This article is from the alt.usage.english FAQ, by Mark Israel email@example.com with numerous contributions by others.
This word is usually "aluminum" /@'lu:m@n@m/ in the U.S. and in
Canada, and "aluminium" /,&lU'mInI@m/ in other English-speaking
People sometimes complain that the American form is inconsistent
with other element names, which end in "-ium". But even in British
spelling, there are elements that end in "-um" not preceded by "i":
lanthanum, molybdenum, platinum, and tantalum (not to mention
argentum, aurum, cuprum, ferrum, hydrargyrum, plumbum, and stannum;
but then those aren't English names, just the names from which the
symbols are derived).
A widespread false belief among those who spell the word
"aluminium" is that theirs is the original spelling, from which the
American version is a later development, perhaps resulting from a
typographical error. The CRC Handbook of Chemistry and Physics
(63rd ed., p. B-5) gives this bit of history:
The ancient Greeks and Romans used alum in medicine as an
astringent, and as a mordant in dyeing. In 1761 [Baron Louis-
Bernard Guyton] de Morveau proposed the name alumine for the
base in alum, and [Antoine] Lavoisier, in 1787, thought this
to be the oxide of a still undiscovered metal. [...] In 1807,
[Sir Humphrey] Davy proposed the name alumium for the metal,
undiscovered at that time, and later agreed to change it to
aluminum. Shortly thereafter, the name aluminium was
adopted to conform with the "ium" ending of most elements,
and this spelling is now in use elsewhere in the world.
Aluminium was also the accepted spelling in the U.S. until
1925, at which time the American Chemical Society officially
decided to use the name aluminum thereafter in their
I used to work for ACS, but I have no idea why they would have
chosen "aluminum" over "aluminium", especially if "aluminium" was
"A Dictionary of American English on Historical Principles"
(University of Chicago Press, 1938, ISBN 0-226-11737-5) gives U.S.
citations of "aluminum" from 1836, 1855, 1889 (two), and 1916, and
says: "This form is in common use in mining, manufacturing, and
the trade in the U.S.; the form "aluminium" is used with practical
uniformity in Great Britain and generally by chemists in the U.S."
"Aluminium" is given as the only form by Noah Webster's 1828
dictionary; and as the preferred form by "The Century Dictionary"
(1889) and by the 9th and 11th editions of the Encyclopaedia
Britannica. The Britannica yearbook switched its index entry from
"aluminium or aluminum" to "aluminum" in 1942.