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General : Columns : The Elements Last Updated: 12, Nov 2008 - 09:56


Sodium: the Salt of the Earth
By Bowser
9, Jun 2002 - 17:53

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I saw a programme recently about a guy who survived 75 days on a life raft after his transatlantic yacht foundered somewhere between the Canaries and Bermuda. Water, water everywhere and all that, but he abandoned ship prepared -he had a solar still in his survival kit. This allowed him to separate the salt from the seawater water drop by drop as he floated from somewhere off the Canaries right across to the West Indies. Excellently gruesome shots of the lost mariner eating the eyes straight from the fish he had speared. Still flipping around the place too by the look of it as he went for the aqueous humour. When you are really thirsty he explained you go straight for the most moist bits. So the eyes and liver, etc., are by far the preferred delicacies when you are thirsty alone on a raft in the middle of the ocean waiting for the next drip from the solar still. Lucky that he also had a spear gun in his survival kit though.
seasalt.jpg
Why is the sea salty?

We all know that too much salt is bad for you, affecting your blood pressure and all that, but what exactly is wrong with drinking seawater? Don't they warn you about losing too much salt say if you are playing in Japan in the World Cup or doing a trans Sahara endurance race? Even in Castlebar electrolyte drinks are advertised for replenishing salts to help athletes avoid hyponatremia or low blood sodium levels. Also didn't Ghandi led a famous march across India in 1930 for the right of Indians to produce their own salt - salt was subject to monopoly control and taxation by the British overlords? In a hot climate especially salt was a key commodity.

So what's the deal? Apparently, according to the raft guy, when you drink seawater your blood becomes saltier than your internal organs and your body tries to balance up the concentration inside and out of organs such as your kidney, liver, heart, pancreas, eyeballs, brain, etc - osmosis. Effectively it sucks the water out of your internal organs in trying to dilute your blood down to match the sodium concentration in the cells in these internal organs. Organ failure will result if you drink too much and into the bargain you will just feel thirstier than ever. Your cells collapse in on themselves and vital life-supporting enzymes stop working with seizures, irregular heart rhythms, brain shrinkage, and eventually coma before you die.

So if you are adrift on a raft don't drink the seawater. That's what they say anyway. The survival manuals also tell you not to drink urine and, just so as you know, dark coloured urine is a sure sign of lack of water.

But I had a distinct recollection that our blood and intracellular sodium concentration is very close to that of seawater because we evolved originally from an ocean cradle. Checking it up though in that amazing medical textbook called Google (quare name but great stuff) it appears that our blood is only about a quarter as salty as seawater. Perhaps the sea has become much saltier over the aeons since our scaly land ancestors first emerged from the sea. A lot of weathering under the bridge since then to make the sea saltier? Of course if we were all created at the start of the Michealmas Term in 4004 BC a la Bishop Wilberforce then we need a different theory to explain why our blood is salty.

My "favourite" use of sodium is as a coolant. Liquid sodium is hot stuff. It liquefies first at 98°C but doesn't boil until almost 1000°C so it can carry heat away from nuclear reactors that run at very high temperatures - particularly fast-breeder reactors that use Plutonium as a fuel. Dangerous bloody things though. Anyone who has dropped a piece of raw solid sodium into a beaker of water and seen take off can appreciate what is likely to happen if 1000°C liquid sodium metal comes into contact with a stream of super-heated steam! China syndrome territory indeed and it could make Chernobyl look like a picnic.

My other favourite use of sodium in salt is a simple method for catching birds. My mother used to say just sprinkle some salt on the bird's tail and he will be yours, as tame as you want. They'll just perch on your hand and be a pet once they get the salt on the tail treatment. I have visions (memories?) of me as a four-year-old running around like mad with a salt cellar trying to catch up with the sparrows outside the back door.

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Magnificent Magnesium

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