FERROUS SULFATEAlso called iron sulfate and green vitriol. It
is a green crystalline material of composition FeSO4 • 7H2O. It occurs naturally as the mineral melanterite and is a by-product of the galvanizing and tinning industries. The specific gravity is 1.898, the melting point is 147°F (64°C), and it is soluble in water. On exposure to the air it becomes yellowish because of the formation of basic iron sulfate, and on heating to 284°F (140°C) it becomes a white powder, FeSO4 • H2O, which also occurs as the mineral szomolnokite. Ferrous sulfate, under the name copperas, is an important salt in the ink industry to give color permanence to the inks. It is also employed in water purification, as a disinfectant, in polishing rouge, as a mordant in dyeing wool, and in the production of pigments. Ferric sulfate is a grayish amorphous powder of composition Fe2(SO4)3 • 9H2O, or Fe2(SO4)3. The specific gravity of the hydrous form is 2.1 and of the anhydrous 3.097. It is very soluble in water and is used as a pigment, as a mordant in dyeing, for etching aluminum and steel, and as a disinfectant. Ferrisul, of Monsanto Co., is anhydrous ferric sulfate used for speeding the action of metal pickling baths and for descaling boilers. In etching steel, the action of anhydrous ferric sulfate is 30 times more rapid than that of sulfuric acid.
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