Geeky Physics, Technostalgia



The pitch drop experiment running at the the University of Queensland, Australia. Image from Wiki

Good morning everyone.

Sometime in 1927, a Professor Thomas Parnell of the University of Queensland in Brisbane, Australia, decided to demonstrate to his students that some materials that appear to be solid at room temperature are actually extremely viscous fluids. The material he chose for his experiment was a variety of pitch called bitumen. At room temperature pitch appears to be a solid, to the point where if you hit it with a hammer it will shatter. Parnell heated up a quantity of pitch and poured it into a sealed funnel, and let it settle for three years (talk about long prep times). He then (in 1930) cut the seal on the funnel and let the pitch flow into a beaker. And flow it does: very, very, slowly. Droplets form and fall at the rate of about 1 per decade, with the eighth drop falling on 28 November 2000. The ninth drop is due literally at any time, and the fact that no one has witnessed any of the drops falling so far must be troubling to the experimenters. The university rigged up a webcam in 2000, but it was glitchy when the most recent drop fell and missed it. Maybe this time…

The current group of experimenters have measured the viscosity of the bitumen pitch for lack of anything else to do, and found that it is about 230 billion (2.3×1011) times the viscosity of water. There may be more viscous liquids in the world, but I can’t think of any offhand (I’ve been up too long and my recollection ability is a bit iffy right now. Urrrgh, too much coffee…). Don’t bring up glass as a candidate because glass is not a liquid but an amorphous solid you myth loving credulous cretin(s). Hmph. Some fool trying to be clever brings that up every year and it’s gotten tiresome.

The Guinness Book of World Records records The Pitch Drop Experiment as the world’s longest continuously running laboratory experiment, and there is evidently enough pitch remaining in the funnel for the experiment to continue for another 100 years or so. This record may stand for a while, eh?

  • jeepjeff

    Now that we have atomic clocks and (hopefully) working 24/7 surveillance, we might be able to get even better data points over the next century. I don't see how anyone would tear this down before the pitch ran out (barring force majeure).

  • OA5599

    "The current group of experimenters have measured the viscosity of the bitumen pitch for lack of anything else to do, and found that it is about 230 billion (2.3×1011) times the density of water. "

    The underlined word should be changed to viscosity. Otherwise, they really need to reinforce their floors.

    • The Professor

      Fixed. Sorry about that. Yeah, that would be pretty interesting stuff, wouldn't it? Damn near degenerate matter.

  • mr. mzs zsm msz esq

    Nice product placement there, it just keeps going and going and… Oh wait, never-mind, just for scale then, I see.

  • "There may be more viscous liquids in the world…."

    <img src=""&gt;

    Indeed, "in the world" is the correct place to look. Silica-rich (rhyolitic) magmas are quite gooey, thanks to pervasive polymerization even when molten. This accounts for much of their tendency to produce violent explosions instead of the comparatively gentle effusions so often associated with basaltic eruptions.

    They're harder to rig up in a funnel under a bell jar, however, so bitumen is the way to go.

    • pj134

      You act like he had a geologist that he could just reach out to if he wanted or something. It's not like anyone that frequently comments here studies that sort of thing and he could have talked to them for further information beforehand.

      I know you're an educator, but you're just in Health and Space Sciences after all.

      • No, The Professor already knows that I don't respond to his emails.

        • pj134

          That's why he's already filling the Freeway with bitumen.

          • The Professor

            Yes, he's absolutely useless as a source of information, unless you're interested in Latin.

          • Fortunately I assume everyone is.

          • pj134

            Watch your mouth! His work has been mentioned in the encyclopedia britannica!

          • It's not clear whether that was me.

    • tonyola

      How is "tar" defined in this chart? Strictly speaking, tar is derived from the fractional distillation of coal, while bitumen is a petroleum product. Bitumen can have a much higher viscosity than coal tar. However, bitumen is also sometimes called "road tar" so there is some ambiguity.

      When I was in civil engineering school, I had a friend who thought that my carrying around a textbook called "Introduction to Asphalt" was the most hilarious thing in the world. Needless to say, he was a political science student.

    • The Professor

      The key phrase is "at room temperature". I was thinking of you when I wrote that bit.

      • That phrase is in an entirely different paragraph, so it would have required some sort of willingness to synthesize a greater contextual understanding of the overall work in order to make use of its significance. I preferred to go with the cheap, lazy way out, thanks all the same.

        • The Professor

          What? You teach at a community college? Pardon my error.

  • dee

    I saw this at The National Physics Laboratory in Teddington about ten years ago. I'm sure the one I saw was older. I cant find any reference to it on Google. Can any one shed any light on this?

  • Glass is the same way. Look at an original window in an old house and you'll see that the panes have become thicker at the bottom than at the top as the glass, ever so slightly, "flows" from gravity.

    • Alas, no, this is not the case. Instead, older methods of making relatively inexpensive sheets of glass produced irregular results, so they looked that way from the start. Occasionally one will even come across an example where the glazier put the thicker part at the top.

      • pj134

        I wonder if as they were were installing panes of glass in past generations they were saying "Hey, make sure you put the thicker end at the bottom in order to confound future generations!"

        Probably not.

      • Well. I've learned something new. Time to go home.

        • <img src=>

        • The Professor

          What, you didn't believe me in the post? Philistine….

          • To be honest, I didn't read that part. I apologize, your Professorship, and will punish myself by consuming a delicious pizza.

          • The Professor

            You're taunting me again? Bastard! The pizza that I just ate was definitely not delicious. My wife bought some new kind of "strip" style pizza that was just horrible.

            /and I didn't get to have beer either….

          • It seems that the punishment was on you!

            I had a delicious pizza, and am enjoying a frosty beer right now.


      • The Professor

        See? There's another fool that thinks glass flows at room temperature. Argh!

    • tonyola

      Actually, the consensus among materials scientists now is that glass is an amorphous solid but does not have the properties of a true liquid. There is a fair amount of old glass (2,000 years old and beyond) that shows no evidence of flowing and even where glass has claimed to have flowed like in windows, the supposed flow patterns do not match experimental data with less-viscous materials.

  • You won't get an argument from this mineralogist. Or, most likely, any mineralogist. Clays are sticky.

  • The Professor

    I don't know if there are any detailed accounts by medieval artisans of their craft. Probably not, as most guilds were pretty secretive back then.

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