II.

Primary Cells

The most common form of primary cell is the Leclanché cell, invented by the French chemist Georges Leclanché in the 1860s. It is popularly called a dry cell or flashlight battery. The Leclanché cell in use today is very similar to the original invention. The electrolyte consists of a mixture of ammonium chloride and zinc chloride made into a paste. The negative electrode is made of zinc, as is the outside shell of the cell, and the positive electrode is a carbon rod surrounded by a mixture of carbon and manganese dioxide. The Leclanché cell produces about 1.5 V.

Another widely used primary cell is the zinc-mercuric-oxide cell, more commonly called a mercury battery. It can be made in the shape of a small flat disk and is used in this form in hearing aids, photoelectric cells, and electric wristwatches. The negative electrode consists of zinc, the positive electrode is of mercuric oxide, and the electrolyte is a solution of potassium hydroxide. The mercury battery produces about 1.34 V.