Sodium Acetate BODY Warmer

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Intro: Sodium Acetate BODY Warmer

Have you ever gone to a football game and frozen your butt off?   While at the game you happen to have brought those little charcoal throw away handwarmers.   You pull it out, open it up, and shake the daylights out of it trying to get it to produce some heat.   Normally the amount of heat you get by shaking the bag warms you up more than the little bag ever will.    The last football game I went to was 30 F so I took one of my body warmer along and it produced 5+ hours of heat!  If your looking for a better solution to help keep you warm during those freezing football games (or other cold outdoor activities) then this is the instructable for you. 

Uses I have found for the body warmer.
1.  Cold football games.
2.  Cold campouts.
3.  My wife takes them to bed with her.
4.  Long lasting localized heat for injuries or sore muscles
5.  Cold car rides to and from work
6. ect.

I have quite a few reasons for making this instructable (explained in later steps), but my main reason is I can't find any instructions anywhere else on how to make a sodium acetate hand warmer from beginning to end.  I want others to share my passion and help me come up with ways to make these body warmers better.   Ultimately I feel the best way to get more ideas flowing on the subject is to put an instructable together that described how to make a decent sodium acetate body warmer.

If you would rather watch how to make it than read it, then go to this youtube video.  (Note: I doesn't include instructions on how to make the insulated bag).
http://www.youtube.com/watch?v=SNF2DO6EXcw

Step 1: Motivation for Making This Instructable

I have a few reasons for making this instructable. 

1.   I think that Sodium Acetate hand warmers are AWESOME and that everyone should have one.  Unfortunately there are quite a few places that show you how to make sodium acetate, but all of them fall short in showing you how to make a decent hand warmer out of the sodium acetate solution.   Those instructions are missing how to make the clicker / activator,  the proper constancy for the solution, and materials that work well for a sturdy durable bag. 

2.   I want to better understand how the clicker / activator works so that maybe I could make a better one.   I have heard vague suggestions on how it works but have not yet as of yet read a good article about how exactly it works.

3.  I want others making these hand warmers and giving me suggestions on how to improve on this design.   For example, I use vinyl for my bags, but vinyl becomes brittle in cold temperatures.   I went camping with scouts in February one year and it was below 0 F.  After we were done using the bags in the morning I was collecting all of the warmers and putting them in my duffel bag.   I happened to throw one of the warmers into the duffel bag and it shattered the plastic on three of the warmers.

4.   Ideas and examples for better accessories.   I have made a few accessories for the hand warmers over the last few years.  One I have included in this instructable is the insulated bag.   I would like a way to keep the insulated bag close to my chest without having to hug it.   I would like a way to easily put the hand warmers into my gloves.

5.  The biggest drawback to sodium acetate hand warmers (ESPECIALLY the large Body Warmers) is how long they take to boil in order to recharge them.   I would like new ideas on how to reheat / recharge the bags.   I have tried heating the bags in 300 degree oil  (that worked until the bag split a seam),  I have tried putting a metal plate in the bag and heating it with an induction cooker.  I had some small success with the cooker, but ultimately it proved difficult and painful (I melted through lots of bags,  rusted out metal plates, and fought with an induction cooker until I gave up).   Another idea I have yet to try is to integrate an internal heating element.

Step 2: Activator / Clicker

The Activator (Clicker) is what makes it possible to make a body warmer in the first place.   The Activator starts the crystallization process thereby releasing the stored heat.   It is easy to start the crystallization process using a seed crystal, but it is impossible to provide a seed crystal in a sealed bag.   I have search all over the internet for the commercial version of these discs but they are difficult to find.  The few times I have been able to find them I would have had to buy them in bulk (1000 at a time).   Since this is cost prohibitive I made my own.

The activator is nothing more than a piece of spring steel with a couple of slits punched into it.  There are a few different places you can easily / cheaply get ahold of spring steel.   The two that I have found readily available is a slap bracelet and a tape measure.   I have tried both and have found that the slap bracelet is better.   The steel in a tape measure is flimsy and wears out quickly.   The steel in the slap bracelet is much thicker and lasts for a few years inside the bag.  You should be able to find slap bracelets at most party stores or Wal-Mart for less than a dollar.

Supplies needed to make the Activator.

