以下为西奥多 格雷（Theodore Gray）的演讲实录：

　　大家好! 今天我想跟大家谈谈我最喜欢的科目——化学，以及组成分子的元素如何通过化学反应构成世界万物。 

　　元素是最纯粹的物质形态，世间万物都由它构成。我们无法将一个元素分成更简单的东西，而当我们将它们组合到一起时，我们就有了一切。每一种元素都是独特的，都有它自己的故事，不过首先我想讲讲我自己的故事。

　　我最开始对化学元素感兴趣是在大概15年前，出于一个有点傻的原因，我们办公室需要一张桌子。在英语中有个关于化学元素周期表的玩笑，“table”一词既可以指吃饭的桌子，也可以指纸上的一堆数字，所以“periodic table”——周期表，用英语表达就很有意思，不过中文体会不到。

　　就是这样一个玩笑，我做了一张有化学元素周期表的桌子。于是我就想，既然我有了一张有化学元素周期表的桌子，那我应该放点元素进去，于是我开始收集元素。

　　接着问题来了，因为有太多元素了，我不知道该如何处理这么多的元素。于是我又想，最好能给每个元素都拍张照，再写下一些关于它们从哪来的小故事，这样我就不会忘记哪个元素是哪个了。

　　于是我就给这些照片写了描述性的文字，然后建了个网站，把所有的照片和故事都放上去。几个月后我接到了《大众科学》杂志编辑的电话，这本杂志是美国发行量最大的科普杂志。

 

　　他们问我：“你想开个关于化学元素的专栏吗？”我想我从没干过这种事啊，我也不知道能否干好，但是管他呢！

　　于是我在往后的十年里，每个月都会写些元素或者与化学有关的其他东西，这一切仅仅是因为我的办公室里需要一张桌子。长此以往，我的专栏就出了书：《疯狂科学》和《疯狂科学 》，这两本书也被译成了中文，挺好的。

　　自那以后，我建立了一个更加完善的科学网站，最后出了一本有关元素的书。因为我发现已经有足够多的素材来把它们出成书，那大概是八年前。

　　现在这本书已经有25种语言的译本，我都不敢相信这是真的，太神奇了！中文版大概是六年前出的。

　　其实，当你写一本书的时候，你首先要学习很多东西。在我写这本书的过程中，我也学到了很多关于元素的知识，也学到了很多关于我自身的东西。

　　举个例子，铁元素。众所周知，这个元素没什么可讲的，每个人都知道铁会生锈，也不用深入去研究什么。但是我花了很长一段时间，去发掘这个元素让我这么伤感的原因——我不喜欢铁，因为它会生锈。

　　生锈就是死亡，是衰竭，是腐烂，是一切事物的终结。一切由铁制成的东西，诸如汽车、桥梁、铁栅栏等等，都无法逃脱这个缓慢锈烂的过程，这让人感觉很悲伤。

　　有位名为Arlo Guthrie的美国流行歌手唱过这样一首歌，歌词里有关于铁生锈的描写，华丽而悲伤。事实上歌里唱的那个地方确实就像歌词写的，有着“堆着生锈汽车的废旧垃圾场”，这让人觉得很伤感。

　　我喜欢这首歌，还因为它是一首关于火车的歌。那列火车通往新奥尔良市，它就从我家几英里以外经过，离我们家房子只有两公里。你甚至真的可以跳上那列火车，然后任它带着你南下千里，去往新奥尔良。旅途所见，皆是锈烂的情景。

　　一个生锈的铁锤，于我而言不是什么好事。然而一把钛锤，那就另当别论了。钛是一种美丽的元素，它很稳定，从不生锈，可以一直保持最初的状态，也就是说它会一直这么美丽。

　　看这些纯度高达百分之99.999纯钛结晶，它们从气体里炼出来。看！没什么能比它更美的了！

　　事实上，人们经常问我：什么是你最喜欢的元素？其实我并不喜欢这个问题，但是既然大家都想知道。我有时就会说，“嗯，钛吧”，因为它从来不生锈，而且好看，闪闪发光，又这么稳定。 

