Pitch drop experiment

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

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. 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. The ninth drop is expected to fall in 2013.

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 pre-dated by two other still-active scientific devices, the Oxford Electric Bell (1840) and the Beverly Clock (1864).

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.

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

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.

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.

To date, no one has ever witnessed a drop fall. The experiment is monitored by a webcam but technical problems prevented the most recent drop from being recorded. 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.

The current drop is expected to fall during the second half of 2013.

Timeline

Date	Event	Duration (months)	Duration (years)
1927	Experiment set up
1930	The stem was cut
December 1938	1st drop fell	96–107	8.0–8.9
February 1947	2nd drop fell	99	8.3
April 1954	3rd drop fell	86	7.2
May 1962	4th drop fell	97	8.1
August 1970	5th drop fell	99	8.3
April 1979	6th drop fell	104	8.7
July 1988	7th drop fell	111	9.3
28 November 2000	8th drop fell	148	12.3

See also

• Long-term experiment
• Rheology
• William James Beal, Botanist who started a long-running seed germination experiment in 1879 that is due to end in 2100

External links

• University of Queensland page (also live webcam)
• Picture of the sixth drop shortly after falling
• Pitch Fever feature article by Trent Dalton - The Weekend Australian, 6 April 2013
• My Putty Drop Experiment