1.  Slap Bracelet
2.  De-Solv-it (or some other solvent)
3.  Scissors
4.  Cardboard
5.  Razor knife
6.  Hammer

Start by removing the fabric / plastic coating on the slap bracelet.   I accomplished this on my fabric bracelet using a razor knife and fingernails.   With the razor knife I cut lengthwise down the center of the bracelet.   Once cut I started at one end and used my fingernails to remove the fabric over the top of one end.   Once I had the fabric off one end off I was able to pull hard on the fabric toward the other end and it came off in one large chunk.   You can watch a better description in my video if you need one.

Once the coating is removed there is a glue residue left behind.   Use the de-solv-it to remove the residue.   Wash off the de-solv-it and the glue.  This should leave you with a gleaming metal slap bracelet.

Now, take your scissors and cut off a square of metal.  Take the square you cut off and round the corners with the scissors.  Finally check for any sharp points on your metal and cut those off.   You are rounding the corners and cutting off the points so that your metal disc does not puncture your bag.

Take your circular metal disc and place it on a couple pieces of cardboard.   The cardboard gives a soft background and allows the razor to puncture through the metal.   Being extra cautious (so you dont cut yourself) take your razor knife and using a lot of pressure, punch two parallel slits in the disc.   The direction of these slits should not matter.  You are trying to make these slits grind / touch each other when the disc is clicked.   Right now the metal around the slits is bent outwards and needs bent back in.   Place the disc on a hard object and pound it flat with the hammer.

And voila!  We have ourselves an activator.



Step 3: Vinyl Bag

Lets make our bag.   I have tried a few different types of bag material.  Some include zip-lock freezer bags, vinyl, 6 mil painters tarp, and one other that I don't remember the name of.   The zip-lock did not last very long before it punctured, the painters tarp melted, the other plastic worked well but seemed prone to getting really small holes.   (If you get even the smallest hole in your bag, the sodium acetate will not stay in solution form).  So far the best plastic I have found is thick vinyl from Wal-Mart (or fabric stores).  Vinyl is cheap, available, and comes in much thicker sheets than the other plastics I have tried.  

While vinyl does have its upsides, it has one major downside.   In very cold temperatures it becomes brittle.   I broke a few of my bags after using them in sub 0 temperatures.  For this reason I would like to try other types of bags.   Some types of plastic I would like to try are 1.  The plastic used in Hydration Bladders (Camelbak).  The problem is I don't know where to get this type of plastic.  2.  Silicone bags.  I am not sure how to seal this type of bag.

If you have any insights for better plastic bags I would love to hear about it.

Enough talk, lets make the bag.

Tools
1.  Scissors
2.  Sealer
3.  Permanent markers
4.  Flat iron (Alternative to Sealer)

Supplies
1.  Clear Vinyl
2.  Metal Disc

Take your vinyl and fold it in half.  Take your scissors and cut a square out of both halves of the vinyl at the same time.   Trim the edges of the vinyl to make yourself a nice looking rectangular bag.   Depending on how much sodium acetate you have will decide how large you should make your bag.  My bag was 10 1/2" by 8"

Next put your favorite sports logo or design on the inside of the bag (for me thats BYU).   If you color on the outside of the bag those colors will leach out and stain your counter when the bag is hot (even though you are coloring with permanent markers).   Draw, trace, or scribble with permanent markers a design on the inside of the bag.  Dont forget that since you are drawing on the inside you need to reverse your letters.   (It would be a good idea to test to make sure your marker really is permanent.   Draw with your permanent marker on a scrap piece of vinyl and then run it under water to make sure it doesn't come off.   I had a marker that said it was permanent that washed off when I put the sodium acetate inside).

Now take your sealer and seal all four edges of the bag.  For my heat sealer I set it up to 9 seconds heat time for thick vinyl.  You will have to experiment to find the right amount of time for your vinyl and sealer.   After the 9 seconds I let the vinyl cool before trying to pull it off the sealer   If you don't let it cool you will stretch out your seam and it will create a weak point in your bag.   Note:  You can test to see if you have a good seal by trying to pull apart the seam.   If it pulls apart you didn't do it long enough.  It should tear before it pulls apart.    

Last, cut off one corner of your bag big enough to fit your metal disc, then insert your disc.   I do it this way is so that when I add the hot sodium acetate to the bag, there is less area to seal.



