Physicochemical studies on dusts. VI. Electron‐optical examination of finely ground silica

Changes in surface structure brought about by removal of the high‐solubility layer from crystallinequartz and fused‐silica (Vitreosil) dusts by 40% hydrofluoric acid, and from Lochaline‐sand dust by a borate buffer (pH 7·5), are studied by electron‐optical methods. The accompanying changes in electron‐diffraction pattern show that the original surface‐layer is amorphous (estimated mean thickness about 0·03–0·06 μ); for quartz and Lochaline‐sand dusts there is some evidence of an intermediate layer of very minute crystallites between the amorphous‐layer and the crystalline core.