430 TRANSACTIONS OF SECTION B. 
where & is the ‘rotation constant’ and A,? the ‘dispersion constant’ for the 
substance. If a is plotted against A,? the curve is a simple rectangular hyper- 
bola, tending to a limiting value a = 0 when A?= @ and to a = @ when A?= A,”. 
If 1 is plotted against a? the curve becomes a straight line. In the 
a 
case of substances, such as ethyl tartrate, which show anomalous rotatory dis- 
persion, two of these terms must be employed, thus :— 
k, Ig 
NASA ln A 
a= 
This is in accordance with Biot’s view that anomalous rotatory dispersion is 
produced by the admixture of two substances differing in rotatory dispersive 
power as well as in the sign of their optical rotations. 
(iii) On Anomalous Rotatory Dispersion. By i. TscHuGAEFF. 
1. There are three different types of anomalous rotatory dispersion. The 
anomaly in question may be due: (a) To the superposition of two (or more) 
different kinds of normally dispersing molecules, differing in rotatory dispersive 
power as well as in the sign of their rotation. This type of anomalous disper- 
sion was first established by Biot. (Ex. mixture of /-menthone and iso-menthone.) 
(b) To the existence of absorption bands in the spectrum of the active substance, 
as it has been pointed out by Cotton, Drude, and others. (Cotton’s phenomenon.) 
(Ex. the xanthates and thiourethanes of menthol, borneol, and fenchol.) (c) To 
the intramolecular superposition of partial rotations corresponding to several 
centres of activity of one and the same molecule, as it has been shown first by 
the author. Experimental evidence in favour of this classification was given. 
2. It has been established that the shape of the dispersion curve is largely 
influenced by constitutive factors, and in the first place by the relative position 
of the centres of activity and of the chromophor groups within the active 
molecule, the whole dispersion curve resulting from the superposition of several 
‘partial’ curves. These results were discussed from the point of view of the 
electronic theory. 
3. The influence of the temperature and the nature of the solvent on the 
rotatory dispersion of the optically active xanthates resembles closely the influ- 
ence exerted by the same factors on the dispersion of tartaric acid and of its 
ethereal salts as studied by Winther and others. There must therefore be an 
intimate analogy in the origin of the anomaly in both cases. 
(iv) Remarks on the Walden Inversion. 
By Professor P. F. Franxuann, F.R.S. 
(v) The Rotation of Active Compounds as modified by Temperature, 
Colour of Light, and Solution in Indifferent Liquids. By T. 8. 
Parrerson, D.Sc., Ph.D. 
Before it can be possible to offer a real explanation of the phenomena of 
optical activity, attention must be devoted to the lowlier task of trying to under- 
stand clearly the main features of the phenomena in question; to study carefully, 
in fact, what may be termed the morphology of the subject. The variation of 
rotation with change in the colour of light, with change of solvent, with change 
of temperature, and perhaps even with change of pressure, must be thoroughly 
examined. 
As regards the last little can be said, but the other three—colour of light 
used, the nature of the solvent, and the temperature—are of the utmost import- 
ance. Even the data available at present seem sufficient to give some idea of the 
general behaviour of optically active compounds with changes of condition, 
and this may be summed up into one scheme, as follows :— 
Tt has been found that the rotation of certain active compounds reaches a 
maximum value at a certain definite temperature. Further, points of inflection 
