Industrially,<unk> rrous sulfate is mainly used as a precursor to other<unk>  compounds. It is a reducing agent, and as such is useful for the reduction of chromate in cement to less toxic Cr(III) compounds. Historically<unk> rrous sulfate was used in the textile industry for centuries as a dye fixative. It is used historically to blacken leather and as a constituent of<unk>  gall ink. The preparation of sulfuric acid ('oil of vitriol') by the distillation of green vitriol <unk> (II) sulfate) has been known for at least 700 years. Medical use Plant growth<unk> (II) sulfate is sold as<unk> rrous sulfate, a soil amendment for lowering the pH of a high alkaline soil so that plants can access the soil's nutrients. In horticulture it is used for treating<unk>  chlorosis. Although not as rapid-acting as<unk> rric EDTA, its effects are longer-lasting. It can be mixed with compost and dug into the soil to create a store which can last for years. It is also used as a lawn conditioner, and moss killer. Pigment and craft<unk> rrous sulfate can be used to stain concrete and some limestones and sandstones a yellowish rust color. Woodworkers use<unk> rrous sulfate solutions to color maple wood a silvery hue. Green vitriol is also a useful reagent in the identification of mushrooms. Historical uses<unk> rrous sulfate was used in the manufacture of inks, most notably<unk>  gall ink, which was used from the middle ages until the end of the 18th century. Chemical tests made on the Lachish letters () showed the possible presence of<unk> . It is thought that oak galls and copperas may have been used in making the ink on those letters. It also finds use in wool dyeing as a mordant. Harewood, a material used in marquetry and parquetry since the 17th century, is also made using<unk> rrous sulfate. Two different methods for the direct application of indigo dye were developed in England in the 18th century and remained in use well into the 19th century. One of these, known as china blue, involved<unk> (II) sulfate. After printing an insoluble form of indigo onto the fabric, the indigo was reduced to leuco-indigo in a sequence of baths of<unk> rrous sulfate (with reoxidation to indigo in air between immersions). The china blue process could make sharp designs, but it could not produce the dark hues of other methods. In the second half of the 1850s<unk> rrous sulfate was used as a photographic developer for collodion process images.
Iron
Zinc
Copper 
Biotin
Folate
Selenous acid
Calamine
Sybil 