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A voltaic pile is the first type of true electric battery capable of a sustained output of electric current. It is named for its inventor, Alessandro Volta who built the first example in 1800, and was based upon previous work by Luigi Galvani. Volta developed it, not to improve upon or validate Galvani's work, but to prove that while Galvani's discoveries had merit, he had incorrectly interpreted their significance. Volta sought to show the true source of the results achieved by his colleague and the mechanism behind them. A voltaic pile consists of alternating discs of zinc and another metal such as copper or silver separated by discs of cardboard or leather soaked in brine. Each unit of one copper disc and one zinc disk with its brine soaked separator will produce a weak electric current and by stacking several such units in series, more current is produced.
Volta's colleague, Luigi Galvani, showed that a circuit of two electrodes and a frog's leg could cause the muscles in the leg to activate. Galvani mistakenly believed that the tissue was the source of the action. Volta constructed the voltaic pile partly to show that there was an electric current present and that the creation of a circuit using electrodes produced the current. Of course, this was not the sole impetus behind his research and the development of his invention as he also sought a method for the production of steady electric current.
The stack of discs in the voltaic pile is held in place by glass rods, which are not conductive. By attaching connected wires to either end of the pile, an electric circuit with a flow of current is created. This is due to the flow of electrons from the zinc discs to the copper discs, facilitated by the liquid held by the cardboard or leather pads. The amount of current produced by an individual cell of two metal discs and a brine soaked separator is roughly equivalent to one volt and was used to define that unit of electromotive force named for Volta. Adding more cells to a voltaic pile increases current output.
This important invention directly led to the first experiments in, and the birth of, the branch of science now called electrochemistry. Two scientists used a voltaic pile to separate water into hydrogen and oxygen atoms by passing a current through it, a process that became known as electrolysis. Other scientists built on this work, expanding this new field and making improvements to Volta's invention, eventually leading to the development of the modern electric battery.