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Pitch is a liquid, finally drips after 69 years

By
Kristen Butler, UPI.com
After 69 years, a tar pitch experiment at Trinity College Dublin is a success. The first drop ever observed proves that pitch is viscous. (Screenshot via Trinity College Dublin)
After 69 years, a tar pitch experiment at Trinity College Dublin is a success. The first drop ever observed proves that pitch is viscous. (Screenshot via Trinity College Dublin)

At Trinity College Dublin, a science experiment started 69 years ago has finally yielded results, after pitch was observed dripping for the first time ever, and proven to be a viscous fluid.

Tar pitch, a carbonic substance also known as bitumen or asphalt, is so thick it appears solid at room temperature.

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Pitch is now estimated to be about 2 million times more viscous than honey and 20 billion times more so than water -- and certainly slower than molasses in January.

The experiment, begun in 1944, has been going so long no one remembers who started it. The pitch was moved to a shelf where it was forgotten, and no one noticed the few drops that fell as it gathered dust.

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To conduct the experiment, pitch is heated and poured into a funnel. After "settling" for up to three years, the funnel is cut and placed over a jar.

Physicists at the college recently began to monitor the pitch again. Professor Shane Bergin remembered the experiment from his time there as a student. He had heard anecdotally that the pitch had dripped before, but it had never been captured on camera.

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He decided to set up webcams to monitor the pitch, so anyone could watch and try to be the first to witness a pitch drop. On July 11, at around 5 p.m., a drop of pitch finally fell.

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A similar, even older, pitch-drop experiment at the University of Queensland in Brisbane, Australia is listed by Guinness as the longest-running laboratory experiment.

John Mainstone has been the experiment's custodian since 1961, though he has yet to personally witness a drip -- which takes anywhere from 7 to 13 years to form. "There were a number of things about [the Dublin video] that were really quite tantalizing for a very long time pitch-drop observer like myself," Mainstone said.

Physicist Thomas Parnell set it up in 1927 to demonstrate the surprising properties of everyday materials. In the 86 years since, the pitch dripped eight drops, with the ninth drop nearly fully formed and about to fall.

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"It was a good old fashioned race," Bergin said of the victory of the Trinity College experiment over their Australian counterparts. "The slowest race in history. We are absolutely delighted."

Asked about the value of the pitch demonstration, Bergin’s colleague Denis Weaire said "curiosity is at the heart of good science, and the pitch drop fuels that curiosity."

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