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影响熔点的因素

    晶体的熔点并不是固定不变的,很多因素会影响晶体的熔点.例如:在盛有小冰块的烧杯里放些盐并搅拌,冰的炫点就会低于零摄氏度.海水冬天结冰的温度比河水低就是因为海水中溶有盐.寒冷的冬天,在汽车发动机的水套中加一些甘油作为抗凝剂,即使温度低于零下二、三十摄氏度,水套中的水也不会凝固.合金可以看做混有杂质的金属,所以合金的熔点比组成合金的每一种金属的熔点都要低.

    又如:将一根两瑞桂有重物的细金属丝挂在冰块上(如图甲所示),金属丝下的冰块熔化,说明增大压强可以使冰熔化.金属丝通过后,冰的熔点又升高了,熔化成的水又凝固成冰,这样,金属丝就可以轻松穿过冰块而不留缝隙.

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    Jackie visited his grandparents on their farm.And he was playing with a slingshot(弹弓)in the woods.He practised in the WOODS but he could never hit the target.As he was walking back,he saw Grandma's pet duck.Without thinking,he shot,hit the duck in the head.and killed it.He was very afraid.He knew Grandma loved the duck.She would be sad or even angry if she knew that her duck was killed.He then hid the dead duck under a tree.His sister Susan saw it all.but she said nothing.

    After lunch that day Grandma said,“Susan,let's wash the dishes.”But Susan said,“Grandma.Jackie told me he wanted to help in the kitchen today,didn't you,Jackie?”And then she whispered(小声说)to him,“Remember the duck?”So Jackie did the dishes.

    Later Grandpa asked if the children wanted to go fishing,but Grandma said,”I'm sorry but I need Susan to help clean the house.”But Susan smiled and said,“Well,that's all right because Jackie told me he wanted to help.”And she whispered again,“Remember the duck?”So Susan went fishing with Grandpa and Jackie stayed.

    These “remember the duck” went on for many days.Then finally Jackie couldn't stand it any longer.He came to Grandma and told her that he had killed the duck.She gave him a hug,and said,“Sweetheart,I know.You see,I was standing at the window and I saw the whole thing.But because I love you,I forgave you.But I just wanted to see how long you would let Susan make a slave of you.”