326 TRANSACTIONS OF SECTION B. 
no carbon atom which is attached to four different groups, but a study of the 
solid model representing the molecular configuration built up in accordance with 
the van ’t Hoff-Wislicenus conclusions reveals the enantiomorphism. 
It is of some importance to note that the configurations assigned to such 
optically active substances as have been mentioned above, on the basis of the 
experimental evidence, are of as symmetrical a character as the conditions 
permit; the Kekulé formula for methane, CH,, in which all five atoms lie in 
the same plane, is not of so highly symmetrical a character as the van ’t Hoff- 
Le Bel configuration in which the four hydrogen atoms are situate at the apices 
of a regular tetrahedron described about the carbon atom as centre. Some 
influence seems to be operative which tends to distribute the component radicles 
in an unsymmetrical molecule in as symmetrical a manner as possible; recent 
work indicates, however, that this is not always true. During the past few 
years Mills and Bain * have shown that the synthetic substance of the constitution 
CH, CH, . CH 
"Sof No: N. 0H 
HY \cH,. CH, 
can be resolved into optically active modifications. The conclusion is thus 
forced upon us that the trivalent nitrogen atom in such compounds is not 
environed in the most symmetrical manner possible by the surrounding com- 
ponents of the molecule; the experimental verification which the conclusions of 
Hantzsch and Werner, concerning the isomerism of the oximes, thus derive, 
constitutes the first really direct evidence justifying their acceptance. 
Quite recently, and by the application largely of the optically active powerful 
sulphonic acids derived from camphor, Werner has made another great advance 
in connection with the subject of optical activity. He has obtained a number 
of complex compounds of chromium, cobalt, iron, and rhodium in optically active 
modifications. 
The foregoing brief statement probably suffices to indicate the progress 
which has been made during the last twenty years in demonstrating that the 
atoms or radicles associated in the chemical molecule do not lie in one plane 
but are disposed about certain constituent atoms in three-dimensional space; 
careful study of the present stage of progress shows that we must attribute to 
molecular configuration, as determined by modern chemical methods, a very 
real significance. It can no longer be supposed to possess the purely diagram- 
matic character which attached to the Frankland-Kekulé constitutional formule ; 
it seems to be proved that the men who developed the doctrine of valency were 
not merely pursuing an empirical mode of classification, capable of various modes 
of physical interpretation, but were devising the main scheme of a correct 
mechanical model of the chemical universe. 
The development of a branch of science such as that now under discussion 
is, to a considerable extent, an artistic pursuit; it calls for the exercise of 
manipulative skill, of a knowledge of materials, and of originality of conception, 
which probably originate in intuition and empiricism, but must be applied with 
scientific acumen and logical judgment. For reasons of this kind many gaps 
occur in our present knowledge of the subject; although so many important 
conclusions find an unshakable foundation on facts relating to optical activity, 
we have as yet no clear idea as to why substances of enantiomorphous molecular 
configuration exhibit optical activity. Great masses of quantitative data 
referring to optical activity have been accumulated; something has been done 
towards their correlation by Armstrong, Frankland, Pickard, Lowry, and 
others, but we still await from the mathematical physicist a theory of optical 
activity comparable in quantitative completeness to the electro-magnetic theory 
of light. Until we get such a theory it seems unlikely that much further 
progress will be made in interpreting quantitative determinations of rotation 
constants. 
That aspect of stereochemistry which has just been so briefly reviewed 
represents a situation which has been attained during the natural development 
‘Trans. Chem. Soc., 1910, 97, 1866. 
