172 Proceedings of the Royal Society of Edinburgh. [Sess. 
XVIII. — The Physical Properties of Mixed Solutions of Independent 
Optically - Active Substances. By Clerk Ranken, B.Sc., 
Carnegie Research Scholar, and W. W. Taylor, M.A., D.Sc. Com- 
municated by Professor Crum Brown, F.R.S. 
(MS. received May 6, 1907. Read same date.) 
The two systems containing one of a pair of optically-active stereoisomers 
and an independent optically-active substance present many points of 
interest and importance, but have not hitherto been investigated with any 
degree of completeness. What is known about them may fairly be said to 
consist of a series of isolated facts. The present communication also con- 
tributes a few more isolated observations, and is, in reality, a preliminary 
to a more systematic examination of the whole subject. 
So far as has been ascertained up to the present time, there seems to be 
some justification for the notion that there is an essential distinction 
between those systems in which the independent optically-active substance 
is capable of entering into definite chemical combinations with each of the 
enantiomorphs, and those systems in which chemical combination is either 
absent or doubtful. 
The method of resolution of racemic acid into its optically-active con- 
stituents by means of an alkaloid, one of the methods first made use of by 
Pasteur, depends upon the difference in solubility, in water or some other 
solvent, of the salt formed by the alkaloid with the dextro-&oid, and of the 
salt formed by the laevo - acid with that alkaloid. There are now known 
innumerable instances of a similar kind. 
Further, Marckwald and McKenzie * found that the rate of esterification 
of ^-mandelic acid and ^-menthol is slower than that of <i-mandelic acid 
and ^-menthol. Similarly, the rate of saponification of £-menthyl 
(i-mandelate by solutions of alkalies in ethyl alcohol is greater than that 
of the £-menthyl ^-mandelate.t M‘Kenzie and Thompson J have just 
shown that the same holds with respect to the corresponding £-bornyl 
mandelates. In these examples there is no doubt about the chemical com- 
bination between the two optically-active substances. 
On the other hand, van’t Hoff§ suggested the possibility of optical 
* Berl. Ber ., 34, p. 469, 1901. 
t M c Kenzie, Ghem. Soc. Jour., 85, p. 1249, 1904. 
X Proc. Chem. Soc., 23, p. 113, April 1907. 
§ Lagerung der Atome im Baume, p. 30, 1894. 
