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“Fixed Points” for all substances?

Discussion in 'Science' started by tesolmath, May 22, 2019.

  1. tesolmath

    tesolmath New commenter

    Hi! I ran across an odd item on a review exam of some sort - a multiple choice item that asked for a label that applied to boiling point (BP) and melting point (MP) for any or all substances. The best answer seems to be “fixed points” but I have been unable to locate a term that applies as generally as used for this item. Specifically, with respect to water at one atmosphere, BP and MP have been used as fixed points to establish Fahrenheit and Celsius systems for measuring temperature. Have BP and MP for other substances also been referred to as “fixed points”? I can’t find a citation or reference. Any input? Thanks!!
  2. phlogiston

    phlogiston Star commenter

    Off the top of my head (and Wikipedia), the Celsius scale was constructed around the boiling and freezing points of water. Fahrenheit's scale had 0 degrees as the melting point of a water, sodium chloride ammonium chloride mix, and 96 degrees as human body temperature. This was refined to the mp and bp of water at 32 and 212.
    I do not think that any other substances are used to calibrate the scales.
    tesolmath likes this.
  3. tesolmath

    tesolmath New commenter

    But ... are the BP & MP of substances (in general) often (or ever) referred to collectively as “fixed points”?
  4. phlogiston

    phlogiston Star commenter

    I've never heard this.
    If I was involved in setting up the calibration of temperature scales, I might well have considered having a fixed point somewhere round the 1000C mark. There's a big difference between water boiling and transition metals melting.
    I am sure there are good reasons why this hasn't happened.
  5. border_walker

    border_walker Lead commenter

    plural noun: fixed points
    1. 1.
      a well-defined reproducible temperature which can be used as a reference point, e.g. one defined by a change of phase.

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