1221 
all solvents is so great, that it was hitherto impossible to prove 
the correctness of Pasrrur’s principle in these cases, just with respect 
to the erystalforms of the antipodes. 
The strongest evidence however in favour of the views previously 
explained about the necessary conditions for the occurrence of 
mirror-image-isomerism, can be deduced from the theoretically com- 
paratively simple cases which for the first time became known asa 
result of A. WerNer’s masterly investigations on the complex-salts, 
and more especially of the /wteo-triaethylenediamine-cobaltic salts *). 
Later on he found analogous phenomena with a number of other 
salts with complex ions, e.g. with the analogous derivatives of oxalic 
acid. Not only did these facts prove the correctness of WeRNER’s 
views considering the spacial arrangement of the six coordinated 
substitutes round the polyvalent central-atom, but they have also 
brought direct proof of the correctness of the other idea, that in the 
question of ‘molecular dissymmetry’, as commonly understood, it 
is not primarily the inequality of the substituents, but exclusively 
their spacial arrangement, which is of importance. 
A new problem is thereby brought to the fore: to find the cireum- 
stances and conditions, which will cause a spacial configuration of 
the atoms in the molecules, which will be different from its mirror- 
image even in those cases where no chemical differences between 
those substitutes are present *). 
1) A. WERNER. Ber. d.d. Chem. Ges. 45. 121. (1912); 47. 1960, 3093. (1914). 
2) In this connection it may be well, shortly to remind of the conditions for the 
occurrence of spacial configurations, which will not be congruent with their mirror- 
images, and to mention the significance there-with of the commonly emphasized 
“Jack of symmetry-planes” in this phenomenon. If one chooses as the descriptive 
“symmetry-elements’ for such spacial arrangements: the symmetry-axes 
2 
(period = =) of the first and of the second class (“axes of alternating symmetry’’), 
: L 
— then one can say that all configurations which do not possess such axes of the 
second class, will be different from their mirror-images. All such configurations, 
which differ from their mirror-images, can possess only axial symmetry. As an 
axis of the second class, for which n = 2, corresponds to a “centre of symmetry”, 
and one for which m= 1, corresponds to a mere mirror-plane, it becomes clear 
that such “enantiomorphic”” arrangements neither possess a centre of symmetry, 
nor a plane of symmetry. But the reverse statement is not true: among the 
32 possible symmetrical groups of crystallography e.g. there are already (ree which 
do not possess any plane of symmetry, and whose configurations, notwithstanding 
that, do not differ from their mirror-images (in the cases apparently, where there 
is only one axis of the second class present, with m= 2, 4 or 6 ). And there 
are several groups, which have no centre of symmetry, and are however identical 
with their mirror images. It can moreover be remarked here, that axes of the 
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