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In sharp contrast with the first period, the second period was characterised
by Mendeleev
s use of a
short form
periodic table (the
Natural System
, Figs.
11.4
and
11.6
). He aimed at an
individual
accommodation of the rare-earth elements, by
converting the rare-earth elements from primary to secondary elements and thus
resolving the undermined periodicity and characterisation issues. He modified
the atomic weights by a valency shift, and withdrew his claims about the rare
earth—transition metal analogy.
To a large extent, the aim of this paper has been to demonstrate how bold and
daring Mendeleev
'
s statements were in 1869. At that time, Mendeleev loved to give
his thoughts free rein and he had all faith in the successful future development of his
system. He clearly believed in atoms and even played with the idea of an internal
matter constituting these atoms (thus pointing to the complexity of atoms). In sharp
contrast with Mendeleev
'
s character in 1869, the more familiar and conservative
Mendeleev of the post-1869 period was very sceptic about the possible existence of
physical atoms (not to mention his disbelief in Prout
'
s hypothesis and the com-
'
plexity of atoms).
84
Acknowledgments The authors would like to extend a very special thanks to the Mendeleev
historian, Michael Gordin, for his invaluable input, detailed comments, feedback and encouraging
suggestions on a previous version of this paper. This paper was first presented by Pieter Thyssen at
the 13th ISPC Summer Symposium of the
International Society for the Philosophy of Chemistry
in
Philadelphia, in August 2009. Pieter warmly thanks the participants of this conference for the
many insightful discussions. Eric Scerri, Eugen Schwarz and Robin F. Hendry, in particular, are
acknowledged for their help. Thanks are also due to the late Johannes W. Van Spronsen and
Masanori Kaji who kindly provided some of the primary source material. Part of this work was
done while Pieter Thyssen was working as a fellow in the Othmer Library of the Chemical
Heritage Foundation (CHF) in Philadelphia, thanks to the generous financial support, provided
by the Chemical Heritage Foundation and the Research Foundation Flanders (FWO).
84
Thyssen, P. “Mendeleev
s Periodic Table and the 19th Century Debates on Atomism.” In
Wald
,
Positivism and Chemistry
. Edited by M. Eisvogel and K. Ruthenberg. W¨rzburg: K¨nigshausen
and Neumann, 2014 (in press).
'
