英文科學(xué)讀本 第二冊·Lesson 21 Some More about Metals

Lesson 21 Some More about Metals

I say, Fred, said Willie, "we didn't finish with the metals last night. Norah would like to hear all about wire, I daresay."

Oh yes, said Norah, "I should, and can you tell me how they make wire, Fred? Father was using some wire today no thicker than sewing thread. I should like to know how they make it."

Well, said Fred, "teacher showed us some coils of wire of all sorts in our lesson, and told us how it is made.

Let us take this piece of iron wire. This was made from a thick round bar of iron a few inches in length. It was first made red-hot in the fire. As it got red hot it became soft. In this state it was taken out with tongs and forced through a hole in a strong steel plate. The hole was smaller than the iron bar itself, and it is easy to see that it squeezed the iron as it went through.

Of course, said Willie, joining in, "this made the iron bar thinner, and at the same time longer."

Yes, I understand. said Norah.

Well, said Fred, "after it had been through this hole, it was forced into a smaller one, and drawn through it, then through a still smaller one, and so on, each hole being smaller than the last."

I think I can understand it all now, said Norah. "Every time the iron was drawn through a hole, it became thinner and longer, until at last it made a great length of this thin wire. But is all wire made like this, Fred?"

Yes, dear, said her brother, "all wire is drawn out through holes in a steel plate in the same way.

Teacher gave us a name for metals which can be drawn out into wire. They are said to be ductile. Ductile means able to be drawn out. They are ductile because they are tough or tenacious, and hold firmly together.

Whenever you see, added Will, "a piece of wire, Norah, you will be able to say at once, 'This metal must be ductile and tenacious, or it could not have been drawn out into wire.’"

SUMMARY

Some metals can be drawn out into wire. We say they are ductile. They must be very tough or tenacious, to hold together while they are being drawn out.