Two electrolytic cells, c 1961.
© Science Museum / Science & Society Picture Library
The cell on the left shows the electrolysis of sodium chloride (common salt) to produce sodium and chlorine gas. The model on the right shows the electrolysis of brine (salt disolved in water) which initially produces sodium and chlorine gas. The sodium then instantly reacts with the water to form the alkali sodium hydroxide (NaOH), also known as caustic soda. Hydrogen gas is also produced.