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World’s Oldest Experiment Drips On

World’s Oldest Experiment Drips On

Australians ask: if it drips every 11 years, is it liquid?

John Mainstone, University of QueenslandIt’s a problem most scientists don’t have; what would happen if your experiment outlived you? For physicist John Mainstone at the University of Queensland, this has become an important question. He’s the leader of what’s being called the world’s oldest experiment.

In 1927, physicist Thomas Parnell became interested in the properties of pitch, a hard, brittle material made from oils and tars in coal and sometimes wood. It’s used for floor coverings, paints and varnishes. And, 83 years ago, Queensland researchers decided they needed to know whether to call pitch a solid or a liquid.

Mainstone, now 78, took over the study in the early 1960s when he came across Parnell’s experiment in a cupboard, quite by accident (Parnell died in 1948). He and his team are watching as the sample of pitch, set up in a glass funnel enclosed in a glass container, slowly creates a drip. And the excitement’s building for the research team; the ninth drop since the experiment started is beginning to form! Any year now!

Pitch Drop 3The pitch’s last drop was in 2000 (13 years ago), and before that, the pitch plopped in 1988. The first drop fell in 1938. Now, three webcams are trained on the pitch experiment, to make sure none of the excitement is missed.

The pitch experiment was set up to illustrate how everyday materials can have unusual properties. Pitch, which once was also used to plug the bottoms of boats, is usually brittle at room temperature, but its more liquid properties show how materials can change over time. Since using a material for 83 years isn’t out of the question, it becomes important to know how materials change over time (in this case, creating a liquid property every 11 to 13 years). Glass, for example, can flow as something like a liquid very slowly, which explains the peculiar shape of glass in 200- or 300-year old buildings.

In 1984, in fact, researchers published a report in the European Journal of Physics that showed they could mathematically predict the rate of dripping for pitch (at least this pitch). They also calculated that the viscosity of pitch is at least 100 billion times greater than water. But it’s still not a solid. And in 2005, Mainstone and the late Parnell were awarded the Ig Nobel award for physics, from the Annals of Improbable Research.

The experiment has not been bereft of hazards, however. Pitch dripping seems to be affected by temperature, and the experiment was never placed in a controlled setting. So when air conditioning was installed in the physics building at the university, this threw off drip creation for a while.

One burning question remains from the pitch experiment; why it happens. Mainstone theorizes that fibrous materials in the pitch may break apart in order to form the drip, but hasn’t confirmed this. Further testing will no doubt be left for Mainstone’s students and protégés.

Sources: University of Queensland, Nature, Improbable.com

Photos: Wikimedia Commons, Philosophy of Science Portal

Edgeworth, R., Dalton, B., & Parnell, T. (1984). The pitch drop experiment European Journal of Physics, 5 (4), 198-200 DOI: 10.1088/0143-0807/5/4/003

university physics experiment, john mainstone

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1 Comment

  • Jack
    May 3, 2013, 17:22

    Didn’t the glass thing turn out to be wrong? I thought the greater thickness of the bottom of glass panels turned out to result from uneven glass forming techniques combined with builders smart enough to put the panes in thick side down?

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