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2. R. A. Lewis: Chem. Eng. Prog., vol. 56, no. 5, 1960, p. 78.
3. G. C. Seager: To be presented at Intl. Aluminum Sym., AIME Annual Meeting, New York, 1962.
4. British Patents, Nos. 784,695, 784,696, 802,471, 802,905.
5. British Patent No. 804,242.