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Related to pyrosulfuric acid: Fuming sulfuric acid
A fuming, dense, oily, colorless to dark brown liquid or hygroscopic crystalline solid, H2S2O7, the primary constituent of oleum, produced by adding sulfur trioxide to concentrated sulfuric acid, and used in petroleum refining and in the manufacture of explosives.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.