There are various haloid derivatives of sulphurous acid.
Tin dissolves readily in strong hot hydrochloric acid as SnC12; aqueous sulphuric acid does not act on it appreciably in the cold; at 150° it attacks it more or less quickly, according to the strength of the acid, with evolution of sulphuretted hydrogen or, when the acid is stronger, of sulphurous acid gas and deposition of sulphur (Calvert and Johnson).
It is decomposed by water into hydrofluoric and sulphurous acids.
Acids, other than carbonic, may promote rusting; this is particularly the case with ironwork exposed to the acids - sulphurous, nitric, &c. - contained in smoke.
The hot springs, among which those of Bagneres de Luchon and Eaux-Chaudes may be mentioned, are sulphurous and mostly situated high, near the contact of the granite with the stratified rocks.