Simon Quellen Field's book Why There's Antifreeze in Your Toothpaste is a fascinating read. I found the part on adding iodine to table salt particularly interesting because while it seems like it should be a simple procedure, it's actually far more complicated than you'd imagine.

Let's back up a bit. So, why is there iodine in table salt anyway? In the early 20th century, researchers figured out that if they added iodine to peoples' diets it would prevent goiters. And the simplest way to do this seemed to be to add the iodine to salt, which was already being used in a variety of foods. By mid-century, most households used iodized salt, and goiters were basically a thing of the past. But the solution wasn't as simple as it sounds.

Here's the problem. The cheapest and most common form of iodine is (1) potassium iodide. Even though only a tiny amount (less than 1/10th of one percent) is added to salt, the compound will break up and the iodine will evaporate after a short while. So, chemists found a solution - adding (2) glucose (sugar) to the mixture to stabilize things. So salt has sugar in it? Yes, albeit a small percentage (again, less than 1/10th of one percent).

On top of that, (3) Calcium silicate is also added to table salt to help keep it from caking together. Salt grabs water from the air, and the water dissolves the salt. When the reaction is over, you end up with a lump of salt instead of the free-flowing grains that we like. The calcium silicate works because it absorbs water but does not dissolve.

The book goes on to remind us that...

salt is used for everything from making ice cream to keeping meat colorful.

And did you know that salt was added to shampoo to alter its viscosity (thickness)? I didn't, and it definitely surprised me. Be sure to check out Why There's Antifreeze in Your Toothpaste here.