18 Proceedings of the Royal Society of Edinburgh. [Sess. 
III. — Researches in Optical Activity. Part I : The Temperature- 
Rotation Curves for the Tartrates at Low Temperatures. 
By T. S. Patterson, D.Sc , Ph.D., Waltonian Lecturer and Lecturer 
in Organic Chemistry, University of Glasgow ; and K. L. Moudgill, 
B.Sc., late Robert Donaldson Scholar, University of Glasgow. Com- 
municated by Professor Andrew Gray, F.R.S. 
(MS. received August 15, 1918. Read November 4, 1918.) 
But a few years ago the diverse phenomena of optical activity, such as 
the changes of rotation which occur with alteration of temperature, of 
colour of light, of solvent, or of concentration in a solvent, appeared, in 
spite of the great accumulation of relative data, to be practically in- 
dependent of each other, and gg,ve very little hope of satisfactory general- 
isation. Quite recently, however, the possibility of bringing into one 
scheme all these different branches of the subject has become more than 
a mere aspiration, and the progress which has been made by several 
investigators reveals clearly the existence of a deep-seated and far- 
reaching regularity underlying the remarkable sensitiveness to external 
conditions of the phenomena in question. 
Some previous work of one of the present authors may be summed 
up as follows:- — 
1. The T-R* curves for a set of homologous active compounds, such 
as the simple tartrates, exhibit maxima which, for the molecular rotation, 
occur mostly at temperatures between 140° and 220°. The slight change 
of constitution, therefore, in passing from one to another, appears to 
cause a comparatively slight shift in the position of the maximum, the 
importance of the maximum lying, of course, in the fact that it is a 
singular point which can be recognised, and which, presumably, represents 
some corresponding or analogous condition in the substances, the behaviour 
of which is represented by the different curves (J.C.S., 1913, 103, 148). 
2. When these esters are dissolved in inactive media the position of 
this maximum is, generally speaking, again shifted, some solvents dis- 
placing it to a higher temperature and a lower rotation value, others 
moving it towards a lower temperature and a higher rotation value both 
in very varying degree (J.C.S., 1908, 93, 1844 et seqq.). 
3. In the region of ordinary temperatures the T — R curve for ethyl 
* Temperature-Rotation. 
