英语听力文摘 English Digest 306、被误解的水蒸气

　　Clouds in the Kitchen
厨房飘着的云朵
Fill a kettle with water, then turn on the burner.
In a while, your kettle will start belching¹ white billowy stuff into the air. What is this stuff? Steam? Actually, no.
Steam is water that’s heated to two hundred twelve degrees Fahrenheit². Believe it or not, steam is invisible–you can see right through it! If you look closely at the end of your kettle’s spout³, you’ll notice that the white stuff doesn’t start right away. It begins billowing about half an inch away from the nozzle, with clear gas in between. This clear gas is the actual steam. The billowy white stuff is what the steam turns into when it hits the drier, cooler air of your kitchen.
Those white billows are, in fact, clouds, not steam. In many ways, they are identical to the clouds you can see in the sky. The white color comes from tiny liquid water droplets⁴ that have condensed from the steam.
More accurately⁵, these billows are a type of cloud called a “mixing cloud.” These can form when two separate air masses–with different temperatures and different amounts of water in them–mix together. In the case of your kettle, the hot, steamy gas cools rapidly in the kitchen air, and this sudden coolness is what makes some of the vapor⁶ condense.
Mixing clouds are pretty common, and they don’t need to start with steam. You see mixing clouds when you “see your breath” on a cold winter day. You’ll find them rising from a bowl of warm soup. Wherever there’s a mixing cloud, you can bet some warm, moist air is mixing with air that’s cooler and drier.

　　译文：
灌满水壶，扭开炉灶。
不一会儿，你会发现水壶向空气喷出滚滚“白气”。这是什么？水蒸气？事实上，不是。
水加温到212华氏度就变成了水蒸气。不管你信不信，水蒸气是透明的。如果你仔细观察壶嘴，会发现“白气”离壶嘴有半英尺远，不是直接从壶嘴喷出，中间还隔着透明的气体。这透明气体才是水蒸气。而翻滚的“白气”是水蒸气遇到厨房的干冷空气凝结而成。
事实上，袅袅“白气”不是水蒸气而是积云。从很多方面比较，和我们看到天空的云朵并无二致。我们会看到白色是因为是水蒸气凝结成的小水滴飘浮在空气中。
更准确地说，我们称翻滚的“白气”为“混合云”。两种温度、含水量不同的云团混合就可以产生。比如，壶嘴中喷出的高温水蒸气遇到厨房空气，迅速冷却，至少水蒸气凝结。
“混合云”很普遍，没有水蒸气也能产生。冬天天冷时，你会发现呼出的气体，变成了“混合云”。同样，热汤也会飘出“混合云”。只要有“混合云”，你就可以肯定某些高温潮湿气体和低温干燥气体相遇且混合。

1 belching   

n. 喷出，打嗝 动词belch的现在分词形式

参考例句：

• The Tartars employed another weapon, the so-called Chinese dragon belching fire. 鞑靼人使用了另一种武器，所谓中国龙喷火器。
• Billows of smoke were belching from the chimney. 巨浪似的烟正从烟囱里喷出来。

2 Fahrenheit   

n./adj.华氏温度；华氏温度计(的)

参考例句：

• He was asked for the boiling point of water in Fahrenheit.他被问到水的沸点是华氏多少度。
• The thermometer reads 80 degrees Fahrenheit.寒暑表指出华氏80度。

3 spout   

v.喷出，涌出；滔滔不绝地讲；n.喷管；水柱

参考例句：

• Implication in folk wealth creativity and undertaking vigor spout.蕴藏于民间的财富创造力和创业活力喷涌而出。
• This acts as a spout to drain off water during a rainstorm.在暴风雨季，这东西被用作喷管来排水。

4 droplets   

n.小滴( droplet的名词复数 )

参考例句：

• Droplets of sweat were welling up on his forehead. 他额头上冒出了滴滴汗珠。 来自辞典例句
• In constrast, exhaled smoke contains relatively large water droplets and appears white. 相反，从人嘴里呼出的烟则包含相当大的水滴，所以呈白色。 来自辞典例句

5 accurately   

adv.准确地，精确地

参考例句：

• It is hard to hit the ball accurately.准确地击中球很难。
• Now scientists can forecast the weather accurately.现在科学家们能准确地预报天气。

6 vapor   

n.蒸汽，雾气

参考例句：

• The cold wind condenses vapor into rain.冷风使水蒸气凝结成雨。
• This new machine sometimes transpires a lot of hot vapor.这部机器有时排出大量的热气。