How to recognize metamorphic ferrous sulfate?

Green vitriol ferrous sulfate is easily oxidized to ferric sulfate in air, which is not easy to be absorbed by crops and then go bad soon. How to recognize metamorphic ferrous sulfate when buying? The simplest method to recognize whether ferrous sulfate go bad is to use potassium thiocyanate as identification reagent. The detailed steps: firstly, pour the ferrous sulfate solution in a beaker, and then slowly trip into potassium thiocyanate solution. If the mixture solution turned red, it means the ferrous sulfate go bad. The simple reason is that this reagent potassium cyanide would become blood red and form a kind of complex which's difficult to decompose when meeting with Fe3+. Potassium thiocyanate method in metamorphic ferrous sulfate identification is simple and accurate. If you doubt your purchased ferrous sulfate heptahydrate and ferrous sulfate monohydrate, you can use this simple method to identify it. The shelf life of ferrous sulfate is generally about half a year. Improper preservation method would cause product deterioration, so stock the well sealled products in cool and ventilated condition after purchasing.