Voltaic pile

The voltaic pile was the first electrical battery that could continuously provide an electric current to a circuit. It was invented by Italian chemist Alessandro Volta, who published his experiments in 1799. Its invention can be traced back to an argument between Volta and Luigi Galvani, Volta's fellow Italian scientist who had conducted experiments on frogs' legs. Use of the voltaic pile enabled a rapid series of other discoveries, including the electrical decomposition (electrolysis) of water into oxygen and hydrogen by William Nicholson and Anthony Carlisle (1800), and the discovery or isolation of the chemical elements sodium (1807), potassium (1807), calcium (1808), boron (1808), barium (1808), strontium (1808), and magnesium (1808) by Humphry Davy.

The entire 19th-century electrical industry was powered by batteries related to Volta's (e.g. the Daniell cell and Grove cell) until the advent of the dynamo (the electrical generator) in the 1870s.

Volta's invention was built on Luigi Galvani's 1780s discovery that a circuit of two metals and a frog's leg can cause the frog's leg to respond. Volta demonstrated in 1794 that when two metals and brine-soaked cloth or cardboard are arranged in a circuit they too produce an electric current. In 1800, Volta stacked several pairs of alternating copper (or silver) and zinc discs (electrodes) separated by cloth or cardboard soaked in brine, which increased the total electromotive force. When the top and bottom contacts were connected by a wire, an electric current flowed through the voltaic pile and the connecting wire. This was the first "true" battery, that gave off continuous charge.

Many scientific instruments that belonged to Alessandro Volta are preserved in the University History Museum of the University of Pavia, where Volta taught from 1778 to 1819; the piles on display, unfortunately, are not original, as the ones preserved in Pavia were lent on the occasion of the centenary of the invention and subsequently lost in a fire.

On 20 March 1800, Alessandro Volta wrote to the London Royal Society to describe the technique for producing electric current using his device. On learning of the voltaic pile, William Nicholson and Anthony Carlisle used it to discover the electrolysis of water. Humphry Davy showed that the electromotive force, which drives the electric current through a circuit containing a single voltaic cell, was caused by a chemical reaction, not by the voltage difference between the two metals. He also used the voltaic pile to decompose chemicals and to produce new chemicals. William Hyde Wollaston showed that electricity from voltaic piles had identical effects to those of electricity produced by friction. In 1802 Vasily Petrov used voltaic piles in the discovery and research of electric arc effects.

Humphry Davy and Andrew Crosse were among the first to develop large voltaic piles. Davy used a 2000-pair pile made for the Royal Institution in 1808 to demonstrate carbon arc discharge and isolate five new elements: barium, calcium, boron, strontium and magnesium.

Because Volta believed that the electromotive force occurred at the contact between the two metals, Volta's piles had a different design than the modern design illustrated on this page. His piles had one extra disc of copper at the top, in contact with the zinc, and one extra disc of zinc at the bottom, in contact with the copper. Expanding on Volta's work and the electro-magnetism work of his mentor Humphry Davy, Michael Faraday utilized both magnets and the voltaic pile in his experiments with electricity. Faraday believed that all "electricities" being studied at the time (voltaic, magnetic, thermal, and animal) were one and the same. His work to prove this theory led him to propose two laws of electrochemistry which stood in direct conflict with the current scientific beliefs of the day as laid down by Volta thirty years earlier. Because of their contributions to the understanding of this field of study, Faraday and Volta are both considered to be among the fathers of electrochemistry. The words "electrode" and "electrolyte", used above to describe Volta's work, are due to Faraday.

The strength of the pile is expressed in terms of its electromotive force, or emf, given in volts. Alessandro Volta's theory of contact tension considered that the emf, which drives the electric current through a circuit containing a voltaic cell, occurs at the contact between the two metals. Volta did not consider the electrolyte, which was typically brine in his experiments, to be significant. However, chemists soon realized that water in the electrolyte was involved in the pile's chemical reactions, and led to the evolution of hydrogen gas from the copper or silver electrode.