英国学生科学读本 第70期:蒸发作用(2)

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　　在你数到十之前, 那根沾有酒精的手指就会变得干燥, 而另外一根沾有水的手指, 则需要一分多钟才能变干。

　　How do your fingers feel after the two liquids have evaporated? They feel cold; for the heat which was needed to make both the alcohol and the water evaporate has been taken chiefly from your hand. This is the reason why one gets a cold so readily by sitting in damp clothes. The clothes dry gradually, but in so doing they rob the body of some of its heat.

　　当这两种液体蒸发之后, 你的手指有何感觉? 你会感到清凉, 因为手指释放了一部分用来蒸发酒精与水的热量。穿着潮湿的衣服, 容易感冒, 原因就在于此。衣服会逐渐变干, 但是在这个过程中, 人体的大量热量就被消耗掉了。

　　If you try such liquids as milk and treacle¹, you will find that they evaporate more slowly than water. I daresay you may have noticed that milk also takes a little longer to boil than water does.

　　用牛奶与糖蜜来做上述的实验, 就会发现, 它们比水的蒸发速度要慢很多。我相信, 你肯定发现了这样一种现象：与水相比, 牛奶沸腾所需的时间比水稍微长一点。

　　Now you can tell why liquids are kept in bottles, and why the bottles are fitted with good stoppers, or with corks². It is to prevent the liquids from evaporating, as well as to keep dust from them.

　　现在你一定明白了, 为什么我们要把液体装在瓶子里, 而瓶子还需要盖上严实的瓶盖或者软木塞。这样做就是为了防止液体蒸发或者沾染上灰尘。

　　If we leave the stopper out of a bottle full of spirit of wine, for instance, we shall find, after a few days or weeks, that the bottle is empty, although no one has touched it. The alcohol will have changed from a liquid into a vapour or gas, and this vapour will have escaped through the open mouth of the bottle.

　　比如, 把一瓶酒精的瓶盖取下, 就会发现：虽然没人去碰这个酒瓶, 但是经过几天或几周, 瓶子一定会变得空空如也。因为酒精会从液体状态变成蒸汽, 从瓶子的开口处挥发出去。

　　Some solids, too, can evaporate, though much more slowly than liquids. Ice and snow are solids; and yet lumps of both ice and snow get smaller and smaller in even the driest and the coldest weather. They slowly change into water-vapour without first melting into liquid water, and this vapour mingles³ with the air and is lost to our sight.

　　有些固体也能蒸发, 当然了, 其速度比液体要慢上许多。冰与雪都是固体；然而, 即便是在最为寒冷的日子里, 一块冰雪也会逐渐变小。它们没有融化成液态水, 而是慢慢变成水蒸气并混入空气之中, 我们就看不见了。

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