Pitch drop experiment

The University of Queensland pitch drop experiment, demonstrating the viscosity of bitumen.

The University of Queensland pitch drop experiment, featuring its then current custodian, Professor John Mainstone (taken in 1990, two years after the seventh drop and 10 years before the eighth drop fell).

The pitch drop experiment is a long-term experiment which measures the flow of a piece of pitch over many years. Pitch is the name for any of a number of highly viscous liquids which appear solid, most commonly bitumen. At room temperature, tar pitch flows at a very slow rate, taking several years to form a single drop.

University of Queensland experiment

The most famous version of the experiment was started in 1927 by Professor Thomas Parnell of the University of Queensland in Brisbane, Australia, to demonstrate to students that some substances that appear to be solid are in fact very-high-viscosity fluids. Parnell poured a heated sample of pitch into a sealed funnel and allowed it to settle for three years. In 1930, the seal at the neck of the funnel was cut, allowing the pitch to start flowing. A glass dome covers the funnel and it is placed on display outside a lecture theatre.^[1] Large droplets form and fall over the period of about a decade.

The eighth drop fell on 28 November 2000, allowing experimenters to calculate that the pitch has a viscosity approximately 230 billion (2.3×10¹¹) times that of water.^[2]

This is recorded in Guinness World Records as the world's longest continuously running laboratory experiment, and it is expected that there is enough pitch in the funnel to allow it to continue for at least another hundred years. This experiment is predated by two other still-active scientific devices, the Oxford Electric Bell (1840) and the Beverly Clock (1864), but each of these have experienced brief interruptions since 1937.

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. Some time after the seventh drop fell in 1988, air conditioning was added to the location where the experiment takes place. The temperature stability has lengthened each drop's stretch before it separates from the rest of the pitch in the funnel.

In October 2005, John Mainstone and the late Thomas Parnell were awarded the Ig Nobel Prize in Physics, a parody of the Nobel Prize, for the pitch drop experiment.^[3]

Professor Mainstone subsequently commented:

I am sure that Thomas Parnell would have been flattered to know that Mark Henderson considers him worthy to become a recipient of an Ig Nobel prize. Professor Parnell's award citation would of course have to applaud the new record he had thereby established for the longest lead-time between performance of a seminal scientific experiment and the conferral of such an award, be it a Nobel or an Ig Nobel prize.^[4]

The experiment is monitored by a webcam but technical problems prevented the November 2000 drop from being recorded.^[5][6] The pitch drop experiment is on public display on Level 2 of Parnell Building in the School of Mathematics and Physics at the St Lucia campus of the University of Queensland. Hundreds of thousands of internet users are checking the live stream each year.^[1]

Professor John Mainstone died on 23 August 2013 following a stroke. He was 78.^[7]

Timeline

Trinity College, Dublin experiment

A similar experiment started at Trinity College, Dublin in October 1944 dripped on July 11th, 2013, marking the first time a pitch drop was successfully filmed.^[8][9]

See also

• Rheology
• William James Beal, Botanist who started a long-running seed germination experiment in 1879

References

External links

• University of Queensland page (also live webcam)
• Picture of the sixth drop shortly after falling
• My Putty Drop Experiment