Paragraph 7 PROCEDURE

Calcium, magnesium, sodium and sulfur in the form of sulfates are extracted from a test sample of 5 g weighed to within 1 mg. However, when the fertiliser contains more than 15% of sulfur (S) i.e. 37.5% SO₃, and more than 18.8% of calcium (Ca) i.e. 26.3% CaO, the extraction of calcium and sulfur is carried out on a test sample of 1 g, weighed to within 1 mg. Place the test sample in a 600 ml beaker.

Add approximately 400 ml of water and, taking care when the sample contains a significant quantity of carbonates, 50 ml of dilute hydrochloric acid (4.1) a small amount at a time. Bring to the boil and maintain for 30 minutes. Allow to cool, stirring occasionally. Transfer quantitatively into a 500 ml graduated flask. Make up to volume with water, and mix. Pass through a dry filter into a dry container, discarding the initial portion. The extract must be completely clear. Stopper if the filtrate is not used immediately.