The Röntgen Rays and Optically Active Substances

Abstract

IN an article in NATURE (February 27) by Prof. J. J. Thomson, it is suggested that the leakage of electricity through non-conductors under the influence of the Rontgen rays is “due to a kind of electrolysis, the molecule of the non-conductor being split up, or nearly split up, by the Rontgen rays, which act the part played by the solvent in ordinary electrolytic solutions.” It has occurred to me that if such ionisation really does take place, independent evidence of it should be obtainable in the case of optically active substances by a change in their rotatory power taking place when they are exposed to the X-rays, as it is well known that the ionised molecules of active compounds are possessed of very different activity from the undissociated molecules themselves. To put this point to the test, Mr. MacGregor and I have polarimetrically examined two optically active compounds, ethylic dibenzoylglycerate and methylic acetylglycerate, interposing a Crookes' focus tube between the polarising Nicol and the column of active liquid; but although the discharge was maintained in both cases for three-quarters of an hour, there was not the slightest change in the rotation observable. To facilitate the passage of the rays, we employed a thin microscope cover-glass to close the polarimeter tube at the end nearest to the Crookes' tube, and that the rays were actually traversing the column of active liquid was demonstrated by obtaining a photographic effect at the other extremity of the tube, whilst the efficiency of the Crookes' tube was further proved by the favourite test of the skeletal photograph of a hand, which yielded an impression of great sharpness and exhibiting a most remarkable amount of detail. It would appear, therefore, that the Rontgen rays either do not give rise to any ionisation at all, or that the concentration of the ions is so small as not to be detectable, by means of a sensitive polarimeter. I have previously shown, in conjunction with Mr. Pickard (Trans. Chem. Soc., 1896), that the active bodies in question exhibit what appears to be a process of ionisation when dissolved in certain organic solvents, which process is accompanied by a very conspicuous change in their rotatory power, so that they appeared to be specially adapted for testing this suggested influence of the X-rays.