THE ICE DESERT

In a single night with a violent northem breeze, the thermometer descended again to - 22º C. Everything was ice. Birds, quadrupeds, amphibians, all disappeared as by enchantment; the holes of the seals closed again, the cracks disappeared; the ice recovered its granite hardness, and the cascades, stopped its fall and became in prolonged crystal icicles. The Ice desert (Julio Verne).

We had seen the peculiar behaviour of the density of the water in the way that if we diminished the temperature below 4º C, water would become less dense, taking place that diminution of density in the point of water freezing. This is due to in freezing state the molecules are structured in a compact form, in such a form that each one is surrounded by other four molecules, so the hydrogen connection which we had seen previously enters in game. When the ice is liquefied, the vibratory energy of molecules break part of this structural arrangement. It allows that some molecules are more compressed and they have more density. Part of this arrangement stays until 4º C. High of this temperature, the water already behaves like another substance more, it diminish its density as we increase the temperature.

That's why we can say that to 0º C the density of the liquid water is 0.9999 g/cm 3 and the one of the ice is 0.92 g/cm 3 , that is to say, a cubical centimetre of ice weighs 0.92 grams , an 8% less than a cubical centimetre of water that would weigh practically 1 gram .

The consequence of this is that, unlike the rest of substances, the congealed water (that is lighter) does not sink in the liquid water completely but a part would be floating over the water while the rest remain submerged as we can observe in icebergs. But what exact proportion remains submerged?

Archimedes was a great Greek mathematician who was born in year 298 A .C. He enunciated a principle which state that a body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid. So, if we have an ice block submerged in water, it is going to be put under two forces, downwards produced by its own weight, and other upwards produced by the principle of Archimedes that will be equal to the weight of the displaced fluid, it means, the weight of the water that would occupy the volume of submerged ice.

If we call V to the total volume of iceberg and V S to the volume that occupy the portion of iceberg that is submerged, we will have, as we can see in the figure, that the weight of iceberg will be worth the product of its volume by its density that since we had seen before for the ice to 0º C has a value of 0.92 g/cm 3 . If we apply the Archimedes´ principle, we will also have an ascending push equal to the weight of the water homeless by the submerged fraction, it means, V s multiply by the density of the water that is 1 g/cm3.

The result is that iceberg will be in a static balance when these two forces are equalled and balanced, it means, V s *1=V*0,92, so we can deduce that the volume of iceberg submerged is worth exactly 92% of the total volume, so 8% of the remaining volume is in the surface which is the one that boats see when they descry an iceberg.

The consequence of this phenomenon is very important for the life in our planet. If the water behaved like a substance more, when the cold winter arrives, the surface from lakes and seas would be the first in cooling off. If water increases its density, it would descend more and more moving the hottest water upwards in order to cool it, so finally all the water would congeal when it reached 0º C and it would become a great compact ice block. The depth of this block, together with the own insulating capacity of the ice, would cause the heat of the warmest stations was not enough to melt a so deep mass of ice and it would only make a fine layer superficial that would isolate to the rest.

Fortunately, the qualities of our miraculous water are other, for that reason when the water cools off and increases its density, this one descends but until reaches 4º C, since a later cooling would make it less dense and it could float on the warmest waters. All of this besides the fact that ice is lighter and tends to float on the water, causes that it is the water of the surface the first one in cooling off and doing of thermal insulator in order to avoid the freezing of the deepest water. Thanks to this, the alive organisms can survive in their habitat during the coldest periods; The winter time would produce the congealed of sea water and summer time couldn't do anything in order to avoid it and finally all ocean would be a great ice block, only with a part of superficial warmer tropical climate water. The life would not exist as we know it in our world and the Earth would be an inert and great ICE DESERT .