　　但真正的事实是，每一种元素都有它之所以如此美丽的原因。比如说，钠元素，钠也是闪闪发光的，看这儿！但是它最有意思的地方不在这儿。当你把它扔进湖里，那才是它最酷的时候。

　　这是我几年前举办过的一个“钠派对”，我邀请了一帮朋友，派对上会发出一些声音。特别是当我们把钠扔进湖里，它爆炸的情景，太壮观了。

　　有时候，一件事物之所以美好，是因为它是一种将人们聚集起来，并向人们展示化学魅力的方式。尤其是当你在其中贡献力量的时候，非常美妙。我之所以喜欢钠，也是因为它是一种将人们聚集起来的方式。当然它也将我们带入了我演讲的第二个部分，那就是元素的集合。

　　我们从四个元素说起，有氢元素，这是一种易爆气体，可以快速燃烧；有碳元素，也就是钻石和石墨；也有氧元素，这是另一种我们呼吸所必须的气体，没有氧气我们就会死；还有氯元素，这是一种会快速痛苦致死的气体，非常危险。

　　大家想想，如果我们把这四种元素结合起来会有什么效果？那我们会得到某种化学分子。这就是元素之间所谓的化学键。这四种元素的组合可以让我们得到成千上万种化学分子。有些是有毒的，有些很无趣，有些很友好，有些是无害的，有些尝起来很美味。

　　下面我们就来说说尝起来很不错的那一部分。

　　这是三氯蔗糖。它是一种人造化学甜味剂，尝起来是甜的，所以它常被用于烘焙食物中、或是巧克力以及其他甜品里。这种东西很有趣，因为它完全是人造的，但是吃起来很美味。

　　另一种尝起来不错的化学制品就是糖。普通的蔗糖来源于甘蔗、甜菜，这是一种天然的化学物质，并且是甜的。这是45千克的白糖，它含17万卡路里，是我们日常所需能量的14000倍。

　　但我们再来看顶上黄色方框里有个小碟子，碟子里放的是4.5克纽甜，它是另一种人造化学物质。它的甜度极高，是一种可作商用的人造甜味剂。4.5克就跟整整45千克的白糖一样甜，知道它的甜度有多高了吧！

　　我个人有一个非常喜欢的对照说法，假设钮甜是一种毒性最高的化学物质，比如VX神经毒气，是人类能力范围内可以造出的毒性最大的化学物质。如果你把这种毒性剧烈的物质，加在一杯咖啡里，让咖啡达到一个比较合理的甜度，然后喝掉，那你可能没什么事。

　　这种甜度，也就是我们假设的毒性，还远达不到致昏的程度，因为就算它的毒性堪比剧毒化学物质，我们摄入的量并不足以致死。我觉得这种对比的说法特别神奇，这也是我并不担心人造甜味剂用量的原因之一。

　　因为我们在食物中能用到的量微乎其微，事实上要想让它达到一个对人体有害的程度还是比较困难的。

　　以上就是关于化学分子的例子。我觉得分子是一种非常有趣的东西，一旦发现什么有意思的，我就会把它写一本书。于是我写了一本关于分子的书，也出了中译本。

　　接下来我想讲几个我特别喜欢的化学分子，因为在我其他的研究中它们十分有用，而且它也能帮助我们理解分子是如何作用的。

　　这是棉花。如果你从一株棉花上拉出其中一丝纤维，大概两到三厘米长，它很短。这是一卷五千米的商用棉线，棉线的纤维也只有两三厘米长，这些纤维并不是粘在一起或是绑在一起的，而是紧紧缠绕，拧在一起。

　　如果你把棉花抽丝剥茧，在不破坏任何一丝纤维的情况下将其分开，像这样轻易地把它们分开，你可以看到聚合物是怎么组合的。

　　聚合物是一种塑料，塑料是由细长的分子组成的，就像棉花由细长的棉纤维组成一样。我们可以通过思考棉线的组合方式，来研究塑料的组合方式。

　　这是一个很普通的塑料袋，商店里就有。你可以轻易地把它撕烂，像这样变成碎片。当你撕扯它的时候，其实没有破坏其中任何一个分子。就像你把棉线扯开，没有破坏其中的任何纤维一样，你只是将它们分开了而已，因为它们结合得太紧密了。

