Why is an ice cube only misty at its centre

Most ice cubes look misty at their centre, but are otherwise quite clear. The ice from which the ice cubes are made is usually obtained from the tap, so it contains dissolved impurities such as chlorine (to ensure its sterility) and gases from the atmosphere. The mist at the centre of the ice cube comprises millions of minute air bubbles containing these gases, principally nitrogen and oxygen. 

Gaseous oxygen readily partitions with oxygen dissolved in solution, in much the same way as the partitioning of CO2 in the fizzy-drink example above. The exact amount of oxygen in solution depends on the value of K(partition) which itself depends on the temperature. 

Tap water is always saturated with oxygen, the amount depending on the temperature. The maximum concentration of oxygen in water - about 0.02 mol dm-3 - occurs at a temperature of 3 °C. The amount of oxygen dissolved in water will decrease below this temperature, since (partition) decreases. Accordingly, much dissolved oxygen is expelled from solution as the water freezes, merely to keep track of the constant decreasing value of K(partition). 

But ice cannot contain much dissolved oxygen, so air is expelled from solution each time an increment of water freezes. This oxygen enters any liquid water nearby, which clearly resides near the centre of the cube. We see how the oxygen from the water concentrates progressively near the cube centre during freezing. 

Eventually, all the oxygen formerly in the water resides in a small volume of water near the cube centre. Finally, as the freezing process nears its completion and even 

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