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.

Comments

Keeps us from getting bored

[tismith]

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.

Re:Keeps us from getting bored

[richie2000]

And you're telling us that not once, NOT ONCE, in 72 years sitting in plain view in a University milling with students of all sizes, shapes, colours and states of mental health, not once, did first-year students open the glass cabinet and replace the pitch with feces? Not ONCE? Not even a little bit? Pull the other one, mate.

Oh wait, this isn't in the US, is it? Nevermind...

Re:Keeps us from getting bored

[machine of god]

I admit, I shook the case, I'm sorry...

The Fluidity of Glass

[richie2000]

glass is not a fluid

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!

Re:The Fluidity of Glass

[flamingmoose]

Q: Is glass solid or liquid?
A: Yes.

Seems like a clear answer to me.

An epiphany!

[echucker]

Ya know, ppl sitting around eating pizza waiting for this to happen is how they get too fat to work for the FBI! ;-)

Kelvin's experiments

[Bazzargh]

Lord Kelvin (William Thomson) created an older pitch experiment: one which had a variety of objects lying on a tray of pitch that are slowly sinking in.

Its usually on show in either the Hunterian Museum or the Department of Physics and Astronomy at Glasgow University.

As I recall, this is considered the oldest continuously running scientific experiment, with the exception only of a wheat-breeding experiment in England? (I can't find references on that, just remember it from back in the mists of time)

BTW: it is more fun to watch paint dry - its faster...

Did michael read his "glass is not a fluid" link?

[pmc]

Apparently not, or the link would have been "Is Glass liquid or solid?", the actual title of the article. I'll repeat the start of its conclusion here:

There is no clear answer to the question "Is glass solid or liquid?". In terms of molecular dynamics and thermodynamics it is possible to justify various different views that it is a highly viscous liquid, an amorphous solid, or simply that glass is another state of matter which is neither liquid nor solid. The difference is semantic.

Couldn't resist...

[Anonymous Coward]

It is pitch black. You are likely to be eaten by a grue.

Cornstarch and Water

[FatAlb3rt]

Reminds me of a cornstarch and water experiment we used to do. Mix it together and you get a weird substance that exhibits properties of solids and liquids. Try it if you're bored...

Re: God's experiments

[cioxx]

I'd consider the universe to be the oldest experiment that I know of, or is it just a very elaborate joke?

In reality God is a hacker who rooted the Universe.

So yes, it's a big experiment (read: Honeypot project)

Pitch is used for polishing optics

[goingware]

Telescope makers and opticians use pitch for polishing glass.

I have a page about telescope making that should give you some jumping off points, but I haven't yet got to the polishing stage of the mirror I'm working on.

One reason for using pitch is that you can press a mirror into it and get a very close fit. Another is that if the mirror is not perfectly spherical, the pitch will flex as the mirror moves across it. And finally, the polishing abrasive (ferrous oxide or cerium oxide) will set in the pitch and have a planing action rather than rolling around and chipping little flakes off as in ordinary grinding.

Pitch is nasty stuff to work with. It takes a lot of practice before a novice telescope maker can make a pitch lap they're happy with.

Re:Pitch is used for polishing optics

[hyacinthus]

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.

coffee

[Tharsis]

Now THAT's how I like my coffee...

Nope

[p3d0]

Do the math. The experiment started in 1927, so the phrase "now, 72 years later" indicates that the web page is three years out of date.

In fact, another page confirms that the 8th drop fell in November 2000, so it is indeed the 9th drop forming.

The glassy state

[infocalypse1]

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.

non-Newtonian fluid

[Kris Warkentin]

That is an example of a non-Newtonian fluid. Normal Newtonian fluids' viscosity is a function of temperature: the colder it gets, the thicker it gets. Non-Newtonian fluids' viscosity is a function of something else, in this case, force. That is, the more force you apply to it, the thicker it gets. If you want a really good and simple 'goop' recipe, try this:

-white glue, mixed with water, 50:50
-tablespoon of borax (from laundry section) in a few cups of water
-(optional) food coloring mixed with glue

pour the glue/water mix into the borax solution and it with thicken up. You'll pull out a slimy, goopy mass that is too watery to play nicely with but if you work it in your hands for a bit to get the excess water out, you'll have some fun. Bounce it around, slap it, tear it and it's more like a solid. Let it sit on your hand and it flows like a liquid. Plenty of fun.