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pets4考前必读阅读文章
随着2017年下半年的到来，pets4下半年的备考也渐渐拉开帷幕。考生在备考时，英语阅读理解是由始至终的重点，下面，小编特地为大家整理了一篇pets4考前必读阅读文章，希望对大家有所帮助。还有更多精彩内容尽在应届毕业生考试网。
Hydrogen and Industries
Hydrogen, the lightest and simplest of the elements, has several properties that make it valuable for many industries. It releases more heat per unit of weight than any other fuel. In rocket engines, tons of hydrogen and oxygen are burned, and hydrogen is used with oxygen for welding torches that produce temperatures as high as 4, 000 degrees F and can be used in cutting steel. Fuel cells to generate electricity operate on hydrogen and oxygen.
Hydrogen also serves to prevent metals from tarnishing during heat treatments by removing the oxygen from them. Although it would be difficult to remove the oxygen by itself, hydrogen readily combines with oxygen to form water, which can be heated to steam and easily removed. Hydrogen is also useful in the food industry for a process know as hydrogenation. Products such as margarine and cooking oils are changed from liquids to semisolids by adding hydrogento their molecules. Soap manufacturers also use hydrogen for this purpose.
Hydrogen is also one of the coolest refrigerants. It does not become a liquid until it reaches temperatures of -425 degrees F. Pure hydrogen gas is used in large electric generators to cool the coils. In addition, in the chemical industry, hydrogen is used to produce ammonia, gasoline, methyl alcohol, and many other important products.
氢与工业
氢作为最轻和最简单的无素，有几种特性对工业非常有用。作为燃料，它每单位重量释放热量最多，在火箭的引擎中，成吨的氢和氧被燃烧掉。氢和氧合在一起用于焊接，能够产生高达华氏四千度的高温而可以切割钢铁。发电的燃料房就是使用氢和氧。
氢也可以用来在金属热处理中通过从中除去氧的方法来防锈。虽然单独除去氧本身是困难的，氢和氧很容易结合成水，而水是可以加热蒸发除去的。氢在食品工业中对于所谓的氢化过程也很有用。人造黄油和食用油的分子中加上氢，就由液态变成半固态。肥皂制造商也为此使用氢。
氢是温度最低的冷冻剂。它要到华氏-425 度才会液化。纯氢被用于大型发电机线圈的冷却。除此之外，在化学工业中，氢被用来制造氨、汽油、甲醇以及其它许多重要产品。
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