Elemental memories

Mar 27, 2019

In order to keep our element writing competition to the forefront in everyone’s minds, I thought I’d re-heat an old post – my first post on The Sceptical Chymist, no less! In that post I look back into the depths of time, at my first ever science lesson in school. Magnesium featured heavily, which is why I’m re-heating the post. The element has already been covered in the In Your Element series ($/£), by organometallic chemist Paul Knochel.

I still vividly remember my first science lesson back when I was a 9 year old, over 20 years ago. The school buildings were quite new (10 or so years old at the time), so the little lab was pretty well kitted out. But what the teacher, Mr Challinor, really tried to instil in us during that first lesson was the fact that science wasn’t just about Bunsen burners or any of the other complicated apparatus we were all seeing for the first time. A scientist’s most important tools, he said, are your eyes, to observe what was happening.

One of the first experiments I remember him showing us was incredibly simple, but also incredibly powerful. He told us about how atoms make up everything around us, and then about how burning something was essentially just adding oxygen to it. He probably briefly mentioned the phlogiston theory – which, like Phil Ball, I don’t think is quite deserving of the laughing and pointing we give it nowadays. After all, I remember during that first lesson thinking that most things end up much smaller after you’ve burnt them – think about how much smaller ashes are than a pile of sticks, for example. So a phlogiston-type theory fits a lot of day-to-day experiences.

In order to prove that things really do get heavier once you’ve burnt them, he carefully weighed some magnesium foil in a crucible, then set fire to it. After the bright white flame died away, he re-weighed the crucible and guess what? The weight had indeed increased.

As well as teaching us about atoms and combustion, something else he did in that experiment also stands out – and it’s probably a more important lesson than correcting what people thought 300 years ago. He got one of the class to watch over his shoulder as he did the weighing (we couldn’t all fit around the balance). This was just to show that he wasn’t making it all up, that we shouldn’t believe him ‘just because he said so’, but to show what he said had happened actually did. That’s a pretty important first lesson in science for anyone, but especially for a 9 year old: don’t just take someone’s word for it, see for yourself.

Now, magnesium was an important part of the experiment, but not the point of the experiment itself. But would I have remembered it as well without that incandescent burning whiteness? I guess I’ll never know, but the whole experience also neatly fits with a recent blogpost at the Guardian, by a teacher and filmmaker who suggests that doing experiments or practicals for the sake of it isn’t the best use of class time. Before we all leap to the defence of our favourite childhood memories, it’s worth noting that the author tries to make it clear that he’s not suggesting ditching all experiments, just making better use of fewer. See what you think.


Neil Withers (Associate Editor, Nature Chemistry)

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