The lead-chamber process is a process for manufacturing sulfuric acid, now superceded by the contact process. Sulfur dioxide, produced by burning sulfur, is mixed with air and nitric oxide (see nitrogen) and passed in turn through the Glover tower, several lead chambers (where steam is sprayed in), and the Gay-Lussac tower, where concentrated sulfuric acid is sprayed in. The mixture of sulfuric acid and nitrosylsulfuric acid from the Gay-Lussac tower is sprayed back into the Glover tower. The net product is impure 70% sulfuric acid, tapped off from the lead chambers. The nitric oxide is catalytic.