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Pioneers of Electricity

Georges Leclanché

b. 1839, Paris - d. Sept. 14, 1882, Paris

Georges Leclanché was the French engineer who, in about 1866, invented the battery that bears his name. In slightly modified form, the Leclanché battery, now called the dry cell, is produced in great quantities and is widely used in devices such as flashlights and portable radios.

George Leclanché was born in Parmain (France) in 1839. He was the son of Léopold Leclanché and Eugenie of Villeneuve. Leclanché was educated in England. He returned to France to continue his study in the Central School of Arts and Manufactures. After completing a technical education in 1860, Leclanché began work as an engineer. Six years later he developed his battery, which contained a conducting solution (electrolyte) of ammonium chloride, a negative terminal of zinc, and a positive terminal of manganese dioxide. In 1866, Georges Leclanche patented a new system, which was immediately successful. Leclanche's original cell was assembled in a porous pot. The positive electrode consisted of crushed manganese dioxide with a little carbon mixed in. The negative pole was a zinc rod. The cathode was packed into the pot, and a carbon rod was inserted to act as a currency collector. The anode or zinc rod and the pot were then immersed in an ammonium chloride solution. The liquid acted as the electrolyte, readily seeping through the porous cup and making contact with the cathode material. Leclanche's "wet" cell (as it was popularly referred to) became the forerunner to the world's first widely used battery, the zinc carbon cell.

The e.m.f. of a Leclanche cell is about 1.5 volts buts its resistance may amount to several ohms when a porous pot is employed. It was used extensively for telegraphy, signalling and electric bell work; and for most work where intermittent current is required and where it is essential that the battery should require very little attention from time to time.

The chemical process that produces electricity begins when the atoms of zinc at the surface of the anode oxidise. A zinc atom oxidises when it gives up both its electrons. It then becomes an ion with a positive charge. The zinc ions move away from the anode. As they do so, they leave their electrons behind on its surface. The anode thus gains an excess of electrons and becomes more negatively charged than the cathode. If a cell is connected to an external circuit, the zinc anode's excess electrons flow through the circuit to the carbon rod. The movement of electrons forms an electric current. After the electrons enter the cell through the rod, they combine with molecules of manganese dioxide and molecules of water. As these substances are reduced (gain electrons) and react with one another, they produce manganese oxide and negative hydroxide ions. This reaction makes up the second half of the cell's discharge process. It is accompanied by a secondary reaction. In the secondary reaction, the negative hydroxide ions combine with positive ammonium ions that form when ammonium chloride is dissolved in water. The secondary reaction produces molecules of ammonia and molecules of water.

The various chemical reactions by which a carbon-zinc cell produces electricity continue until the manganese dioxide wears away. After this cathode material has been "used up," the cell can no longer provide useful energy and is dead. Dead cells should be removed immediately. Even after a cell stops working, its electrolyte continues to eat away at the container and may puncture it. If the electrolyte leaks out, it can damage the equipment.

A carbon-zinc cell, like most primary batteries, cannot be recharged efficiently. But a device called a battery charger may extend the life of a cell for a short time. It partially restores the cell's ability to produce electricity. A battery charger functions by passing a current through the cell in a direction opposite to that of the flow of electricity during discharge. Leclanche's invention, which was quite heavy and prone to breakage, was steadily improved over the years. The idea of encapsulating both the negative electrode and porous pot into a zinc cup was first patented by J.A. Thiebaut in 1881. But, it was Carl Gassner of Mainz who is credited as constructing the first commercially successful "dry" cell. Variations followed. By 1889 there were at least six well-known dry batteries in circulation. Later battery manufacturing produced smaller, lighter batteries, and the application of the tungsten filament in 1909 created the impetus to develop batteries for use in torches.

In 1867 George Leclanché gave up his job to devote full time to his invention; a year later it was adopted by the telegraph service of Belgium. He subsequently opened a factory to produce the battery and other electric devices; the business was taken over by his brother Maurice upon George's death in 1882.

This text has been compiled from the biographies of Leclanché available in the Internet.

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