sulphur trioxide

British  

noun

1. Systematic name: sulphur(VI) oxide.  a white corrosive substance existing in three crystalline forms of which the stable ( alpha- ) form is usually obtained as silky needles. It is produced by the oxidation of sulphur dioxide, and is used in the sulphonation of organic compounds. Formula: SO 3

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sulphur trioxide

SO2 is called sulphur dioxide, to distinguish it from SO3, sulphur trioxide.

From An Introduction to Chemical Science by Williams, Rufus Phillips

It is therefore analogous to sulphur trioxide which forms sulphuric acid in a similar way: SO3 + H2O = H2SO4.

From An Elementary Study of Chemistry by McPherson, William

Union takes place at once, and the strongly fuming sulphur trioxide escapes from the jet at the end of the tube, and may be condensed by surrounding the receiving tube with a freezing mixture.

From An Elementary Study of Chemistry by McPherson, William

The acid commonly used is made by the "contact" process, in which sulphur dioxide is oxidized to sulphur trioxide, and then, with the addition of water, changed to sulphuric acid.

From The Automobile Storage Battery Its Care And Repair by Witte, Otto A.

The olefines—ethylene, &c.—are generally absorbed by a very strong sulphuric acid prepared by adding sulphur trioxide to sulphuric acid to form a mixture which solidifies when slightly cooled.

From Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 4 "G" to "Gaskell, Elizabeth" by Various