This method is applicable to products in Groups 5(a) and 5(b) of Section A of the Table in Schedule 1 of the Fertilisers Regulations (Northern Ireland) 1990(1).
The sample is dissolved in a measured quantity of standard hydrochloric acid, the excess of which is titrated with a standard solution of sodium hydroxide.
Hydrochloric acid, 0.5 N solution.
Sodium hydroxide, 0.5 N solution of carbonate free).
Phenolphthalein indicator solution: dissolve 0.25 g phenolphthalein in 150 ml 95% ethanol and dilute with water to 250 ml.
Rapidly grind 50 g of the representative lime sample to pass through a 1 mm sieve.
5.1 Weigh to the nearest 0.001 g, 0.5 g of the prepared sample and transfer to a 300 ml conical flask. Add 50 ml of 0.5 N hydrochloric acid (3.1), cover the flask with a watch glass and boil the contents gently for five minutes. Cool the mixture to room temperature, add two or three drops of the phenolphthalein indicator (3.3) and titrate with 0.5 N sodium hydroxide solution (3.2) to the end point of the indicator.
Determine the amount of hydrochloric acid consumed by the sample. 1 ml 0.5 N hydrochloric acid = 0.01402 g calcium oxide (CaO).
The neutralising value is expressed as a percentage by weight of calcium oxide (CaO), and refers to undried sample as received.