What is Sodium Sulphate?

Anhydrous sulphate is a white crystalline solid also known as the mineral thenardite, while the decahydrate Na₂SO₄.10H₂O has been known as Glauber’s salt or mirabilis.

Na₂SO₄.7H₂O is transformed to mirabilite when it is cooled. Mirabilite is the natural mineral form of the decahydrate. About two-thirds of the world’s production of sodium sulphate is obtained from mirabilite. It is also produced from by-products of chemical processes such as hydrochloric acid production.

Meaning of Anhydrous

Anhydrous literally means “no water.” In chemistry, substances without water are labelled as anhydrous. The term is most often applied to crystalline substances after the water of crystallisation is removed. 

The name and function of salt compounds change with the presence or absence of water in their crystalline structures. For example, sodium sulphate, NaSO4, is called anhydrous sodium sulphate when free of water and is used as a drying material. That same compound in its decahydrate iteration is called “Glauber’s salt,” and is used to make glass. A molecule with no water molecule in it usually absorbs moisture from the salt to which it comes in contact with and hence use as a dehydrating agent.