Edwin Hill

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In existographies, Edwin Hill (105-26 BE) (1850-1929 ACM) (CR:5) (LH:2) (TL:7) was an American chemist, noted for his “Hill order” system (1900) of classifying molecular formulas, in respect to alphabetical element ordering.


Hill order

See main: Hill order

In 1900, Hill, in his “On a System of Indexing Chemical Literature”, in order to organize the ordering of the elements in various chemical formulas being sent in to the US patent office, after giving a short history of formula ordering variations, stated the following:

“I have modified the purely alphabetical scheme, and have adopted the following general rule for indexing : reject the water of crystallization, and rewrite the empirical formula in the alphabetical order of the chemical symbols, except that in carbon compounds write C first and H second; follow this rewritten formula with the constitutional formula, when given, adding the water of crystallization, if any, but arrange the titles alphabetically by the rewritten formula.”
— Edwin Hill (1900), “On a System of Indexing Chemical Literature” (pg. 480) [1]

In the 1970s, Hill's method began to be employed as a standard for formula indexing, referred to as: "Hill order formula index" (1970)[2], or "Hill system order" (1985)[3], in 1994 the following definition appeared:

“When molecular formulas are written in ‘Hill order’, C appears first, H second (if present), and the other element symbols in alphabetical order.”
— David Linde (1994), Hand Book of Organic Solvents (pg. 11) [4]

In 1995, the CRC Reference Handbook provided CAS registry numbers, names, synonyms (about 135,000), and molecular formulas for 27,489 organic compounds, with each molecular formula written in “Hill order”.[5]

CHNOPS+ molecular formulas

In 2000, Robert Sterner and James Elser calculated the first attempt at a molecular formula for a human (see: human molecular formula), using 22-elements.

In 2002, Libb Thims, independently, derived a 26-element human molecular formula, based on known mass compositions and known element functionality in humans.

In 2005, Thims, in his molecular evolution table, calculated the molecular formulas for a dozen chemical species, including methanol, urea, DNA, bacteria, fish, monkey, and human.

In these calculations, Hill ordering comes into conflict with the mass composition dominance of each element. Resultingly, the Hill order scheme tends to be employed only for the element CHNOPS elements, give or take one or two more elements, then mass dominance defines the ordering of each element in the formula.


Hill completed his BA in 1875 at Yale University, followed by an MA, after which he served as a lawyer and civil engineer for various railroads prior to 1895. In 1901, he switched gears, and completed an MS in chemistry, with a thesis on “Properties of Compounds of Antimony”, followed by a PhD in 1903, with a dissertation on “The Constitution of Certain Halogen Oxyacids as Inferred from Thermochemical Data”, both at George Washington University, where after he became a professor of chemistry, remaining there until 1926.[6]

End matter


  1. Hill, Edwin A. (1900). “On a System of Indexing Chemical Literature; Adopted by the Classification Division of the US Patent Office” (Ѻ), Journal of the American Chemical Society, 22(8):478-94.
  2. Kent, Allen; Lancour, Harold. (1970). Encyclopedia of Library and Information Science, Volume Four (pg. 487). Publisher.
  3. Author. (1985). “Molecular Formulas” (pg. 38), Using CAS Online. Publisher.
  4. Linde, David. (1994). Hand Book of Organic Solvents (pg. 11). Publisher.
  5. Lide, David; Milne, G.W.A. (1995). Names, Synonyms, and Structures of Organic Compounds (Hill order, pg. #). Publisher.
  6. Staff. (1929). “Obituary: Edwin Allston Hill” (abs), Chemical Engineering News, 7(21):11.

Further reading

  • Hill, Edwin A. (1907). “The Chemical Card Index of the Patent Office”, US Patent Office.

External links

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