1224 
from Werner’s well-known octahedrical arrangement of the six 
equivalent coordination-places round the central cobalt-atom. 
\ 
\ 
Fig. 1. 
A more detailed study of the real symmetry of these spacial 
arrangements, in connection with the perfectly symmetrical atomistic 
configuration of the ethylenediamine-molecule itself, shows how these 
complex cations are rather highly “symmetrical”; they possess the 
following symmetry-elements: one bipolar ternary principal axis, 
and three polar binary axes in a plane perpendicular to the ternary 
axis, intersecting each other at angles of 60° (or 120°). In fig. 1 
the plane of these three polar axes is drawn parallel to the face 
of the octahedron, lying in the octant right- and left-above. There 
is no symmetry-centre nor any symmetry-plane present in the 
configuration. The symmetry deduced is the same as in erystallo- 
eraphy is described as characteristic of the forms of the ¢rigonal- 
trapezohedrical class, which symmetry is shown also e.g. by the 
erystals of cinnabar, quartz and some camphora-species, etc. Just as 
in the case of these substances, both the cations here schematically 
drawn are not identical with their mirror-images, and it is for this 
reason, that the salts derived occasionally occur in two modifications, 
which are to each other in the relation of right- and left-handed 
forms. It may be remarked that a slight indication of the trigonal 
symmetry of these cations may be observed in the fact, that under 
the racemic compounds the chloride and bromide, erystallising with 
three water-molecules, and also the racemic nitrite, possess an appar- 
ent or real trigonal symmetry (vid. paper IH). However the corre- 
sponding antipodes of the bromide unhappily erystallise with two 
molecules of water, while the tetragonal or rhombic symmetry of 
these optically active salts, which occurs in several cases, can more- 
