Pickling salt by John Spottiswood.

This is similar to table salt, but lacks the iodine and anti-caking additives that turn pickles dark and the pickling liquid cloudy. Pickles made with table salt would still be good to eat, but they wouldn't look as appetizing. Pickling salt is available in large bags or boxes in supermarkets, but it's hard to find in cities. In addition to pickling or canning with it, you can also use pickling salt just as you would ordinary table salt, though without the anti-caking agents it may get lumpy if exposed to moisture. To prevent lumps, put a few grains of rice in your salt shaker. To get rid of lumps, spread the salt on a cookie sheet and bake in an oven. Don't substitute reduced-sodium salt for pickling salt when making pickles.