A process once used for the large-scale manufacture of sulphuric acid by the oxidation of sulphur dioxide with air using a potassium nitrate catalyst in water. This involved burning iron pyrites, FeS2, or some other source of sulphur such as zinc sulphide, ZnS, to produce sulphur dioxide which was then oxidized in large lead chambers to sulphuric acid by the action of air, oxides of nitrogen, and water:
The process was carried out in expensive lead chambers but produced only dilute acid. The process was invented by English physician and industrialist John Roebuck (1718–94) in 1746 and was later replaced by the more economic contact process in 1876.