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Summary Article: Volta, Alessandro Giuseppe Antonio Anastasio (1745-1827) from The Hutchinson Dictionary of Scientific Biography

Place: Italy

Subject: biography, physics

Italian physicist who discovered how to produce electric current and built the first electric battery. He also invented the electrophorus as a ready means of producing charges of static electricity.

Volta was born in Como on 18 February 1745. He received his early education at various religious institutions but showed a flair for science, particularly the study of electricity, which had been brought to the forefront of attention by the experiments and theories of Benjamin Franklin. Volta began to experiment with static electricity in 1765 and soon gained a reputation as a scientist, leading to his appointment as principal of the Gymnasium at Como in 1774 and, a year later, as professor of experimental physics there. In 1778, Volta took up the same position at Pavia and remained there until 1819. In 1799, the conflict between Austria and France over the region caused him to lose his post but he was reinstated following the French victory in 1800. Volta then travelled to Paris in 1801 to demonstrate his discoveries in electricity to Napoleon, who made him a count and awarded him a pension. Volta retained his academic post when Austria returned to power in 1814, but retired in 1819. He died in Como on 5 March 1827.

Volta's first major contribution to physics was the invention of the electrophorus in 1775. He had researched thoroughly into the nature and quantity of electrostatic charge generated by various materials, and he used this knowledge to develop a simple practical device for the production of charges. His electrophorus consisted of a disc made of turpentine, resin, and wax, which was rubbed to give it a negative charge. A plate covered in tinfoil was lowered by an insulated handle on to the disc, which induced a positive charge on the lower side of the foil. The negative charge that was likewise induced on the upper surface was removed by touching it to ground the charge, leaving a positive charge on the foil. This process could then be repeated to build up a greater and greater charge. Volta went on to realize from his electrostatic experiments that the quantity of charge produced is proportional to the product of its tension and the capacity of the conductor. He developed a simple electrometer similar to the gold-leaf electroscope but using straws so that it was much cheaper to make. This instrument was very sensitive and Volta was able to use it to measure tension, proposing a unit that was equivalent to about 13,500 volts.

Volta's next important work did not concern electricity but the air and gases. In 1776, he discovered methane by isolating and examining the properties of marsh gas found in Lake Maggiore. He then made the first accurate estimate of the proportion of oxygen in the air by exploding air with hydrogen to remove the oxygen. Later, in about 1795-96, Volta recognized that the vapour pressure of a liquid is independent of the pressure of the atmosphere and depends only on temperature. This anticipated the law of partial pressures put forward by John Dalton in 1801.

Volta's greatest contribution to science began with the discovery by Luigi Galvani in 1791 that the muscles in dead frogs contract when two dissimilar metals (brass and iron) are brought into contact with the muscle and each other. Volta successfully repeated Galvani's experiments using different metals and different animals, and he also found that placing the two metals on his tongue produced an unpleasant sensation. The effects were due to electricity and in 1792, Volta concluded that the source of the electricity was in the junction of the metals and not, as Galvani thought, in the animals. Volta even succeeded in producing a list of metals in order of their electricity production based on the strength of the sensation they made on his tongue, thereby deriving the electromotive series.

Volta's tongue and Galvani's frogs proved to be highly sensitive detectors of electricity - much more so than Volta's electrometer. In 1796, Volta set out to measure the electricity produced by different metals, but to register any deflection in the electrometer he had to increase the tension by multiplying that given by a single junction. He soon hit upon the idea of piling discs of metals on top of each other and found that they had to be separated by a moist conductor to produce a current. The political upheavals of this period prevented Volta from proceeding immediately to construct a battery but he had undoubtedly achieved the ‘voltaic pile’, as it came to be called, by 1800. In that year, he wrote to the president of the Royal Society, Joseph Banks, and described two arrangements of conductors that produced an electric current. One was a pile of silver and zinc discs separated by cardboard moistened with brine, and the other a series of glasses of salty or alkaline water in which bimetallic curved electrodes were dipped.

Volta's discovery was a sensation, for it enabled high electric currents to be produced for the first time. It was quickly applied to produce electrolysis, resulting in the discovery of several new chemical elements, and then led throughout the 1800s to the great discoveries in electromagnetism and electronics that culminated in the invention of the electrical machines and electronic devices that we use today. Volta's genius lay in an ability to construct simple devices and in his tenacity to follow through his convictions. He was not a great theoretician and did not attempt to explain his discovery. However, he did see the need for establishing proper measurement of electricity, and it is fitting that the unit of electric potential, tension, or electromotive force is named the volt in his honour.

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