SCHEDULE 2 METHODS OF ANALYSIS

8b. DETERMINATION OF DIFFERENT FORMS OF NITROGEN IN THE SAME SAMPLE — IN THE ABSENCE OF CYANAMIDE NITROGEN

“4.26    REAGENTS

Indicator solutions:

Mixed indicator

• 4.26.1 Solution A: dissolve 1 g methyl red in 37 ml 0.1 N sodium hydroxide solution and make up to 1 litre with water.

• Solution B: dissolve 1 g methylene blue in water and make up to 1 litre.

• Mix 1 volume of solution A and 2 volumes of solution B; this indicator is violet in acid solution, grey in neutral solution, and green in alkaline solution; use 0.5 ml (10 drops) of this indicator.

4.26.2 Methyl red indicator solution:

dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and filter if necessary; 4 — 5 drops of this indicator can be used instead of the previous one.