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2. Neblette, C. B. “Photography its Materials and Processes”, 6th Edn., Van Nostrand Company, Inc., New York, 1962, p. 2.
3. Kaspaul, A. F., and E. E., Trans, 10th National Vacuum Symposium of the A.V.S., Oct. 16-18, 1963, Macmillan Co., New York, p. 422.
4. Philips, Brit. Pat., 1,175,747(1969).
5. Shuman, D. C., and James, T. H.Phot.Sci.Eng.15, 42 (1971). These authors supplemented the view of Faerman and Voeikova (ref. 5) by stating that, apart from their electronic properties, the adsorption characteristics of the various types of nuclei (metallic, sulphidic) must be considered in evaluating catalytic activity.