英文科學讀本 第一冊·Lesson 24 Rock-Salt—Table Salt

Lesson 24 Rock-Salt—Table Salt

I want to have a talk tonight, said Fred, "about the salt we use at our meals. Shall we, Norah?"

Oh, that's just what I wanted, said his sister. "I have been looking at the lump of white salt in the cupboard all the week. I can't make out where it came from."

Well then, Fred went on, "teacher tells us that, deep down in the earth, there are great solid beds of salt that stretch for many miles."

Yes, Will joined in, "but it is not lean, white salt, like the salt we see. It looks like stone, it is smooth and shiny, and it is brown, not white. Teacher showed us a piece of it. It is called rock-salt, for it is like rock."

Teacher put a piece of this rock-salt in water, and we saw it dissolve, like other salt, said Fred. "I wonder whether Norah forgets the name for water with salt in it."

Oh no, said his sister quickly, "we call it brine."

Well now, said Fred, "teacher asked us to think about the rain. It falls on the ground, but what becomes of it then?"

Why, it soaks into the earth, said Norah, "because the earth is porous, and absorbs it."

We are making our little girl very clever, said Fred, "but she is quite right. Isn't it jolly, Will, to have a fine teacher? We couldn't tell Norah all these things, if he did not take a lot of trouble to make it easy for us."

That's what I say, said Willie.

Now tell us, Norah, said Fred, "suppose some of this water, as it soak down into the earth, comes to one of these beds of rock-salt. What would it do to the salt?"

Why, I suppose it would dissolve the rock-salt, and make brine, said his sister.

You are right, said Fred. "That is just what it does. Teacher says when men want to get this brine, they bore a hole through the ground, till they come to the bed of salt. Then they put a long pipe down the hole. The brine runs into the pipe, and then they pump it up."

I think I can tell you the rest, said Norah, who was busy thinking. "They boil the brine, and the salt is left behind."

Yes, they do, said Fred. "They boil it in great pans as big as this room. And that is how we get salt for the table."

SUMMARY

Rock-salt is dug out of the earth. It looks like a piece of smooth, shiny stone. Water is always soaking through the earth. Some of this water, as it soaks through, dissolves the rock-salt, and makes brine, and then we get a brine-spring. Men pump up this brine and boil it. The water boils away, and leaves the salt behind. This is the white salt we see on the dinner table.