书城教材教辅科学读本(英文原版)(套装1-6册)
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第157章 第二册(74)

"Lead is very flexible. See, too, how easily I can cut it with the knife. The workman can bend it, cut it, and hammer it into any shape he pleases.

"Sheet-lead is used for the roofs and gutters of houses, and for lining water cisterns, and you can see now why it is useful for these purposes.

"Here, look at this piece of lead pipe," he added. "This is used for gas and water. Lead is more useful for this purpose than any other metal, because it can be easily fused, bent, cut, and hammered, just as the workman pleases.

"Teacher showed us that the very reasons, that make lead useful for these purposes, make it useless in another way. Why don"t we use lead wire?""Lead is a soft metal and breaks easily," said Willie. "It is not ductile, so that it cannot be drawn out. It is not tenacious, so that it would not bear to be pulled." "Do you see this spoon?" said Fred. "It looks like lead, but it is not lead. It is made of pewter. Pewter is made by melting lead and tin together. Pewter is used for making drinking vessels, and many usefulthings for the house.

"You must remember that lead, like most metals, is found as an ore. It must be smelted, to remove the earthy matters before it can be of use."SUMMARY