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Paragraph 4 REAGENTS

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4.1

Hydrochloric acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid (ρ = 1.18 g/ml) with an equal volume of water.

4.2

Sulfuric acid, 0.05 M solution.

4.3

Sodium or potassium hydroxide, 0.1 M solution, carbonate free.

4.4

Sulfuric acid solution, approximately 30% H2SO4 (W/V), ammonia free.

4.5

Powdered iron reduced in hydrogen. (The prescribed quantity of iron must be able to reduce at least 0.05 g nitrate nitrogen.)

4.6

Sodium hydroxide solution, 30 g per 100 ml, ammonia free.

4.7

Indicator solutions:

Mixed indicator:

4.7.1

Solution A: dissolve 1 g methyl red in 37 ml 0.1 M 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).

Methyl red indicator solution:

4.7.2

Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and filter if necessary.

  • This indicator may be used (4-5 drops) instead of the preceding one.

4.8

Anti-bump granules of pumice stone, washed in hydrochloric acid and ignited.

4.9

Sodium nitrate.