1219 
and as Guynr’s suggestive ideas prove, they even tried to point out 
an immediate connection between the more or less considerable 
degree of such molecular dissymmetry, and the more or less palpable 
differences, e. g. in mass, which can be stated between those 7 un- 
equal atoms or radicals"). In that case the idea is evidently always 
present, that a chemical molecule possessing such ‘‘unsymmetric 
atoms’, will necessarily be characterized by a complete lack of 
symmetry, and thus can be defined in the full sense of the word, 
as an “unsymmetric’ molecule. 
As long as one is of opinion, that in this question the ordinary 
chemical differences of the radieals-which are linked to the multivalent 
atom, will really be the predominant factor, it perhaps is allowable 
to consider such a molecule as a spacial complex which does not 
possess any more symmetry-properties. But it must immediately be 
pointed out here, that this conclusion is by no means an inevitable 
one: it must be considered to be quite precipitate, to suppose the 
molecules of this kind as necessarily unsymmetrical ones for all 
kinds of physical properties, just because we do not know the 
undoubtedly very complicated structure of the atoms themselves. 
The more, as the “absence of symmetry-planes”’, commonly brought 
to the fore on this oceasion, will by no means involve the absence 
of any symmetry in such a spacial system, nor will this single 
condition be sufficient to make the presence of two modifications, 
which relate to each other as mirror-images, a necessary consequence.’) 
In connection with these erroneous conceptions about the conditions 
which will imvolve the mirror-image-isomerism in the case of such 
spacial systems, it must be esteemed of the highest importance that we 
have begun to understand that the presence of an ‘“unsymmetric” 
multivalent atom, as defined by the conception of LeBeL and vaAN 
1) PH. A. Guye. Compt. rend. 110. 744 (1890); Thèse Paris, (1891). 
4) If for instance one accepts the idea that the atoms of the chemical elements, 
notwithstanding their different nature, contain some structure-elements which are 
common to all of them, and that it will principally depend just on the spacial 
arrangement of those common constituents (e.g. systems of electrons), which will 
determine the symmetry of the physical properties or at least of some of them 
in the resulting substances, — then it does by no means follow from the chemical 
inequality of the substitutes in the molecule, that the spacial system of those 
determining structure-elements of the atoms, necessarily represents a non-sym- 
metrical complex. As long as we do not know, on what particular circum- 
stances the physical dissymmetry of the molecules properly depends, it is not 
allowable in my opinion to consider the chemical inequality of the substitutes as 
the necessary condition of the physical dissymmetry of the substance; it can at 
pest be esteemed a very favourable moment for it. 
S1 
Proceedings Royal Acad. Amsterdam. Vol. XVII. 
