We have #S(IV^+)# rather than the #S(VI^+)# observed for #"sulfuric acid"#, #H_2SO_4#. #H_2SO_3# is #"sulfurous acid"#, or the hydrate of #"sulfur dioxide"#, i.e. #O_2S*OH_2#. I think that solutions of this salt have a pleasant, pharmaceutical smell.