THE tendency of optically active compounds t o become racemised when undergoing chemical change presents a serious obstacle to the preparation of their derivatives, and the difficulty is much enhanced by the fact that" except in a few instances, the exact conditions under which racemisntion occurs are imperfectly known. It is generally recognisecl that in dealing with such substances high ternperatures and violent actions are to be avoided ; but, even when every precaution has been taken, and

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... active derivative obtained, there is always a risk of its activity having been impaired by the prodaction of more 013 less of the racemoid form, the presence of which cannot in molst cases be directly detected. In preparing such derivatives with the view of determining their constants of activity, it is therefore essential either to recover the compounds from which the derivatives under investigation were obtained, so as t o compare their activities with those of the original substances used, or, if this is impossible, to employ various methods of preparation, and to show that the activity of the different specimens is identical. In recent times, numerous series of optically active ethereal salts have been prepared in connection with the interesting questions raised by Guye's theory. In some iustances, as, for example, that of the active glycerates prepa.red by Frankland, of the amylic ethereal salts prepared by Guye and Chavanne (Compt. rend., 1894,119, 906) , and by Walden (Zeit. physikat. Chem., 1894, 15, 6&) ,1 precautions of the kind referred to, have been adopted, but in numerous other cases no evidence o€ t h e absence of the racernoid compound appears t o halve OF OPTICALLY ACTIVE MALIC AND LACTIC ACIDS. although the conditions observed were such as, it might have been supposed, would preclude the occurrence of any such change. The method used W~E I that described by Scbreiner (An~zalen, 1879,197,l'L) for the preparation of the corresponding inactive compounds, namely, the action of sodium alkylate at the ordinary temperature on