These are the sulphite group, viz., sulphur dioxide and sulphurous acid, sodium sulphite, sodium bisulphite, and sodium thiosulphate (hyposulphite). The sulphites absorb oxygen to form sulphates. They will destroy many colors, but these on exposure to the air tend to be restored through reoxidation. Ferrous sulphate is of this group, as it takes up oxygen; its chief use is in water-closets, sinks, and cess-pools.

Sulphur dioxide (So2), formed by burning sulphur, is used for the disinfection of rooms. It bleaches fabrics, though these may slowly regain their color on exposure to the air. As a disinfectant it is not very efficient, but the New York Department of Health allows room disinfection with eight hours' exposure to the fumes of 4 pounds of sulphur for each 1000 cubic feet of air-space. It has the greatest disinfectant power when used with steam or moist air, but then is more destructive to fabrics and colors. The dry sulphur dioxide is effective in destroying vermin, but it does not readily penetrate cracks.