The Fertilisers (Sampling and Analysis) Regulations 1991

REAGENTS

4.—4.1 Sulphuric acid (d = 1.84 g/ml).

4.2 Powdered iron reduced in hydrogen.

4.3 Potassium sulphate, finely pulverised.

4.4 Sulphuric acid, 0.1 N solution. } for variant (a) (page 15)

4.5 Sodium or potassium hydroxide, 0.1 N solution, carbonate free. } for variant (a) (page 15)

4.6 Suplhuric acid, 0.2 N solution. } for variant (b) (page 16) (see Note on page 15)

4.7 Sodium or potassium hydroxide, 0.2 N solution, carbonate free. } for variant (b) (page 16) (see Note on page 15)

4.8 Sulphuric acid, 0.5 N solution. } for variant (c) (page 16) (see Note on page 15)

4.9 Sodium or potassium hydroxide, 0.5 N solution, carbonate free. } for variant (c) (page 16) (see Note on page 15)

4.10 Indicator solutions:

4.10.1 Mixed indicator:

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

• Solution B: dissolve 1 g of methylene blue in water and make up to 1 litre. Mix 1 volume of A and 2 volumes of B.

• This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution.

• Take 0.5 ml (10 drops) of this indicator solution.

4.10.2 Methyl red indicator:

4.10.2 dissolve 0.1 g of methyl red in 50 ml of 95% ethanol, make up to 100 ml with water and filter if necessary. This indicator (4 to 5 drops) may be used instead of the preceding one.

Solution of stannous chloride:

4.11 Dissolve 120 g of stannous chloride (SnCl².2H²O) in 400 ml concentrated hydrochloric acid (d = 1.18 g/ml) and make up to 1 litre with water. The solution must be completely clear and prepared immediately before use. It is essential to check the reducing power of the stannous chloride. Dissolve 0.5 g of stannous chloride in 2 ml concentrated hydrochloric acid (d = 1.18 g/ml) and make up to 50 ml with water. Then add 5 g of Rochelle salt (potassium sodium tartrate) and a sufficient quantity of sodium bicarbonate for the solution to show an alkaline reaction to a litmus paper test.

• Titrate with 0.1 N iodine solution in the presence of a starch solution as an indicator.

• 1 ml of iodine solution 0.1 N corresponds to 0.01128 g SnCl₂.2H₂O.

• At least 80% of the total tin present in the solution thus prepared must be in a bivalent form. For the titration at least 35 ml of 0.1 N iodine solution should be used.

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

Standard nitrate-ammoniacal solution:

4.13 Weigh out 2.500 g of potassium nitrate and 10.160 g of ammonium sulphate and place them in a 250 ml graduated flask. Dissolve in water and make up to 250 ml. 1 ml of this solution contains 0.010 g of nitrogen.

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