The world's longest running lab experiment has been going for 85 years

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The world’s longest running lab experiment has been going for 85 years

In 1927, Thomas Parnell started the pitch-drop experiment to demonstrate to his students that pitch, a derivative of coal so brittle it can be shattered with a hammer, is actually a highly viscous fluid. And for 85 years, Parnell’s pitch has been dropping through a funnel at a rate of about one drop every eight or nine years.

Parnell melted the pitch, poured it into a glass funnel, let it cool (for three years), hung the funnel over a beaker, and waited. Eight years later, a dollop of the pitch fell from the funnel’s stem. Nine years after that, another long black glob broke into the beaker. Parnell recorded the second drop but did not live to see the third, in 1954. By then, his experiment had been squirreled away in a dusty corner of the physics department.

The pitch-drop experiment might have fallen into obscurity (or a wastebasket) had it not been for John Mainstone, who joined the physics department at Queensland in 1961. One day a colleague said, “I’ve got something weird in this cupboard here” and presented Mainstone with the funnel, beaker and pitch, all housed under a bell jar. Mainstone asked the department head to display it for the school’s science and engineering students, but he was told that nobody wanted to see it. Finally, around 1975, Mainstone persuaded the department to take the bell jar out for the world to see.

Today the experiment is broadcast on a live webcam. Some of its fans send Mainstone e-mails within minutes if the screen goes black. Despite their efforts, on November 28, 2000, the eighth, and most recent, drop of pitch fell during a camera malfunction. To this day, no one has actually witnessed the moment a drop of pitch has detached and fallen. Mainstone says it’s impossible to predict when future drops will occur, especially because the lapses between will grow longer as gases in the pitch escape and the weight of the pitch in the funnel decreases. He expects, however, that the ninth drop won’t break off before 2013. The experiment is far from complete. Says Mainstone, “It has at least 100 years left if someone doesn’t throw it out.”

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