This Is The World's Purest Water Drop

Image: TU Wien / EurekaAlert

You might think glacial water melted by a virgin flame (whatever that is) would give you the purest H2O. Not quite. In fact, it'd be utter bilge compared to this delicious, laboratory-made dew, created using a combination of a vacuum chamber, titanium dioxide and a "cold finger".

The trick is to start with a very clean surface and pure ice, according to Professor Ulrike Diebold of Vienna University of Technology's Institute of Applied Physics. You also need a vacuum, as contact with air introduces impurities:

"In order to avoid impurities, experiments like these have to be carried out in a vacuum," [says Diebold]. "Therefore, we had to create a water drop that never came into contact with the air, then place the drop on a titanium dioxide surface that had been scrupulously cleaned down to the atomic scale."

This task was made even more difficult by the fact that water drops evaporate extremely quickly in a vacuum, regardless of the temperature.

In order to get the water to stick around for a while, researchers came up with something called a "cold finger". No, it's not what you think, you dirty, dirty people:

The tip of this metal finger is cooled to around -140°C and ultra-pure water vapour is then allowed to flow into the chamber. The water freezes on the tip of the cold finger, producing a small, ultra-clean icicle. The titanium dioxide sample is then placed beneath the finger. When the icicle melts, ultra-pure water drops on to the sample.

So, what's the point of doing all this? Are they releasing a brand of bottled water so clean it'll put Evian and Fiji out of business? Actually, it was to figure out where "molecular dirt" — a layer of acetic and formic acid that forms on a surface when it touches air — comes from.

Using this ultra-pure water (and one made from soda water), there was no "dirt" to be found:

The surface was then investigated using high-powered microscopes, but the scientists saw no traces of the unknown molecules ... This means that the molecules must come from something other than water or carbon dioxide.

Cool. I'd still like a sip, though.


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