| Themes > Science > Physics > Electromagnetism > Electrostatics > Electric field > The voltaic pile |
By 1795, Volta convinced himself that a continuous flow of electricity took place whenever two different metals were in contact with each other and with a moist conductor. In 1796, he showed that if two metal plates were simply held in contact with each other, by insulating handles, and then pulled apart, each one carried an equal and opposite charge, as evidenced by the deflection of a very delicate electrometer. And in a famous letter to the Royal Society, dated March 20, 1800, Volta described the discover of a new technique for greatly amplifying the effect. What he described was an assemblage of three good conductors, two metals and a moist conductor, layered so that the metals alternate but each has a moistened layer in between. He emphasized the identity of effects produced by his pile with those produced by "common" electricity. Not only did he demonstrate shocks and sparks and the necessity of providing a continuous, electrically conducting path from one side of the pile to the other (just as such a path was necessary from one side of the jar to the other), but he also showed that the sensitive electrometer could be charged positively at one end of the pile and negatively at the other. In particular, Volta emphasized the continuity of the process, but not having an instrument for the direct detection of continuous flow of electrical charge, he had to adduce as evidence only his physiological sensations in grasping the terminals and allowing conduction to take place through his own body. The voltaic pile, which we now recognize under the name of "electrical battery," produced an immediate sensation and revived the lagging research in electricity. Within a short time, scientific apparatus houses were offering Volta's piles as regular items of equipment for research and demonstrations. Very shortly after receipt of Volta's letter in London, Nicholson and Carlisle, having constructed a pile in accordance with Volta's instructions, followed up the chance observation of evolution of gas at the terminals of the pile where the connecting wires had been wetted with water to provide a better electrical connection. They led conductors from the ends of the pile into a vessel of water, acidified to render it a better conductor, and detected hydrogen being evolved at one conductor and oxygen at the other. (The steady evolution of gas at the conductors further dramatized the fact that a continuous process was taking place in the system when electrical connection was made between the terminals of the pile, and this is further reinforced by the observation of continuous heating of the connecting wires, soon noted by many investigators.) Nicholson and Carlisle thus discovered the phenomenon of electrolysis of water into its component gases. Humphry Davy, in his chemical researches at the Royal Institution, seized upon this device for decomposing other materials, and discovered the metals sodium and potassium by electrolyzing their molten salts. Gradually it came to be realized that chemical effects taking place outside the pile always occurred at the expense of simultaneous chemical change within the pile itself. Although a good theoretical model was still far in the future, it was clear that the electrical effects associated with Volta's pile had a deep underlying relation to what was then called chemical affinity-the tendency of certain substances to enter into chemical combination with each other-and motivation was provided for further research on the role of electricity in the structure of matter. Thus, physical research in electricity came to be joined to the science of chemistry. This is a story, though, for later. Let's pursue now other physical aspects of Volta's discovery. |
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