Seven Decade-Long Experiment Catches Tar Dripping For First Time
July 19, 2013

Seven Decade-Long Experiment Catches Tar Dripping For First Time

[Watch Video: Pitch Drop Experiment Comes To An End]

Brett Smith for - Your Universe Online

Set up by Ireland's Trinity College in 1944 and Australia's University of Queensland in 1927 -- a very specific event had never been witnessed before. Even an attempt to catch it with a webcam in 2000 failed because of an equipment malfunction. It represents the world's longest running experiment.

If you're thinking "get to the point!" then you might know the frustration of observers who have been watching for the climax of a seven-decade experiment -- a single drop of highly viscous tar pitch falling from a funnel into a glass jar below.

And last week, it finally happened.

Tar pitch is a hard organic material that can shatter when hit with a hammer, but can have liquid properties under certain conditions.

"Nobody has ever witnessed a drop fall in such an experiment -- they happen roughly only once in a decade!" said a statement on the experiment's official website.

In 1944, a scientist at Trinity College in Dublin heated some tar pitch and placed it in a funnel. The funnel was placed over a jar and the wait began. Over the years, scientists and students would track the progress of the pitch -- hoping to catch that single moment when a drop separated from the funnel and fell into the jar below. It eventually became known as the Pitch Drop.

Catching a pitch drop has proved notoriously difficult over the years. At a similar experiment in Australia, University of Queensland professor John Mainstone took a tea break from watching a precipitously hanging drop only to come back into his lab after 15 minutes and see that it had fallen. Years later, Mainstone and his colleagues set up a webcam to catch another drop. An unfortunately timed equipment malfunction led to another unwatched drop falling.

In May, Dublin researchers noticed that a new drop had begun to form at their pitch drop experiment and a webcam was set up. On July 11, the event was finally seen and captured on video.

"For me, it summed up why I like being a scientist," pitch drop curator Shane Bergin of Trinity's School of Physics told RTE News. "It acts as a catalyst for curiosity, and that's, for me, what the driving force of science is."

With Trinity's drop finally caught, the university's physicists were able to calculate tar pitch's precise viscosity -- about 2 million times the viscosity of honey. The scientists have published a report of their findings in the journal Nature.

For those who missed the Dublin drop, a webcam is still trained on the Queensland pitch drop, which is 83 years in the running. The ninth drop has just formed and appeared quite precipitous at last check.

"If you're interested in trying your luck, or at least just having a look at the experiment, you can watch the live view," said a statement on the webcam's official site. "You can also see students of The University of Queensland milling around outside the cabinet, so it is more exciting than watching grass grow!"