# Which Oxalic Acid do I use?



## Hillside (Jul 12, 2004)

The testing has been done and the formulations are calibrated with the dihydrate form. If you use the anhydrous, you will have a higher percentage of acid in your solution. It's also a lot more difficult to store the anhydrous form since, over time, it will pull moisture out of the air and become the dihydrate.


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## Dave W (Aug 3, 2002)

If you are preparing say a 3-1/2% solution, couldn't you use "any form"?


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## Sundance (Sep 9, 2004)

This is what I get.......... I am pretty sure it is dihydrate.

At the time it was also the best price I could find. A 7 pound bucket for $20 which lasts a long, long, time.

http://www.chemistrystore.com/oxalic_acid.htm


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## Hillside (Jul 12, 2004)

> If you are preparing say a 3-1/2% solution, couldn't you use "any form"?


Yes you can, but since the gram atomic weight of the dihydrate is 36 grams greater than the anhydrous, if you use the anhydrous acid with a dihydrate formula, you won't get the right concentration. It'll be a little over 30% too concentrated.

You would have to recalculate the formula and since the anhydrous form is difficult to store without it taking on water, using the dihydrate is a lot easier.

Instructions for the dihydrate can be found here.
http://www.honeycouncil.ca/users/folder.asp?FolderID=5204


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## megank (Mar 28, 2006)

I understand that the anhydrous will make a stronger solution...which may or may not be harmful.

I guess my real question is...What form of OA do you get when you purchase it from your local hardware store?

I've checked the container and it's not listed...

Any ideas?


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## Hillside (Jul 12, 2004)

From the hardware store it's the dihydrate. You would have to go to a chemical supply place to get the anhydrous.


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## Dave W (Aug 3, 2002)

Are there difference "concentrations" of the dihydrate form?

If so, how do know what you have?

To mix a 3-1/2% "working solution", a different formula is needed for a 99% pure and a 75% pure dihydrate form of OA.


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## Hillside (Jul 12, 2004)

The only oxalic acid I have bought has been labeled as wood bleach. The label states that it is 100% oxalic acid dihydrate. Of course, no industrial grade chemical is really 100%, but this particular type has worked well for me. Heck, reagent grade chemicals aren't really 100% either. 

The wood bleach oxalic acid comes in a plastic tub with a snap on lid that seals quite tightly. I put the sealed tub in a plastic zip lock bag for extra protection from moisture. I use a cheap, electronic postal scale to weigh out what I need.

I've also run into wood bleach where the label says "non-acid" and "contains no chlorine". It doesn't really say what is in it, only what isn't. I have no idea what's in that stuff, but I'm obviously not going to buy it. 

I was not able to the get oxalic acid type wood bleach at Menards. I had to go to the local hardware store. They had a bunch of it.


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## Dave W (Aug 3, 2002)

It is my guess (not sure) that if you use “food grade” OA that meets U. S. P specification, all of the contents (every thing in container) will be OA and the purity of the OA chemical will be 99%+.

But, CONTENTS of “hardware-store-commercial grade” OA is probably UNKNOWN and probably VARIES (from source to source, batch to batch). The AMOUNT of OA in the contents probably VARIES, while the purity of the OA present may 100% pure, that too may vary.

I have heard (pure rumor) that some dihydrate forms only contain 70% or so OA.
If so, mixing formula to produce a 3.5% working solution will vary wildly.
Wrong formula would mean a stronger or weaker solution. 

Is this why we haven’t seen U.S. OA registration?


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## megank (Mar 28, 2006)

SO using the dribble OA formula using OA bought from the hardware store is just fine?


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## Dick Allen (Sep 4, 2004)

yes, the OA purchased at the hardware store as wood bleach is just fine to use.


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## Hillside (Jul 12, 2004)

Another source for oxalic acid is the chemistry store. They have an MSDS that indicates this is pure oxalic acid dihydrate. They actually have a pretty decent price.

www.chemistrystore.com/oxalic_acid.htm

The trouble with this site is that the CAS # they list is for the anhydrous, but the MSDS is for the dihydrate. It would be nice if people could get their act together.


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## Dave W (Aug 3, 2002)

If you have a formula for mixing a 3.5% OA solution, "run the numbers" and see if it uses 100% or 70% OA. Then all you have to "guess about" is IF the material in the hardware store is 100% or 70%.

Using 100% OA w/ a formula designed for 70% will give you a MUCH higher strength solution. The other way around, it will be so WEAK that . . .

Oh well


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## Dave W (Aug 3, 2002)

To determine the percentage (weight/volume) of OA in a syrup solution, divide the actual amount of OA (weight of OA x 0.714) by total volume of sugar solution. (Example: 75 g of OA x 0.714 = 53.55 / 1.67 liters of sugar solution = 32.06 or 3.2%)


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