I recently watched one of the better known chemistry demonstration shows, which, I confess left me in part underwhelmed, but also rather appalled. Part way through the lecture the famous SF6 floating boat demo was carried out. If you haven’t seen it then look on YouTube. It is astonishing. No question. But should we be doing it?
I’m sure you are aware of the problem. SF6 is one of the most robust molecules ever discovered/invented. Its six S-F bonds are tightly packed around the central sulfur in such a way that virtually nothing can get in there to interfere with the sulfur – it’s a molecular armadillo – and that makes it brilliant as a blanketing gas for smelting magnesium – it’s astonishing that not even hot magnesium will bite it. But it also means that if you release it into the environment it will hang around forever and a day – the atmospheric lifetime is 3200 years according to the EPA.
But at the same time, the S-F bonds are actually highly polarized – there is a lot more negative charge on the fluorine than there is on the sulfur. That means that when the atoms move they can couple very strongly with infrared radiation. In other words, it’s one hell of a greenhouse gas.
Coupled with its atmospheric lifetime that gives it a global warming potential of 34000 compared to CO2 (which has a value of 1).
So why the hell is anyone doing this demo any more? But even worse, how can one do this demo without talking about the chemistry of SF6 and all the implications of using it? Sure you only use a few litres, which is nothing compared to what industry does, but does that make it right? By that argument then it’s OK to pour mercury waste down the sink “because it’s not much really”. There are some demos that may pass our current obsession with Health and Safety and yet which I just don’t think should be done.
Did I go and tell the guy what I thought? I’m afraid I didn’t. And that was partly because the last thing you need after giving a talk is some arrogant nutter out of the audience giving you grief. But when (not if) I’m in the bar with him one of these days, I will tell him. And I hope that if I do something that you feel I shouldn’t, come and tell me. Just be gentle. I’m not an armadillo.
I did this demo for a TV show about ten years ago, and only later learned about the greenhouse implications. Doing the maths, I worked out that the item we’d filmed was equivalent to driving my car 100,000 miles. OK, it was a Mini, but that’s still a significant output. Following this sobering realisation, I promised myself that henceforth, along with the habitual risk assessment, I’d also conduct an environmental impact assessment of all my projects.
Of course, I never did. Not really. It’s hard to take on an onerous job like that if nobody’s going to give you any credit for it, and it’s not even clear how one might go about doing it. But I do think the idea has some validity.
Thanks Jonathan. I’m impressed that you did the back of the envelope calculation – hats off to you. And I agree, that it would be pretty cumbersome to try to do a footprint calculation on everything we do.
But my point is two fold. If we know that something has wider implications we need to think about it in a wider context. Should I accept an invitation to fly New Zealand or St Louis all expenses paid to do a demo in front of a live audience? I have gently turned those opportunities down, because my talk starts to vere towards the SF6 demo.
But more importantly, I think my point is that if you’re going to do a demo like the SF6 demo then for God’s sake talk about molecular weights, vapour densities, diffusion of molecules and the speed of mixing, the refractive index of gases, oscillator strengths of infrared transitions, climate change and the importance of trace gases, atmospheric lifetimes, kinetic versus thermodynamic control in chemical reactions…….. (bejayzus I think I have a one hour lecture here just round SF6……..). In other words, milk it for all it’s worth
Simply to do it “because it’s cool” is an incredible waste of an opportunity to show people the big picture.
You know, there’s an amazing show to be written building up to a demo that you know is brilliant, that you’ve terrific props for, that you convince the audience will be one of the most amazing things they’ve ever seen… but when you get there, the audience themselves demand that you don’t do that demo. That you leave the pandora gas in the cylinder.
That could be an amazingly powerful show.
(It’s the demo lecture equivalent of the art installation that featured goldfish swimming in food blenders. The question there was: would anybody push the button to turn the blender on?)
Cheltenham next year?
I love it.
Let’s DO it!
If we do, can we use the word ‘amazing’ fewer times than I just did in that reply? (sheesh, and I call myself a writer…)
Alom knows how to contact me if you’re serious. I could be: there’s something in this. It’d have to be sold as a show culminating in a flying boat – the audience have to come to see that, to want to see that, then finally deny themselves the experience as a deliberate choice. No mean feat to pull off.
Get it right, though, and it’d be a hell of a moment.
Incidentally, I once made an Irish science magazine series aimed at teens, and one of the shows was based around our calculations of the carbon emissions involved in making the show. Which became rather amusingly recursive at one point. A whole bunch of consultants offered to do the calculations for us (for a fee…), but in the end we picked the most chatty of them and said, “No, we’ll do the sums, then you can give us your reaction. On camera.”
Turns out it’s rather easy to calculate emissions if you add a carbon column to your budget, as long as the budget doesn’t hide anything much. You have to decide how far down the rabbit hole you go – do you cover staff commuting emissions? How about the upstream emissions caused by the production of the office coffee? – but that’s a general problem anyway.
I’ve meant to double bottom line account everything since then, and hence offset my projects so they’re carbon neutral. Maybe it’s time I made good on that too…
Carbon neutrality. Now there’s a question. I’ll be posting graphs of domestic emissions over the next little while as I have data going back several years. I keep track of travel emissions, but I haven’t actually costed up chemicals I use when I do demos……… stuff to think about.
Andrea and Jonathan – although, done well, this demo can create a powerful emotional response, I share your environmental concerns. I agree it’s a real shame because it is such an amazing demo.
I think that if you are going to use this demo responsibly then it may be possible to justify it as a one-off *if* – the audience is very large; you take advantage of the opportunity to discuss the environmental damage the gas causes; and you moderate this damage by donating to an off-setting scheme.
Hmmm… letting the audience vote if you should do the environmentally irresponsible finale demo is certainly a novel and intrigiung show format. Like Jonathan I’d love to see how it works. I’d have two main concerns in practice – the age of the audience being played to (some teenage audiences, although inherently green in theory, can be extremely preverse and oppositional if they sense any agenda of being preached to); and the actual impact of the demo is much stronger than “making a foil boat float on a gas” tease sounds so we’re not really testing their environmental resolve very strongly. Do we reward them with a video of the demo at the end so they know what a stunning demo they resisted from seeing live? Dramatically tricky to pull off the ending of this show obviously, but that’s not a reason for not trying.
If only there was a talented chemistry demonstrator and an experienced TV producer of science demos who could record a beautifully-shot version of this demo and make it available for teachers and science presenters to use in lieu of using the gas themselves….