Sodium hydroxide production. Schematic diagram of the membrane cell method for the chlor-alkali electrolytic process to produce sodium hydroxide. Salt solution (brine, sodium chloride, blue) is piped in at upper left (26%) and out at lower left (23%). Electrolysis produces chlorine gas (dark green) at the anode (left), and hydrogen gas (pale green) at the cathode (right). An ion-exchange membrane (yellow) separates the two halves of the electrolysis cell. Sodium hydroxide (pink) is piped in and out of the cell: arrives at upper right, 32%; leaves at lower right, 35%. This is a net gain of sodium hydroxide, a chemical that is widely used in the chemical industry. Chlorine and hydrogen are also important products.