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.