The Pitch Drop Experiment: The World's Slowest Drip

Strange Science · September 29, 2026

In 1927, Thomas Parnell, the first physics professor at the University of Queensland in Australia, heated a sample of pitch and poured it into a sealed glass funnel. Pitch is a tar derivative. At room temperature it looks solid, and if you hit it with a hammer it shatters like glass.

Parnell wanted to show his students that pitch is actually a liquid, just an extremely slow one. He let it settle for three years, then cut the funnel's stem in 1930 and let it drip.

Nine drops in almost a century

The pitch drips about once every ten years. The drops so far fell in December 1938, February 1947, April 1954, May 1962, August 1970, April 1979, July 1988, November 2000, and April 2014. The gaps were shorter, about eight years, before air conditioning was installed in the building. After that the room stayed cooler, the pitch got thicker, and the gaps stretched to twelve or thirteen years.

Parnell died in 1948. Two drops fell in his lifetime, but he never saw either one.

The caretaker who kept missing it

John Mainstone took care of the experiment from 1961 until his death in 2013, a total of 52 years. He never saw a drop fall. In 1979 he watched it through the weekend, went home on Sunday evening, and by Monday morning it had come down. In 1988 he stepped out for a drink and missed it again.

In 2000, a webcam was finally set up. Then a thunderstorm in Brisbane disrupted the power just as the drop was falling, and the live feed went dark. Sources differ on the exact details of what failed, but most agree the storm interrupted the camera feed.

Mainstone died in August 2013. In April 2014, about eight months later, the ninth drop came down. It did not cleanly free-fall: it touched the previous drop in the beaker and separated later, during a beaker change.

A record, and a caveat

Guinness World Records lists the experiment as the longest-running laboratory experiment. The apparatus now sits in a glass case in the Parnell Building at the University of Queensland.

One fair caveat: "nobody has ever seen a drop fall" applies to the Queensland experiment. A similar pitch drop experiment at Trinity College Dublin, started in 1944, was filmed mid-fall in July 2013.

As of the last checks we could find (late September 2026), the tenth drop had not yet fallen. The university expects it sometime in the 2020s. A live stream is at thetenthwatch.com.

Sources