boots hand warmers

[mollykins]

I got hand warmers from boots for christmas, but me ( and 2 science teachers ) can't work out how they work and with what kind of chemicals (non are listed on the packaging).

They have a clear gel in them aswell as this little metal disc, that you pop to activiate them. Once activated, the gel becomes hard, white and warm, which lasts for about 40 minutes. After which they go cold but stay white, and you have to boil them for ten minutes to recharge them, after which they do go clear again, and they can be reused.

Any ideas as to why/how this works and what chemicals could be inside?

[redcrx]

here you go Molly.

You can print it off to show your science teachers

http://en.wikipedia.org/wiki/HotBag

[mollykins]

Thanks.