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Water Triple Point 273.1598?

  1. Apr 5, 2012 #1
    Water triple point T is 272.16K


    But several internet pages say that water triple point is at 273.1598 K
    http://temperaturemeasurement.wordpress.com/2010/07/08/international-temperature-scale/http://www.duncaninstr.com/pdfs/Temperature%20Measurement.pdf [Broken]

    Which is the source of this number 273.1598?
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Apr 5, 2012 #2


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    Staff: Mentor

    Perhaps a historical artifact? Original definition of deg C used melting and boiling temperatures of water, perhaps 273.1598 is a triple point measured using these old degrees. In 1954, after Kelvin was defined as exactly ##\frac 1 {273.16}## both Celsius and Kelvin slightly changed. But I am just guessing.
  4. Apr 5, 2012 #3
    they are so closed numbers not to to much go through that :D
  5. Apr 5, 2012 #4


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    Gold Member

    The first site you reference states
    which I take that the one temperature is exact.

    I think Borus is correct. The defining of the Kelvin scale left the Celcius scale to be redefined as the triple and boiling point of water and that was "assumed" to be 273.16 K. Experimentation afterwards found the actual triple point was not 0.01 C and therin lies the descrepancy.
  6. Apr 5, 2012 #5
    It seems that the question is "what is the source of the 272.16 value" that you show here.
    I looked at the first link indicated in the post. I did not read it all, it's a long pdf. However it refers several times to the triple point temperature as 273.15..
    The second link does not work for me.

    It is somehow interesting that the triple point of the ionic liquid 1-Methylimidazole is reported as 272.16. Is it possible that you confused some values?
    The link is here:

    For water it is about 273.16K
    Last edited by a moderator: May 5, 2017
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