A higher temperature decomposes this body into carbon dioxide and itaconic acid, C 5 H 6 0 4, which, again, by the expulsion of a molecule of water, yields citraconic anhydride, C 5 H 4 0 3.
When distilled with phosphoric anhydride they yield nitriles.
Four oxides of sulphur a.re known, namely sulphur dioxide, S02, sulphur trioxide, S03, sulphur sesquioxide, S203, and persulphuric anhydride, S 2 0 7.
Although this acid appears to be derived from an oxide S203, it is not certain that the known sesquioxide is its anhydride.
Persulphuric anhydride, S207, is a thick viscous liquid obtained by the action of the silent discharge upon a mixture of sulphur trioxide and oxygen.