If you don't have a sealer I have successfully sealed bags using a flat iron.  IF you decide to try the flat iron instead of a sealer, first don't hold me responsible if this process ruins it.  2nd, either get permission to use it (they can be expensive) or buy a cheap one from walmart.  3rd, be careful, those flat irons are hot.  I take no responsibility.   It is hard to tell how hot to make the iron in order to melt the vinyl together.   Experiment with it and come up with the right heat/time/pressure for yourself.  (As said above try pulling apart two pieces that you seal.  If it comes apart then it wasn't good enough.  You want it to rip before it comes apart).   Once you have made your bag I would recommend that you fill it with water, seal the bag, and stand on it to make sure your seals will withstand the test of time.  If it passes then cut the corner and let the water out.

Step 4: Prepare the Sodium Acetate

Now onto the Sodium Acetate Solution.

You can either mix vinegar and baking soda in the proper proportions to make your sodium acetate or you can buy it online or at a chemical shop.  I have mixed my own before and it worked quite well but it took FOREVER and stunk the house up.   It would take a long time to make enough sodium acetate to fill a large bag.   There are a number of sources for sodium acetate such as where I bought it here -- http://www.hvchemical.com/ -- which is local to me.   I have also seen it on ebay for fairly good prices.   You want to buy Sodium Acetate Anhydrous.   We are making Sodium Acetate Trihydrate when we mix it with water.

Tools
1.  Pot
2.  Measuring Cup
3.  Tool to pound out the lumps (I used a meat pounder)

Supplies
1.  Sodium Acetate Anhydrous
2.  Water

The ratio of Water to Sodium Acetate is approximately 1 cup water to 1 1/4 cups sodium acetate.    For my larger bag I used 2 cups water to about 2 1/2 cups sodium acetate.  

So add your water to the pot and bring it to a boil.  Then add your sodium acetate.  Stir and pound out the lumps until everything has disolved.   At this point your solution should be near boiling and there should be a super thin crystalline layer across the top of the solution.   You want your solution right at the point where this layer appears.  You can play with the consistency by adding more water,  boiling water off, or adding more sodium acetate.

If you make the solution too thin then the heat reaction wont be as strong.  So it will still crystalize and get hot, but it wont get as hot or stay as hot as long.

If you make the solution too thick then your solution will look like a gel when cool.   It also has a tendency to form interesting crystals in the solution when it is too thick.  These two side effects can actually be pretty cool, and don't seem to change the heat reaction.

Step 5: Testing Your Solution and Activator (optional)

I added this step for those of you who are impatient and want to see results NOW!!!   So lets give you your results now.  Simply put we are going to create a temporary hand warmer.

Tools
1.  Measuring Cup
2.  Bowl full of ice water

Supplies
1.  HOT sodium acetate solution
2.  Freezer Zip-Lock bag
3.  Clicker / Activator

Open your ziplock bag and insert your clicker / activator.   Take the measuring cup and put some of the sodium acetate solution in the bag.  Seal the bag and then place it in the ice water.   Leave it there until it has cooled off.   Once cool pull out the bag and try out your clicker.  INSTANT HEAT.   USUALLY.    Sometimes the clickers are temperamental and take a little more effort in order to activate your solution.   If needed click, twist, and/or bend your activator until you get the reaction to take place.   

Step 6: Finish the Hand Warmer

Finally we are ready t put the solution in the bag.

Tools
1.  Funnel
2.  Container for pouring the sodium acetate.
3.  Leather Gloves
4. Sealer
5. Wet Paper Towel ( or rag)

Supplies
1.  Hot sodium acetate
2.  Vinyl bag with one edge cut and clicker / activator inside.
3.  Food Coloring (optional)

DISCLAIMER:  While I wouldn't consider making a body warmer very dangerous, if there were a dangerous part this would be it.   The solution is VERY hot and can burn you.   If you get the solution on you it will initially burn because it is hot, but then it will also crystalize and continue to burn.   Just be ready to run to your sink and wash off the sodium acetate if you happen to get it on yourself.   Also, the bag and the funnel will get very hot when your pouring the solution into the bag.   I would recommend using gloves during this part.

Step 1, transfer the solution from the pot into something that is easier to pour with.   This step isn't necessary but I find that pots have a tendency to drip the solution down the bottom of the pan instead of into the funnel.

Step 2,  insert the funnel into your vinyl bag.  hold the funnel in the bag with your fingers.

