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How Does Salt Melt Ice
為什么鹽可以用于地面除冰
Now that winter’s here, the weather fiends out there are waiting for the next big snowstorm.But before the flakes fall, armies of trucks are loaded full of one of the most important road safety tools out there – salt.
現在，冬季即將來臨。喜愛冬天的人們正在期待下一場暴風雪的來臨。但是在雪花飄落之前，大量卡車會裝滿最重要的道路安全工具——鹽。
Along with keeping our French fries on point,salt, like sodium chloride,has actually saved a lot of lives,and probably even more fenders thanks to its incredible deicing abilities.
除了讓我們的炸薯條更美味之外，鹽就像氯化鈉一樣，由于其除冰能力，實際上挽救了許多人的生命，拯救的擋泥板就更多了。
So here’s a truck throwing salt all over a wintery road.
看看，這里有一輛卡車，在冬季整個結冰的道路上撒鹽。
Like everything else in the picture,you can bet that that salt is pretty cold.
就像畫面上其他任何地方一樣，你可以肯定這些鹽絕對非常冷。
This begs the question – how be that something that isn’t hot is melting the ice?
那就出現一個問題——這種并不熱的東西是如何融化冰的呢？
Turns out, salt isn’t actually about melting.It’s all about freezing.
事實表明，鹽的作用并不是融化冰。而是防止結冰。
The freezing point of pure water rests at 32 degrees Fahrenheit, or 0 degrees Celsius.
純水的冰點是華氏32度，也就是0攝氏度。
When the temperature of water reaches the freezing point, its normally free-flowing molecules get trapped into an organized crystal structures.
當水的溫度到達冰點時，正常情況下自由流動的分子被困為一個有組織的晶體結構。
This is how ice is formed. Salt disrupts this process. Upon hitting water,salt breaks up into two ions:one sodium and one chloride.
這就是冰的形成過程。而鹽就是擾亂這個過程。遇到水之后，鹽會分解為兩個離子：一個鈉離子和一個氯離子。
These two ions then move around and take up space in between water molecules, pushing them apart and frustrating their potential links to form ice. This disruption is called freezing point depression.So to put it simply, salt lowers the freezing point of water.
然后這兩個離子四處游動，在水分子之間占據空間，將它們分開，打破他們鏈接形成冰的可能性。這種擾亂過程叫做凝固點降低。簡單地說，鹽可以降低水的冰點。
But there’s a limit.Salt can only act as a stable deicer in temperatures above 16 degrees Fahrenheit (-9 C).
但是也有一個限制。鹽只能在華氏16度（零下九攝氏度）以上作為穩定的除冰劑。
And there’s another drawback to salt.
鹽還有另外一個缺點。
Considering that over 20 million tons of road salt is used annually in the U.S.,all that salt has to go somewhere in the spring.
考慮到美國道路每年要使用超過2000萬噸鹽，到了春天的時候，這些鹽總要有去處。
Of those two ions split from dissolved salt,the chloride ions can have a potentially negative effect on the environment.
融化的鹽釋放的兩個離子中，氯離子可能對環境產生負面影響。
Chloride can kill small aquatic critters,dehydrate and kill plants,alter the composition of ground soil near roads, and can limit water circulation that keeps lakes healthy.
氯可能會殺死小型水生生物，使植物脫水甚至死亡，改變道路附近的土壤構成，限制保持湖泊健康的水循環。
All that salt is also corrosive to metal,wreaking havoc on infrastructure.And oh yeah, your wheels too.
這些鹽還會腐蝕金屬，對基礎設施造成嚴重破壞。是的，你的車輪也會受到損壞。
For these reasons, sand is used as an abrasive for an alternative.
由于這些原因，沙子有時作為研磨料也用來替代鹽。
Sand is often used because it’s cheap and maybe cuz folks want to avoid the chloride issues.
通常用沙子是因為比較便宜，也可能是為了避免氯產生的問題。
The thing is, salts have a chemical advantage: because you get 2 or more ions when they dissolve,you get way more melting power for the same handful of deicer.
問題是，鹽有著化學方面的優勢：因為鹽融化的時候會分解為兩個或更多離子，同樣的一把除冰劑，鹽的融冰能力更強。
So sand might be cheap, but you have to use way more of the stuff, and that can leave quite the mess.
所以，沙子或許便宜，但是必須使用更多，可能會導致路面亂七八糟。
Now for super cold temperatures,sodium chloride in sand won’t do the job.Some alternatives that melt ice better include Magnesium Chloride, Calcium Chloride,Potassium Chloride, and Potassium acetate.
對于特別寒冷的溫度，沙子中的氯化鈉不能發揮作用。一些可以更好地融冰的替代品包括氯化鎂，氯化鈣，氯化鉀和乙酸鉀。
Potassium acetate is particularly incredible at deicing because it works at temperatures as low as -75 degree Celsius, while the rest of the bunch work around the -20 degree mark.
乙酸鉀的除冰能力非常強，因為在低至零下75攝氏度的氣溫也能發揮作用。而其他幾種只能在零下20度的溫度下工作。
Although these alternative chemicals are better at deicing at lower temperatures, most of them have that environment damaging Chloride too,not to mention that they cost way more than that table salt.
盡管這些替代化學品可以在更低的溫度下除冰，然而，大部分都會產生對環境有害的氯離子，更不要提其成本遠遠高于食鹽。
And if you’re buying 20 million tons a year of the stuff… well,that’s a lot of money!
而如果你每年要購買2000噸，那要多少錢啊！
So people, keep your eyes on the road, and thank salt for the fine driving conditions.
所以，伙計們，多關注一下路況，多虧鹽改善了駕駛環境。
Or, on the other hand, you can shake your fist at it, if you didn’t get that snow day you know you DESERVE.
另一方面，你也可以揮拳慶祝，如果寒冬沒有迎來大雪。
