SOLUBILITY VERY SOLUBLE IN WATER ID PASSES TEST RESIDUE AFTER IGNITION MAX. 0.03% CHLORIDE MAX 0.001% NITRATE MAX. 0.002% PHOSPHATE MAX. 0.0005% SULPHATE MAX. 0.02% HEAVY METALS MAX. 0.002% IRON MAX. 0.001% SUBSTANCE DARKENED BY SULPHURIC ACID TO PASS TEST