Explain about principle and reactions involved in carius method of estimation of sulphur.

Explanation

Carius method:
(i) Principle: A known mass of the organic substance is heated strongly with fuming `HNO_(3)`. C and H get oxidized to `CO_(2)` and `H_(2)O` while sulphur is oxidised to sulphuric acid as follows.
`Cunderset(ΗΝΟ_(3))overset("Fuming")rarrCO_(2)`
`2Hunderset(ΗΝΟ_(3))overset("Fuming")rarrH_(2)O`
`SrarrSO_(2)overset(O+H_(2)O)rarrH_(2)SO_(4)`
(ii) The resulting solution is treated with excess of `BaCl_(2)` solution, `H_(2)SO_(4)` present in the solution is converted into `BaSO_(4)` . From the mass of `BaSO_(4)`, the percentage of sulphur can be calculated.