91- 6303239042
$$\text{Na}_2\text{S} + \text{Na}_2[\text{Fe(CN)}_5\text{NO}] \to \text{Na}_4[\text{Fe(CN)}_5\text{NOS}]$$
$$\text{S}^{2-} + [\text{Fe(CN)}_5\text{NO}]^{2-} \to [\text{Fe(CN)}_5\text{NOS}]^{4-} \quad \text{(Deep Violet / Purple)}$$
Concept: When a freshly prepared solution of sodium nitroprusside ($$\text{Na}_2[\text{Fe(CN)}_5\text{NO}]$$) is added to the alkaline sodium fusion extract (Lassaigne's extract) containing sulfide ions ($$\text{S}^{2-}$$), a complexation reaction takes place. The sulfide ion coordinates to the iron complex to form sodium thionitroprusside, resulting in a distinct deep violet or purple color.
