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These hand warmers are great to stick in a cold coat pocket.  You just grab a rock, clean it off, stick it in the oven, wrap in foil to control the loss of heat, then put it in your pocket.  I like to use them on camp outs, except you put it over the fire there.  
how long time how warm in the oven?
Friends & I do basically that same thing when we have get-togethers. We almost always have a bonfire to heat the rocks, but we wrap them in newspaper. It insulates them so that you don't burn yourself with it and the heat also lasts longer. Of course you don't want to carry a stack of newspaper on a hiking trip, then you could use a couple socks or something along that line that you would be packing anyway.
Oh, these would be sooo nice and toasty after a hockey game!=] I wonder if they might stay warmer if I kept them in my solar oven while I'm outside(?) =^..^=
Toasty. <br> very effective, works every time <br>
Nice entry!
That rocks!
What's with people and irony humor. :p :)
Pay attention to the aluminum foil.<br>Aluminum is a VERY GOOD termal conductor, so it will release the heat very well, meaning it will not protect your hand muck while you touch it.<br>If hot stones can boil water (depends how hot you heat them) then, if wrapped in foil, they can burn your fingers.<br><br>Take a look at:<br>http://en.wikipedia.org/wiki/Aluminium<br>http://en.wikipedia.org/wiki/Thermal_conductivity<br><br>Why hot a woole sock ?
Just don't leave it in there forever
Do these get really hot because of the foil?
rocks can get VERY hot, hot enough to boil water. The foil acts as an insulation to help keep in the heat
They used to do this type of thing with bricks in the days before central heating... putting them into the bed to warm them up. Nice work.

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Bio: I'm still working on my electronics skills. If you see a flaw in any of my crazy plans, feel free to let me know!
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