75 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。
76 MARS
Mars According to the best evidence gathered by space probes and astronomers, Mars is an inhospitable planet, more similar to Earth's Moon than to Earth itself - a dry, stark, seemingly lifeless world. Mars' air pressure is equal to Earth's at an altitude of 100,000 feet. The air there is 95% carbon dioxide. Mars has no ozone layer to screen out the Sun's lethal radiation. Daytime temperatures may reach above freezing, but because the planet is blanketed by the mere wisp of an atmosphere, the heat radiates back into space. Even at the equator, the temperature drops to 50℃ ( 60 ) at night. Today there is no liquid water, although valleys and channels on the surface show evidence of having been carved by running water. The polar ice caps are made of frozen water and carbon dioxide, and water may be frozen in the ground as permafrost. Despite these difficult conditions, certain scientists believe that there is a possibility of transforming Mars into a more Earth like planet. Nuclear reactors might be used to melt frozen gases and eventually build up the atmosphere. This in turn could create a "greenhouse effect" that would stop heat from radiating back into space. Liquid water could be thawed to form a polar ocean. Once enough ice has melted, suitable plants could be introduced to build up the level of oxygen in the atmosphere so that, in time, the planet would support animal life from Earth and even permanent human colonies. "This was once thought to be so far in the future as to be irrelevant," said Christopher McKay, a research scientist at
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