Dry ice, or Cardice – as British researchers call it, is a solid form of carbon dioxide. When carbon dioxide is cooled below temperatures of -78.5 degrees centigrade, the gas gets directly frozen into a solid form. -78.5 degrees centigrade is extremely cold, and handling dry ice without proper protection can be very dangerous – could cause frostbite / burns. The point being, it’s extremely cold.
Since it’s too cold compared to something at room temperature, even everyday objects at room temperature can make it vaporize. A simple metal coin at room temperature would feel like a hot pan to dry ice. So, when a coin is shoved into a piece of dry ice, it creates a funny sound, just like water would, on a very hot pan; or, you could say the sound be very much like a hot metal ball being dropped into a cold bath of water (the temperature difference being much less in this case, of course).
This is how it works: The metal piece at room temperature vaporizes some amount of carbon dioxide from the piece of dry ice when it comes in contact. There’s a pressure difference (Bernoulli’s principle) associated with this process and the gas tries to escape. This makes the metal vibrate very fast, creating that funny sound. This is how it sounds…
Metals work best because they have a good thermal conductivity. For the sake of trying it out yourself, if you have a piece of dry ice lying unused, you could dip a spoon in hot water and make it touch the piece of dry ice. A slightly warmer spoon will probably give you a better effect. And then the spoon will be singing…
An experiment so slow that a professor overseeing it, died without having seen the results for half a century! The Pitch Drop experiment, started by Professor Thomas Parnell of the University of Queensland in the year 1930, is the probably slowest science experiment and also holds the Guinness World Record for the world’s longest continuously running experiment ever.
What is the experiment?
It is an experiment designed to measure the flow of a solid looking piece (image) which is actually an extremely viscous liquid (actually a Viscoelastic Polymer) with a viscosity of approximately 230 billion times that of water. The name used for this class of extremely viscous liquids is, Pitch – Bitumen, Asphalt, Resin and Rosin are a few examples (not Glass). These things are so viscous that you can strike them with a hammer and see them shatter into sharp flakes (like glass), but it flows. The experiment is explained in detail, in the first few minutes of this radio show attached below. (the second half is pretty interesting too, but that is for some other day)
Other unbelievable materials previously covered in this series – Aerogels and Superhydrophobic surfaces.
Side note: The overseer of this experiment, Prof. John Mainstone actually lived through the drops of pitch falling three times, but unfortunately missed watching it happen every time (for 3 times in 50 years). In all, 8 drops have fallen since 1930.
- 1979 – He missed it because he wasn’t in the laboratory for the weekend.
- 1988 – Missed it because he went out for a tea break.
- 2000 – A camera was installed as a precautionary measure, the equipment malfunctioned; missed again!
He recently died waiting to see it in action. Since then, three web cameras have been installed as a fool proof measure to record the extremely rare event. You can watch it happening online here, although you might have to wait for several years to see it happening. (To confirm the live stream, look at that clock in in it and confirm with time here). There is also a time-lapse from 28th April 2012 – 10th April 2013 compressed into a 10-second-long video of the drop forming, embedded below.
A parallel experiment running at Trinity College, Dublin also wasn’t able to capture the rare scientific event on camera in spite of several drops falling since the commissioning of the experiment (1944). Finally, after 70 years of patient wait, on July 11, 2013 it was recorded on camera.