How do they get the salt and water apart? O, just as easily. They ask the wind to help them. They cut brush about four feet long, and pile it up twenty feet high and as long as they please. Then a pipe with holes in it is laid along the top, the water trickles down all over the loose brush, and the thirsty wind blows through and drinks out most of the water. They might let on the water so slowly that all of it would be drunk out by the wind, leaving the solid salt on the bushes. But they do not want it there. So they turn on so much water that the thirsty wind can drink only the most of it, and the rest drops down into great pans, needing only a little evaporation by boiling to become beautiful salt again, white as the snows of December.
There are other minerals besides salt in the beds in the mountains, and, being soluble in water, they also come down the tiny railroad with musical laughter. How can we separate them, so that the salt shall be pure for our tables?
The other minerals are less avaricious of water than salt, so they are precipitated, or become solid, sooner than salt does. Hence with nice care the other minerals can be left solid on the bushes, while the salt brine falls off. Afterward pure water can be turned on and these other minerals can be washed off in a solution of their own. No fairies could work better than those of solution and crystallization.
MORE GRAVITATION
At Hutchinson, Kan., there are great beds of solid rock salt four hundred feet below the surface. Men want to get and use two thousand barrels a day. How shall they get it to the top of the ground? They might dig a great well--or, as the miners say, sink a shaft--pump out the water, go down and blast out the salt, and laboriously haul it up in defiance of gravitation. No; that is too hard. Better ask this strong gravitation to bring it up.
But does it work down and up? Did any one ever know of gravitation raising anything? O yes, many things. A balloon may weigh as much as a ton, but when inflated it weighs less than so much air; so the heavier air flows down under and shoulders it up. When a heavy weight and a light one are hung over a pulley, the light one goes up because gravity acts more on the other. Water poured down a long tube will rise if the tube is bent up into a shorter arm.
Exactly. So we bore a four-inch hole down to the salt and put in an iron tube.
We do not care about the water. It is no bother. Then inside of this tube we put a two-inch tube that is a few feet higher. Now pour water down the small longer tube. It saturates itself with salt, and comes flowing over the top of the shorter tube as easily as water runs down hill. Multiply the wells, dry out the water, and you have your two thousand barrels of salt lifted every day--just as easy as thinking!
We want a steady, unswerving force that will pull our clock hands with an exact motion day and night, year in and year out. We hang up a string, and ask gravitation to take hold and pull. We put on some lead or brass for a handle, to take hold of. It takes hold and pulls, unweariedly, unvaryingly, and ceaselessly.