Noun
oleum (countable and uncountable, plural oleums)
(inorganic chemistry) A solution of sulfur trioxide in sulfuric acid.
Concentrations of oleum are either expressed in terms of % SOmain (called % oleum) or as % Hmain SOmain (the amount made if Hmain O were added); common concentrations are 40% oleum (109% Hmain SOmain ) and 65% oleum (114.6% Hmain SOmain ). Source: Internet
Sulfuric acid and SO 3 combine to give oleum, a solution of pyrosulfuric acid (H 2 S 2 O 7 ) in sulfuric acid. Source: Internet
The oleum is then diluted with water to form concentrated sulfuric acid. Source: Internet