A neutral salt with the formula Na2SO4. It has several hydrates. Its common name is "salt cake" because of its cake-like consistency. It is a by-product of one of the types of hydrogen chloride production processes, shown below.

2NaCl(aq) + H2SO4(aq) ---> Na2SO4(aq) + 2HCl(g)

It has limited industrial use. However, because it can exist as a hydrate, it can be used as a dehydrating agent. It is also a quite effective electrolyte; the sodium and sulfate ions are very resistant to electrolytic breakdown.