The ninth pitch drop fell

What I’m about to describe is supposedly the world’s longest-running scientific experiment, and, although we already know the result, it gets demonstrated repeatedly: once every decade on average.

In 1927, Professor Thomas Parnell of the University of Queensland set up an experiment to demonstrate that some substances that appear to be solid, like pitch, are really liquids, and flow at an extremely slow rate. At room temperature, for example, pitch is solid, brittle, and can be shattered with a hammer. But Parnell wanted to show that it was really a liquid in the technical sense.

So, in 1927 Parnell heated up some pitch, poured it into a sealed funnel, allowed it to congeal for three years, and then snipped the neck of the funnel. Over the next 86 years (Parnell died 21 years into the experiment), generations watched the pitch slowly drip from the funnel (nobody’s actually seen a drop fall).

Here’s a photo of the setup:

Screen shot 2014-04-22 at 6.57.43 AM

Longtime custodian of the famous experiment, the late Professor John Mainstone. (Photo from the University of Queensland.)

Up until last week, there had been eight drops, but a ninth just fell on April 10. Here’s a time-lapse video taken over the last two years:

Sadly, the fall isn’t so dramatic, as the latest drop simply glopped onto the one below it, still adhering to the funnel. They need to move that funnel higher up!

There’s another description of the experiment at the University of Queenland’s site, which gives a bit more information:

The experiment was set up as a demonstration and is not kept under special environmental conditions (it is actually kept in a display cabinet in the foyer of the Department), so the rate of flow of the pitch varies with seasonal changes in temperature. Nonetheless, it is possible to make an estimate of the viscosity of this sample of pitch (R.Edgeworth, B.J. Dalton and T. Parnell, Eur. J. Phys (1984) 198-200). It turns out to be about 100 billion times more viscous than water! The first picture in the slide show above is of the late Professor John Mainstone, longtime custodian of the experiment. In the 83 years that the pitch has been dripping, no-one has ever seen the drop fall.

The history (from Wikipedia):

Screen shot 2014-04-22 at 6.46.06 AM

By the way, I’m told that very old windows are thicker at the bottom than at the top, supposedly the result of glass itself flowing downward. I have no idea whether this is true.

h/t: Robert

50 Comments

  1. Greg Esres
    Posted April 22, 2014 at 9:35 am | Permalink

    “I’m told that very old windows are thicker at the bottom than at the top, supposedly the result of glass itself flowing downward. I have no idea whether this is true.”

    Nah, this is a myth. It has to do with the way the glass was manufactured in the middle ages. There are far older glass objects that show no signs of sagging.

    • Charles Jones
      Posted April 22, 2014 at 9:41 am | Permalink

      It is a very appealing myth that was in at least some earlier editions of the introductory geology textbook by Stan Chernicoff. I’ve not checked to see if it has since been removed!

      • Greg Esres
        Posted April 22, 2014 at 9:54 am | Permalink

        It is very appealing and I know that I have repeated it myself. I sure wish it were true!

    • The Militant One
      Posted April 22, 2014 at 9:43 am | Permalink

      I beg to differ, sir. I have a 107 year old house with some of the original windows (I have slowly been replacing them) made from float glass manufactured at the time. And there is indeed a variance in thickness from top to bottom, as measured with a micrometer – something that I did just for shits and giggles.

      • Greg Esres
        Posted April 22, 2014 at 9:53 am | Permalink

        It still is a manufacturing thing, not a flowing thing.

        Glass is technically an “amorphous solid” and it does flow, but would take millions of years to be noticeable.

        • Greg Esres
          Posted April 22, 2014 at 10:03 am | Permalink

          Also, if your expectation is that the bottom should be thicker, it’s easy enough to close the micrometer a little less tightly.

        • WT
          Posted April 22, 2014 at 10:04 am | Permalink

          http://scitation.aip.org/content/aapt/journal/ajp/66/5/10.1119/1.19026

          “The conclusion is that window glasses may flow at ambient temperature only over incredibly long times, which exceed the limits of human history.”

      • madscientist
        Posted April 22, 2014 at 3:28 pm | Permalink

        There is quite an inconsistency of the thickness throughout. However, if you find the bottom part in the installation is consistently thicker then that would have been a deliberate act by the person installing the glass.

    • Posted April 22, 2014 at 10:21 am | Permalink

      As stated, the medieval manufacturing meant that the glass tended to be thicker at one end. It appears that the window installers preferred to put the thicker end at the bottom, thus leading to the mistaken conclusion of flow.

      I believe the Dictionary of Misinformation even states that glass doesn’t flow even in geologic time.

