1. Egyptian directions for preparing alloys resembling silver and gold are given in ref. 67a
2. G.M. Ross, ‘Leibniz’, Oxford University Press, Oxford, 1984
3. J. Lenihan, ‘Science in Action’, The Institute of Physics, Bristol and London, 1979, pp. 179–180
4. E.R. Caley,J. Chem. Educ., 1926,3, 1149–1166; 1927,4, 979–1002
5. J.R. Partington, ‘A Short History of Chemistry’, 3rd Ed., Harper & Brothers, New York, 1957, p, 17