World Library  
Flag as Inappropriate
Email this Article

Clark cell

Article Id: WHEBN0003319776
Reproduction Date:

Title: Clark cell  
Author: World Heritage Encyclopedia
Language: English
Subject: List of battery types, Weston cell, Battery (electricity), Voltage reference, Mercury (element)
Collection: Battery Types, Mercury (Element)
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Clark cell

Clark cell (1897)

The Clark cell, invented by English engineer Josiah Latimer Clark in 1873, is a wet-chemical cell (colloquially: battery) that produces a highly stable voltage. In 1893, the output of the Clark cell at 15 C was defined by the International Electrical Congress as 1.434 volts, and this definition became law in the United States in 1894. This definition was later supplanted by one based on the Weston cell.[1]

Contents

  • Chemistry 1
  • Construction 2
    • Original cell 2.1
    • H-form cell 2.2
  • Characteristics 3
  • Sources 4
  • References 5

Chemistry

Clark cells use a zinc, or zinc amalgam, anode and a mercury cathode in a saturated aqueous solution of zinc sulfate, with a paste of mercurous sulfate as depolarizer.

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 Lord Rayleigh in 1882. It was set up in an H-shaped glass vessel with zinc amalgam in one leg and pure mercury, surmounted by a layer of mercurous sulfate paste, in the other. The vessel was filled, nearly to the top, with zinc sulfate solution. Electrical connections to the zinc amalgam and the mercury were made by platinum wires fused through the lower ends of the legs.

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.

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

References

  1. ^ 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. 
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.