system 1. Series 1: 3 ml 1.92 ? 10 ?4 M manganese(III) sulphate + 0.1 ml 30 l g ml ?1 ascorbic acid + 1.5 ml 10 ?4 M diphenylamine + 0.5 ml 5 M sulphuric acid, diluted to 10 ml with water. Series 2: 3 ml 1.92 ? 10 ?4 M manganese(III) sulphate + 0.4 ml 30 l g ml ?1 ascorbic acid + 1.5 ml 10 ?4 M diphenylamine + 0.5 ml 5 M sulphuric acid, diluted to 10 ml with water. Series 3: 3 ml 1.92 ? 10 ?4 M manganese(III) sulphate + 0.8 ml 30 l g ml ?1 ascorbic acid + 1.5 ml 10 ?4 M diphenylamine + 0.5 ml 5 M sulphuric acid, diluted to 10 ml with water