Clark cell
The Clark cell, invented by English engineer
Chemistry
Clark cells use a
Construction
Original cell
Clark's original cell was set up in a glass jar in a similar way to a gravity Daniell cell. The copper cathode was replaced by a pool of mercury at the bottom of the jar. Above this was the mercurous sulfate paste and, above that, the zinc sulfate solution. A short zinc rod dipped into the zinc sulfate solution. The zinc rod was supported by a cork with two holes — one for the zinc rod and the other for a glass tube reaching to the bottom of the cell. A platinum wire, fused into the glass tube, made contact with the mercury pool. When complete, the cell was sealed with a layer of marine glue.
H-form cell
The H-form cell was introduced by
Characteristics
The cell yields a reference EMF of 1.4328 volts at a temperature of 15 °C (288 K). Reference cells must be applied in such a way that no current is drawn from them. The design had two drawbacks—a rather large temperature coefficient of −1.15 mV/°C, and corrosion problems caused by the platinum wires alloying with the zinc amalgam connections where they enter the glass envelope.[citation needed]
In 1905, Clark cells were supplanted as a voltage standard by the more temperature-independent Weston cell.[1]
Sources
- Practical Electricity by W. E. Ayrton and T. Mather, published by Cassell and Company, London, 1911, pp 198–203
See also
References
- ^ a b Hamer, Walter J. (January 15, 1965). Standard Cells: Their Construction, Maintenance, and Characteristics (PDF). National Bureau of Standards Monograph #84. US National Bureau of Standards.