648 
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, CHa 
ee SCN OE 
HH?) Cry pCi 
can be resolved into optically active modifications. 
The conclusion is thus forced upon us that the tri- 
valent nitrogen atom in such compounds is not en- 
vironed in the most symmetrical manner possible by 
the surrounding components 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 con- 
stituent atoms in three-dimensional space; careful 
study of the present stage of progress shows that we 
must attribute to molecular configuration, as deter- 
mined by modern chemical methods, a very real 
significance. It can no longer be supposed to possess 
the purely diagrammatic character which attached to 
the Frankland-Kekulé constitutional formula; 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 
cheniical 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 manipu- 
lative 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 con- 
clusions find an unshakable foundation on_ facts 
relating to optical activity, we have as yet no clear 
idea as to why substances of enantiomorphous mole- 
cular 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, Frank- 
land, 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 or rotation constants. 
That aspect of stereochemistry which has just been 
so briefly reviewed represents a situation which has 
been attained during the natural development of 
organic chemistry by methods which have now be- 
5 Trans. Chem. Soc., 1910, 97, 1866. 
T 2 
NO. 2238, 
NATURE 
[AUGUST 20, 1914 
come traditional; progress has been made by the 
application of strictly logical methods of interpreta- 
tion to masses of experimental data, and each new 
conclusion has been checked and verified by fhe 
accumulation of fresh contributions in the laboratory. 
The sureness of the methods adopted could not fail 
to lead to the intrusion of stereochemistry into ad- 
jacent fields of scientific activity; bio-chemistry, the 
study of the chemical processes occurring in living 
organisms, is already largely dominated by stereo- 
chemistry, and the certainty with which stereo- 
chemistry has inspired us as to the reality of the 
molecular constitution of matter is exerting a power- 
ful influence in other branches of natural science. 
Quite possibly, however, the acquaintance which every 
chemist possesses of the great progress already made 
upon one particular set of lines is to some extent an 
obstacle to his appreciation of new directions in which 
further great stereochemical advances may _ be 
anticipated. 
A little reflection will show that the study of the 
relation between the crystalline form and chemical 
‘ constitution or configuration of substances in general 
may confidently be expected to lead to important: ex- 
tensions of our knowledge of the manner in which 
the atoms are arranged in molecular complexes. The 
earlier crystallographic work of the nineteenth century 
led to the conclusion that each substance affects some 
particular crystalline form, that the regular external 
crystalline shape is an expression of the internal 
structure of the crystal, and that a determination of 
the simpler properties—geometrical, optical, and the 
like—of a crystalline material constitutes a mode of 
completely characterising the substance. Later work 
during the last century demonstrated that the proper- 
ties of crystalline substances are in entire harmony 
with a simple assumption as to the manner in which 
the units or particles of the material are arranged; 
the assumption is that the arrangement is a geo- 
metrically ‘‘homogeneous”’ one, namely, an arrange- 
ment in which. similar units are uniformly repeated 
throughout the structure, corresponding points pre- 
senting everywhere a_ similar environment. The 
assumption of homogeneity of structure imposes a 
definite limitation upon the kinds of arrangement 
which are possible in crystals; it leads to the inquiry 
as to how many types of homogeneous arrangement 
of points in space are possible, and to the identification 
of these types with the known ‘classes of crystal 
symmetry. The final conclusion has been attained 
that there are 230 geometrically homogeneous modes 
of distributing units, or points representing material 
particles, throughout space; these, the so-called 230 
homogeneous ‘‘point-systems,’’ fall into the thirty- 
two types of symmetry exhibited by crystalline solids. 
The solution of the purely geometrical problem here 
involved was commenced by Frankenheim in 1830, 
and finally completed by Barlow in 1894; it brings us 
face to face with the much larger stereochemical 
problem—that of determining what the units are 
which become homogeneously arranged in the crystal, 
why they become so arranged, and in what way a 
connection can be established between chemical con- 
stitution and crystal structure. 
Since the conception of homogeneity of structure 
alone is clearly insufficient for the interpretation of 
the more advanced problem, some further assumption 
must be made as a foundation for any really compre- 
hensive attempt to collate the quantities of. isolated 
facts bearing upon the subject. Of the many assump- 
tions which have been made in this connection only 
one, which may now be stated, has as yet proved 
fruitful in the sense that it serves to correlate large 
| numbers of. known experimental facts, and that it 
1 
al ll 
Sore 
