Pitch drop caught on camera after 69-year wait

It took 69 years, but at last we've seen the pitch drop. One of the world's longest-running experiments climaxed last week, when a finger-sized bulb of pitch (bitumen) separated from its parent bulk and dropped into a beaker. For the first time ever, this fleeting event has been recorded on video.

The pitch drop experiment was set up at Trinity College Dublin, Ireland, in 1944. The original version of the experiment, at the University of Queensland in Australia, has been running since 1930, but various glitches have prevented that team from actually seeing a drop separate.

"No one has ever seen a drop fall anywhere in the world," says Trinity's Shane Bergin, whose webcam recorded the event on 11 July. "It's one of the oldest experiments ? an oddity, a curiosity."

Pitch shatters if hit with a hammer at room temperature. Physicist Thomas Parnell set up the Queensland experiment to illustrate that, although it appears solid, pitch is actually an incredibly viscous liquid. (Recent experiments showed that the same is true for "Gorilla Glass", used in smartphones and tablet screens.)

In 1927 Parnell heated a blob of pitch and poured it into a glass funnel with a sealed stem. After letting the material settle for three years, Parnell cut the stem to allow the pitch to drip out and fall. Gravity has since drawn out a gloopy drop about once a decade, and a ninth is expected to fall sometime this year. The long-running experiment has since been added to the Guinness Book of World Records and won an IgNobel prize in 2005.

Perfect pitch

Parnell died having never seen a drop separate, and John Mainstone, the current custodian of the Queensland experiment, has had no luck capturing such an event on camera.

No one recalls who set up the Trinity experiment, which sat on a shelf largely unwatched for years. Bergin recently rekindled excitement in the project and set up a webcam last year so that anyone around the world could join the vigil. The video shows that the drop actually fell in two stages, says Bergin. "There was one heavy fall, and then there was a tiny thread left that was still connected. That broke while I was there."

His colleagues Denis Weaire and Stefan Hutzler immediately started analysing the drop footage, measuring its development over time to figure out that their pitch is two million times more viscous than honey, and two billion times more viscous than water. Weaire has suggested that Trinity hold an annual party on 11 July to commemorate the pitch drop, and to check in on the next drip.

"We have great plans for the next drop and a decade to put them into action," says Bergin. "Within ten years, God knows what kind of technology will be available. We'll be keeping up with that to capture the next one in all its stunning beauty."

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