... in water, with light nitrogen oxides-like odour. Oxalic acid forms fine colourless crystals, readily soluble in water, ... with light nitrogen oxides-like odour.Oxalic acid dihydrate begins to dissociate at temperature over 30 ... and avoid water,solarization.ParameterGradeOxalic acid 1 2 3Purity (H2C2O4·H2O)99.6%99.4%99.0%SO4-2 % ≤0 ... % ≤0.0012Fe+3 % ≤0.00120.0020.01 Oxalic acid (99.6%, 99.4%,99%)