Step 3,  pour the solution down the funnel and into the bag.  Note don't overfill the bag, this makes it incredibly hard to seal the bag.   I wouldn't fill it more that 1/2 to 3/4 full.  Remove the funnel.

Step 4,  If you want to change the color of the sodium acetate now is the time to do it.   Add drops of food coloring to the bag.   It might help to experiment with water first to know what color you want to create.

Step 5, Any sodium acetate in the area of the final seam (crystalized or not) will prevent a good seal.   When you seal the bag the water evaporates and the sodium acetate crystalizes in the seam.   I prevent any problems by wiping out the seal area with a wet paper towel.   Simply wet a paper towel and wipe the inside of the bag where the seam will go.   Make sure to do a good job cleaning the inside of that seam.

Step 6,  Force any excess air out of the bag  (making sure not to get sodium acetate in the area of the seam, a little air is ok) and seal the final seam.

And thats it, your bag is done.   You might put your bag in cold water so that you can cool it down and try it out.   Often times after you initially seal the bag the solution will crystalize and you will have to heat the bag up in boiling water to melt all of the crystals before testing it.

Step 7: ReHeating the Body Warmer

To reheat or reactivate your body warmer all you have to do is boil it.    Essentially what your trying to do is melt the crystals.  Sodium Acetate Trihydrate  (what me made with Sodium Acetate Anhydrous and water) melts at 58 C or 136 F.

Tools
1.  Pot of boiling water
2.  Strainer
3.  Tongs

Fill your pot will water and heat up the water.   Add some sort of barrier into the pot (a strainer, or a rag).   The barrier is to prevent the vinyl from sticking to the bottom of the pot and becoming too hot and melting.   Next add your bag to the water and put the lid on the pot and let it boil for a while.    You need to let it boil past the point where you can see any crystals (even little tiny ones).  Finally once it is all solution again take it out with your tongs and let it cool.

You can help speed up the melting process by taking the bag out of the pot and mixing the solution in the bag around.  This helps to distribute the heat inside the bag.

During the boiling process you can test the solution in the bag to see if it is completely melted by taking the bag out of the water and hold it up by one corner.   Then using a pice of ice cool down the corner of the bag you are holding.   If the solution crystalizes in that corner then it is not ready to take out.

Step 8: Insulated Bag

Normally the body warmers cool off fairly quick and only gives 30-45 minutes of heat.  To help the body warmer keep heat as long as possible and to slow down its heat loss I have created a bag to put the body warmer into.   Using this insulated bag and heating up the body warmer before activating it, I gotten 5+ hours of usable heat out of the body warmer.

Tools
1.  Razor Knife
2.  Scissors
3.  Permanent marker
4.  Hot glue gun

Supplies
1.  Mylar Bag  (you can use aluminum foil tape instead, but it takes longer).   I have bought these a a food storage center near my house for really cheap.
2.  Padded Envelope ( flexible packing foam is a good alternative)
3.  Duct Tape (of your favorite color)
4.  Velcro strips

Cut and seal your mylar bag so that it is just longer then the padded envelope and wide enough to just barely fit your padded envelope.   Insert your envelope into your mylar bag.  Cut the the top of the mylar bag off so that it is one inch longer than the inserted padded envelope.   Now cut off one side of of that top 1 inch so that it creates a flap at the top of the mylar bag that you can fold over to close the bag.

Draw a fairly large square on one side of the mylar bag.   This will be the window that allows heat to escape (and keep you warm).   Use the razor knife to cut out the square.  Be careful not to cut too deep, you only want to cut through one side of padded envelope.

Now take your duct tape and tape the inside edges of the window.   This will keep the mylar bag and the envelope from ripping.   The mylar bag edges are somewhat rigid and sharp so cover all the edges of the mylar bag with the tape.  

Finally cut out 4 strips of velcro. Hot glue two of the strips onto the outside of the flap of the bag.   Now hot glue the other two strips to the front of the bag so that you can fold the flap over and have it stay down because of the velcro holding it down.

Thats it!   Now you have a body warmer and a bag to keep it hotter longer.

Step 9: Tips/Tricks/Finish

Last but not least, a few tips I have picked up along the way.

1.   If you heat up your bag before you use it, it will stay hot MUCH longer.  
2.   If you heat up your bag and put it in the insulated bag it will stay hotter EVEN LONGER.  

