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there appears to be a constancy in the valency number, although the atomic
weights of the congeners are changing regularly and gradually. The same can be
said for the iron group, the palladium group, the platinum group, and the erbium
group. In conclusion, the generality of the periodic law got undermined due to the
presence of primary groups in the periodic system. This was one of the core
problems of the rare-earth elements, which lay at the basis of their problematic
accommodation.
11.1.11 Characterisation Issues: Primary Versus
Secondary Elements
The dual sense of the epistemological concept of chemical elements has been the
focus of much philosophical debate and research by contemporary philosophers of
chemistry. Although this debate goes back to the 1931 paper by Paneth,
39
the main
idea was clearly already present in the Mendeleev corpus.
40
It is therefore interest-
ing to investigate to what extent the rare-earth crisis forced Mendeleev to change
his points of view with regard to the nature and concept of elements.
Summarising Mendeleev
s philosophical viewpoints, one could state that
Mendeleev clearly recognised the dual sense of the nature of chemical elements.
He thus clearly distinguished between the elements as
simple substances
and as
basic substances
. Simple substances could be characterised by the plethora of
secondary properties (i.e. colour, taste, smell, etc.), and were therefore observable
and isolable. Basic substances on the other hand were completely unobservable to
our senses. This did not imply however that they were completely devoid of
properties. Mendeleev was of the opinion that the more abstract, basic substances
were characterised by the atomic weight, and he therefore used this property in
'
39
Paneth, F. A. “
¨
ber Die Erkenntnistheoretische Stellung Des Chemischen Elementbegriffs.”
Schriften der Ko¨nigsberger Gelehrten Gesellschaft
8, no. 4 (1931): 101-125. An English transla-
tion can be found in Paneth, F. A. “The Epistemological Status of the Chemical Concept of
Element (I).”
The British Journal for the Philosophy of Science
13, no. 49 (1962a): 1-14 and
Paneth, F. A. “The Epistemological Status of the Chemical Concept of Element (II).”
The British
Journal for the Philosophy of Science
13, no. 49 (1962b): 144-160. More recently, Paneth
'
s paper
has been republished in Paneth, F. A. “The Epistemological Status of the Chemical Concept of
Element.”
Foundations of Chemistry
5, no. 2 (2003): 113-145.
40
See Paneth, F. A. “Chemical Elements and Primordial Matter: Mendeleeff
'
s View and the
Present Position.” In
Chemistry and Beyond
:
Selection from the Writings of the Late Professor
F.A. Paneth
, edited by Herbert Dingle and G. R. Martin, 53-72. New York: Wiley Interscience,
1965. See also Bensaude-Vincent, B. “Mendeleev
s Periodic System of Chemical Elements.”
The
British Journal for the History of Science
19, no. 1 (1986): 3-17, Scerri, E. R. “Realism,
Reduction, and the “Intermediate Position”.” In
Of Minds and Molecules
,
New Philosophical
Perspectives on Chemistry
, edited by N. Bhushan and S. Rosenfeld, 51-72. New York: Oxford
University Press, 2000, Scerri, E. R. “Some Aspects of the Metaphysics of Chemistry and the
Nature of the Elements.” HYLE 11, no. 1-2 (2005): 127-145.
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