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continued to be primary elements, Mendeleev withdrew his claims about the rare
earth—transition metal analogy. More importantly, by destroying the primary
group of rare-earth elements, and accommodating them on an individual basis,
Mendeleev created three new secondary groups, where the differences in atomic
weight between lanthanum, boron and yttrium, for example, were big enough to
use them as a characteristic, differentiating property. This removed the need to
speculate about the existence of atoms, or the complexity of the elements.
11.2.6 Mendeleev
'
s Active Rare-Earth Research
The improved format of Mendeleev
s table had revealed a number of interesting
relationships between the properties of the elements. Encouraged by this new
information, Dmitrii Ivanovich began to focus all his attention on predicting the
properties of the as yet undiscovered elements (i.e. eka-boron in III-2,
eka-aluminium in III-3, and eka-silicon in IV-3, Fig.
11.4
). He finished writing
his paper
Concerning the Natural System of the Elements and Its Application in
Determining the Properties of Undiscovered Elements
on the 29th of November
1870 and he presented his work during a meeting of the
Russian Chemical Society
in early December 1870.
With the predicted properties at hand, Mendeleev soon embarked upon his quest
for the unknown elements. The position of eka-silicon (IV-3) implied that its
properties would lie midway between those of titanium and zirconium, and
Mendeleev therefore thought it best to initiate his hunt for this element in the
minerals of titanium and zirconium. Two days after the meeting of the
Russian
Chemical Society
, on the 5th of December 1870 to be exact, Mendeleev sent a
petition to the rector of the University of St. Petersburg, K. F. Kessler, requesting
him a number of minerals for his future investigations. “My observation of the
periodic dependence between the properties and the atomic weights of simple
bodies gives the possibility to predict the existence and to guess the properties of
some simple bodies that have not yet been discovered, about which I communicated
at an extraordinary session of the
Russian Chemical Society
”, said Mendeleev.
70
“Desiring to verify at least part of the conclusions expressed [at this meeting], I
need to undertake investigations of several rare minerals, and therefore request that
you contact the Mining Institute to ask them for some of these minerals needed
for my scientific work which they have in stock.”
71
Mendeleev continued how especially important it was for him “to obtain as large
an amount of titanium minerals as possible, together with their place of origin, if
possible. Specifically: rutile [TiO
2
], ilmenite [FeTiO
3
], and also other minerals:
zirconium [Zr], orthite, or cerite and eschynite.”
72
Dmitrii Ivanovich quickly
'
70
Brooks (2002), op. cit., p. 138. (note 10)
71
Loc. cit.
72
Loc. cit.
