Sulphuric Anhydride.

Sulphuric Anhydride. SO₃ is obtained by distilling fuming Nordhausen sulphuric acid, a fibrous mass of silky crystals being deposited in the receiver. It may also be prepared by the distillation of anhydrous bisulphate of soda. It is a tough solid, melting at 65° (18·3° C.), and possessing none of the properties of an acid, not even affecting the skin. In contact with moisture much heat is developed, and it then possesses the corrosive properties of sulphuric acid.