Bichromate cell, 1876.
© Science Museum / Science & Society Picture Library
The simplest form of one-fluid cell with a liquid depolariser is the bichromate cell invented by Robert Bunsen (1811-1899) and Johann Poggendorf (1796-1877). The bichromate battery was one of a number of different types developed from about 1840 onwards to supply a relatively large current for a long period of time - with earlier types of battery, the current dropped quickly in continuous use, though recovered when disconnected for a while. Bichromate cells were made in several different forms.