The Voltaic Pile
                                                      Middlebury College           St. Patrick's College, Ireland   Transylvania University
   About 1791-92 Luigi Galvani (1737-98), a biologist and professor at the University of Bologna, noticed that frogs' legs, impaled on brass hooks, contracted when the legs came in contact with an iron lattice. Unfortunately, he made the assumption that the source of the effect was in the animal tissue.

   In the last years of the 18th century Alessandro Volta (1745-1827) of the University of Pavia showed that any moist, porous material between two dissimilar metals would produce the same effect. 

In the Pile that Volta described in 1800, a disk of copper is placed at the bottom, followed by a disk of cloth soaked in brine or acidulated water, followed by a disk of zinc. More sets of copper-cloth-zinc disks is placed on top, until the pile reaches a height of about 30 cm. The positive end of the pile is the bottom copper disk, and the negative end is the top zinc disk. The three glass rods serve to confine the disks into a vertical pile.

   An alternative arrangement of the metallic disks is Volta's Crown of Cups.

   The voltaic pile at the left, in the collection at Dartmouth College in Hannover, New Hampshire, is unusual in its provision of a built-in spark gap.

    Electrochemical Cells, which were developed from Volta's basic idea of dissimilar metals separated by an electrolyte, were developed in the first half of the 19th century.

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