'The differences between the two isotopes, H2O and D2O, given here shows the importance of nuclear quantum effects', says Kyung Hwan Kim, postdoc in Chemical Physics at Stockholm University. Now we have found such a maximum, which means that there should also be a critical point at higher pressures.'Īnother remarkable finding of the study is that the unusual properties are different between normal and heavy water and more enhanced for the lighter one. 'For decades there has been speculations and different theories to explain these remarkable properties and why they got stronger when water becomes colder. 'What was special was that we were able to X-ray unimaginably fast before the ice froze and could observe how it fluctuated between the two states', says Anders Nilsson, Professor of Chemical Physics at Stockholm University. It is this ability to shift from one liquid state into another that gives water its unusual properties and since the fluctuations increase upon cooling also the strangeness increases. The water fluctuates between these states as if it can't make up its mind and these fluctuations reach a maximum at -44☌. Water is unique, as it can exist in two liquid states that have different ways of bonding the water molecules together. Now researchers at Stockholm University, with the help of ultra-short x-ray pulses at x-ray lasers in Japan and South Korea, have succeeded in determining that water reaches the peak of its strange behaviour at -44☌. Many more properties such as compressibility and heat capacity become increasingly strange as water is cooled. If you continue to cool pure water (where the rate of crystallization is low) to below 0, it continues to expand - the expansion even speeds up when it gets colder. If you chill water below 4 degrees, it starts to expand again. Strangely enough for the liquid state, water is the densest at 4 degrees C, and therefore it stays on the bottom whether it's in a glass or in an ocean. However, if we look at a glass of ice water, everything is upside down, since we expect that water at 0☌ being surrounded by ice should be at the bottom of the glass, but of course as we know ice cubes float. We would therefore expect that water would have high density at the freezing point. We all are aware that all matter shrinks when it is cooled resulting in an increase in the density. How water's density, specific heat, viscosity and compressibility respond to changes in pressure and temperature is completely opposite to other liquids that we know. Water, both common and necessary for life on earth, behaves very strangely in comparison with other substances. The findings will be published in the journal Science. At -44☌ these fluctuations reach a maximum pointing to the fact that water can exist as two different distinct liquids.

Using x-ray lasers, researchers at Stockholm University have been able to map out how water fluctuates between two different states when it is cooled. Temperatures are specified by the notation ( T s/ T r) with T s representing the temperature at which the sample's density was determined and T r the temperature at which the reference (water) density is specified.Video: Professor Anders Nilsson explains how, using x-ray lasers, researchers at Stockholm University have been able to map out how water fluctuates between two different states when it is cooled. For true ( in vacuo) relative density calculations air pressure must be considered (see below). It is nearly always the case that measurements are made at nominally 1 atmosphere (101.325 kPa ignoring the variations caused by changing weather patterns) but as relative density usually refers to highly incompressible aqueous solutions or other incompressible substances (such as petroleum products) variations in density caused by pressure are usually neglected at least where apparent relative density is being measured.

The density of substances varies with temperature and pressure so that it is necessary to specify the temperatures and pressures at which the densities or masses were determined. Temperature dependence See Density for a table of the measured densities of water at various temperatures. Occasionally a reference substance other than water is specified (for example, air), in which case specific gravity means density relative to that reference.

Density of water at 4c