My earlier experiments on the relation between constitution and optical activity were made with the menthyl esters of various acids ; more recently, I have worked with derivatives of citronellal, of carvoxime, myrtenol, and methylene-camphor. One of my English colleagues has pointed out that we cannot expect clear answers to our questions except by using optically active compounds with only one asymmetric carbon atom, and that these must be liquid and give liquid compounds, so that no solvent

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... necessary::: But this is an ideal we are not able to attain in every case. Moreover, the same author has pointed out in a recent paper t that the influence of homologous groups on optical rotatory power is sometimes developed in a more striking way in solution than when no solvent is used. Again, whilst it is a most desirable thing to work with compounds containing only one asymmetric carbon atom, the influence on rotatory power of several asymmetric carbon atoms in one molecule is as yet very little understood. I have made a comparative table of corresponding series of compounds with one, two, and three asymmetric carbons, but have not been able to come to any conclusion about it, the material being as yet not sufficient. At the present time I am in agreement with Hiiditch, when he says that the number of asymmetric atoms in a given molecule has little bearing upon the changes of rotatory power produced by constitutive influences. Here, indeed, we find a subject for future researches.