英語聽力文摘509 輕輕的，它縮水了！
Sublimation
Sublimation on this moment of science.
Pop quiz, everybody put away your books, and keep your eyes on your own radio.
You fill the ice tray up to the rim and put it in the freezer. The ice that results will be
a.) at the rim
b.) over the rim
c.) under the rim.
Answer? It depends.
I know, you hate that. But it does depend — it depends on how long you wait before checking on the ice again. My guess would be that most folks chose answer b: over the rim. That is correct, if you checked on the ice trays after only a couple hours. That’s because water expands when it turns into ice, as you know if you ever put a soda bottle in the freezer and came back to find it exploded all over the fish sticks.
But if you were to leave the ice tray untouched for a couple of months, you might find the ice to be under the rim, or lower than the water was.
Huh? Didn’t we just say water expands when it freezes? Initially, yes. But frozen water can do something else as well: it can sublimate. To sublimate is to go from one state to another without passing through the usual intermediary state.
By adding heat, ice can be melted into liquid water, which can be evaporated. That’s three states: solid, liquid, gas. But given enough time, ice can also turn into a gas without melting first! When your ice cubes seem to have shrunk, it’s because they are sublimating: the frozen water is slowly evaporating off the cubes, without ever actually melting.
Will this work in any freezer? Next time.
升華現象
今天我們的節(jié)目要講的是：升華現象。
各位，請放下你們手中的書本，專心聽收音機，我們來做一個突擊測驗。
用水將冰格填得滿滿的，漫過冰格的邊緣，然后再將冰格放到冰箱的制冷室里，最后結成的冰會：
a.) 剛好齊邊
b.) 邊緣以上
c.) 邊緣以下
答案是?要看情況而定。
我明白，你們不喜歡這樣的答案。但是，實際情況確實如此——答案取決于你要過多長時間去查看。我猜，很多人都會選擇b選項：邊緣以上。如果你在放入制冷室僅兩個小時之后去查看的話，這個答案就是正確的。這是因為水在變成冰的時候會膨脹。就像大家所知道的，如果將一瓶汽水放在制冷室中，回頭去看的時候會發(fā)現，汽水已經炸開了，整個制冷室中到處都是汽水。
但是，如果你將冰格放在制冷室中，好幾個月都不動它的話，你會發(fā)現，冰在邊緣以下，或是低于你之前裝的水的高度。
哈?我們剛剛不是才說了水在變成冰的時候會膨脹嗎?最開始的時候，會。但是冷凍之后的水也會有其他的變化：升華。升華也就是物質不經中間狀態(tài)直接從一個狀態(tài)轉變成另一個狀態(tài)。
通過加熱，冰可以化成液態(tài)水，液態(tài)水可以被蒸發(fā)為水蒸氣。這是三個狀態(tài)：固態(tài)，液態(tài)，氣態(tài)。但是，如果時間足夠的話，冰可以在不被融化的情況下轉變?yōu)闅鈶B(tài)。如果你的冰“縮水”了，那是因為被升華了：在沒有被融化的情況下，固態(tài)水以非常緩慢的速度在蒸發(fā)著。
這種現象在任何的制冷器中都會出現嗎?下次再談。
