Phosphate Rocks Chapter 33: Equilibrium

Before we investigate what happened next, a word about thermodynamic equilibrium. 

Equilibrium is a beautiful thing. 

For a pure liquid in equilibrium with its vapour, if you know the pressure, you automatically know the temperature and vice versa. If warm ammonia liquid were to spill on to the ground at sea level, vapour would flash off leaving the liquid at exactly minus thirty-three degrees centigrade³⁷. 

The temperature in the spheres at Leith Fertiliser Works was kept just above zero degrees centigrade, so the pressure inside was about four atmospheres. You would experience equivalent pressure if you were to dive down thirty metres in a freshwater lake – Wastwater in Cumbria would do – or twenty-eight metres in the lightly salty North Sea, or twenty-five metres in the saline soup of the Dead Sea. 

On the top of Mount Everest, with a lower atmospheric pressure, the liquid would be even colder, but I don’t recommend carrying a flask of anhydrous ammonia all the way up there just to check. Better to take food, water and oxygen. Trust me on this one.