　　但如果你去拉扯塑料袋，把它拉到一个特定的长度，比如拉到一个纤维那么长，你会感到有一个特定的点。在这个特定点上，塑料袋拉不动了，它变得很结实。

　　再使劲拉，你的手就会被割伤，因为在那个点上很难将它拉长，而这个特定点，就是分子伸展拉伸构成特定排列组合的点。

　　这个点使分子们缠绕在一起，保证它们不会轻易被分开。当你达到那个点的时候，你可以感受到这种结合的力量，绷紧的感觉。这就是化学长分子式中的碳碳键在将分子往回拉，这种结合非常稳定，他们远强于那些让高分子聚合在一起的相互作用力。

　　这是一种认识分子级力量的很好的方法，因为我们可以真实地感受到它。

　　我们回到棉花，它是由一种叫做纤维素的分子构成的。像所有的聚合物一样，棉花分子中有很多重复的小单元，这是其中一个单元，那纤维素中重复了很多次的分子到底是什么呢？

　　其实我们几分钟前才见过它，实际上这种单元就是葡萄糖，也就是糖。棉花是由百分之百的糖分子构成的。那为什么棉花吃起来不甜呢？为什么我们不吃棉花呢？

　　因为如果我们想从棉花中得到糖分，就必须把棉花分子分解成极小的糖分子，我们没办法做到，人类的胃也没有可以消化棉花的酶，只有一种特定的细菌能做到。

　　所以如果你想从棉花中得到糖分，可以把棉花喂给牛，然后你再把牛吃掉。我们称这种化学过程为——养牛。

　　现在明白了吗，这是两种棉花，一种是普通的棉花，一种是棉花糖。它们俩都是由百分之百的糖构成的。只是糖分子在二者中的结合方式不同罢了。我们再说回甜的东西。

　　这里有四种高甜度的无糖甜味剂，其中两个是天然的，从植物中提取的，另外两个是人造化学物质，是两种很小的化学分子。

　　人们总是会问人造甜味剂是不是不健康，我们该不该吃人造甜味剂。事实上大多数人更喜欢人造化学物质的味道，因为它们吃起来比植物提取物味道更好。

　　那为什么人们还总是担心人造甜味剂健不健康、该不该吃它呢？其实在我看来，这根本就是个错误的问题。人们该关注的，不应该是甜味剂是人造还是天然的问题，而是这是一种好的还是坏的化学物质，而非这些物质是怎么来的。

　　其实人造化学物质有好有坏，天然化学物质亦然。 

　　比如说这种不好的人造化学物质——醋酸铅，它很可怕，毒性极强，以前常古罗马人把它用作人造甜味剂，这并不是一种明智的做法，这会让他们铅中毒。

　　下面是一个关于不好的天然化学物质的例子：甘草甜素。

　　黑甘草在中国并不流行，但在美国它是一种很流行的甜味剂。黑甘草的味道主要来源于甘草甜素，然而它毒性很强。

　　如果你一天食用100克黑甘草，这已经很多了。虽然现实中你吃不了那么多，当你持续这样吃了几个月，就会造成不可逆的肝、胃、心脏损伤，这就是黑甘草的毒性。

　　如果黑甘草是人造化学物质，那肯定要被禁用。但正因为它是天然的，没有相应的限制标准，人们就可以在食物里面想放多少放多少。

　　所以与其去争论是天然的还是人造的，更应当关注的是这种物质有没有毒。事实上，这四种众所周知毒性很强的化学物质中，三种都是天然的。只有第四种，VX神经毒气是人造的。

　　大自然显然比我们更擅长制造有毒物质。另一点我们应该记住的是，其实所有人都喜欢化学物质的味道，大家都喜欢。我很喜欢吃芦笋，如果你也喜欢，其实你喜欢的是其中的化学物质，这些化学物质的味道。

　　所有的食物都由许许多多的化学物质构成，这些物质有些有毒，有些无毒，有些有味道，有些可以用于杀菌，或者其他功能。我们希望能够按照每种化学物质性质的标准衡量它们的好坏，而非去担心它们的来源。

