* * * * *

VIII.

IV.—­THE OCTAHEDRAL GROUPS.

These groups are at the turns of the spiral in Sir William Crookes’ lemniscates (see p. 28).  On the one side is carbon, with below it titanium and zirconium; on the other silicon, with germanium and tin.  The characteristic form is an octahedron, rounded at the angles and a little depressed between the faces in consequence of the rounding; in fact, we did not, at first, recognize it as an octahedron, and we called it the “corded bale,” the nearest likeness that struck us.  The members of the group are all tetrads, and have eight funnels, opening on the eight faces of the octahedron.  The first group is paramagnetic and positive; the corresponding one is diamagnetic and negative.  The two groups are not closely allied in composition, though both titanium and tin have in common the five intersecting tetrahedra at their respective centres.

[Illustration:  PLATE XV.]

CARBON (Plate III, 5, and XV, 1) gives us the fundamental octahedral form, which becomes so masked in titanium and zirconium.  As before said (p. 30), the protrusion of the arms in these suggests the old Rosicrucian symbol of the cross and rose, but they show at their ends the eight carbon funnels with their characteristic contents, and thus justify their relationship.  The funnels are in pairs, one of each pair showing three “cigars,” and having as its fellow a funnel in which the middle “cigar” is truncated, thus loosing one atom.  Each “cigar” has a leaf-like body at its base, and in the centre of the octahedron is a globe containing four atoms, each within its own wall; these lie on the dividing lines of the faces, and each holds a pair of the funnels together.  It seems as though this atom had been economically taken from the “cigar” to form a link.  This will be more clearly seen when we come to separate the parts from each other.  It will be noticed that the atoms in the “leaves” at the base vary in arrangement, being alternately in a line and in a triangle.

{ left 27
CARBON:  One pair of funnels { right 22
{ centre 1
—­
54
4 pairs of funnels of 54 atoms 216
Atomic weight 11.91
Number weight 216/18 12.00
TITANIUM (Plate III, 6, and XV, 2) has a complete carbon atom distributed over the ends of its four arms, a pair of funnels with their linking atom being seen in each.  Then, in each arm, comes the elaborate body shown as 3 c, with its eighty-eight atoms.  A ring of twelve ovoids (3 d) each holding within itself fourteen atoms, distributed among three contained globes—­two quartets and a sextet—­is a new device for crowding in material.  Lastly comes the central body (4 e) of five intersecting tetrahedra, with a “cigar” at each of their twenty points—­of which only fifteen can be shown in the diagram—­and a ring of seven atoms round an eighth, that forms the minute centre of the whole.  Into this elaborate body one hundred and twenty-eight atoms are built.