"All right, I hope it will turn out well. Meantime, I'll take the cast net and get some shrimps and possibly some fish, and then if I had any thing to bait with, I would set some rabbit traps or something of that sort. But I haven't, and so I can't. Charley can carry on the salt-works while you do whatever it is you mean to do."
The salt-works consisted of nothing more than the kettle. Filling this with clear sea-water, Ned set it to boil, saying:
"Now, Charley, as it boils down add more water, and toward night we can stop adding water and let the salt settle. It will begin to settle before that time, and when it does you can dip the wet salt up from the bottom and spread it out on a plank to dry."
"All right. I'll make a dipper out of a tin cup by fastening a stick to it for a handle. But what makes the salt settle?"
"Why, don't you see? You can only dissolve a certain amount of salt in a certain amount of water; if you put more in it sinks to the bottom, being heavier than water, and stays there. When a liquid has as much of any thing dissolved in it as it can hold, it is said to be saturated; we call it a saturated solution. Now when you boil sea-water it evaporates, and the quantity of water steadily decreases. After awhile so much of the water is evaporated that we have a saturated solution, and then if you evaporate half a pint more of it the salt that a half pint of water can hold in solution must settle to the bottom. It is a curious fact that water which is saturated with one substance, so that it can not hold any more of it, is still capable of dissolving other substances and holding them in solution. Sometimes, in making salt, men take advantage of that fact."
"How?" asked Jack, who had become interested in Ned's explanation.
"Why, by washing out the impurities of the salt with salt water. Having a quantity of impure salt they put it into a funnel-shaped vessel with a small hole in the bottom; then they take clear water and pure salt and make a saturated solution of that; this water cannot dissolve any more salt, but it is still capable of dissolving the other substances which constitute impurities; so it is poured into the vessel that contains the impure salt, and as it passes through it dissolves and carries off the impurities, but doesn't dissolve any of the salt."
"Why can't we purify our salt in that way?" asked Charley.
"Because we have no pure salt with which to make the solution."
"That's so, but I didn't think of it. I wish I knew as much as you do about such things."