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 1^st 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:  Fe^III, Al (from sulfate), Ga, Ti^IV, 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, Cb^V, and Ta^V.  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.