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bulrush
05-20-2008, 10:15 AM
Saw this on "Rough Science" volume 1 DVD. This makes a heat pack so hot it melted a ziplock bag on the show. My guess is it will not last long, about 30 minutes tops. But this is just a guess.

- Cook chalk (sidewalk chalk, school chalk) over heat for 8-12 hours to remove all water vapor. This creates slaked lime. Heat must reach 2000F-2500F.
- Mash up the slaked lime into a powder.
- Put in heat safe can. Add about 1/2 cup lime powder, and several tablespoons of water. CAUTION: this melted a plastic bag on the show.

This creates an exothermic reaction and heat.

EDIT: Found this on http://www.pbs.org/weta/roughscience/series3/ice/handwarmers.html

Chalk must be heated between 2000 and 2500°F (1200 - 1400°C). This means, you will need to make or buy a blower-powered forge to get those temperatures. It explains why it didn't work when I used a hobo stove this weekend.

Everyone: what common metal melts at 2000F to indicate we have reached the right temperature?

The melting point of Iron is 1538C, enough for our experiment. The melting point of Copper is 1084C, not enough for this experiment. The melting point of gold is 1084C, not enough. The melting point of silver is 962C, not enough.

For sources of pure (or mostly pure) iron to go http://periodictable.com/Elements/026/index.html .

Examples are: railroad spike, hammer head, nuts? bolts? nails? slingshot ammo, BB gun ammo, old fashioned iron, old tea pot, some trivots, some cast iron toys.

RangerXanatos
05-20-2008, 11:09 AM
This may sound dumm but is this chalk as in board chalk and sidewalk chalk?

grundle
05-20-2008, 12:01 PM
Sorry but both chalks are the same. Side-walk chalk just comes in bigger chunks and is a little bit less refined

Ken
05-20-2008, 12:36 PM
[QUOTE=bulrush;48452]

- Cook chalk over medium heat for 8-12 hours to remove all water vapor. QUOTE]

How much chalk do we use?:confused:

crashdive123
05-20-2008, 12:47 PM
So it doesn't heat up until the water is added right? Is this something for long term storage in your first aid kit or make it as you need it? If you can cook it for 8-12 hours and need a heat pack now - hot compresses. I may be missing something (probably am)

bulrush
05-20-2008, 01:52 PM
- Yes this is any kind of kids chalk, for the sidewalk or board. They are both calcium carbonate? in (compressed) powder form. The Romans used to heat limestone in chunks, when making cement. It takes higher temperatures and longer time to bake but it still works.

- Correct. It heats up only when water is added.

- Yes, you can make up batches of the slaked lime ahead of time, but I think it may be hygroscopic, meaning it attracts water. So put it in an airtight container ahead of time, I mean really, really air tight. If water gets absorbed into it, it won't work. Adding a moisture absorber (like silica gel) inside the container wouldn't hurt either.

Do your own experiments. Make this stuff up, store it for a year, and see if it works later after you add water. Does it get as hot as last time?

When I saw the show I didn't think it would get real warm for real long, but it managed to melt the plastic baggie they had put it in.

Now before you go out there asking "Wouldn't portland cement work the same?" My guess is (and it's a guess) that it might have too many impurities in it to heat up well, but you can try it.

Also, adding 2 (concentrated) acids together, also produces heat. But you have the added danger of the acid splashing on you, or melting your container. Acids you buy in the store (like muriatic acid) may not be concentrated enough to make heat.

grundle
05-20-2008, 02:28 PM
You are slightly incorrect, it is when you add an acid and a base together for a neutralization reaction that heat is generated. Two acids don't do much since the aqueous solution is already H+

Probably more information than you cared for, but there you go.

bulrush
05-20-2008, 02:38 PM
Hmm. That makes sense. I think I got that info (about 2 acids) from Instructables.com, which is sometimes incorrect.

RangerXanatos
05-20-2008, 04:48 PM
We have some meals like MRE's that have that have a compound that heats up when water is added to them. Do you think it would be possible to dehydrate them again to remove the water to make them active again? Just curious...

crashdive123
05-20-2008, 05:27 PM
Do you think it would be possible to dehydrate them again to remove the water to make them active again? Just curious...

Don't believe they can. The chemical reaction with the iron, magnesium, salt and water causes the expenditure of much of the material (causing heat).

bulrush
05-27-2008, 03:25 PM
Everyone, I updated the original post, post #1 with more information. Chalk needs to get to 2000F, which is why it did not work for me this weekend.

RobertRogers
05-27-2008, 04:55 PM
Interesting. It would be great to be able to make this stuff easily at home.

BraggSurvivor
05-27-2008, 05:20 PM
I make heat packs from Keenan dry mustard powder. Make into a paste, wrap in a towel and apply to the area you are trying to heat. The more mustard the hotter it gets.

http://www.ehow.com/video_2167480_mustard-plaster-relieve-chest-congestion.html

Rokas
07-12-2008, 03:46 PM
Well if you have access to these chemicals, witch I'll mention later, you could make another heater too... Take water, add CuSO4+7H20 (cuprum(cupric) sulphate) and make solution in which any more CuSO4+7H2O could melt. Than add salt until this solution makes very green colour. Than add sawdust (to keep the warm longer than liquid). after you done, pour this substance into container with good seal. when you want to activate the exothermic reaction just drop aluminium foil or any aluminium thing and it will start to heat... At home I dropped in this solution aluminium penny. This substance will heat to 100-150 or even more degrees Celsius.. I even once break my flask with heat... The heat should stay about 15-30 minutes depending on your liquid mass and amount of aluminium. The final product of this reaction will be H2 O2 Al2O3 and Cu.
Chemist :D

Rokas
07-12-2008, 03:50 PM
And one more receipt: you'll need sodium acetate and water. heat up the water until it boils. than add sodium acetate until no more of it could melt. then cool the substance down and drop few crystals into this liquid. this liquid will solidify and heat. Do not try this at home! try this at wilderness :D