[cookaburra (OP)]

On BBC Breakfast TV this week there was an experiment that I didn't see but was reported to me by a non-scientist involving the reaction of a powder with a what I presume was an alkene that produced Iodine as a vapour.  I am a technician in a secondary school and would like to try this as it was apparently quite impressive.  Can you tell me what it was?

[RD]

The item may have been a promo for the BBC TV science series "bang goes the theory" ... http://www.bbc.co.uk/bang/

[mcjhn]

is it this one?

aluminium and iodine

[Bored chemist]

Rather more likely to have been the reaction of iodine with turpentine.

[iwannabeavet]

It was probably iodine and turpentine. You pile iodine crystals or iodine powder, if you prefer, onto a lab table and smother it with liquid turpentine, which causes an impressive purple smoke cloud to billow into the classroom. The smoke stings a little so it is best done under a fume hood.