The Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1991

4a DETERMINATION OF THE TOTAL NITROGEN IN CALCIUM CYANAMlDE — IN THE ABSENCE OF NITRATE

1.    SCOPE

This method is for the determination of total nitrogen in nitrate free calcium cyanamide.

2.    FIELD OF APPLICATION

Exclusively to calcium cyanamide (nitrate free).

3.    PRINCIPLE

After Kjeldahl digestion, the ammoniacal nitrogen formed is displaced by sodium hydroxide, and collected in a standard solution of sulphuric acid. The excess sulphuric acid is titrated with a standard solution of sodium or potassium hydroxide.

4.    REAGENTS

Sulphuric acid solution 50% (V/V): dilute an appropriate volume of sulphuric acid (d = 1.84 g/ml) with an equal volume of water.

Potassium sulphate.

Copper oxide (CuO) — 0.3 to 0.4 g for each determination or an equivalent quantity of copper sulphate pentahydrate, from 0.95 to 1.25 g for each determination.

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

Sulphuric acid, 0.1 N solution. Sodium or potassium hydroxide, 0.1 N solution, carbonate free.	for variant (a) (page 19)
Sulphuric acid, 0.2 N solution. Sodium or potassium hydroxide, 0.2 N solution, carbonate free.	for variant (b) (page 19) (See Note on page 18)
Sulphuric acid, 0.5 N solution. Sodium or potassium hydroxide solution, 0.5 N, carbonate free.	for variant (c) (page 19) (See Note on page 18)

Indicator solutions:

Mixed indicator:

4.11.1 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 A with 2 volumes of 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:

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

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

Potassium thiocyanate.

5.    APPARATUS

Distillation apparatus. See Method 2.

6.    PREPARATION OF SAMPLE

See Method 1.

7.    PROCEDURE

Preparation of the solution

7.1  Weigh to the nearest 0.001 g, 1 g of the prepared sample and place it in the Kjeldahl flask. Add 50 ml 50% sulphuric acid (4.1), 10-15 g potassium sulphate (4.2) and one of the prescribed catalysts (4.3). Heat slowly to drive off the water, boil gently for two hours, allow to cool, and dilute with 100—150 ml water. Cool again, transfer quantitatively the suspension to a 250 ml graduated flask, make up to volume with water, shake, and filter through a dry filter into a dry flask.

Determination

7.2  According to the variant chosen (see Method 2) transfer with a pipette 50, 100 or 200 ml of the solution to the distillation apparatus and add sufficient sodium hydroxide solution (4.4) to ensure a considerable excess. Distil the ammonia and titrate the excess acid as described in Method 2.

Blank test

7.3  Make a blank test (omitting only the sample) under the same conditions and allow for this in the calculation of the final result.

Control test

7.4  Before carrying out the analysis, check that the apparatus is working properly and that the correct application of the method is used, using an aliquot part of a standard solution of potassium thiocyanate (4.13), approximating to the concentration of nitrogen in the sample.

8.    EXPRESSION OF THE RESULT

Express the result as the percentage of nitrogen (N) contained in the fertiliser as received for analysis.

Where A = millilitres of sodium or potassium hydroxide used for the titration.
Variant (a):	N% = (50−A) × 0.7
Variant (b):	N% = (50−A) × 0.7
Variant (c):	N% = (35-A) × 0.875