Sulphur is estimated by Carius method. The organic compound containing sulphur is heated with fuming nitric acid. The sulphur in the compound is oxidised to sulphuric acid, which is then precipitated as barium sulphate by adding excess of barium chloride solution. The precipitate is filtered, washed and dried. From the weight of barium sulphate formed, the percentage of sulphur in the organic compound can be estimated.

Moles of `BaSO_4 = (text(Weight of)quad H_2SO_4)/(text(Molar mass of)quad BaSO_4) =` Moles of `S` in `BaSO_4`

= Moles of `S` in organic compound.

Mass of sulphur in organic compound `= (text(Weight of)quad BaSO_4)/(text(Molar mass of)quad BaSO_4) xx 32`

Percentage of sulphur `= (32 xx text(wt. of) Ba SO_4)/(text(Molar mass of) Ba SO_4 xx text(wt. of organic Compound)) xx 100`

`= (32 xx text(wt. of)quad BaSO_4)/(233 xx text(weight of organic Compound) xx 100)`