The other day I went to a BYU football game where the temperature outside was 30 F.   Before I left for the game I boiled my body warmer to get it hot before I left.   So I left for the game at 7:00 PM.   While at the game I was nice and bundled and kept the body warmer in my coat pressed up against my chest.   It was nice and warm.   I ended up getting home from the game at about 12:15 AM and the body warmer was STILL HOT!!!   Not just warm, it was hot!   That is 5+ hours of useable heat.  Now thats what I am talking about!!!  

Throughout the game I was warm except by half time my toes were a little cold.   By the end of the third quarter my toes were very cold.   I happened to have another body warmer on me, so I took it out, activated it and placed it on my shoes.   That worked somewhat, so I took my feet out of my shoes and placed the warmer directly on them.  AHHH that felt good.   After 5 minutes of that, no more cold toes.

3.  If your body warmer will not stay in solution no matter how long you heat it up, this would suggest that you have a hole in your bag.   Even the smallest hole will cause your sodium acetate solution to crystalize when it cools down.


If you need more instructions here is a youtube video I made of the process.

http://www.youtube.com/watch?v=SNF2DO6EXcw

2 People Made This Project!

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85 Discussions

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Laserfoot

8 months ago

I have a purchased sodium acetate handwarmer that sat around without being used for a couple of years (at least). I went to activate it tonight by flexing the disc and nothing is happening. I suspect the seed crystals trapped in the metal disc eventually totally dissolved through lack of activation. Do you have any idea on how I can re-introduce crystals into the sealed handwarmer? I could just go buy new ones, but I'm getting stubborn about this and want to see if there is something that can be done. Right now the handwarmer is outside in -19F cold but still no crystallization when the disc is flexed. The solution is fully liquid. Any help is appreciated. Thanks.

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kevin_micLaserfoot

Reply 8 months ago

I don't think there are seed crystals stuck in the disc, instead flexing the disc somehow creates sites for seed crystals to form. When I have a stubborn disc I flex and twist the disc rather than clicking it and that usually works. I try and not deform the disc but I do flex/twist it up to the point of deforming it.

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Laserfootkevin_mic

Reply 8 months ago

Thanks a bunch Kevin. Perseverance, like you suggested, along with some extra muscle did the trick! This is a palm-sized hand warmer which is really helpful for barn runs in -20C weather, but I'd like to use your methods to make some finger disks to drop in the fingers of a work glove.

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badon

1 year ago

Have you tried using a pressure cooker?

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67chevl

1 year ago

Just a couple thoughts on your bag. You can buy those Space Age silver heating blankets at the dollar store which would work for the boil bag. Have you tried lining the inside of your padded bag with the foil so it reflects the heat back to the middle? Then you wouldn't have to cut the large hole and lose heat faster. Or if you wanted holes could you use a hole punch and put several smaller holes?

For reheating the bag I would think that a steamer pot (you know the ones for veggies, 2 part pot, the lower is filled with water and then you put on the upper pot that has holes in the bottom of it). The steam would reheat faster and the bag shouldn't melt touching the bottom. Great write-up!

2 replies
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kevin_mic67chevl

Reply 1 year ago

Thanks for the suggestion on the steamer. I have a rice cooker I could try that with.

For the padded bag I was using a mylar bag outer bag to reflect the heat back. The hole in the middle was to direct the heat toward my body. If I fully enclosed it then I didn't feel the heat at all.

My biggest problem these days is the vinyl bag. Vinyl is cheap and available but their seams usually fail after a few months.

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67chevlkevin_mic

Reply 1 year ago

I think you would get better heat if you had the vinyl bag in the reflective foil bag and then put that in a cloth bag (denim) of some sort for padding that isn't to thick. The heat can't pass through the padded envelope. Kinda like the rice bags that are used in homes if you know what they are. I do upholstery (part time) and I would think that you could use some of the clear window covering that is used in Jeep soft tops and in tent trailers. It does get a lil stiffer in the cold but with the bag being warm it shouldn't break. It can withstand over 100 deg and well below freezing. The only thing you would have to do is make sure you had a good seal on it. There are different thicknesses you can get, the thicker one would work better for your bags. It can be purchased at any upholstery shop. I get ours from Silver State Supply in SLC if you can't find another. I am going to have to make some of these for work. I have a co worker that has one that he purchased and it is pretty cool. I can't have the "Y" at my work though. I could put an "A" on it though. :)

Lots of suggestions to consider. For the person that wants to do one with what they have at home your design looks spot on.

