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ArrowDavy Electrolysis

The invention of the voltaic pile – the first primitive battery – at the dawn of the 19th century enabled scientists to conduct experiments that were never possible before possible. Just six weeks after Alessandro Volta demonstrated the pile to the Royal Society of London, English scientists William Nicholson and Anthony Carlisle copied his design to make a voltaic pile of their own. By experimenting with the apparatus, they became the first men to separate water into its component elements —hydrogen and oxygen. Shortly thereafter, English chemist Humphry Davy used a similar process to separate a number of other compounds into their basic components. The process first invented by Nicholson and Carlisle and then perfected by Davy is known as electrolysis, and involves the use of an electric current to cause a chemical reaction.

Davy Electrolysis

To perform electrolysis, Davy used a special trough such as the one illustrated here. In it he placed a liquid and a pair of electrodes connected to a voltaic pile. One electrode, called the cathode, carried a negative charge (a surplus of electrons); the other, termed the anode, had a positive charge (a deficit of electrons). Liquids (as well as gases and solids) that are electrolytes are made up of ions (charged atoms), and can therefore conduct an electric current by passing electrons from one ion to another. Whenever Davy applied a voltage to an electrolyte in his trough, chemical reactions occurred at the immersed electrodes. Each electrode attracted oppositely charged ions. Ions coming into contact with the cathode tended to gain electrons, those that touched the anode tended to lose electrons. As a result, different elements or compounds became isolated around the opposing electrodes.

Through electrolysis, Davy became the first to isolate potassium, sodium, calcium, magnesium and other elements from liquid compounds. Perhaps even more importantly, Davy changed the very definition of what an acid was by discovering that hydrogen and chlorine are the only elements in hydrochloric acid (known at the time as muriatic acid). Before Davy’s discovery, most scientists believed Antoine-Laurent Lavoisier’s theory that oxygen was an essential part of all acids.

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