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

譯者: Lilian Chiu 審譯者: Helen Chang

Sitting around a campfire, you can feel its heat,

坐在營火的旁邊， 你可以感受到它的熱度，

smell the woody smoke, and hear it crackle.

聞到燒木材的煙味， 聽見木材被燒裂的聲音。

If you get too close,

如果你太靠近，

it burns your eyes and stings your nostrils.

你的眼睛會感到灼燒， 你的鼻孔會感到灼痛。

You could stare at the bright flames forever

你可以目不轉睛一直 盯著明亮的火焰看，

as they twist and flicker in endless incarnations.

因為它們會在扭曲、 閃爍中無限循環。

But what exactly are you looking at?

但你到底是在看什麼？

The flames are obviously not solid,

很明顯，火焰並不是固體，

nor are they liquid.

它們也不是液體。

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

和空氣混合在一起， 它們比較像是氣體，

but more visible--and more fleeting.

但比空氣更可見——也更短暫。

And on a scientific level, fire differs from gas

就科學上來說，火和氣體不同，

because gases can exist in the same state indefinitely

因為在同樣的狀態下 氣體可以無限期地存在，

while fires always burn out eventually.

而火最終都會燒盡。

One misconception is that fire is a plasma,

有一種誤解是認為火是電漿，

the fourth state of matter in which atoms

物質的第四種相，在這種相中，

原子被剝去了電子。

are stripped of their electrons.

Like fire and unlike the other kinds of matter,

和火一樣，但和其他物質不一樣，

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

電漿不會在地球上 存於穩定的狀態中。

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

電漿的形成，只會發生在 氣體接觸到電場時，

或是加熱到數千、 數萬度的高溫時。

to temperatures of thousands or tens of thousands of degrees.

By contrast, fuels like wood and paper burn

相對之下，用木材 和紙當燃料來燃燒，

at a few hundred degrees —far below the

只會有幾百度的高溫——

遠低於一般認定的電漿標準。

threshold of what's usually considered a plasma.

所以，如果火不是 固體、液體、氣體，

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

or a plasma, what does that leave?

或電漿，那還剩什麼可能性？

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

結果發現，其實火根本不是物質。

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

火是我們對某種 化學反應的感官體驗，

這種化學反應叫做燃燒反應。

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

某種方面來說，火就像是 秋天樹葉改變顏色、

the smell of fruit as it ripens,

水果成熟時的氣味，

or a firefly’s blinking light.

或是螢火蟲的閃光。

All of these are sensory clues that a

上述這些都是感官線索，

chemical reaction is taking place.

表示有一項化學反應正在發生。

What differs about fire is that it engages a lot of

火的差別在於它同時連結了 我們的好幾種感官，

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

創造出一種生動的體驗， 讓我們以為是來自實體。

experience we expect to come from a physical thing.

Combustion creates that sensory experience

燃燒創造出那感官體驗，

using fuel, heat, and oxygen.

用的是燃料、熱，以及氧氣。

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

在營火中，當木料被加溫到 它們的點火溫度時，

the walls of their cells decompose,

它們的細胞壁會分解，

releasing sugars and other molecules into the air.

把糖以及其他分子釋放到空氣中。

These molecules then react with airborne oxygen

這些分子接著會和空氣 傳播的氧氣發生作用，

to create carbon dioxide and water.

創造出二氧化碳和水。

At the same time, any trapped water in the logs

同時，木料中含有的任何水份

vaporizes, expands, ruptures the wood around it,

都會蒸發、擴張，並造成 它周圍的木頭破裂，

and escapes with a satisfying crackle.

然後跑出來， 發出的令人滿足的霹啪聲。

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

隨著火的溫度上升，燃燒造成的

created by combustion expand.

二氧化碳和水氣會擴張。

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

現在它們的密度比較低， 會以越來越細的柱狀形式上升。

Gravity causes this expansion and rising, which gives

地心引力造成這種擴張和上升，

flames their characteristic taper.

所以火焰的特徵之一 就是頂端是尖細的。

Without gravity, molecules don’t separate

若沒有地心引力， 分子不會因為密度而分開，

by density and the flames have a totally different shape.

火焰的形狀就會完全不同。

We can see all of this because combustion

我們能看到這些， 是因為燃燒也會產生光。

also generates light.

Molecules emit light when heated,

分子被加熱時會發射出光，

and the color of the light depends

光的顏色會依分子的 溫度而有所不同。

on the temperature of the molecules.

The hottest flames are white or blue.

最熱的火焰是白色或藍色。

The type of molecules in a fire can

火中的分子類型也會 影響火焰的顏色。

also influence flame color.

For instance, any unreacted carbon atoms from the logs

比如，木料中若有 未作用的碳原子，

form little clumps of soot that rise

就會形成一叢一叢的煤煙， 上升到火焰中，

into the flames and emit the yellow-orange

並發散出我們在想像營火時 會想到的橘黃色光。

light we associate with a campfire.

Substances like copper, calcium chloride,

像是銅、氯化鈣， 以及氯化鉀這些物質

and potassium chloride can add their

會有它們自己獨特的顏色， 造成不同的混合色。

own characteristic hues to the mix.

Besides colorful flames,

除了多彩的火焰之外，

fire also continues to generate heat as it burns.

火一邊燒也會一邊持續產生熱。

This heat sustains the flames by keeping

這些熱就會讓燃料 保持在點火溫度之上，

the fuel at or above ignition temperature.

進而維持著火焰。

Eventually, though, even the hottest fires

不過，最終，再熱的火

run out of fuel or oxygen.

也會燃料或氧氣用盡。

Then, those twisting flames give a final hiss

接著，那些扭曲的火焰就會 發出最後的嘶嘶聲，

and disappear with a wisp of smoke

隨著一縷煙消失，

as if they were never there at all.

好像從來沒有在那裡存在過一樣。