... , Feso: 7H2O - traits: turquoise single crystal, soluble in water, glycerin, not soluble in alcohol, easy ChaoXie, in air oxidation ... strong, can be the following proportions of chromium-containing waste water reduction hexavalent chromium cr3 +, replace expensive by sodium sulfite ... ferrous sulfate (usually 1/1000, namely 1000 ml of water, add 1 gram, specific drug with pollutant concentration, ...