Thermal degeneration of the X-ray haloes in liquids

Abstract

The theory of X-ray diffraction in fluids put forward some years ago by the writer with Dr. Ramanathan (Proc. Ind. Assoc. Cult. of Science, vol 8, pp. 127-162 1923) indicates that the diffraction halo exhibited by liquids under ordinary conditions should be strikingly modified by rise of temperature. As explained in that paper, it follows from thermodynamic considerations that at ordinary temperatures the molecules of a liquid are ordered in space with a high degree of regularity, and the comparative sharpness of the X-ray halo at such temperatures is a consequence of this fact. With rise of temperature, however, the molecules are thrown into increasing disarray, as is shown by the considerably enhanced scattering power of the liquid for ordinary light. Accordingly, we should expect the X-ray halo to become more diffuse and faint; it should also contract to some extent, owing to the diminished density and consequent increase of the mean distance between neighbouring molecules. Vice versa, if the liquid is supercooled until it congeals into a glassy solid, we should expect the halo to become sharper and brighter, and at the same time to dilate somewhat.