A Grenet cell or bichromate cell consists of a flask like glass jar with a hard rubber, porcelain or wood cover. From the cover two flat retort carbon or graphite plates are suspended parallel with an amalgamated zinc plate hanging between them. The zinc plate is supported by a brass sliding rod which allows the zinc to be drawn entirely out of the electrolyte. The electrolyte consists of water, potassium dichromate and sulphuric acid. The E.M.F. of the cell is between 1.92 to 2.20 volts.
The cell was actually invented by German physicist Johann Christian Poggendorff in 1842. It bears the name of Eugene Grenet, Jr. of Paris, France who made it more practical. He was granted a patent in 1859.
The patent number is #25,503.
For those of you interested, the action of this cell is represented by the following equation:
3Zn + K2Cr2O7 + 7H2SO4 = Cr2(SO4)3 + 7H2O + K2SO4 + 3ZnSO4
If you want to mix up a bichromate electrolyte, use 10 parts of water, 1 part of potassium bichromate, and 3 parts of sulphuric acid.
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