Volta's pile

The roots of Volta's invention go back to the discovery by his fellow Italian, Luigi Galvani, of frog legs fame. A full account was published in 1791 and caused great excitement amongst both physicists and the medical fraternity. The latter wondered if the "vital principle" had at last been found and pondered the possibilities for new treatments. Galvani was the second to report what we would now recognise as an electrochemical effect, the Swiss J.G. Sulzer having noted in 1762 that two dissimilar metals placed on the tongue gave a sensation of taste.

At first, Volta considered Galvani's reports to be unbelievable. Pressed by colleagues, he at last investigated the phenomenon and, by the April 1, 1791, had begun the series of careful step-by-step experiments which led him to the electric battery.

Galvani explained the excitation of the dead frog's legs as being caused by animal electricity, an explanation which Volta firmly rejected. Volta was led to believe that the current flow was caused by the contact of two different metals. In that he too was wrong. It was another Italian, G.V. Fabroni, who got the right explanation by pointing to a chemical action between the liquid, which always seemed to be present in both Galvani's and Volta's work, and the two different metals.

Volta repeated Sulzer's as well as Galvani's work. In one experiment he brought insulated zinc and copper discs into contact and found that they were charged on separation. By experiment he found that zinc and silver discs best suited his purpose and eventually he arranged pairs of them in a pile. Each pair was separated from neighbouring pairs by a piece of cardboard soaked in water or brine to provide, as he believed, a conducting path between the pairs. Letting all pairs touch one another, he knew, provided only the same effect as a single pair of discs.

The finished pile of discs and cardboard multiplied the effects of a single pair many times and he was able to receive a shock from his pile similar to that from a charged Leyden Jar capacitor. The vital differences were that Volta's pile did not need to be immediately recharged and could give a continuous current.

News of the invention was announced in a letter to the Royal Society in London: "The apparatus of which I speak," wrote Volta, "will doubtless astonish you." The continuous current almost appeared as perpetual motion, "but it is nonetheless true and real, and can be touched with the hands.”

Volta's pile, "as high as can hold itself without falling," consisted of 30, 40, or 60 cells. From such primitive origins grew today's huge international industry. As an alternative to the pile, Volta also used pairs of metals soldered together with each end dipping into water or brine contained in glasses; this arrangement he called the crown of cups. Again, 30 or more cells could be arranged to produce a battery of cells. The word battery had, of course, been used earlier, not only for a battery of guns but for a battery of charged Leyden Jars.

Improvements were soon made by others. For greater voltages more cells were needed in the pile, which increased the weight and squeezed out the electrolyte from the cardboard discs. In Germany, J.W. Ritter turned up the edges of his metal discs and obtained batteries which lasted for two weeks! A horizontal wooden trough provided an even better battery: zinc plates, for example, could be fixed vertically to a support and lowered into the trough between vertical plates of the other metal. This trough arrangement has been suggested as the origin of our circuit symbol for the battery.

Volta received many honours in his lifetime, including recognition by learned societies in London, Paris and Berlin. His financial rewards from his university salary were boosted in 1805 by the annuity he received from Napoleon and, in 1809, by his senatorial salary. For the last two decades of his life he had the income of a wealthy man.

Task I

Speak on Volta’s scientific interests and experiments.

Task II

Dscribe Volta’s pile and explain its work.