英文科学读本 第二册·Lesson 09 What Starch is

Lesson 09 What Starch is

You remember our chat about starch, Norah? asked Fred. "Would you like to see me make some starch now?"

Ah, said Norah, "I know you are a very clever brother, but I don't think you can make starch."

Then watch me, and see, said Fred. "Look, this is some flour. I will tie it up in this piece of muslin. All I have to do is to work it up between my fingers and thumb in this basin of water. See, the water is getting white and milky-looking, because I am washing the starch out into it. This flour—the flour that makes our bread—contains starch."

Teacher made some starch from a potato, said Willie. "He says the potato contains more starch than the flour."

Let us have another look at the basin. said Fred.

Why, said Norah, "the water is not white like milk now; it is quite clear. Where is the starch?"

Look at the bottom and you will see it, said Fred. "See, I will pour off the clear water. The thick, wet, solid stuff at the bottom is the starch."

Teacher, you see, showed us how to get starch from flour and potatoes, said Willie, joining in. "But he told us too that it is found in all plants. Some plants contain more starch than others. The plants store up this starch as a supply of food for themselves."

He told us too, said Fred, "that the starch is always in tiny grains, too small to be seen with, the naked eye.

We saw a picture of these grains as they would look, if our eyes were sharp enough to see them. They are really little bags of starch. You remember, sister," he added, "that starch will not dissolve in cold water. It dissolves in boiling water. The boiling water makes the little bags swell and burst. This sets free the real starch inside the bags and it dissolves. Cold water only loosens the little bags one from another, so that they float about. It does not burst them."

SUMMARY

The flour, from which our bread is made, contains starch, and so does the potato. We can wash the starch out of some flour in a basin of water. The starch is in the form of tiny grains or bags, too small to be seen with the naked eye. Boiling water bursts these bags, and so dissolves the starch.