How will you detect the presence of sulphur in an organic compound by Lassaigne's test?
Lassaigne’s test: This test involves following two steps:
(i) Preparation of Lassaigne’s or sodium extract (As described under detection of nitrogen in :
Sulphur present in the organic compound combines with sodium on fusion to form sodium sulphide. 
Test for sulphur: The extract is divided into two parts and tested for sulphur as follows:
(i) Lead acetate test: A portion of the Lassaigne's filtrate is acidified with acetic acid and then lead acetate solution is added. Formation of black precipitate confirms the presence of sulphur in the organic compound. 
(ii) Sodium nitroprusside test:To another portion of the Lassaigne's filtrate, few drops of sodium nitroprusside are added. The appearance of purple colour confirms the presence of sulphur in the organic compound.
