A sample of raw material contain `NaNO_(3)`. It contains some `NaIO_(3)` also. The `NaIO_(3)` can be used as a source of iodine, produced in the following reactions:
`IO_(3)^(-)+HSO_(3)^(-) to I^(-)+SO_(4)^(-)`...................(1)
`I^(-)+IO_(3)^(-) to I_(2)+H_(2)O`............(2)
One litre of sample solution containing 396 g `NaIO_(3)` is treated with stoichiometric quantity of `NaHSO_(3)`. Now a substantial amount of solution is added to reaction mixture to bring about the reaction (2).