The Fertilisers (Sampling and Analysis) Regulations 1991

REAGENTS

4.—4.1 Potassium sulphate.

4.2 Iron powder, reduced with hydrogen (the prescribed quantity of iron must be able to reduce at least 50 mg nitric nitrogen).

4.3 Potassium nitrate.

4.4 Ammonium sulphate.

4.5 Urea.

4.6 Sulphuric acid, 0.2 N solution.

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

4.8 Sodium or potassium hydroxide, 0.2 N solution, free of carbonates.

4.9 Sulphuric acid (d = 1.84 g/ml).

4.10 Hydrochloric acid solution: dilute an appropriate volume of hydrochloric acid (d = 1.18 g/ml) with an equal volume of water.

4.11 Glacial acetic acid.

4.12 Sulphuric acid, solution approximately 30% (W/V) H₂SO₄.

4.13 Ferrous sulphate, crystalline FeSO₄.7H₂O.

4.14 Sulphuric acid, 0.1 N solution.

4.15 Octan-1-ol.

4.16 Potassium carbonate, saturated solution.

4.17 Sodium or potassium hydroxide, 0.1 N solution.

4.18 Barium hydroxide, saturated solution.

4.19 Sodium carbonate solution, 10 g per 100 ml.

4.20 Hydrochloric acid, 2 N solution.

4.21 Hydrochloric acid, 0.1 N solution.

4.22 Urease solution: suspend 0.5 g active urease in 100 ml distilled water. Using 0.1 N hydrochloric acid (4.21), adjust pH to 5.4, measured with pH meter.

4.23 Xanthydrol solution, 5 g per 100 ml in ethanol or methanol (4.28) (do not use products giving a high proportion of insoluble material). The solution can be kept for 3 months in a carefully stoppered bottle in darkness.

4.24 Catalyst: copper oxide (CuO), 0.3 to 0.4 g per determination, or an equivalent amount of copper sulphate pentahydrate, 0.95 to 1.25 g per determination.

4.25 Anti-bump granules of pumice stone washed with hydrochloric acid and ignited.

4.26 Indicator solutions:

4.26.1 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:

4.26.2 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.

4.27 Indicator papers: litmus, bromothymol blue (or other papers sensitive to pH 6-8).

4.28 Ethanol or methanol, 95% (V/V).