1. Treatise on Chemistry, Vol. 1, Macmillan, London, 1881, p. 14.
2. General Chemistry: An Introduction to Descriptive Chemistry and Modern Chemical Theory, 2nd ed., W. H. Freeman, San Francisco, 1953, p. 120.
3. The Spirit of Chemistry: An Introduction to Chemistry for Students of the Liberal Arts, Longman Green, London, 1930, p. 143.
4. General Chemistry, Prentice-Hall, Englewood Cliffs, 1975, p. 5.