The Fertilisers (Sampling and Analysis) Regulations 1996

6. DETERMINATION OF THE NEUTRALISING VALUE IN LIMING MATERIALS

SCOPE AND FIELD OF APPLICATION

1.  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 1991.

PRINCIPLE

2.  The sample is dissolved in a measured quantity of standard hydrochloric acid, the excess of which is titrated with standard solution of sodium hydroxide.

REAGENTS

3.1  Hydrochloric acid, 0.5 M solution.

3.2  Sodium hydroxide, 0.5 M solution (carbonate free).

3.3  Phenolphthalein indicator solution: dissolve 0.25 g phenolphthalein in 150 ml 95% ethanol and dilute with water to 250 ml.

PREPARATION OF SAMPLE

4.  Rapidly grind 50 g of the representative lime sample to pass through a 1 mm sieve.

PROCEDURE

Determination

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 M 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 M sodium hydroxide solution (3.2) to the end point of the indicator.

EXPRESSION OF RESULTS

6.  Determine the amount of hydrochloric acid consumed by the sample. 1 ml 0.5 M 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 the undried sample as received.