Selenium Cell

   Selenium was discovered by the chemist Berzelius in 1817, and in 1873 Smith found that its resistivity was a function of the intensity of the illumination falling on the surface of the material. The first selenium cell was made by Siemens in 1876, and was made by winding two thin platinum wires to the surface of a sheet of mica, and then covering the surface with a thin film of molten selenium. The large surface-to-volume ratio was necessary because photoconductivity is a surface effect, while the resistivity of the selenium is quite high.

   The selenium cell was used as the detector for an optical communication system developed by Alexander Graham Bell in 1879-80. This example at the right is at Kenyon College; the active area is the small dark rectangle in the black-surfaced base. A very similar cell was sold by Max Kohl of Chemnitz about 1900 for 40 Marks.

   On the right is a selenium cell made by Kips of Delft, Holland, and in the collection of Denison University.

REFERENCE: Thomas B. Greenslade, Jr., "The Photophone", Phys. Teach., 17, 382-382 (1979)
   The selenium cell at the left is exactly like the cell at the right, above. Here it is mounted on a stand and is shown with its sliding cover closed. 

   It is in the Greenslade Collection.

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