The pitch experiment: if whisky dropped into Alf’s glass at this pace, he would turn teetotal

Alf has been fascinated since first learning of an experiment begun across the Tasman in 1927. Actually, he is more fascinated by the people who find it fascinating.

It demands much more patience than watching paint dry or grass grow and the Daily Mail today asks: Is this the most boring experiment ever?

It involves scientists watching drops of pitch form.

There have been eight drops in 75 years.

But the rate of fall is slowing. The last drop fell 12 years ago.

The current custodian of the experiment is a Professor John Mainstone.

He has been watching since the 1960s, although he is bound to have muttered “bugger” on five occasions, because he has missed all five drops that have fallen in that time.

The experiment is on public display at the University of Queensland in Brisbane, if you are looking for excitement next time you are in that city.

And what is it intended to establish?

Wait for it, folks…

Drum roll, please…

It is designed to prove pitch is a liquid.

The Daily Mail describes it as the world’s longest-running experiment and says

… the very, very patient scientists in charge are waiting for a single drop of pitch to fall, 12 YEARS after the last one fell.

The ‘pitch drop’ experiment began in 1927 and was designed to show that solid-looking pitch was, in fact, a liquid.

The experiment has been running now for 85 years and it is estimated that it will last for another century.

The Daily Mail explains that a lump of the black substance, which can be broken with a hammer, was put into a glass funnel away back, and the waiting began.

It is estimated the experiment will last for another century

A decade after the late Professor Thomas Parnell, formerly from Cambridge University, began the process, the first of eight drops fell.

The viscous liquid continued its incredibly slow, but inexorable, journey downwards, and in 1947 the second drop fell.

The next drops occurred in 1954, 1962, 1970, 1979, 1988 and lastly in 2000 when the webcam that was trained on the experiment broke at the crucial stage.

Professor Mainstone hopes to be present when the next drop falls from the funnel – it has grown into a perfect teardrop shape and he believes it could fall this year, but 2013 is a better bet.

Here’s the thing that bemuses Alf.

The experiment is attracting a global audience.

Since the webcam was erected next to the experiment it has attracted a large and devoted following of barmy boffins and amateur enthusiasts from around the world.

Indeed, Professor Mainstone was surprised to receive emails from the Inuit people who were watching the experiment online.

Professor Thomas Parnell (1881-1948) conceived the Pitch Drop Experiment as a demonstration experiment

Prof Mainstone, 77, is friendly with Parnell’s son, who is now in his 80s.

‘He said that other people in the physics department didn’t take much interest in it. The students probably laughed at him.

‘It became something of a real oddity and was hidden away in a cupboard and when I started I had to convict the department to put it on display. There were people who thought it should just be thrown out.

‘Before he died in 1948, Parnell would have been there for two drops, so I’ve been there for many more than him. But no one has ever actually watched one fall.

‘The last time it happened I was in London and I got an email saying it was getting close, but I wasn’t worried because we had a camera on it.

‘Then I got an email to say it had happened, which was followed by another email to say the camera had not worked. Hopefully the technology is better now.

‘The closest I have been to seeing a drop live is five minutes away, and on another occasion I left the university thinking it would not drop at least until the next day, but when when I arrived in the morning it had happened.

‘It is very difficult to judge when it is going to drop. But as it gets nearer the pitch hangs by filaments and when one of those breaks it goes.”

As to when the next one will fall, the prof is sanguine:

“It’s got a mind of its own. You’ve got to be a bit philosophical about it.”

He hopes it continues to run after he has gone.

“I think there are another 100 years left and the gaps between drops will get longer and longer.”

For the physics buffs among his constituents, Alf can recommend a scientific paper published here.

THE PITCH DROP EXPERIMENT

R. Edgeworth, B.J. Dalton and T. Parnell

Department of Physics, University of Queensland, St. Lucia, Qld 4067, Australia

Abstract
An account is given of an experiment, begun in 1927, to illustrate the fluidity of pitch.

Introduction
In the foyer of the Department of Physics at the University of Queensland in Brisbane is an experiment to illustrate, for teaching purposes, the fluidity and the very high viscosity of pitch, set up in 1927 by Professor Thomas Parnell, the first Professor of Physics there.

The pitch was warmed and poured into a glass funnel, with the bottom of the steam sealed. Three years were allowed for the pitch to consolidate, and in 1930 the sealed stem was cut. From that date the pitch has been allowed to flow out of the funnel and a record kept of the dates when drops fell. The observations which appear in the illustration are brought up to date in table 1. The pitch in its funnel is not kept under any special conditions, so its rate of flow varies with normal, seasonal changes in temperature.

An estimate can be made of the viscosity of pitch assuming that the flow through the stem (length l, diameter d) obeys Poiseuille’s law as modified to take into account the weight of the pitch in the stem itself. As the volume of pitch in the funnel is relatively large, the pressure at the top of the stem of the funnel is assumed to be given by the hydrostatic expression P_A + \rhogh, where \rho is the density of pitch, h is the depth of pitch in the funnel and P_A is the atmospheric pressure. The pressure at the exit of the stem is taken to be P_A, thus ignoring for the present the possible change in the pressure at this point due to the formation of the pendant drop of pitch. With these assumptions the volume V of pitch that flows through the tube in time T is given by

V/T = (pi d^4 \rho g)/(128 \eta)*(1 + h/l)

And there’s lots more where that came from.

Fair to say, this is an award-winning bit of physics.

Two awards, at least.

The Brisbane Times reported on the experiment earlier this year and mentioned the awards.

Having dripped just nine drops in 81 years, it is recognised by the Guinness Book of World Records as the longest running experiment in the world.

Having won Professors Mainstone and Parnell a Ig Nobel Prize in 2005, it currently sits proudly in the lobby of the Physics Department, needing no special attention apart from being kept at room temperature.

The Ig Nobel Prizes honor achievements that first make people laugh, and then make them think.

The official website says prizes are intended to celebrate the unusual, honour the imaginative — and spur people’s interest in science, medicine, and technology.

Alf prefers his own experiment.

He wants to know how long it takes for a nip of scotch to fall into a glass when poured from a bottle just four inches above the top of the glass, and then for the glass to be emptied.

Ooh look. No time at all.

This just goes to show…

… that liquor pours quicker than pitch.

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One Response to The pitch experiment: if whisky dropped into Alf’s glass at this pace, he would turn teetotal

  1. Anon says:

    With regard to your experiment, good scientific practice is to repeat experiments to ensure they are generalizable… 🙂

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