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Element of Surprise
Who doesn't enjoy watching fireworks? Noisy, exciting, colorful. It seems hard to imagine today, but once upon a time people used to make their own fireworks. When I went to school it was still possible to buy the essential ingredients: saltpeter (potassium nitrate), sulfur, charcoal, and iron filings, and my friends and I experimented with them. Of course the fireworks we made were not very impressive -- a fizz and a few yellow sparks were all we produced -- and the reason was that we knew no chemistry.
When eventually I was taught chemistry at school, things became much clearer, and the more chemistry I learned, the more interested I became. So what is it about fireworks that make them such a good advertisement for the chemical elements? The most obvious link between them is that three of the traditional ingredients (sulfur, charcoal, and iron filings) are simply pure chemical elements, as is magnesium powder, which is used to create a brilliant white flame. But if you want color, then you need to know a little more about some of the other chemical elements, such as strontium, whose compounds burn with a bright red flame; or barium and copper, which burn green; or sodium, which can color flames a bright yellow.
And blue? No element burns with a purely blue flame, and if you attend a firework show you might notice how few of the bursts of stars that light up the sky are blue in color. Indeed, one of the skills of a practiced firework maker is to produce a blue display, and it is done by a careful combination of other colors, which are blended so as to appear blue.
We now know of 114 chemical elements, although only 85 or so are to be found on Earth, and it's from these that everything we see around us is made. About a dozen of them are used in firework manufacture. Even more are needed to create a human being, and while there are at least a few atoms of 90 elements in our bodies (and that includes gold and uranium), most are not essential to life and are simply there because there are minute traces of them in the foods we eat. Nevertheless, 25 elements are vital, and that goes for cobalt (the metal we normally associate with the pigment cobalt blue used by artists), chromium (of chrome plating), and nickel (used in coins and stainless steel), although the amounts of these in our bodies are tiny.
A lifelong career in chemistry has led me to collect all kinds of interesting facts about the chemical elements, and these I have turned into the book Nature's Building Blocks. In it I tell the fascinating story of each element, under headings such as cosmic element, human element, food element, medical element, historical element, economic element, element of war, environmental element, and, or course, chemical element. And at the end of each section I include an "element of surprise," with a fact so surprising that I felt it needed special note.
For example, we think of uranium as a modern element, essential for generating nuclear power and atomic bombs. Yet 2,000 years ago, in the time of Christ and the Roman Empire, a workman who made the tiles for mosaic floors used a uranium pigment to color some of them a fluorescent green. Where he got his uranium from we will never know, and those who stood on the floors of villas he decorated with his mosaics were happily unaware that the wonderful new color they so admired was giving them a daily dose of radiation! (John Emsley)
