书城教材教辅科学读本(英文原版)(套装1-6册)
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第118章 第二册(35)

"When it dries it becomes very hard-as hard as the stone itself.""The stone mason," added Willie, "always uses a special sort of mortar. It is made from chalk and lime mixed with clay. He calls it cement. It is mixed up with sharp sand and then made into a paste withwater, just as the bricklayer makes his mortar. It is used where great strength is wanted. It becomes as hard as the stone itself when it dries."SUMMARY

Cements are adhesive substances that stick things together. Glue is a cement for wood; mortar is a cement for bricks and stone.

Lesson 17

Wheat and Rice

"You remember our flour in the muslin bag, Norah?"asked Fred.