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2. Idem. ibid.
26 (1991) 704.
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4. D. Barby, J. A. R. Griffiths and D. Pawson, in “The Modern Inorganic Chemicals Industry”, edited by R. Thompson (Chemical Society, London, 1977) p. 320.
5. R. Iler, in “The Chemistry of Silica” (Wiley, New York, 1977) p. 116.