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vations which bear upon the properties of the racemic and tartric 
acids and their salts, — have led to that more detailed conception 
of the spacial arrangement of the atoms in the molecules, which 
has finally obtained expression in the stereochemical views of modern 
times. The conclusion to which Pastrur was led can be shortly 
expressed in this way: in all cases where a substance is characterised 
by a dissymmetrical arrangement of the composing atoms in its 
molecules, the possibility can be foreseen of the existence of two 
modifications of that substance, whose physical properties can be 
described by spacial systems of vectors, which are in the relation 
to each other of right- and lefthand-systems. 
This statement has proved to be satisfactorily general and so 
indefinite as to have led to numerous remarks and even to misunder- 
standing. With respect to the second part of the above-mentioned 
conclusion, there can hardly be any divergence of opinion: it is of 
course quite apparent, that here only can be question about vectorial, 
never about sca/ar quantities. Thermical, caloric, and volumetrical 
constants, e.g., will thus be identical with the two modifications in all 
cases; and from those properties which are expressed by means of 
vectors, only such can be taken into account, whose descriptive 
-vector-systems will not coincide with its mirror-images; the pyro- 
and piezo-electrical phenomena, etc, which cannot be described by 
centrically-symmetrical, but only by “polar” vectors. 
The first part of Pasrrur’s conclusion however will immediately 
lead to the question: what is the proper meaning of the expression 
“molecular dissymmetry’, and under which circumstances will it 
manifest itself? It becomes clear on fuller examination, that the 
introduction of the word ‘“dissymmetry’’ in these cases, has often 
caused misconceptions, and that it has led to erroneous or at least 
incomplete statements, even with well-known authors; and what is 
more, it seems continually to lead to unintelligibility about the 
conditions which will determine the isomerism indicated, notwith- 
standing the evident feeling of incertitude, which can occasionally 
be stated *). 
The doctrine of the so-called ‘“unsymmetric atoms” of Le Bet and 
vAN “tT Horr brought, as is well-known, a first rational explanation 
of that “molecular dissymmetry”. Since then the presence of an 
n-valent atom, saturated by 2 unequal substitutes, has begun to be 
considered as the necessary condition which must be fulfilled, if the 
case of a possible isomerism as foreseen by Pasteur, is to be realized; 
1) Conf. Ga, M. van DEventER, Chem. Weekblad 10. 1046, (1913). 
