Its negative complement consists of nitrogen, vanadium and
niobium, and we have again to note that nitrogen, like hydrogen and oxygen,
departs from its group type. Two other triad groups, the positive
aluminium, gallium and indium (the fourth unexamined) and the negative
phosphorus, arsenic and antimony (the fourth unexamined), have also six
funnels opening on the faces of a cube.
IV. _The Octahedron._--The simplest example of this is carbon (5 on Plate
III). We have again the funnel with its ovoids, but now there are eight
funnels opening on the eight faces of the octahedron. In titanium (6 on
Plate III) the form is masked by the protruding arms, which give the
appearance of the old Rosicrucian Cross and Rose, but when we look into the
details later, the carbon type comes out clearly. Zirconium is exactly like
titanium in form, but contains a large number of atoms. We did not examine
the remaining two members of this group. The group is tetratomic and
positive. Its negative pendant shows the same form in silicon, germanium
and tin; again, the fourth was unexamined.
[Illustration: PLATE IV.]
V. _The Bars._--These characterise a set of closely allied groups, termed
"inter-periodic.
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