processes in which glass parts are strengthened by ion exchange with cations in a molten salt bath are improved by removal of the small amounts of moisture and other forms of the hydroxyl group present in the salt melt by either chemical or electrolytic means , prior to the ion exchange . the chemical means involve reacting the hydroxyl - containing compounds with the chlorine - containing gas , while the electrolytic means involve electrolysis to gaseous hydrogen and oxygen . preferred embodiments further include a gas purge prior to the chemical or electrolytic treatment .