    • Nick
      Posted April 22, 2014 at 2:56 pm | Permalink

      Glass does have some interesting properties though. I remember as a kid (12 or 13)finding out, and subsequently amazing my friends with demonstrations, that I could cut a piece of window glass with a pair or scissors if both were underwater. Anyone else done this?

      • Posted April 23, 2014 at 6:54 am | Permalink

        Well, then!

        /@

        • merilee
          Posted April 23, 2014 at 7:28 am | Permalink

          way cool!! Now I just have to think up a reason to cut some glass…

        • Diane G.
          Posted April 23, 2014 at 6:11 pm | Permalink

          Why on earth is this not more widely known?!

  2. Barry
    Posted April 22, 2014 at 9:41 am | Permalink

    The glass flowing sounds reasonable too. I know I’m 68, and now much thicker at the bottom than the top.

  3. Posted April 22, 2014 at 9:50 am | Permalink

    Is it just me, or does the data from that table suggest that the pitch is slowing down? Any suggestions as to why this might be so?

    My first thought is that it could have to do with airconditioning….

    b&

    • Isaac
      Posted April 22, 2014 at 9:59 am | Permalink

      What comes to mind right away is that fact that, as more pitch is emptied from the funnel, the less weight there is on the remaining pitch pressuring it downward.

    • WT
      Posted April 22, 2014 at 10:12 am | Permalink

      According to Wikipedia (http://en.wikipedia.org/wiki/Pitch_drop_experiment):

      “The experiment was not originally carried out under any special controlled atmospheric conditions, meaning that the viscosity could vary throughout the year with fluctuations in temperature. Some time after the seventh drop fell in 1988, air conditioning was added to the location where the experiment takes place. The temperature stability has lengthened each drop’s stretch before it separates from the rest of the pitch in the funnel.”

      • Posted April 22, 2014 at 10:38 am | Permalink

        Woo-hoo! I guessed right! Yay me!

        b&

    • John Scanlon, FCD
      Posted April 22, 2014 at 10:24 am | Permalink

      No, it’s global cooling! The so-called climate scientists have the trend in surface temperature since the 1970s exactly backwards!! They’ve been HIDING THE DECLINE!!!

  4. Posted April 22, 2014 at 9:51 am | Permalink

    My understanding is that the glass is thicker at the bottom because of the manufacturing process.

    The molten glass was poured into sand or clay to make a sheet. Then the sheet was either cut. Or the glass was poured into a form of the correct dimensions in sand or clay.

    The thicker part was always at the bottom during the install process.

    Although, if the measurement is only determinable via micrometer, then I’m not sure how the glass installers would know to put it in thicker side at the bottom.

    That’s just what I’ve heard.

    • Greg Esres
      Posted April 22, 2014 at 10:00 am | Permalink

      “Although, if the measurement is only determinable via micrometer, then I’m not sure how the glass installers would know to put it in thicker side at the bottom. ”

      Could be an effect that disappears with double blind protocols. :-)

  5. Drew
    Posted April 22, 2014 at 9:56 am | Permalink

    Glass is not a high viscosity liquid:

    http://en.wikipedia.org/wiki/List_of_common_misconceptions#Materials_science

  6. potaman
    Posted April 22, 2014 at 10:01 am | Permalink

    http://www.cmog.org/article/does-glass-flow

    Here is a nice article from the guys at the corning museum of glass that explains the whole thing.

    • JBlilie
      Posted April 22, 2014 at 11:00 am | Permalink

      Excellent article!

    • JBlilie
      Posted April 22, 2014 at 11:02 am | Permalink

      The money quote:

      “Some years ago, I heard a remark attributed to Egon Orowan of the Massachusetts Institute of Technology. Orowan had quipped that there might, indeed, be some truth to the story about glass flowing. Half of the pieces in a window are thicker at the bottom, he said, but, he added quickly, the other half are thicker at the top.”

    • gravityfly
      Posted April 22, 2014 at 1:02 pm | Permalink

      Great article. Thanks!

    • Ronaldo
      Posted April 22, 2014 at 3:58 pm | Permalink

      And the Corning Museum of Glass is a great place to visit. You get to see glass in art, science, history and technoly. From old egyptian and roman glass to Tiffany, fiber optics, a 200″ telescope mirror… I visited in 2010 and loved it.

  7. Neil
    Posted April 22, 2014 at 10:01 am | Permalink

    Greg is correct, window glass does not flow at any measurable rate; the relaxation time constant of window glass is a ridiculous number. And he is also correct that the thickness variation is due to the way they used to manufacture it.