　　所以在我在演讲开头就已经向各位保证，我演讲的所有东西都跟化学有关，我们身边处处皆化学。刚才我们讨论了元素和分子，现在该说说化学反应了。

　　我给大家展示一些不同的化学反应。这是我最喜欢的化学反应之一。我们需要一些铝粉，它是一种纯粹的元素。还需要一些氧化铁，这是一种常见的铁氧化粉末。

　　我们把这两样东西混合在一起，然后放入混凝土罐中，然后点燃，反应就开始了。

　　这是铝原子它正在将铁原子中的氧偷走，于是大量的热量释放出来，最后我们就得到了氧化铝。因为氧元素转移到了铝元素上，反应得到白色的、温度极高的液态铁，过几秒再看罐子底部，铁流了出来。

　　

　　这就是铝和氧化铁的反应。然后我们将铁水从底部倒入模具，我们为什么要这么做？

　　这是一个相当精密的过程，期间释放了大量能量。我们移走模具后，就能知道答案了，这是火车的两条铁轨，这是当它冷却下来打磨抛光之后的样子。高铁轨道就是这样连接在一起的。

　　在世界上，人们用这种化学反应去生产液态铁，使它们熔化，使铁轨的两端熔合在一起。这就是为什么坐在高速上你会觉得非常平稳，不会感觉到颠簸的原因——一段一段的轨道都熔合成一整条连贯的轨道。所以这个化学反应是多么实用啊。

　　不过我喜欢这个反应的真正原因，是因为它是一种与生锈相反的化学反应。生锈是指铁与氧气相结合，形成氧化铁，而这种反应使得氧化铁重新变回铁，也就是“反生锈”作用。这太酷了。

　　这是一个金属燃烧的反应，它生锈得很快，在这个案例中，锂金属与氧气结合，就像生锈反应一样，但是更快。

　　其实我们可以让铁也锈得那么快，这就是一件很普通的钢丝绒，从商店就能买到，如果将其点燃，它就会剧烈燃烧。

　　这种化学反应其实就跟生锈的反应同理，只是反应机理略有不同。它之所以反应得这么快，就是因为热量高使得其快速爆炸，爆炸的关键在于氧气。

　　于是液氧就可以用来做很多有趣的事，比如说在普通的木炭粉中加上几滴液氧，持续滴入，直到它爆炸。

　　如果往纯氧气瓶中加入木炭粉，也是一个无与伦比的化学实验。当木炭粉掉入氧气瓶中时，粉末会因为得到了足够的氧而突然发出剧烈的光。

　　即使是空气中的氧气也足以快速爆炸，前提是粉末要足够纯。这是石松粉，是炼金师最喜欢的粉末。

　　炼金师就像古代的魔术师，他们总把手伸进火里，拿出一个大火球，皇帝会觉得他们有神奇的力量。不过那就是一堆孢子。它确实很神奇，毕竟火球非常漂亮。我喜欢这种特定的结果，在新书《化学反应》里面，就有大量的关于这种反应的照片。

　　我先给大家看一些照片，因为石松粉是我最钟爱的粉末之一，相信在图片中的孩子也是这么想的。看啊！这种神奇的粉末。

　　还有一个非常漂亮的化学反应，它看上去像是燃烧但其实没有氧元素在里面。这是铝溴反应，也就是把铝溴反应成溴化物。

　　不过我真的很想让大家看看这个实验，这是我见过最美丽的化学反应了。

　　它也不是那么有意思，就单纯是个很美丽的化学反应而已。

　　下面我要给大家看另一个漂亮的，但并非燃烧的化学反应。相信你们的化学老师肯定也做过这种实验——将碘化钾和硝酸铅溶于水。

　　这个反应的结果就是生成金色的碘化铅沉淀，因此这种化学反应也常被叫做金戒指反应。

　　如果你在烧杯中做这个实验，那就像把金戒指扔进去一样，但是如果把这种“金戒指”滴到田地里，将会有非常可怕的后果。因为碘化铅有毒，会长时间污染土壤。

　　因此，每当我想到化学，想到这种火光，其实是因为这种反应真的很美丽。人类总会被火光所吸引。它无处不在，甚至在橙子皮里面都有。

　　看，如果你把橙子皮团在一起，你会得到一个很漂亮的火球。

　　当然了，最美的火光，在我《化学反应》的书中有提到，我是指那种古代中国艺术里的化学技术，也就是烟花。

　　烟花其实就是不同的化学物质，诸如火药、闪光粉、火星的混合物，不同的元素、不同的颜色构成了这种神奇的反应。你就会看到这样一种景象，并且知道，这就是化学，就是化学之所在。这种火光与美的爆炸，其实随处可见，但只有烟花能将其完美表达。

