weewee has some very rarefied properties . Its solid phase is less dense than its liquid one , for lesson , which is why icebergs float . It also flows more easily when compress . These features are beneficial , perhaps even essential for life . We get it on these oddities are the product of localise arrangements ride by hydrogen bonds , but we have not supervise to form a complete account . Now , an sometime hypothesis about why water has such unusual properties has gained some new evidence .
Decades ago , scientist proposed that if there are two different forms of very stale liquid piddle , it would explicate some of the features we do n’t translate . If so , there should be acritical pointon a temperature - insistence graphical record where these two meet , just as there is for the spiritual rebirth of weewee to ice . However , attempts to find this distributor point have failed , leaving the theory of different water forms controversial . Now Princeton’sProfessor Pablo Debenedetticlaims to have found the critical point ’s location .
Another weewee oddity is that it can be cool well below 0ºC ( 32ºF ) without solidifying , provided it lacks any impurities around which ice crystals can start to form . This supercooling is apopular science demonstrationand supercooled water droplet in eminent - altitude clouds avail shape the weather condition .
Under the conditions available in a school science lab , supercooling means exact water a few degrees below zero . However , under high pressure level and very clean stipulation , it ’s possible to go a lot low-toned than that , and this liquidness - liquid critical point is thought to be at temperatures that would dash even the bravest penguin . Unfortunately , it ’s arduous to make measurements under these shape , so nothing has been through an experiment confirmed .
InScience , Debenedetti and colleague report model the chilling of water under 2,000 times the atmospheric pressure at ocean degree . The two models concord that somewhere between 170 and 190 Kelvin ( -103ºC and -83ºC / -153ºF and -117ºF ) a critical point exists . One of the paper ’s writer , Professor Francesco Sciortino of Sapienza University of Rome , proposed something along these lines in 1992 , but at the time information processing system were not remotely powerful enough to offer anything beyond crude confirmation .
Two computer simulations ( top and bottom jury ) showed large swings in density as supercooled piss oscillates between two fluid phases . Fig B ( justly ): The simulation disclose a critical compass point between the two limpid phases on graphs of temperature and pressure . PG Debenedetti et al , Science
The complexity of the chore of pose the interaction of so many molecules is so bang-up that even today 1.5 years ' worth of research information processing system ' time go into this paper . " Now I can log Z’s well , because after 25 years , my original approximation has been support , " Sciortino aver in astatement .
The paper conclude that when water gets cold enough , it swings between tetrahedral structures of five generally bound particle and a sixth molecule wring inside , producing wild swings in density . Although this occur in conditions far from our everyday experience , Debenedetti say a decisive pointedness ’s existence shape the dimension of a substance under quite different temperature and force per unit area .
Even the serious computer models are not the same as the real earth , and work will cover to confirm these claims by experimentation . The models disagree by about 10 percent on the temperature at which the vital point lies , so they provide only a rough guide on where experimentalists should be looking .
