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Finding the Viscosity of Pitch
ColdChrist writes "The University of Queensland has a page about a 72-year-old experiment on the fluidity of pitch. There's a webcam where you can try to become the first person ever to see a drop of the pitch fall; eight drops have fallen since 1930 and the ninth is now forming. The experiment 'demonstrates the fluidity and high viscosity of pitch, a derivative of tar once used for waterproofing boats. At room temperature pitch feels solid - even brittle - and can easily be shattered with a blow from a hammer', but it does flow, as the pictures demonstrate." I know this is going to bring up glass comparisons, so we'll head those off: glass is not a fluid.
The experiment is sitting in a glass cabinet just outside one of the lecture theatres used for a lot of first and second year engineering and science lectures.
When I started in first year (1999), the pitch had formed into an interesting drop, and it provided students with a pretty geeky talking point while waiting for lectures to start.
I remember when we went for holidays one year, and came back to find that the drop had fallen! Everyone was a bit pissed (understandably) that it had fallen during uni hols.
Apparently the rate of drop formation is slowing down due to the air conditioning in the building. Or at least thats a rumour circulating around UQ.
Well, from that very link one can glean: 'There is no clear answer to the question "Is glass solid or liquid?".'. Of course, that does not absolutely preclude the possible truth of michael's assertion, but it does make it seem a little ambigous. Oh, the semantics!
Money for nothing, pix for free
The whole "glass is a liquid" thing is a classic example of one of thos things that people say without really understanding understanding what they mean. This article, which is well written, addresses the two main points that you need to prove that glass isn't a "liquid".
It then refutes the common and to my knowledge ONLY evidence for glass "flowing" on human timescales, the thickness difference in the top and bottom of old windowglass. Windows that are OPPOSITE what one would expect to find and the fact that hanging the windows with the thick edge down was common practice neatly debunks this evidence.
So, READ the whole article before you quote without understanding context...
+++ ATH0 +++
In fact, another page confirms that the 8th drop fell in November 2000, so it is indeed the 9th drop forming.
Patrick Doyle
I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....
As a UQ student, I'm lucky enough to see it once a week. Since its last drop, there's now a big long tail from the drop to the funnel. I imagine that, just like before a drop, the physics staff and students will gather round and place bets on when they think it'll break off. Apparently there is a fair bit of money in it...
/.ed will probably land me (or somebody else) in a great deal of trouble. And of course, no visit to UQ is complete without a visit to kewn.
And this is just one example of how our Federal Government's massive spending cutbacks on higher education, and the consequent reduction in spending on research, can produce breakthroughs in science. But of course, our biggest breakthrough is our Scramjet program -- NASA's hundreds of millions of dollar and hundreds of brilliant scientists and engineers, we did for A$1.5 million (that's about US$7.84), a couple of basements full of shock-tunnels, some second-hand rockets, and a handful post-grad students.
Finally, seeing as everybody enjoys looking at UQ web cams so much, you can also view FoyerCam, an incentive to make us messy students keep out foyer clean in our computer science building. There's more cams here, but having 2 servers
As a glass scientist, I wanted to add my 2 cents worth. Almost any substance can occur in a glassy state if quenched fast enough. This includes most metals, plastics, and pitch. Below a critical temperature (the glass transition temperature Tg) a glass is a brittle, perfectly Newtonian solid. At temperatures above Tg, viscosity decreases to the point where relaxation can occur, and the substance becomes rubbery, then fluid. The apparent viscosity at Tg is ~ 10^13 poise. Real motion is observed at ~10^8 poise. The Tg of optical pitch is a bit below room temperature, and the room temperature viscosity is ~10^9 poise. The problem with the experiment cited is that temperature fluctuations change the viscosity exponentially. Droplet formation time will vary accordingly.
I've done some amateur optical work myself, and I know the properties of pitch first-hand. It's worth mentioning that the stuff sold as "pitch" these days isn't really pitch. Proper pitch is a pine-tar product; it smells nice and piney, but it's abominably sticky and subject to enormous changes of viscosity with respect to temperature, and also dangerously flammable. When the old writers like Rev. Ellison write about pitch, this is the material they mean.
Since then, high-boiling coal-tar and petroleum fractions have been formulated which resemble pitch in their physical qualities, but which are much more predictable and constant in their properties, and safer to work with (but smell like roofing tar when they're hot.) "Gugolz" pitch is a petroleum product. "Asphalt" would be a more accurate name, but "pitch" has come to mean any dark-colored organic tar.
One nit: ferric oxide (iron(III) oxide), not ferrous oxide, is the composition of red optical rouge. The cerium oxide used for polishing is the quadrivalent oxide, ceric oxide (cerium(IV) oxide), I believe.
One of the old writers (Ellison, maybe?) writes that if you put a cork at the bottom of container of pitch, the cork will eventually rise to the top. I don't know if this experiment has ever been tried.
My own mirror-making project eventually failed, by the way. I never got a good polish and eventually I gave up.
hyacinthus.