英国学生科学读本 第35期:蒸汽往上冒(1)

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　　第35课 蒸汽往上冒！

　　Do you want to know what steam is? Let us get a lump of ice, or a snow-ball, and place it in a saucer in a warm room. It soon melts, and then the saucer is half full of water. If we leave the saucer in the warm room for a few hours, we shall find that it has become quite empty.

　　小朋友，你想知道蒸汽是什么东西吗？咱们拿一块冰或者一个雪球，放在一个碟子里，放到温暖的房间里。冰雪很快就会熔化，碟子里会盛上半碟子水。要是把碟子留在温暖的房间里几个小时，里面就会空了。

　　The ice or snow was solid water. The heat changed it into liquid water, such as we drink. And then, by more heat, the liquid water was changed into water-vapour, which mixed with the air and was lost to our sight.

　　冰和雪都是“固态”水。热量让固态水变成了“液态”水，就是我们喝的水。然后，如果再加热，液态水就会变成“水蒸气”，水蒸气和空气混在一起，我们就看不见了。

　　This shows that water can exist in three forms—first, as the solid we call ice or snow; second, as the liquid water we drink; and third, as the gas we call water-vapour.

　　这说明，水的存在形态有三种——第一种，我们叫做冰雪的“固态”；第二种，我们喝的“液态”；第三种，我们叫水蒸气的“气态”。

　　If we put the liquid water into a little sauce-pan on the fire, the heat of the fire will change it into vapour in a few minutes. Vapour made by the boiling of water is called steam.

　　要是我们把液态水倒进汤锅，放在火上煮，火焰的热量，只要几分钟，就能把液态水变成水蒸气。水开了散发出来的水蒸气，就是三点水的“蒸汽”。

　　Now hold a tea-spoon, or something cold, in the steam as it rises. In a moment the spoon will be covered with little beads¹ of water. The cold spoon has turned the steam back into water. Heat turns water into steam; cold turns steam into water again.

　　拿一把茶匙或者别的冷东西，放在往上冒的蒸汽里面。马上，茶匙就会盖上一层小水珠。冷的茶匙又把蒸汽变回了水。热可以把水变成蒸汽，冷又能把蒸汽变回水。

　　Suppose we were to put some water into a kettle, and then close up its spout², fasten down its lid, and put it over a hot fire, what do you think would happen?

　　假如，我们把水倒进水壶，堵住壶嘴，封死了壶盖，再放在火上烧，会发生什么事？

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