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nanoBorg88

6 years ago on Introduction

Some ideas for warming it:
Could you use a kettle, you would have to modify it slightly to make sure you protect the bag from the actual heating element.
Cars give off a lot of heat, could you make a safe little compartment under (or even on, if you want) your bonnet so when you've arrive at your cold destination you have a useable warmer.
I dont know how long these things take to warm but I imagine the keetle might need more than one go.
Also just out of curiousity would a pen clicker set off the reaction?

1 reply
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ata1antananoBorg88

Reply 2 years ago

Pen clickers are generally plastic so they probably wouldn't work.

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cre8tivefix

2 years ago

Your instructable was great. Lots of good info. I started looking up sodium acetate for a totally different reason, but landed here and after a few days made myself a warmer after having some real science fun with my kids. Ran into a few challenges after getting it close, so I thought I would add what I learned. I used baking soda and vinegar to get my SA, so it was helpful to filter it and rinse it with isopropyl alcohol to get rid of particles that were causing it to solidify prematurely. Next, I didn't have a slap bracelet around and wasn't willing to wait for one, so I made a snap disc out of a can lid and a ball pein hammer. It worked but not reliably, so my end fix was just to throw two pennies in the bag and rub them together to start the reaction. Works perfectly. I used an old curtain bag for the vinyl. And our food saver vacuum thing to make the seals (putting a small strip of cardboard in on side for the funnel to fit through then sealing it again after filling). May not last long, but for now it's great fun. Thanks so much for putting this up.

1 reply
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kevin_miccre8tivefix

Reply 2 years ago

Hey, thanks for the info. I will try the alcohol method for cleaning the next time I try it from scratch.

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jjsnow

2 years ago

I love this idea - has anyone tried to 3D print with PLA (flexible) or Silicon and then inject the sodium acetate into it? or better yet, print it like a pillow form with a stopper or resealable tab/screw through which the activator and the liquid could be inserted? The plastic could be printed to be very thin but would probably hold up better than plastic bags or plastic wrap. Just a thought, I know 3D printing with silicon is still fairly limited but when I read everyone's comments I thought it might be a good application for this particular challenge.

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Laral

3 years ago on Introduction

I see a lot of people trying to make their own sodium acetate with less than stellar results. Why would you bother? You can't make it any way near as pure as a chemical company can and purity is absolutely mandatory for this use. Impurities will interfere with the crystallization process. You can buy 4 oz. of 99% pure food grade sodium acetate on eBay for $8.95.

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kevin_micLaral

Reply 2 years ago

I agree that it is much easier to buy it, though i disagree that it has to be absolutely pure for the reaction to work. The ratio of water to sodium acetate is main factor in how well it works.

Also I would recommend you buy it in crystal form (trihydrate) so that you arent paying for water that is very easy to add. Also, that is a really crappy price. I saw 2 lbs (32 oz) on ebay for $14.

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Laralkevin_mic

Reply 2 years ago

The more impurities, the greater the chance of them precipitating the reaction. FYI, it is the trihydrate (3 water molecules) form that has 3 water molecules added to the anhydrous (0 water molecules) form, which is the one you want. If you go to the eBay link, you will see that the $14 for 2lbs that you mention is the TRIHYDRATE form. It is probably still cheaper per lb in that form if you want a lot. The water content is around 40% by weight. Both these forms are crystalline forms.

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kevin_micLaral

Reply 2 years ago

You are right, i meant anhydrous.

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PhebeEve

2 years ago

Without the preheating, how long do the warmer bags extend the "life" of the heaters?

1 reply
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kevin_micPhebeEve

Reply 2 years ago

I don't understand your question. The "life" of the heater is as long as your bag lasts (since it is reusable). Temperature of the bag doesnt affect tge bag's life. Temperature of the bag does affect how long the bag stays warm during a single use.

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Laral

3 years ago on Introduction

I am playing around with sodium acetate and would like to make something like this. There are some good ideas here. Thanks.

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ccronkhite

3 years ago on Introduction

Have you tried the vacuum sealer bags for preserving food? The bags we use seem to be pretty tough. It definitely holds up in the freezer and I'm pretty sure the material can stand hot temperatures too.