Paragraph 3 PRINCIPLE

Cobalt^III combines with 1-nitroso-2-naphthol to give a red precipitate Co(C₁₀H₆ONO)₃.2H₂O. After the cobalt present in the extract has been brought to the cobalt^III state, the cobalt is precipitated in an acetic acid medium by a solution of 1-nitroso-2-naphthol. After filtration, the precipitate is washed and dried to constant weight and then weighed as Co(C₁₀H₆ONO)₃.2H₂O.