英語(yǔ)聽力文摘 為什么鹽會(huì)結(jié)塊？

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為什么鹽會(huì)結(jié)塊?

You probably noticed that sometimes the salt gets clumpy. If it’s really humid outside–there may even be condensation on top of the salt shaker.

The reason this happens is that salt is hygroscopic. Hygroscopic means that salt absorbs water vapor from the surrounding air.

Eventually, the salt attracts enough water vapor that the gas changes into liquid, and the salt partially dissolves and starts to clump together. To combat this tendency, manufacturers put additives in salt that keep it from liquefying.

Sugar is hygroscopic, too. This is partly the reason cake doesn’t go stale as quickly as bread. You see, when baked goods such as bread or cake lose water, the starch molecules in them undergo a chemical change that make them hard and stale.

But because cake contains more sugar than bread, and sugar is hygroscopic, it retains water better and stays fresh a little longer.

This also explains why saltines and cookies get soft when they go stale instead of hard–because they’re absorbing water from the air around them.

生活中，你可能發(fā)現(xiàn)鹽有時(shí)會(huì)結(jié)塊。如果室內(nèi)很潮濕的話，在鹽瓶上甚至?xí)a(chǎn)生液滴。

產(chǎn)生這種現(xiàn)象的原因是：鹽吸濕。吸濕的意思就是鹽從周圍空氣中吸收水蒸氣。

最終，鹽吸收了足夠多的水蒸氣后氣體就會(huì)變成液體，鹽就會(huì)局部溶解并結(jié)成一團(tuán)。為了避免這種情況，生產(chǎn)商在鹽中加了添加劑防止其溶解。

糖也吸濕。這也是蛋糕比面包更難保鮮的部分原因。要知道，焙烤食品像面包或者蛋糕失去水分后，其淀粉分子就會(huì)發(fā)生一種化學(xué)變化使起變得堅(jiān)硬，不新鮮。

但是因?yàn)榈案庵泻械奶欠直让姘?，糖又吸濕，蛋糕就保持了充足的水分，所以保鮮的時(shí)間長(zhǎng)些。

鹽薄餅干和餅干不新鮮了就會(huì)變軟兒不是變硬。因?yàn)樗鼈兾樟酥車諝饫锏乃帧?/p>