Edwin A. Hill (1900). "On a system of indexing chemical literature; Adopted by the Classification Division of the U.S. Patent Office". J. Am. Chem. Soc.22 (8): 478–494. doi:10.1021/ja02046a005.
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Hill, John W.; Petrucci, Ralph H.; McCreary, Terry W.; Perry, Scott S. (2005), General Chemistry (4th ed.), Upper Saddle River, NJ: Prentice Hall, p. 6, ISBN978-0-13-140283-6