　　

 

以下为演讲英文实录：

　　Hello! So today I’m going to talk about my favorite subject chemistry, and      how everything in the world is made of elements, which are assembled into  molecules, and then set in motion by chemical reactions.

　　Elements are the pure substances, from which everything else is built. You can’t divide an element into anything simpler, and when you put them together, you get everything. Every element is unique. Every element has its own story .But first a little bit of my story.

　　I first became interested in elements about 15 years ago for a completely silly reason.We needed a table for my office. In English you can make a joke about the periodic table, because in English the word “table” means both the thing that you sat at maybe you have dinner, and it also means when you write a bunch of numbers together on paper. So you see “periodic table”, that is funny in English, not in Chinese, but, you know.

　　So it was a joke, I made a “periodic table” table. And then I thought, well, you know, I have a periodic table table, I should put elements on it. So I started collecting elements and I just kept going.

　　And it became unreasonable. I had too many elements, I didn’t know what to do with them all. So I thought I’d better take a picture of everyone, and I should write a little bit about a little story about where these elements come from, because otherwise I’ll forget what they are.

　　So I wrote all these descriptions to the pictures and I made a website, where I put up all the pictures and all the stories. And then just a month or two later I got a phone call from the editor of Popular Science Magazine which is the largest circulation science magazine in the US.

　　And they said, “Do you want to write a column every month about elements?” I thought, “I don’t know. I’ve never done that before.” I have no idea, but you know, whatever.”

　　So I spent the next ten years every month writing something about some element or something to do with chemistry. Basically because we needed a table in my office, that was the only reason. So that became two books, Mad Science, Mad Science , Both which are available in Chinese, which is very nice.

　　Then I made a better website, periodictable.com, and it looks nicer and better URL. Eventually I wrote a book about elements, because I figure out that I have enough stuff now, I’ve written enough about different elements and I could make a book. That was 8 years ago? So that book has now been translated into 25 languages, which I just can’t believe that! It’s amazing!

　　Including Chinese, something like 6 years ago. When you write a book, you are forced to learn a lot about many things. So I learnt a lot about elements in the process of writing this book. And I also learnt a lot about myself.

　　For example, iron. You know, there’s not that much to learn about iron. Iron rusts. Everybody knows that. You don’t have to study it. But what took me a long time to realize is why iron makes me so sad all the time. I don’t like iron. The reason is because of rust.

　　Rust is death, and dying, and decaying, and the end of things. Every car, every bridge, every iron fence … everything made of iron is dying slowly, is rusting away. And this is very sad.

　　Actually there is a very nice song by a popular folk singer in America named Arlo Guthrie that has beautiful line about iron in it, about iron rusting. So I’m gonna play you a little bit of that song. So there is “the graveyards of rusted automobiles” exactly like in the song, very sad.

　　I love that song because it is a song about the train, and the name of the train is City of New Orleans. That train goes right about mile away from my house. That train goes right about mile away from my house. You really can get on that train and it will take you a thousand miles south to New Orleans, and the whole time you will see rust everywhere.

　　So a rusty hammer, this to me is a sad thing. A titanium hammer, on the other hand, that is a wonderful thing. Titanium is a beautiful element, it’s strong, it never rusts. It will last forever. And it will be beautiful forever. These are crystals of 99.999% pure titanium, grown from the gas. I mean, just look at it! There’s no more beautiful element!

　　In fact people often ask me, what is my favorite element? I don’t really like this question, but everyone wants to know. Sometimes I just say, “well, titanium, because it doesn’t rust. And it’s beautiful, it’s shiny and it’s strong.”

