PROCEDURE: 
Cobaltous chloride CS (Red solution)
(Mol. Formula: CoCl2.6H2O, Mol. Wt: 237.93)
Reagents:
(1) Hydrogen peroxide TS: Pipette 10 mL of 30% hydrogen peroxide solution into a 100 mL volumetricflask, dilute to volume with purified water.
(2) Sodium hydroxide solutio