A voltaic pile is a set of individual voltaic cells placed in series. The voltaic pile, invented by Alessandro Volta in 1800, was the first electric battery. Building on Galvani's 1780's discovery of how a circuit of two metals and a frog's leg can cause the frog's leg to respond, in 1791 Volta demonstrated that when two metals and brine-soaked cloth or cardboard are arranged in a circuit they produce an electric current. In 1800 Volta literally piled up several pairs of alternating copper (or silver) and zinc discs (electrodes) separated by cloth or cardboard soaked in brine (electrolyte) to increase the electrolyte conductivity. When the top and bottom contacts were connected by a wire, an electric current flowed through the voltaic pile and the connecting wire. The strength of the pile is expressed in terms of its electromotive force, or emf, given in volts. Volta characterized the emf of a pair of metals in terms of the difference in their voltages, which he could measure. His 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.
On March 20, 1800, Volta wrote to the London Royal Society to describe the technique for producing electrical current using his pile. On learning of the voltaic pile, William Nicholson and Anthony Carlisle used it to discover the electrolysis of water. Humphrey 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.
Because Volta believed that the emf 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 the work of his mentor Davy, in the early 1830s Faraday studied voltaic cells in detail. This led to his founding of the area of electrochemistry. The words "electrode" and "electrolyte", used above to describe Volta's work, are due to Faraday.
A number of high-voltage dry piles were invented between the early 1800s and the 1830s in an attempt to determine the source of electricity of the wet voltaic pile, and specifically to support Volta’s hypothesis of contact tension. Indeed Volta himself experimented with a pile whose cardboard discs had dried out, probably accidentally. The first to publish was Johann Wilhelm Ritter in 1802, albeit in an obscure journal, but over the next decade it was announced again and again as a new discovery.