Animation showing the contact process, the industrial process that makes sulphuric acid from sulphur. Sulphur enters a roasting tower on a conveyor belt. The air supply from bottom produces sulphur dioxide, which is piped to the oxidising tower. Catalytic oxidation (450 degrees Celsius and 1-2 atmospheres of pressure) occurs in the presence of vanadium pentoxide to produce sulphur trioxide gas, with more air supplied from bottom. This is then pumped into a tank of concentrated sulphuric acid (final stage, right). The sulphur trioxide dissolves in the sulphuric acid to form oleum (fuming sulphuric acid), which is diluted with water to form sulphuric acid.