22 
NATURE 
[APRIL 2, 1914 
and Ritchey being finally adopted. The report gives 
a brief résumé of the work of the various branches 
accomplished during the year, and an appendix con- 
tains a table giving the corrections to the Norddeich 
and Eiffel Tower wireless time signals. The report is 
accompanied by some good reproductions of some of 
the larger telescopes, and two pictures of the annular 
solar eclipse of April, 1912, secured by Prof. A. 
Schwassmann with the Lippert astrographic instru- 
ment. 
OPTICAL ROTATORY POWER. 
HE Faraday Society has adopted in recent years 
the policy of organising a series of general dis- 
cussions on physico-chemical subjects, to which inves- 
tigators of all countries are invited to contribute. The 
ninth of these discussions, on optical rotatory power, 
was held in the rooms of the Chemical Society on 
Friday, March 27. At the afternoon session the chair 
was occupied by Prof. Armstrong, who contributed 
an introductory address; the evening session was pre- 
sided over by Prof. Frankland. Papers were read 
by Prof. H. Rupe, of Basle, on the influence of certain 
groups on rotatory power, by Prof. H. Grossman, of 
Berlin, on the rotatory dispersion of tartaric and malic 
acids, by Dr. T. M. Lowry and Mr. T. W. Dickson, 
on simple and complex rotatory dispersion, by Dr. 
T. M. Lowry and Mr. H. H. Abram on an enclosed 
cadmium arc for use with the polarimeter, by Dr. 
R. H. Pickard and Mr. Joseph Kenyon, on the rota- 
tory powers of the members of homologous series, and 
by Dr. T. S. Patterson, on the dependence of rotation 
on temperature, dilution, nature of solvent, and wave- 
length of light. Papers were also communicated by 
Prof. L. Tschugaeff, of St. Petersburg, on anomalous 
rotatory dispersion, by Dr. E. Darmois, of Paris, on 
the existence of racemic tartaric acid in solution, by 
Dr. G. Bruhat, of Paris, on the rotatory power of 
tartaric acid, and by Prof. A. Cotton, of Paris, on the 
constitution of liquid mixtures and their rotatory 
power. 
Two distinct schools of research were conspicuous 
in the papers and in the discussion. The attempts to 
find a relationship between chemical constitution and 
the rotatory power of compounds for sodium light 
received its greatest impetus from the theory put for- 
ward in 1892 by Crum Brown and Guye, to whom, 
at the suggestion of Prof. Armstrong, greetings were 
sent from the meeting; this school of research was 
well represented by Prof. Frankland, who had no 
difficulty in showing that results of very great value 
had been obtained from observations made with light 
of one colour only, that of the sodium-flame. Prof. 
Rupe gave a masterly summary of his work on the 
influence of unsaturated groups on rotatory power ; 
this work had also been done mainly with sodium 
light, but there was no reason to suppose that the 
results would have been essentially different if light 
of other: colours had been used. Dr. Patterson, in 
describing his observations on the influence of tem- 
perature and of solvents on the rotatory power of the 
tartrates for sodium light, was able to show that there 
is an essential unity in the effects produced bv these 
two widely different factors; this unity could be ex- 
tended to include some features in the behaviour of 
these liquids towards light of different colours, as 
recorded by Winther and others. 
An element of novelty attached to the description 
of several series of researches which depended on the 
measurements of rotatory dispersion—a subject which 
has come suddenly to the front, both in England and 
on the Continent, during the course of the last two 
or three years. The apparatus required for measur- 
NO? 2308, VO no) 
ing rotatory dispersion was exhibited by Mr. Abram, 
who also succeeded in showing an enclosed cadmium 
arc in actual operation. This arc is likely to be of 
great value in experiments on rotatory dispersion, be- 
cause it provides a pair of lines, Cd 5086 (green) and 
Cd 6438 (red), which can be read with the same 
accuracy as the mercury lines, Hg 4359 (violet) and 
Hg 5461 (green). Thus it has been used to prove that 
a-methylglucoside, a compound which contains five 
asymmetric carbon atoms, obeys strictly the simple 
dispersion law given by the formula, 
This law also holds good for a long series of alcohols 
prepared and described by Dr. Pickard and Mr. Ken- 
yon, the dispersive power of which remains constant 
over wide ranges of temperature, and may persist 
almost unchanged throughout the whole range of a 
homologous series. 
Rotatory dispersion has usually been classified as 
normal when the rotation increases steadily as the 
wave-length diminishes, and as anomalous when in 
any part of the spectrum the rotation diminishes with 
the wave-length. The most familiar examples of 
anomalous rotatory dispersion are (i) tartaric acid, for 
which a remarkable series of data were recorded in 
M. Bruhat’s paper; (ii) ethyl tartrate, studied exhaus- 
tively by Dr. Patterson; and (iii) methyl malate, which 
has been examined by Grossman in nearly one hundred 
different solvents. More recently Dr. Pickard and 
Mr. Kenyon have detected the same phenomenon in 
the simple esters of their optically active alcohols, and 
also in the a-naphthylmethylearbinol, 
C,,H,.CH(OH).CH,, 
when this is examined in the superfused state. 
Dr. Patterson protested against a_ classification 
which represented ethyl tartrate as showing “‘ normal ”’ 
dispersion in some solvents and ‘‘anomalous”’ disper- 
sion in others. He argued that it was merely a 
matter of accident whether the maximum of optical 
rotation occurred within or without the region of the 
spectrum used for the polarimetric observations. This 
contention was supported by Dr. Lowry and Mr. 
Dickson, who were able to quote cases in which the 
camera had revealed a maximum beyond the limits of 
visual observation. They proposed to describe as 
simple rotatory dispersion all those cases to which the 
formula, 
hy 
as 
VAL 
can be applied. All cases in which two or more terms 
are required to express the dispersion, thus— 
hy hy 
a = 
A2—AZ— 2)?’ 
were to be described as complex rotatory dispersion, 
whether the curves were anomalous or apparently 
normal in the region investigated. Simple rotatory 
dispersion may be detected very easily by plotting r/fa 
against ’*, when the experimental data are found to 
fall on a straight line. When two terms, with con- 
stant values of 4,7, and 4,7, are sufficient to express 
the rotatory dispersion of a substance over a wide 
range of experimental conditions, the ‘‘ characteristic 
diagram’”’ of Armstrong and Walker will plot out to 
a series of straight lines, but this will no longer be 
the case if three ‘‘ dispersion-constants,’”’ ,?, A,7, A537, 
are required. 
The cause of anomalous rotatory dispersion was 
discussed by Prof. Tschugaeff. It can be produced 
by mixing two substances of opposite rotatory power 
and unequal dispersion (Biot) or by superposing two 
a= 
