书城教材教辅科学读本(英文原版)(套装1-6册)
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第126章 第二册(43)

"I found my pocket knife just now. Here it is. Ilost it a few days ago in the garden; but look at it. It is no longer bright and shining. It is covered withred rust. Iron and steel soon rust if they are left out in the weather.""Do all the metals rust like this?" asked Norah. "No," said her father, who had been listening tothe children. "Look at these gold and silver coins. They never rust. They would not rust if I left them out in the garden for a week.

"We call gold and silver the precious metals," father added, "because they never rust. All the others are called common metals.""Teacher showed us a sheet of gold leaf, thinner than the thinnest paper I ever saw," said Fred. "It was beaten out thin with hammers.

"I have here a piece of lead. Watch while I beat it flat with this hammer. You know," he added, "if I had beaten a piece of coal it would have broken in pieces, for it is brittle. The metals then cannot be brittle. Teacher gave us a new word for all the metals that can be hammered out thin. We say that they are malleable."SUMMARY