    • Kevin
      Posted April 22, 2014 at 10:31 am | Permalink

      Agreed. The time scales for flow at room temperature are far too long to be measured. Bond energies – on the order of eV. Room temperature – on the order of 1/40 eV. Poisson fluctuation – on the order of <10^-9 eV in a macroscopic object (10^23 particles). Not going to happen for a long time. Though I am not sure this rigorously negates the possibility of flow at room temperature for all time….though it seems unlikely.

      • JBlilie
        Posted April 22, 2014 at 11:01 am | Permalink

        The Corning glass museum shows just how slow. Really, really slow. The age of the universe is need to produce a measurable effect.

        • Greg Esres
          Posted April 22, 2014 at 11:52 am | Permalink

          “age of the universe is need to produce a measurable effect.”

          So, 6,000 years. Gotcha.

          • Mark Joseph
            Posted April 22, 2014 at 8:41 pm | Permalink

            Yes, it’s incredible that every scientific fact reminds us of something idiotic that creationists say and/or believe.

            The first thing I thought of when I read this post was, “Gee, did any creationists ever do an experiment lasting 80+ years?” Nah, they’re too busy riffling through writings of real scientists, trying to find something they can whine about.

  8. Posted April 22, 2014 at 11:28 am | Permalink

    There is a 127 year old experiment still running at Glasgow University. It is a pitch glacier experiment, essentially the same as the pitch drop, started by William Thomson, Lord Kelvin. The experiment continues in the Hunterian Museum in the university. Some give the start date as 1882, but the majority agree on 1887 as its start.

  9. Diane G.
    Posted April 22, 2014 at 11:43 am | Permalink

    Fun and fascinating experiment. However it looks like the third longest; see chart at the end of this article:

    http://www.npr.org/2012/11/23/165030844/experiments-that-keep-going-and-going-and-going

  10. Merilee
    Posted April 22, 2014 at 11:44 am | Permalink

    Why does the clock in the time-lapse seem to be moving backwards?
    Great background music, btw;-)

    • Posted April 22, 2014 at 12:05 pm | Permalink

      The webcam’s clock and the alarm clock are not running at the same rate. It’s why wagon wheels move backwards in old Westerns.

      b&

      • Merilee
        Posted April 22, 2014 at 1:49 pm | Permalink

        Hmmm..had never noticed that in old westerns. Thanks for da clarification:-)

  11. oskar
    Posted April 22, 2014 at 12:14 pm | Permalink

    If the glass thing were true every stone age arrowhead would be a puddle when found

    • madscientist
      Posted April 22, 2014 at 3:32 pm | Permalink

      They were flint, not glass.

      • Posted April 22, 2014 at 3:59 pm | Permalink

        Many were obsidian — or at least, in certain parts of North America if not elsewhere.

        b&

  12. Torbjörn Larsson, OM
    Posted April 22, 2014 at 12:22 pm | Permalink

    I’m confused. Last year I learned that Beale’s seed germination is a longer running experiment. [ http://en.wikipedia.org/wiki/William_James_Beal ] The linked wiki page refers to it. So why shouldn’t we count that?

    But this year I learn from the links that there are still older running experiments. The oldest has been running since 1840 a physics experiment barely beeting the oldest biological (1843). [ http://en.wikipedia.org/wiki/Long-term_experiment ]

    • Torbjörn Larsson, OM
      Posted April 22, 2014 at 12:23 pm | Permalink

      Edit: The oldest has been running since 1840, a physics experiment barely beating the oldest biological (1843).

      • WT
        Posted April 22, 2014 at 1:32 pm | Permalink

        Yeah, there’s definitely some qualifiers on that “oldest running” title. Wikipedia says the pitch drop experiment is “recorded in Guinness World Records as the world’s longest continuously running laboratory experiment.” It appears that the Oxford Electric Bell (1840) and the Beverly Clock (1864) experiments have each had interruptions. I’m not sure why the Beal germination experiment doesn’t qualify. Maybe it isn’t considered to be a “continuously running” experiment?

  13. godsbelow
    Posted April 22, 2014 at 12:23 pm | Permalink

    Well, it’s nice to see that my alma mater is contributing to science.

    (But this doesn’t make up for UQ’s awarding Ken Ham a Diploma of Education, and the air of legitimacy that comes with it.)

    • Tim Anderson
      Posted April 22, 2014 at 1:12 pm | Permalink

      It was the honorary doctorate for Banana Joh that did it for me.

      • godsbelow
        Posted April 22, 2014 at 1:48 pm | Permalink

        I know someone who was in the Senate that awarded Joh that degree. Needless to say, he’s still deeply ashamed.

  14. marksolock
    Posted April 23, 2014 at 8:13 pm | Permalink

    Reblogged this on Mark Solock Blog.


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