An iron anticathode was used. The lines correspond to a face-centred cubic structure with lattice constant a = 6.18 A. The cell contains 4 molecules hydrogen iodide; the calculated density is 3.59.

IN a previous letter to NATURE (July 19, 1930, p. 97) I communicated some preliminary results upon the crystal structure of hydrogen iodide. I have now repeated, with greater accuracy the X-ray ...