3636.     ---------------.  [WEISER, H. B., AND MILLIGAN, W. O.]  Electron-Diffraction Study of Hydrous Oxides Amorphous to X-Rays.  Jour. Phys. Chem., vol. 44, 1940, pp. 1081-1094; Chem. Abs., vol. 35, 1941, p. 951.

        Hydrous oxides that give X-ray-diffraction patterns of the amorphous type may be grouped in 2 classes; (a) Oxides that give relatively sharp ring electron-diffraction patterns and (b) oxides that give electron-diffraction patterns of the amorphous type.  The oxides of the 1st class are crystalline, but the primary crystal size is so small that the X-ray-diffraction pattern consists of broad bands.  The precipitates oxides of the following metals belong in this class:  FeIII, Al (from sulfate), Ga, TiIV, and probably Be.  The oxide gels of the 2d class are amorphous in the sense that glasses are amorphous, the atoms arranging themselves in the form of a network lacking the periodicity and symmetry that characterize a crystal lattice.  The following precipitated oxides belong in this class:  Cr, Si, CbV, and TaV.  Fe2O3 gel thrown down at room temperature consists of minute crystals of a-Fe2O3.  The oxide gel from Al2(SO4)3, like that from AlCl3 and Al(NO3)3, is γ-Al2O3.H2O.  Gallia gel precipitated at room temperature is made up of minute crystals of a-Ga2O3.