英文科學(xué)讀本 第二冊(cè)·Lesson 11 Soluble and Insoluble

Lesson 11 Soluble and Insoluble

I want to have another chat tonight, said Fred, "about things which we can dissolve. I suppose Norah can name some of them?"

Oh yes, said Norah. "We can dissolve salt, sugar, alum, lime, and soda."

What do we say about them, because we can dissolve them?

We say they are soluble, said his sister.

Suppose we dissolve salt. Can you tell me what we get?

We get a solution of salt. If we dissolve sugar, we get a solution of sugar.

Teacher told us in our lesson today, said Willie, "that the water which dissolves these things is called a solvent."

Now you know, said Fred, "we once put some bits of flint, wood, iron, and glass into water. Did they dissolve?"

No, said Norah, "they did not dissolve. We cannot dissolve them. They are not soluble."

We have found out, too, said Willie, "that chalk and starch will not dissolve. They are not soluble. Teacher told us that the right word for this is insoluble. Insoluble means not soluble."

I'll try and show you something now that teacher showed us today, said Fred. "Look at this greasy oil-bottle. Suppose we wish to clean it out— to get rid of all the oil. What shall we do?"

Wash it out with hot water, said Norah.

Very well, said Fred, "I'll fill the bottle with hot water and shake it up. I wonder whether the oil has gone," said he, after shaking it well. "No, it has not gone. It is still hanging to the sides of the bottle. The oil is insoluble.

Now I will put some pieces of soda into the water. Look what happens when I shake up the bottle.

Why, the oil mixes up with the water now, said Norah.

Yes, said Fred, "the soda breaks up the oil into tiny drops, and dissolves it.

Water will not dissolve oil; but soda is a solvent for oil and fats of all kinds.

SUMMARY

Flint, wood, and iron, like chalk and starch, will not dissolve in water. They are insoluble. Water is a solvent for sugar, salt, and other things, because it dissolves them. Soda is a solvent for fat and oil.