http://www.legislation.gov.uk/nisr/1991/540/schedule/2/part/II/crossheading/extraction-of-phosphorus-by-mineral-acids-total-phosphorusn2/paragraph/3.1/madeThe Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1991Local GovernmentGovernment Printer for Northern Ireland2016-09-06AGRICULTURESCHEDULE 2METHODS OF ANALYSISPART II5a.EXTRACTION OF PHOSPHORUS BY MINERAL ACIDS (TOTAL PHOSPHORUS)REAGENTS3.1Sulphuric acid (d = 1.84 g/ml).