　　But really, the fact is that every element has some reasons why it’s nice and good and beautiful. So for example, sodium. Sodium also is shiny, right here, but that’s not why sodium is interesting. What’s really cool about sodium is that you can throw it in the lake.

　　This is some video from a sodium party that I had a few years ago, where basically I invited a bunch of people, sometimes there is sound. And basically when you throw sodium in the lake and it explodes, and that’s great.

　　One thing is nice about it is that it is a way of sort of bringing people together and showing them the power of chemistry. What you can do if you know a little bit about the chemistry. And that’s fine. So I like sodium because it is a way of bringing people together and which brings us to the next part of my talk, which is bringing elements together to the next part of my talk, which is bringing elements together.

　　Let’s say we start with four elements. We have Hydrogen, which is an explosive gas, burns very fast. We have Carbon, which is diamonds or graphite. We have Oxygen, which is another gas that we need to breathe, we die without oxygen. And we have Chlorine, which is a gas that will kill you painfully and quickly, very dangerous stuff.

　　What do you think we get if we combine all four of these elements together? Well, you get a molecule. That is what’s called when you make chemical bounds between elements. There’re millions of different molecules that you could get by combining those four elements. Some of those are poisonous molecules and some are very boring and good for anything. Some of them are harmless. Some of them taste good.

　　This happens one of them taste good. It’s sucralose. Sucralose is an artificial sweetener, a synthetic chemical. That tastes sweet to us. It’s used in many baked goods, in chocolates as an artificial sweetener. It’s interesting because it is completely synthetic and doesn’t exist in nature, yet it tastes very good to us.

　　Here’s another example that chemical tastes good to us. This is sugar. Ordinary table sugar that comes from sugarcane, sugar beets. It’s a natural chemical, and it’s sweet. But actually it is not very sweet by standards. This is about 45 kilograms of sugar. And it’s 170000 calories, 14000％ of your recommended daily energy in take.

　　But you see the little thing on the very top. The tiny little dish up there in the yellow zone. So this is four and a half grams of neotame, which is another synthetic chemical. It is the most intensely sweet, commercially available artificial sweetener. That four and a half grams is as much sweetness as the entire 45 kilograms of sugar. How intense is that！

　　Here’s a comparison that I really love. Suppose the neotame were as poisonous as the most poisonous-known synthetic chemical, which is VX nerve gas, a chemical specifically designed to be as poisonous as we could possibly make it. If you were to use that, you know, incredibly poisonous version of neotame, and sweeten a cup of coffee with it to a reasonable level of sweetness, and drink it, you will probably be fine.

　　It’s well below the lethal dose, because even it’s as poisonous as the most poisonous-known synthetic chemical, poisonous-known synthetic chemical, you still don’t need enough of it to be sweet enough that it will actually be likely to kill you.

　　I think that’s amazing and one reason I don’t worry about artificial sweeteners because they are so little used when you put them in your food, that it actually will be difficult to design one that will be harmful. So that’s the example to molecule.

　　I find molecules very interesting, and I think something is interesting, apparently I will write a book about it. So I’ve written a book about molecules, which is also available in Chinese. I’m going to talk about a couple of molecules, here’s one of my favorites, because how useful it is in my other projects. And because it helps understand how molecules work in the world.

　　This is cotton. If you pull a fiber off a piece of cotton off a cotton plant, it’s about 2 or 3 centimeters’ long. It’s very short. This is five kilometers of cotton thread on a commercial spool. All the fibers in there are still only 2 or 3 centimeters long. This is five kilometers of cotton thread on a commercial spool. All the fibers in there are still only 2 or 3 centimeters long. They are not glued or knotted or tied or anything like that, they are just twisted around each other.

　　And if you untwist cotton fibers, you can actually take it apart, without breaking any of the fibers. You just untwist them and they come apart. This turns out actually to be quite a good way of thinking about the way certain polymers a certain kind of plastics work. Plastics are made out of long thin molecules. Just like cotton fibers that are made out of long thin fibers. You can actually sort of understand how plastic behaves by thinking about the way that thread behaves.

　　So this is an ordinary grocery bag, like you get from the store. You can pull it apart pretty easily. It just separates. And when you do this, you’re probably not breaking very many of the molecules. Just like when you untwist the cotton thread, you are not breaking the fibers.

