iron sulphate
(US iron sulfate)
noun
1Iron (ii) sulphate (ferrous sulphate), FeSO4, a green crystalline solid used in dyeing, nutritional supplements, water purification, etc.
2Iron (iii) sulphate (ferric sulphate), Fe2(SO4)3, a yellow crystalline solid used as a mordant in dyeing.
Origin
Mid 19th century; earliest use found in The Mechanics' Magazine.