Paragraph 6 SPECIAL CASES
Fertilisers comprising a blend of several categories of crystals
In this case, separation frequently occurs. It is therefore absolutely essential to crush and pass the sample through a sieve with apertures of 0.2 mm (for example, mixtures of ammonium phosphate and potassium nitrate). The grinding of the whole of the final sample is recommended in the case of these products.
Residue which is difficult to grind and does not contain fertilising substances
Weigh the residue and take account of its mass when calculating the final result.
Products which decompose on heating
Grinding must be carried out in such a way as to avoid any heating. It is preferable in this case to use a mortar for grinding (for example, compound fertilisers containing calcium cyanamide and urea).
Products which are abnormally moist or made into a paste by grinding
To ensure homogeneity, a sieve is to be chosen which has the smallest apertures compatible with the destruction of lumps by hand or with the pestle. This may be the case for mixtures, certain ingredients of which contain water of crystallisation.