Study: Water’s really 2 liquids

Water is a funky molecule. You’re probably familiar with some of water’s strangeness: It is the only compound that exists naturally in three phases (ice, liquid, gas) on Earth. Solid water floats in liquid water; for most molecules, the solid form would sink. There are dozens of physical properties that separate water from other liquids.

And our knowledge of water’s oddities just got a little deeper. Liquid water is not just one liquid but two, reported an international group of scientists Monday in the journal Proceedings of the National Academy of Sciences.

In 1985, a team of Canadian chemists first proposed that water might have this dual nature. Since then it has “heavily been debated,” said Anders Nilsson, a physicist at Stockholm University in Sweden and an author of the new study. But Nilsson and his team said they were able to show the transition between the two liquid forms.

They shot X-rays at an unusual type of ice, called amorphous ice, as it transitioned from high to low densities at supercool temperatures (around minus 226 Fahrenheit). The way that the X-rays scattered off the water revealed that the ice became a viscous liquid and then flipped to a less dense but far more viscous liquid. Water can convert between two types of liquid, in other words.

When asked to imagine what it would be like to pour the liquids into a cup, Nilsson said, “If we could hypothetically do such a simple thing there would be a huge effect. The two liquids would separate as oil and water with an interface in between. The difference in density is 25 percent, which is huge.”