The Morton Salt Compant instroduced a logo and slogan for advertising its salt in 1911. This is one of the oldest and most successful ad campaigns ever, but what does it mean and where and why did they come up with it?
(describe the chemical basis for it)
One of the difficult things to do when storing salt is to keep it dry, a small amount of moisture will cause the crystals to clump together so that the salt does not flow. This is especially annoying to diners in restaurants who want the salt to flow freely from the salt cellar.
The logo shows salt flowing freely from a salt container while the girl is under an umbrella in the rain. Thus demonstrating that the salt will flow freely even when the air is damp.
The salt manufacturers add a small amount of a compund that forms a crystalline hydrate. So this material picks up the water, rather than the salt. A typical material added is magnesium carbonate or sometimes magnesium sulfate. Magnesium carbonate forms a number of hydrates see http://en.wikipedia.org/wiki/Magnesium_carbonate
Hope this is useful