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posted by chromas on Sunday June 09 2019, @08:08AM   Printer-friendly
from the Celsiius-AND-Fahrenheit! dept.

The Mysterious Crystal that Melts at Two Different Temperatures:

In a little-known paper published in 1896, Emil Fischer—the German chemist who would go on to win the 1902 Nobel Prize in Chemistry for synthesizing sugars and caffeine—said his laboratory had produced a crystal that seemed to break the laws of thermodynamics. To his puzzlement, the solid form of acetaldehyde phenylhydrazone (APH) kept melting at two very different temperatures. A batch he produced on Monday might melt at 65 °C, while a batch on Thursday would melt at 100 °C.

Colleagues and rivals at the time told him he must have made a mistake. Fischer didn’t think so. As far as he could tell, the crystals that melted at such different points were identical. A few groups in Britain and France repeated his work and got the same baffling results. But as those scientists died off, the mystery was forgotten, stranded in obscure academic journals published in German and French more than a century ago.

There it would probably have remained but for Terry Threlfall, an 84-year-old chemist at the University of Southampton, UK. Stumbling across Fischer’s 1896 paper in a library about a decade ago, Threlfall was intrigued enough to kick-start an international investigation of the mysterious crystal. Earlier this year in the journal Crystal Growth and Design, Threlfall and his colleagues published the solution: APH is the first recorded example of a solid that, when it melts, forms two structurally distinct liquids. Which liquid emerges comes down to contamination so subtle that it’s virtually undetectable.

Many, many years ago I learned that "If it can't be what (where) it has to be, then it has to be what (where) it can't be!"

The linked story reads like a modern-day whodunnit mystery with false leads and a surprise ending. Knowledge of chemistry is helpful, but is not really required.


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  • (Score: 0) by Anonymous Coward on Sunday June 09 2019, @09:56AM (1 child)

    by Anonymous Coward on Sunday June 09 2019, @09:56AM (#853343)

    This phenomenon adds a fourth category to the relationship between crystalline solids and their melting behavior. Two samples of identical composition of a crystalline solid show:

            Identity if the same crystal structures melt to the same melt

            Isomerism if different crystal structures melt to different melts

            Polymorphism if different crystal structures melt to the same melt

            The curious case discussed here, if the same crystal structures melt to different melts

    • (Score: 2) by Muad'Dave on Monday June 10 2019, @11:52AM

      by Muad'Dave (1413) on Monday June 10 2019, @11:52AM (#853639)

      > The curious case discussed here, if the same crystal structures melt to different melts

      Not exactly. TFA says "Overall, the starting solid is the same, the finishing liquid is the same, and the amount of energy used is the same. The laws of the universe are safe."

      What's different is the energy pathway that the substance takes when melting due to impurities.

  • (Score: 2) by Dr Spin on Sunday June 09 2019, @11:59AM (2 children)

    by Dr Spin (5239) on Sunday June 09 2019, @11:59AM (#853357)

    If it can't be what (where) it has to be, then it has to be what (where) it can't be!

    Or, as Shirlock Holmes wisely put it:

    "When you eliminated the possible, only the impossible remains!"

    --
    Warning: Opening your mouth may invalidate your brain!
    • (Score: 2) by Immerman on Sunday June 09 2019, @12:42PM (1 child)

      by Immerman (3985) on Sunday June 09 2019, @12:42PM (#853365)

      Actually
      "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth?"

      • (Score: 2) by Dr Spin on Sunday June 09 2019, @08:21PM

        by Dr Spin (5239) on Sunday June 09 2019, @08:21PM (#853457)

        My mum's version is much better.

        --
        Warning: Opening your mouth may invalidate your brain!
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