In previous communications1-3 we have shown that rnandelic acid and many of its derivatives carrying simple nuclear substituents, and several analogous acids derived from larger aromatic nuclei, such as naphthalene, anthracene and diphenylene oxide, are resolved without difficulty on wool. In all these instances, the acids carried hydroxyl groups, and there was the possibility that the difference in the degree of absorption of the two forms of the anion was due to a difference in the extent of the interaction of their hydroxyl groups with the protein. Our present result shows that the occurrence of resolution is not restricted to the hydroxy acids. Indeed, the degrees of resolution of oc-methoxy-phenylacetic acid and mandelic acid are of the same order under the same conditions.The a-methoxyphenylacetic acid used in our experiments was prepared by Reeve and Christoffel's method4 ; it melted at 70 (literature : m.p., 70-5-71). Wool (30 gm.) was immersed in a solution of the (ij-acid in 500 c.c. of a mixture of equal volumes of water and alcohol, and after a time the amounts of the acid absorbed and not absorbed, and the rotations of the two fractions, were determined. Exp. 1 Exp. 2Initial weight of acid in solution Period of immersion Weight of acid absorbed " " " unabsorbed Rotation of acid absorbed " " " unabsorbed 7-31 gm. 18 hr. 2-54 gm. 4-76 gm. + 0-19 - 0 19 7-83 gm. 24 hr. 2-45 gm. 5-10 gm. + 0-20 - 0-20 The rotations were measured in a 2 dm. tube in a Hilger model, Type ikf 413, polarimeter, each of the two fractions being dissolved in 17-5 c.c. of alcohol. They are of the same order as those obtained with mandelic acid3 in similar circumstances, and if the molecular rotations of the two acids do not differ greatly it would follow that mandelic acid and its methyl ether are resolved to almost the same degree ; MD : '(.)-mandelic acid, - 159-73, in water5; (.)-mandelic acid, +156-40, in water6; (.)--hexadecoxymandelic acid is not resolved at all3. Similarly, many acids containing azo-groups are not resolved on wool9'10. The resolution of acids on proteins and the extent to which it occurs is of considerable interest for the theory of biochemical processes. It has always appeared feasible that the difference in behaviour of the optical antipodes of the a-amino-acids, the a-hydroxy acids and other acids in natural processes could be related to the preferential absorption of one or other of the two enantiomorphs. Our results do not support this view ; for although we have demonstrated the resolution of acids on proteins, the degree of resolution has always been small and insufficient to account for the striking differences in biochemical properties which are often observed, unless the degree of separation can be increased in natural processes, as by continued resolution at a succession of surfaces.