1805

Electroplating

Alessandro Volta (1745–1827), Luigi Brugnatelli (1761–1818)

Electricity was at the frontier of technology in the late 1700s and early 1800s. Luigi Brugnatelli, an Italian professor and friend of electrical pioneer Alessandro Volta, used the new voltaic pile battery on various chemical solutions, and in 1805 he discovered that he could cause gold metal to deposit in a thin film on other metal objects if they were dipped into a solution of gold salts while they were wired to the negative terminal of the battery. (He was even able to electroplate nonmetallic things such as insects and flower petals if he covered them first with a thin layer of metal-based paint to conduct the electricity.)

Brugnatelli’s discovery, now called electrochemical reduction, is another application of oxidation and reduction chemistry. Iron smelting, for example, involves both reactions: carbon is oxidized (combines with oxygen) when it burns, forming carbon monoxide (CO), which in turn strips the ore of oxygen, reducing the iron oxides down to the elemental metal. In the case of electroplating, the electrons at the negative end of the battery reduce the (positively charged) gold ions back down to elemental gold as they come near the surface of the metal object, causing a very thin layer of new gold to build up.

This is the sort of discovery that you might think would make someone wealthy and famous, but it was not to be. Brugnatelli presented his work to the French government (i.e., Napoléon Bonaparte), and there was some sort of catastrophic disagreement, so Brugnatelli’s results were suppressed throughout Napoleonic Europe. Electroplating wasn’t rediscovered for nearly twenty-five years. There were many variables to be worked out (voltage and current, the types of metal salts to use, and what sorts of materials would best take the new electroplated layer), but by the 1840s gold and silver plating was a commercial success, thanks partly to the discovery that cyanide solutions could dissolve large amounts of the metals. These and other metals are still electroplated on a large scale throughout the world, and electrochemistry has evolved into its own branch of science.

An early voltaic pile, made with alternating zinc and copper disks. This sort of battery provided the power for the first electroplating experiments and many other types of experiments as well.