Decades in the making. The world's slowest dripping liquid revealed

Pitch, often mistaken for black stone due to its appearance, is, in fact, a liquid with a very high viscosity when exposed to high temperatures. But how can one demonstrate that this "stone" is actually a dense liquid? This curiosity led Prof. Thomas Parnell to establish what would become the longest ongoing scientific experiment in history.

The experiment was initiated at the University of Queensland in Australia in 1927. Prof. Thomas Parnell aimed to reveal that pitch, despite its stone-like appearance and the way it hardens and crumbles upon impact, is fundamentally a liquid. To do this, he placed a sample of pitch inside a sealed glass funnel, allowed several years for the funnel's outflow to fully fill, then opened the outflow, covered the setup with a glass dome, and simply waited.

The wait continued until 1938, when, 11 years after the experiment had started, the first drop finally detached from the funnel. Prof. Parnell also witnessed a second drop fall in 1947 before his death, yet his experiment carried on.

Since then, the pitch-sample funnel has remained under watch. Over the years, certain conditions have evolved – notably, the room housing the funnel has been air-conditioned since the mid-80s. This introduction of a stable and slightly cooler environment has substantially slowed the rate at which subsequent drops detach.

• 1927 - Experiment begins
• 1938 - The first drop falls
• 1947 - The second drop falls
• 1954 - The third drop falls
• 1962 - The fourth drop falls
• 1970 - The fifth drop falls
• 1979 - The sixth drop falls
• 1988 - Seventh drop falls
• 2000 - Eighth drop falls
• 2014 - Ninth drop falls

Almost a hundred years have passed since the outset of this unique study. During this lengthy period, nine drops of pitch have fallen. Prof. John Mainstone, who looked after the experiment until his death in 2013, famously experienced terrible timing.

In 1988, during the World Expo 88 exhibition, the experiment was on display when the seventh drop fell after 111 months of anticipation. Unfortunately, in an ironic twist of fate, Prof. Mainstone was out for a drink at the crucial moment, and the event was only captured after the fact.

Since the year 2000, such unfortunate occurrences have been avoidable thanks to the experiment being under continuous camera surveillance. Footage from the camera is available online, provided by the University of Queensland.

Today, anyone can observe The Pitch Drop experiment, although the anticipated tenth drop is not expected to happen for a few more years. Nonetheless, people from all corners of the globe remain eager spectators, with 31 people watching the livestream at the time this article was written.