The discovery of electrolysis
As soon as the news of Volta’s invention of the simple cell reached London a professor of anatomy named Sir Anthony Carlisle constructed a voltaic pile consisting of silver half-crowns, zinc discs and cardboard soaked in brine. While experimenting with this he decided to place a drop of water on the top disc for the purpose of improving the electrical contact made with the connecting wire. He was surprised to notice that bubbles of gas rose from the wire when it was allowed merely to dip into the water drop without touching the disc. Sir Anthony had a friend named William Nicholson, who had also constructed a voltaic pile, and the two
decided to work together in making a further investigation of this new phenomenon, now called electrolysis.
In one experiment they connected the pile to two platinum wires dipping into a shallow vessel containing water to which a few drops of sulphuric acid had been added. Clouds of bubbles arose from each wire and were collected in separate bottles. When the gases were tested it was found that the wire connected to the zinc (-ve) disc gave off hydrogen, while that connected to the silver disc (+ve) gave oxygen.
It was already known that water consisted of hydrogen and oxygen in chemical combination. This had been demonstrated by several chemists, who, at various times, exploded mixtures of hydrogen and oxygen and obtained the formation of a dew which proved to be water. Now, for the first time, Nicholson and Carlisle had shown that water could be decomposed into its elements by an electric current. It was a discovery of first-class importance. The obvious inference was that it might be possible to decompose other substances by this means and hence discover their chemical composition. This was done with striking success a few years later by Sir Humphry Davy. He isolated the metals sodium and potassium by passing an electric current through molten sodium hydroxide and potassium hydroxide respectively.