Fluorsulphonic acid, SO 2 F OH, is a mobile liquid obtained by the action of an excess of hydrofluoric acid on well-cooled sulphur trioxide.
Persulphuric anhydride, S207, is a thick viscous liquid obtained by the action of the silent discharge upon a mixture of sulphur trioxide and oxygen.
It is decomposed readily into sulphur trioxide and oxygen when heated.
In small works the cupellation is finished in one furnace, and the resulting low-grade silver fined in a plumbago crucible, either by overheating in the presence of air, or by the addition of silver sulphate to the melted silver, when air or sulphur trioxide and oxygen oxidize the impurities.
It combines directly with sulphur trioxide to form a complex of composition TeC1 4.2SO 3.
