# Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1996, Paragraph 5: PROCEDURE Sample for analysis 5.1 Weigh approximately 10 grams of ammonium nitrate to the nearest 0.001 gram. Removal of carbonates 5.2 Place the sample for analysis in the reaction flask (B). Add 100 ml of sulfuric acid (3.2). The prills dissolve in about 10 minutes at ambient temperature. Assemble the apparatus as indicated in the diagram: connect one end of the absorption tube (A) to the nitrogen source (4.2) via a non-return flow device containing 5 to 6 mm of mercury and the other end to the feed tube which enters the reaction flask. Place the Vigreux fractioning column (C') and the condenser (C) with cooling water supply in position. Adjust the nitrogen to provide a moderate flow through the solution, bring the solution to boiling point and heat for two minutes. At the end of this time there should be no more effervescence. If effervescence is seen, continue heating for 30 minutes. Allow the solution to cool for at least 20 minutes with the nitrogen flowing through it. Complete assembly of the apparatus as indicated in the diagram by connecting the condenser tube to the Drechsel bottle (D) and the bottle to the absorption vessel F1 and F2. The nitrogen must continue to pass through the solution during the assembly operation. Rapidly introduce 50 ml of barium hydroxide solution (3.4) into each of the absorption vessels (F1 and F2). Bubble a stream of nitrogen through for about 10 minutes. The solution in the absorbers must remain clear. If this does not happen, the carbonate removal process must be repeated with a fresh barium hydroxide solution. Oxidation and absorption 5.3 After withdrawing the nitrogen feed tube, rapidly introduce 20 grams of chromium trioxide (3.1) and 6 ml of silver nitrate solution (3.3) via the side arm of the reaction flask (B). Connect the apparatus to the suction pump and adjust the nitrogen flow so that a steady stream of gas bubbles passes through the sintered-glass absorbers (F1) and (F2). Heat the reaction flask (B) until the liquid boils and keep it boiling for 90 minutes. It may be necessary to adjust the suction-regulating valve (G) to control the nitogen flow since it is possible that the barium carbonate precipitated during the test may block the sintered glass discs. The operation is satisfactory when the barium hydroxide solution in the absorber (F2) remains clear. Otherwise repeat the test. Stop heating and dismantle the apparatus. Wash each of the distributors both inside and outside to remove barium hydroxide and collect the washings in the corresponding absorber. Place the distributors one after the other in a 600 ml beaker which will subsequently be used for the determination. Rapidly filter under vacuum firstly the contents of absorber F2 and then absorber F1 using the sintered glass crucible. Collect the precipitate by rinsing the absorbers with water (3.10) and wash the crucible with 50 ml of the same water. Place the crucible in the 600 ml beaker and add about 100 ml of boiled water (3.10). Introduce 50 ml of boiled water into each of the absorbers and pass nitrogen through the distributors for five minutes. Combine the water with that from the beaker. Repeat the operation once to ensure that the distributors are rinsed thoroughly. Measurement of the carbonates originating from organic material 5.4 Add five drops of phenolphthalein (3.8) to the contents of the beaker. The solution becomes red in colour. Add hydrochloric acid (3.5) drop by drop until the pink colour just disappears. Stir the solution well in the crucible to check the pink colour does not reappear. Add five drops of bromophenol blue and titrate with hydrochloric acid until the solution turns yellow. Add a further 10 ml of hydrochloric acid. Heat the solution to boiling point and continue boiling for a maximum of one minute. Check carefully that no precipitate remains in the liquid. Allow to cool and titrate with the sodium hydroxide solution (3.6). --- Source: https://www.legislation.gov.uk/nisr/1996/513/schedule/2/part/I/chapter/14c./paragraph/5 (the official version) Page: https://openlegislation.uk/fertilisers-sampling-and-analysis-regulations-northern-ireland-1996/schedule-2/part-I/chapter-14c./paragraph-5 Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.