Pitch drop experiment

In 1927 physicist Thomas Parnell at the University of Queensland set up a funnel of pitch to show that this seemingly solid black material is really an extremely thick liquid. It drips about once every ten years or so. Nine drops have fallen since it began, the ninth in April 2014.

Pitch is roughly 100 billion times thicker than water. Check the university's page for any drop after April 2014.

Context

Parnell poured the heated pitch into a sealed funnel in 1927 and let it settle for three years before cutting the stem in 1930. The first drop fell in December 1938, and the gaps between drops have been roughly eight to fourteen years, with the time varying with room temperature.

The pitch is far thicker than water, and the UQ team quotes a viscosity about 100 billion times that of water, while published estimates differ. Temperature matters because warmer pitch flows faster, so the gaps between drops depend partly on room conditions.

Parnell died in 1948, and physicist John Mainstone looked after the setup for decades until his death in 2013. A similar experiment at Trinity College Dublin, started in 1944, recorded a drop in 2013, which explains why Queensland's is described as the longest-running one. The long wait between drops is why the experiment is often cited as a lesson in patience and in how slowly some materials flow.