Reduction of nitro group to amine
Hyperconjugation accounts for the somewhat greater negativity of the 4-nitro-group compared with the 2-nitro-group in 2:4-dinitrotoluene; in consequence, selective reduction of the former by alkaline sulphides produces mainly 2-nitro-4-aminotoluene, although some 4-nitro-2-aminotoluene is also formed. In acid medium the 2-nitro-group becomes relatively negative in comparison with the 4-nitro-group, owing to the inductive (+I) effect having the chief role, with resultant preferential salt formation to give the very positive $\ce{-NO2H}$ group at 2-position and preferential reduction of it by acid stannous chloride.


Quoted from Coloration Technology 62 (1946) 114 

As for how ammonium sulphide reacts see this answer:  Selective nitro reduction of poly nitro compounds