书城教材教辅科学读本(英文原版)(套装1-6册)
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第24章 第一册(24)

"All these things are made of clay. Clay is earth. This is why we sometimes call the things earthenware.""What a useful substance clay is," said Norah. "I suppose all these things are molded into the right shape while the clay is moist and pliable. But how are they made hard, like this plate?""They have to be baked in very hot ovens." said Fred. "Bricks, after they are molded, are piled in a great heap, and a big fire is made in the middle of them. This fire is kept burning for weeks. When the baking is over, the things are hard and firm, and will always keep their shape.

"If we drop the cups and saucers on the floor they break into pieces. They are brittle as well as hard. The moist clay was not brittle, for we could throwit down, or even strike it with a hammer, without breaking it.""Did the baking make it brittle, Fred?"

"Yes, it did," said Fred, "and it did something more. The moist clay was pliable. But could I mold this piece of flowerpot into any other shape?""No," said Norah.

Willie, who had been very quiet for some time, joined in now and said, "Don"t forget, Norah, that the clay, after it is baked, will never be pliable again."SUMMARY