2603.     PERNOUX, E.  [Examination Under the Electron Microscope of Some Kieselguhrs Utilized as Catalyst Supports.]  Compt. rend., vol. 228, 1949, pp. 1,646-1,647; Chem. Abs., vol. 43, 1949, p. 8,831.

        About 50 samples of 4 different commercial kieselguhrs were examined under the electronic microscope:  A crude Filter-Cel, an acid-treated Filter-Cel, an acid-treated Filter-Cel followed by treatment with 5% Na₂CO₃, and a crude Filter-Cel treated with 5% Na₂CO₃.  A magnification of 6,000 was adopted.  The micrographs are described but not illustrated.  Taking account of the fact that the kieselguhrs are made up of 95% of hydrated amorphous silica to which are added some silicates and various impurities (Al₂O₃ and Fe oxide), the following interpretations can be made.  The acid treatment of the crude product causes the superficial formation of a silica gel, which seals the pores.  This silica is redissolved by treatment with 5% Na₂CO₃.  The direct carbonate treatment of the initial product involves only a small part of the silica consisting of the most finely divided portions.  The microscopic examination thus confirms the conclusions made by Teichner.