　　You’re just separating them from each other. But if you instead pull it and sort of stretch it until it gets longer, it kind of becomes like a fiber almost, you will feel, you should try this at home sometime, you will feel a certain point, that’s the point of which molecules all become elongated and line up with each other.

　　And they are sort of twisted around each other and they can’t slide any more. When you reach that point, you actually feel a bounce. It’s sort of a little bounciness to it. That’s the carbon-carbon backbone of those long molecules pushing back at. Those bounds are very very strong. They are much stronger than the bounds, the forces, that are holding together the polymer molecules. So it is a very nice way of seeing a sort of molecular level of thing that you can actually feel.

　　So cotton again, cotton, it’s made of molecules called Cellulose. Like all polymers, there’s many units repeated over and over again. This is one unit there. So what is the molecule that repeated many many times in cellulose? Well, we’ve seen that before, just a minute ago. The unit is actually Glucose, it’s sugar. Cotton is made of 100% sugar. So why doesn’t cotton taste sweet? Why don’t we eat cotton?

　　Because if you want to get the sugar energy out of it, you have to break it up into individual sugars. We don’t have any way of doing that. We don’t have any enzymes in our stomach that can break up cotton. Only certain bacteria can do that.

　　So if you want to get food energy from cotton, you have to feed it to cows. And then eat the cows. This form of chemical processing is that we called cattle ranching .So now you’ve learn something. This is two kinds of cotton. One is regular cotton. The other is cotton candy. They are both made of 100% sugar. It’s just that sugar is bounded together in a different way between the two .So back to sweet things.

　　These are four examples of non-sugar sweeteners of high intensity sweeteners. Two of them are natural products from plants. And two of them, the two smaller molecules are synthetic chemicals. They taste better than the plant extracts.

　　But what people usually worry about is whether they are healthy or not. Should I eat them? And I think this is really the wrong question. It’s not a question of synthetic verses artificial you should be asking. You should really be asking is that is this a good chemical or bad chemical, not where did they come from.

　　The fact is that there are good and bad synthetic chemicals, and there are good and bad natural chemicals. This is an example of bad synthetic chemicals, lead acetate. It’s terrible, poisonous. It was used as an artificial sweetener by the Romans. And it poisoned them with lead. It was not a good idea.

　　This is an example of bad natural chemical. It’s Gycyrrhizin. Apparently black licorice is not popular in Chinese. But this is a very popular candy in the US. The taste of licorice is gycyrrhizin. And it’s very poisonous.

　　If you eat 100 grams of black licorice a day, which is a lot, but not impossible, for a few months, you can have irreversible liver and kidney damage, heart damage. It’s very poisonous. If it were synthetic, it will never be allowed. But because it is natural, there’s no regulation and people can put as much as they want in their food. Because natural verses artificial is the wrong question and what we should be looking at was poisonous or not poisonous.

　　The fact is that of the four most poisonous-known chemicals, three of them are natural. It’s only the fourth-most poisonous VX nerve gas, that’s synthetic. Nature is much better at making poisonous chemicals than we are. The other thing to remember is that all of us like the taste of chemicals. The other thing to remember is that all of us like the taste of chemicals.

　　If you like asparagus, that is favorite of mine, I really love asparagus. And if you like asparagus, those are the chemicals that you like the taste of, and that you enjoy eating. All food is made of many many many chemicals. Some of these are poisonous, some of them are not. Some have flavor, some are for killing bacteria, or fungi, whatever.

　　You know, we really want to evaluate each chemical in its own right as a good or bad thing without really worry about where they came from. So at the beginning of this talk, I promised you the whole story of chemical, of chemistry. So we have elements, we talked about molecules, now it’s time for reactions.

　　I’m gonna show you a somewhat random collection of different reactions. This is one of my favorite reactions of all. We start with two main ingredients, aluminum powder, which is a pure element, and iron oxide, which is a compound of iron and oxygen. You mix these things together, you pour them in a concrete pot, and you light it, and then this happens.

