Division 7.2.3.2 F1

Stopper with a loosely inserted stopper, shake, and heat in a boiling water bath (5.7) for 10 minutes, then cool in a 20 ^o C water bath (5.4) for 20 minutes and analyse spectrophotometrically (5.12) in a 1 cm cuvette (5.13) at 420 nm against the comparative solution (7.2.1.4).