The pitch drop experiment began in 1927 when Professor Thomas Parnell of the University of Queensland in Brisbane, Australia, set out to demonstrate to his students that some substances that appear to be solid are in fact very high viscous fluids. He used tar pitch, a derivative of coal once used to waterproof boats, in an experiment to prove his point. At room temperature, pitch appears to be solid and can even shatter if hit with a hammer, but despite its look and feel, pitch can also flow at room temperature, albeit extremely slowly.
For his experiment, Parnell melted some pitch into a glass funnel with a sealed stem and allowed it to cool for three years. In 1930 he cut the sealed stem, hung the funnel over a beaker, and waited. It took eight year before the first drop fell into the beaker and another nine years before the second drop hit. Parnell didn’t live to see the third drop fall in 1954, as he passed away in September 1948. By then, the experiment was stored away in a cupboard of the physics department.
The Pitch Drop Experiment with its current custodian, John Mainstone in a picture taken in 1990.
The pitch-drop experiment might have fallen into obscurity had it not been for John Mainstone, who joined the University of Queensland physics department 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 publicly display the experiment in a cabinet in the foyer of the department building.
Today the experiment is broadcast on a live webcam. The eighth and most recent drop fell on November 28, 2000, but it couldn’t be recorded as the camera malfunctioned when it fell. To this day, no one has actually witnessed the pitch drop fall, but you could try your luck.
The Pitch Drop Experiment on webcam
The experiment was not originally carried out under any special controlled atmospheric conditions, meaning that the viscosity could vary throughout the year with fluctuations in temperature. However, sometime after the seventh drop fell in 1988, air conditioning was added to the location where the experiment resided. The temperature stability has lengthened the interval between each drop.
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. Mainstone says that it has at least 100 years left if someone doesn’t throw it out.
In October 2005, John Mainstone and the late Thomas Parnell were awarded the Ig Nobel Prize in Physics, an America parody of the Nobel Prize, for the pitch drop experiment.
The experiment is also recorded in the Guinness Book of Records as the world's longest continuously running laboratory experiment.
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