David Charveny, age 9, of Winston Salem, North Carolina, for his question: 

Is the salt we eat like the salt in the ocean?

A shipwrecked sailor may drift for days on a lonely raft. He may be parched with thirst under the scorching sun.  But he will not take a sip of water from the salty sea. The human body is poisoned by sea water. Yet the most plentiful chemical in the ocean is salt ordinary, harmless table salt.

Dozens of different chemicals drift around in the salty sea. They are broken into fragments too tiny for our eyes to see and dissolved in the water. Most of these dissolved chemicals are particles of salt, just like the snowy crystals of salt that we sprinkle on our food. If we let the water dry up, we can find this ordinary salt in the sea. The evaporated sea water leaves behind a layer of dry and solid chemicals, all mixed together. There is a lot of drdinary salt in the mixture. In fact, more than three quarters of it is the kind of salt we use on our food.

Let's see what happens when we trap a smallish lake of sea water and let the water dry up in the sun. As the water evaporates, it turns into vapor and goes off to mingle with the other gases of the air. But the chemicals dissolved in the water do not dry up and disappear. They are left behind and the shrinking lake gets saltier and saltier. When ' the last drop of water disappears,the chemicals are spread in powdery layers on the floor of the dry lake. Most of these dry dregs are ordinary salt.

Suppose we started our drying up test with one cubic mile of sea water. This is enough water to fill a lake more than 20 feet deep, 10 miles wide and 26 miles long. When the last drop of water evaporated, we could scoop up the powdery drags and weigh them. We would have about 166 million tons of dry chemicals. We would need dozens of freight cars to haul all this material away. We would need lots of know how and a few chemical tricks to separate the powdery particles of table salt from the assortment of other chemicals in the mixture. When the tricky job of separating was done, we would have more than 125 million tons of pure salt, fit to sprinkle on our potatoes.

Scientists use the word "salt" for many different chemicals. Only one of these chemical salts is ordinary table salt. Some of the others are downright harmful. The fancy scientific name for our table salt is sodium chloride. This name tells an expert what its snowy white crystals are made of. They are built from tiny molecules, and each molecule is a  salt in ocean for Thursday, February 15, 1968 package of one atom of sodium and one atom of chlorine. Dissolved in the sea, along with many other chemicals, there is enough sodium chloride to cover every country in the world with a layer of table salt 150 feet thick.

Every year, America uses up about 31 million tons of sodium chloride. We get more than half our supply from the salty water of brine wells. More than a quarter is mined from rocky layers of salty minerals in the ground. We get about five million tons of our yearly quota of salt from the sea. And all of this material is exactly the same sodium chloride that we call table salt.

We need only a trace of table salt on our daily menu and Americans do not sprinkle the yearly harvest of 31 million tons on their food. Most of these mountains of salt are used in science and industry. Shoe makers use salt to prepare their leather. Soap makers, paper makers and glass makers use salt to prepare and process their products. Tons of ordinary salt are used to purify gasoline and soften water. More countless tons are used to create rayon and other textile goods. Besides its duties in the kitchen, sodium chloride has more than 400 other chores in the world of industry.