A black coloured compound (A) on reaction with dil. H₂SO₄ gives a gas (B) and almost a colourless solution from which a pale green compound crystallizes out. Gas (B) on passing through a solution of an acid (C) gives a white turbidity (D). Gas (B) when passed through an acidified solution of a compound (E) gives a precipitate (F) soluble in dilute HNO₃. After boiling this solution, addition of an excess of NH₄OH results in an intense blue coloured compound (G). A chocolate brown precipitate (H) is obtained when acetic acid and aqueous K₄[Fe(CN)₆] is added to the solution containing (G). On addition of an aqueous solution of BaCl₂ to an aqueous solution of (E) a white precipitate insoluble in dilute HCl is obtained. 

Compounds A, D and F respectively are

Compounds G and H respectively are

 

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