here is the stuff notion; since at least the late eighteenth
century, chemistry has been characterized as the enterprise concerned with the
property changes of stuff by most of its practitioners. The Belgian chemist Jean
Timmermans (1882-1971), for example, who was concerned with standardization
topics in chemistry in an international framework, gave the following practically
motivated list of questions as a general outline for his topic on the general
characterization of chemical species: “(1) How may a given physical-chemical
system be defined without ambiguity? This is the problem of chemical species;
(2) How may such a system be realized? This is the problem of pure materials;

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19

Gomberg 1928 , 164. In his monograph on philosophy of chemistry, the Dutch philosopher Jaap
van Brakel refers to a similar view. In a footnote referring to discussions of USSR philosophers of
chemistry such as Kedrov he states: “Here, the material carriers of chemical change are assumed to
be atoms, molecules, radicals and ions (both of atoms and atom groups)”, van Brakel 2000 , 25.
20 Note that in fact any analytical work incorporates necessary synthetic steps, that is, the
“analytical” methodology like in Schummer s description should be read theoretically rather

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than empirically .
21 Note that this is the case for many pure substances, for example the chemical elements during
the very first occasion of their discovery or preparation.