AbstractThree methods are described for preparing une of the transition forms of alurtlina, the δ‐fornt, in a comparatively advanced state of crystallinity. In these preparations the crystal structure is sufficiently well‐developed for complete X‐ray powder diffraction spacing and intensity data to be compiled, and these data are presented. The methods of preparation comprise:(a)Heat treatment of a dense form of high‐purity alumina monohydrate in air at about 950° over an extended period.(a)Ignition of ammonium aluminium sulphate impregnated with ammonium molybdate at 950°.(a)Heat treatment at 1100° in air of a flame‐sprayed alumina displaying the cubic gamma structure.The spherulized alumina described by Plumnier in the preceding paper contains a high proportion of cryst