Laundry sour

A laundry sour is a chemical added to clothing during the final rinse cycle of a washing machine to lower the pH of the water and to assist with the removal of detergent rust and or mineral residues that clinged on the fabrics. Most such sours are fluoride-based, including ammonium silicofluoride, ammonium bifluoride, and hydrofluosilicic acid; glycolic acid is also used. The US Department of Defense recognizes two "types" of laundry sours: type I is sodium silicofluoride and sodium acid fluoride in powdered, crystal, or flake form; type II is ammonium bifluoride in flake form.