The University of Queensland has a display containing… Longest running Laboratory experiments in the world. It had gone on for so long that two of his guardians died before they saw any results.
The experiment began in 1927 by Thomas Parnell, the university’s first physics professor. Intended as a showcase for highly viscous materials, Parnell took scraps of pitch material Coal tar distillation – Warm it, put it in an airtight glass funnel, then wait three years for it to settle into the shape of the container. This may seem like a long time to wait for the experience to start, but given the planned length of the demo, it was just a blip.
in 1930, Parnell cut off the stem of the funnel, allowing the highly viscous liquid to slowly flow from the bottom. The experiment has been going on ever since, very slowly. The first drop fell eight years after the start of the experiment, and then fell another five years during the following years 40 years. This experiment has been running now for nearly 100 years, and has been under the responsibility of many different guardians. Parnell and his successor Professor John Mainstone died without seeing the fall for themselves, Professor Andrew White being the present trustee.
But the experiment is now under constant webcam surveillance, which means someone might witness the next experiment. The last drop (until another drop happens) occurred in 2014, as seen here in very quick snapshots.
So, can the experiment tell us anything interesting?
Although the experiment was less controlled than ideal (it is subject to room temperature fluctuations, and the inner diameter of the stem cannot be accurately measured without risk of damaging the experiment), it did hold some surprises for us.
Taking a number of factors into account, it is possible to make a reasonable estimate of the viscosity of a pitch.
“The pitch viscosity is then calculated as q = (2.3 +0.5) x 108 Pa s, which is a huge amount compared to common liquids.” paper On experience he explains. “Water at 20°C has a viscosity of 1.0 x 10-3 Pascal. However, it should be noted that (apart from the superfluidity) it is close to the geometric mean of the range of values considered by physicists – the effective viscosity of the Earth is on the order of 10.20 Ba s.”
This does not fit well with previous expectations.
“The viscosity result from the pitch drop experiment does not agree well with predictions based on it [previous] “The measurements even allow for the enormous variation in viscosity with temperature and the somewhat unknown temperature history of the experiment.” The team writes. “A possible explanation lies in the different viscosities of different bitumen samples – they could have varying proportions of volatile hydrocarbons trapped and this would affect the viscosity.”
if you want to Watch the experience live, you can. Right now, there is a very large bubble forming – but we do not recommend watching for too long as the next decline is expected to come sometime in the 2020s, and there is still plenty of decade left to go.
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