Is fire a solid, a liquid, or a gas? - Elizabeth Cox

翻译人员: Yifan L 校对人员: janice zhu

Sitting around a campfire, you can feel its heat,

坐在篝火旁， 你能感受到它的热度，

smell the woody smoke, and hear it crackle.

闻到木头冒烟的味道， 还能听到它劈啪作响。

If you get too close,

要是离得太近，

it burns your eyes and stings your nostrils.

火会烧到你的眼睛， 熏疼你的鼻子。

你毫不厌倦的盯着这明亮的火焰，

You could stare at the bright flames forever

as they twist and flicker in endless incarnations.

看它闪烁摇曳， 不断变换身姿。

But what exactly are you looking at?

但是， 你在看的到底是什么？

The flames are obviously not solid,

火焰显然不是固体，

nor are they liquid.

也不是液体。

Mingling with the air, they’re more like a gas,

当与空气混合， 它们更像一种气体，

but more visible--and more fleeting.

但更显眼—也更短暂。

And on a scientific level, fire differs from gas

从科学的角度来说， 火不同于气体，

because gases can exist in the same state indefinitely

因为气体能以一种恒定的状态存在，

while fires always burn out eventually.

而火最终总会熄灭。

One misconception is that fire is a plasma,

有一种错误认识， 认为火是一种等离子体，

the fourth state of matter in which atoms

后者是原子被剥夺电子后

are stripped of their electrons.

产生的第四种物质形态。

Like fire and unlike the other kinds of matter,

与其他物质形态不一样， 等离子体更像火，

plasmas don’t exist in a stable state on earth.

它们不是以一种稳定的状态 存在于地球上。

They only form when gas is exposed to an electric field or superheated

它们只在气体暴露于电场，

或者被过度加热到 成千上万度时才会产生。

to temperatures of thousands or tens of thousands of degrees.

By contrast, fuels like wood and paper burn

相比之下， 类似木柴和纸张之类的燃料

at a few hundred degrees —far below the

几百度时就能燃烧—

远低于通常认为的 等离子体存在的临界温度。

threshold of what's usually considered a plasma.

So if fire isn’t a solid, liquid, gas,

如果火不是固体、液体、气体，

or a plasma, what does that leave?

也不是等离子体， 那它到底是什么呢？

It turns out fire isn’t actually matter at all.

事实上， 火都称不上是一种物质。

Instead, it’s our sensory experience of a chemical reaction called combustion.

相反，它是我们对一种 名为燃烧的化学反应

所产生的感官体验。

In a way, fire is like the leaves changing color in fall,

某种程度上， 火就像叶子在秋天的颜色变化、

the smell of fruit as it ripens,

果实成熟时散发的气息，

or a firefly’s blinking light.

或是萤火虫发出的亮光。

All of these are sensory clues that a

这些都是感官上的提示，

chemical reaction is taking place.

表明一种化学反应正在发生。

What differs about fire is that it engages a lot of

火的不同之处在于

它同时调动人体的多项感官，

our senses at the same time, creating the kind of vivid

创造出一种我们希望从实体中获得的 生动的体验。

experience we expect to come from a physical thing.

Combustion creates that sensory experience

燃烧能创造那样的感官体验，

using fuel, heat, and oxygen.

只需要燃料、温度、氧气。

In a campfire, when the logs are heated to their ignition temperature,

当篝火中的木材被加热到燃点，

the walls of their cells decompose,

其内部的细胞壁分解开来，

releasing sugars and other molecules into the air.

向空气中释放糖类和其他分子。

These molecules then react with airborne oxygen

这些分子随后与空气中的氧气反应，

to create carbon dioxide and water.

生成二氧化碳和水。

At the same time, any trapped water in the logs

同时， 被困在木材中的水分

vaporizes, expands, ruptures the wood around it,

蒸发、扩散、 撑破周围的木质，

and escapes with a satisfying crackle.

最终伴着满意的噼啪声逃脱。

As the fire heats up, the carbon dioxide and water vapor

随着火温度升高，

燃烧所产生的 二氧化碳和水开始扩散。

created by combustion expand.

Now that they’re less dense, they rise in a thinning column.

现在它们没那么拥挤， 它们从一条细长的圆柱体中上升。

Gravity causes this expansion and rising, which gives

重力导致了这种扩散和上升，

flames their characteristic taper.

形成了特有的锥形火焰。

Without gravity, molecules don’t separate

如果没有重力， 分子就不会因密度不同而分离，

by density and the flames have a totally different shape.

火焰也会是全然不同的形状。

We can see all of this because combustion

我们能观察到这些，

是因为燃烧也会产生光。

also generates light.

Molecules emit light when heated,

分子被加热时会发光，

and the color of the light depends

而光的颜色

on the temperature of the molecules.

取决于分子的温度。

The hottest flames are white or blue.

温度最高的火焰是白色或蓝色的。

The type of molecules in a fire can

火中分子的种类

also influence flame color.

也会影响火焰颜色。

For instance, any unreacted carbon atoms from the logs

例如， 木料中未发生反应的碳原子

form little clumps of soot that rise

会生成小簇煤烟，

into the flames and emit the yellow-orange

从火焰中蹿升，

发出我们在篝火中常看到的 橙黄色光芒。

light we associate with a campfire.

Substances like copper, calcium chloride,

而像铜、氯化钙、

氯化钾一类的化学物质，

and potassium chloride can add their

能把它们特有的颜色混合进去。

own characteristic hues to the mix.

Besides colorful flames,

除了多彩的火焰，

fire also continues to generate heat as it burns.

火还会在燃烧中持续产生热量。

This heat sustains the flames by keeping

这种热量能将燃料温度 保持在燃点以上,

the fuel at or above ignition temperature.

从而维持火焰不灭。

Eventually, though, even the hottest fires

然而，即使是温度最高的烈火，

run out of fuel or oxygen.

最终也会耗尽燃料或者氧气。

Then, those twisting flames give a final hiss

接着，这些摇曳的火焰 发出最后的咝咝声，

and disappear with a wisp of smoke

消失在一缕轻烟中，

as if they were never there at all.

仿佛它们从没来过。