Okay, it’s pop quiz time. What mineral is used in greater quantities and for more purposes than any other?

Give up? I’ll give you a hint: it’s the only mineral we sprinkle on both our roads and our French fries.

That’s right: salt. Those innocuous little white crystals in the shaker on your table are actually one of the cornerstones of our civilization–not to mention our own bodily well-being.

Common table salt–sodium chloride to its friends–isn’t called common for nothing. It’s found all over the place, especially in the oceans, which contain enough of it to cover the Earth’s surface with a layer of salt 35 centimetres deep should they ever dry out. It’s also found in rivers, inland lakes and seas, as a crust in swamps and dry lake bottoms, and in massive underground beds where ancient bodies of salt water dehydrated. Not only that, more of it is being formed all the time by the actions of rivers and streams on rocks containing chlorides and compounds of sodium.

From a human perspective, the importance of salt begins in our own bodies, which are awash in a saline–salt–solution we call “blood.” The sodium component of salt helps keep the right amount of water in our cells and prevents excessive water loss, while the sodium and chlorine components both play a role in the proper transmission of nerve signals. Salt literally keeps our hearts beating.

Our need for salt explains why our tongues are dotted with clumps of salt-sensitive cells. Our bodies can’t store salt the way they can (unfortunately) store fat, so we have to eat some salt every day. Our built-in desire to stimulate these salt-sensitive taste cells ensures that we get the salt we need. And only sodium chloride is able to fully activate these cells, which is why salt substitutes such as potassium chloride, while they’re better than nothing for those on a sodium-reduced diet, just don’t work as well.

The presence of these salt-sensitive cells also explains why salt makes other food taste better. A plain French fry isn’t able to activate these cells; a salted French fry does, so you get an extra burst of flavor.

Humans have craved salt so much over the centuries that it has even been used as a form of currency–and, governments being what they are no matter what era you live in, heavily taxed. In fact, the English word “salary” originally referred to a soldier’s money allowance for the purchase of salt, and in turn was derived from the Latin word “salarium,” which referred to the salt allotment that was issued to soldiers serving in the Roman army. In those days, when they said someone was “worth his salt,” they meant exactly that.

Salt was valued not only for making food taste good, but also for its preservative qualities, an important consideration in those pre-refrigerator days. High levels of salt are toxic to most cells, so bacteria settling on salted meat, for example, absorb the salt and must then expend a lot of energy pumping it out again–energy that might otherwise be used to produce toxins or reproduce. As well, salt binds itself to whatever water molecules are present, literally drawing them out of microorganisms, dehydrating them.

These days, though, we have a lot more uses for salt than just preserving and enhancing food. Industrially, salt is the principal source of chlorine and its compounds and sodium and its compounds, which is to say salt is vital to the production of such important substances as hydrochloric acid, chloroform, carbon tetrachloride, bleaching powder, washing soda and baking soda.

Salt is used in most textile dyes to keep the colors from running, in soap, glass, plastic and pottery, and to preserve leather hides. It’s used in some refrigeration techniques and to help melt ice off the streets in winter. Both of those uses rely on the fact that the presence of salt lowers the freezing point of water–or, if you prefer, the melting point of ice.

Salt is produced commercially three ways: rock-salt mining, solar evaporation, or solution mining. Rock-salt mining, like any other form of underground mining, basically involves drilling a vertical shaft, blasting out horizontal galleries, and hauling out the debris, in this case, salt. It can then be crushed into several commercial sizes, from 19-millimetre chunks to fine powder.

Solar salt is produced by the evaporation of water from the ocean or inland salt lakes. It tends to be coarser than salt produced by other methods.

In solution mining, naturally occurring underground salt water is pumped to the surface, or water is directed into an underground salt deposit and the resulting brine is pumped to the surface. In either case, the salt solution is purified by the addition of chemicals, then condensed in a series of vacuum evaporators that take away the water but leave the salt behind. How quickly the water is evaporated determines the final size of the salt crystals being produced.

As you’d expect, given the myriad uses for the stuff, vast amounts of salt are produced every year: more than 200 million metric tonnes, worldwide. Does this mean we could soon be facing a salt crisis?

Unlikely; unlike most other minerals, salt is a renewable resource. All our salt originally came from the oceans, lakes and streams, and that’s exactly where it most of it ends up again. The salt we put on the roads washes into the gutters, into the river, and eventually into the sea. Even the salt we eat eventually gets excreted as sweat or urine, and is washed or flushed away–once again, eventually ending up in the sea.

Why, there’s no telling how many exotic places the salt you sprinkle on your French fries might have been before it ended up in your mouth!

Hmm. Maybe I’ll go with the ketchup, instead.

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