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TED-Ed 074・・The deadly irony of gunpowder （火薬の破壊的皮肉）

ご存知の内容でわかり易い。 ただしスタートが錬金術とは！

易・・03分・・165wpm　　2014/05/28 新出
　

★下記英文はｸﾞｰｸﾞﾙのマウスオーバー辞書が使えます｡　　　　　　

Everybody loves fireworks -- the lights, the colors, and, of course, the big boom. But the history of fireworks isn't all hugs and celebrations. Long before epic fireworks displays, chemists in China invented the key ingredient that propels those bright lights into the sky.

That invention was what we now call gunpowder. Our story begins back in ancient China in the mid-ninth century where early Chinese alchemists（錬金術師） were trying to create a potion for immortality. Instead, what they created was a flammable powder that burned down many of their homes.

They quickly realized that this black powder, which they called fire medicine, was precisely the opposite of something that would make you live forever. In these early days, the Chinese hadn't yet figured out how to make the powder explode; it was simply very flammable, and their armies used it to make flaming arrows and even a flamethrower（火炎放射器）.

But once they figured out the right proportions of ingredients to create a blast, they began using the powder even more, creating fireworks to keep evil spirits away and bombs to defend themselves against Mongol invaders. It was these Mongols, most likely, who spread the invention of gunpowder across the world.

After fielding Chinese attacks, they learned how to produce the powder themselves and brought it with them on their conquests in Persia and India. William of Rubruck, a European ambassador to the Mongols, was likely responsible for bringing gunpowder back to Europe around 1254.
　　（William of Rubruck：ウィリアム・ルブルック 仏の修道士。「東方諸国旅行記」 ）

From there, engineers and military inventors created all kinds of destructive weapons. From bombs to guns to cannons, gunpowder left its mark on the world in some pretty terrible ways, in contrast to the beautiful marks it can leave in the air.

So, how does black powder propel fireworks into the sky? You might have seen old Westerns or cartoons where a trail of gunpowder is lit and it leads to a large and obviously explosive barrel. Once the fire gets to the barrel, a large boom occurs.
　　（trail：A long thin line stretching behind from something　ここでは導火線の意味）

But why doesn't the trail itself explode? The reason is that burning the powder releases energy and gases. While the trail is burning, these are easily released into the surrounding air. But when the gunpowder is contained within the barrel, the energy and gases cannot easily escape and build up until BOOM!

Firework canisters provide a single, upward-facing outlet to channel this explosive energy. The wick ignites the gunpowder and the energy takes the easiest exit from the canister, launching the firework high into the sky. The flame then makes its way through the firework's encasing and the same reaction occurs high above our heads.

So, while the Chinese alchemists never found the compound for eternal life, they did find something that would go on to shape all of civilization, something that has caused many tragic moments in human history, and yet still gives us hope when we look up in celebration at the colorful night sky.