Salts burn with characteristic coloured flames, in this demonstration photographed at the Centre for Life, Newcastle.

Flame colours

A scary article in the NY Times last Friday about a chemistry demo they refer to as “the rainbow”:

“With about 30 students watching from their desks, a snakelike flame tore through the air, missing the students closest to the teacher’s desk, but enveloping Alonzo Yanes, 16, searing and melting the skin on his face and body, according to witnesses. He was in critical condition on Friday[…]”

Just weeks ago, the article relates, the demo was the focus of a safety bulletin from the US Chemical Safety Board, and this film:

Here in the UK, I think we’d more commonly refer to the demo as “Flame colours”, and at the head of this post is a photo I took of it a few years ago. As best I can tell, the cause of the accidents in the US has been demonstrators topping up the flame straight from the methanol bottle, leading to the ignition of a large volume of fuel vapour.

Now, I’d hope most people reading this blog will be wincing right now. It was drilled into us (in school) that you never open a bottle of fuel near a naked flame, and that the correct procedure here is to ensure the watch glasses are cold before adding a small amount of fuel (typically with a pipette), then sealing the fuel bottle and removing it to a safe distance, before lighting the mixture in the watch glasses.

That would be standard lab practice, and it’s near-inconceivable that a teacher would pour meths from a bottle directly onto a flame. However, one thing we learned from SciCast is that we’re into the second generation of science teachers who’ve never really ‘done’ practical science. Recent science graduates don’t necessarily know how to handle flammable materials; they may never have been taught.

That generational knowledge gap was one impetus behind the demonstration films Alom and I have been making for the National STEM Centre and others, and also for this website. So pass this on, please, and let’s not make assumptions.

Oh, and if you’re a teacher in the UK, the version of this demo you should do is probably the one with ethanol spray bottles. That’s the version the Royal Society of Chemistry and Nuffield promote, but – as ever – check with CLEAPSS for their standing advice.

[EDIT 9/1/2014 – The RSC’s Education in Chemistry blog has picked up the story. Their post includes a quote from Steve Jones, Director of CLEAPSS.]

[EDIT 2 15/1/2014 – I somehow missed the NY Times’ follow-up story about the school involved in the incident above being inspected by the Fire Department, and being given notices to improve on a range of issues. Also, for the UK audience I should note that the Scottish equivalent of CLEAPSS is SSERC.]

One thought on “Flame colours”

  1. Astonishing. I get jumpy if I am cooking in the kitchen (gas) and my daughter is using nail varnish remover in another room. My science club version of this experiment does not require the solvent – I use fuel tablets on a heat-proof board, and gently sprinkle a small amount of the salt powder into the flame. Stronger colour and lasts for a while.

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