　　So what’s happening here is that the aluminum atoms are stealing oxygen away from the iron atoms. You are getting a lot of heat released, a lot of heat released. At the end the result of this reaction is aluminum oxide because the oxygen is moved over to aluminum from iron, but not just any iron, what you get is white hot liquid iron. And just in a few seconds if you watch the bottom down there, you’re gonna see the iron come out.

　　That’s liquid iron. It was produced by the reaction and is now pouring out the bottom of that pot and here it’s going into the mold ,So why are we doing this?

　　It’s fairly elaborate procedure and a lot of energy is released. The answer is…so this is what that looks like after the mold has been removed. The thing you see in the left and right side there are two ends of train track. This is what it looks like after it’s cooled down and it’s been ground and polished. This is actually how high speed train tracks are joined to each other.

　　All around the world, they use this chemical reaction as a way of creating enough liquid iron to fuse, not just weld together, but actually melt together two ends of train tracks. When you go on a high-speed train, and it’s very smooth when you’re going on. You don’t feel any bumping. It’s because all the tracks has been melted together into one continuous piece. So it’s a very useful chemical reaction.

　　But really the reason that I like it is because it is the exact chemical opposite of rusting. Rusting is iron combing with oxygen to form iron oxide. Thermite is iron oxide being pushed back into iron. So it’s unrusting the iron, which is cool.

　　This is another example of metal burning, rusting very fast. In this case, lithium metal combines with oxygen, the same kind of reaction as rusting, but faster. You can actually make iron rust that fast. This is just an ordinary steel wool, you can buy it in the store .If you light it, it will burn!

　　And the reaction that happens is exact the same reaction slightly different mechanism but same reaction as rusting. It’s happening so fast that the heat makes the blow up like a glow like that. The key to burning is always oxygen. So you can do fun things with liquid oxygen that this is just ordinary charcoal with drops of liquid oxygen dropping into it until it flares up. A particularly beautiful demonstration of that is if you drop charcoal powder, this is a glass that’s filled with pure oxygen gas, so when the charcoal falls into it, suddenly it will brighten up because it is getting more oxygen.

　　But even the oxygen in the air is plenty to burn rapidly like that, if you have very very fine powder. The powder that we’re seeing here, is lycopodium powder. It was the favorite of the alchemists, the ancient magicians, that you will have a handfull of it, throw it in the fire, and there is big fire balls. And the emperor will be very impressed and think you are powerful wizard.

　　And really it is just actually the spores of club moss, it’s a moss spore. But it’s so fine that it makes beautiful fire balls. I like this particular sequence because we got several very nice photographs to use in the Reactions book.

　　I’m showing you a bunch of them because lycopodium is my favorite powder, and the kid was great in the photo should also…Beautiful powder, very much recommended.

　　So here is an example of a beautiful chemical reaction that it looks like burning but there’s no oxygen involved. It’s a reaction of aluminum and bromine to form aluminum bromide. But really I’m showing you because I think it is the most beautiful reaction that I’ve ever filmed.

　　It’s not really that interesting as a reaction, but it is very pretty. Here’s another very beautiful reaction, which is not burning. Your chemistry teacher may have done this for you students, that it’s a reaction between potassium iodide and lead nitrate. The result is lead iodide which is a beautiful gold color. This demonstration is sometimes is called the golden rain demonstration.

　　If you do in the beaker, because it looks like golden rain drops falling down. But it will be a very bad idea if that sort of “rain” would have fall on your farm, for example. Because it’s lead iodide, it will poison your farm field for generations.

　　So, really, when I think about chemistry, what I think about is fire, and that’s mainly because fire is so interesting. And human have always be drawn to fire. It’s everywhere. It’s even in an orange peel.

　　Look at that. I mean, you get an orange peel and squeeze it and you get a beautiful fire ball. The best fire, of course, the best chemical fire, is what in my Reactions book, I refer to as the ancient Chinese art of chemical arranging, which is of course, fireworks.

　　Fireworks are just different chemicals, gun powder, flash powder, stars, with different elements, for color, arrange just right carefully by a master. You get things like this. And you know, this is chemistry.

　　This is what chemistry is about. This is beautiful explosion of fire and beauty, which we see everywhere around us, but quite literally in the art of fireworks. So thank you very much for coming to see what I have to say.

　　Thank you!

　　

　

 

 

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