Lassaigne's Test for Sulphur

Formula / Core Reaction:

$$2\text{Na} + \text{S} \xrightarrow{\Delta} \text{Na}_2\text{S}$$

$$\text{Na}_2\text{S} + \text{Na}_2[\text{Fe}(\text{CN})_5\text{NO}] \rightarrow \text{Na}_4[\text{Fe}(\text{CN})_5\text{NOS}]$$

Concept: Organic sulfur is converted into sodium sulfide ($$\text{Na}_2\text{S}$$) upon sodium fusion. Treatment with sodium nitroprusside yields a deep purple/violet complex.

Notation / Key Observation:

• $$\text{Na}_2[\text{Fe}(\text{CN})_5\text{NO}]$$: Sodium nitroprusside reagent;
• $$\text{Na}_4[\text{Fe}(\text{CN})_5\text{NOS}]$$: Sodium thionitroprusside complex (Purple/Violet coloration).