Making formalin from paraformaldehyde - help

iranzi · Jul 31, 2011

Hello,

i'm trying to make 37% formalin from paraformaldehyde but it doesn't go into solution. I used 37g paraformaldehyde, 100ml water, heated it up to about 70-80C and stirred for almost 30 minutes. Now i have a bottle of it, 2/3 sediment and 1/3 clear liquid.

Can someone point out what am i doing wrong? Perhaps pH should be adjusted?

I couldn't find the answer here, and got some confusing information from some other sites, eg:

"For all other uses of formalin made from paraformaldehyde, please refer to the formalin variant fixatives. They may be substituted directly, keeping in mind that it requires 40 grams paraformaldehyde in a litre of water to make 10% formalin (4% formaldehyde)." etc. etc...

Photo Engineer · Jul 31, 2011

Your formula and method are incorrect. 37 grams of Paraformaldehyde + 100 ml of water will not make a 37% solution. It will be more dilute than that. See here: http://en.wikipedia.org/wiki/Paraformaldehyde

Take about 50 ml of warm water and add a drop of 37% Sulfuric Acid to it. This is common battery acid. Then add 37 grams of Paraformaldehyde to that in small amounts while stirring. It should dissolve. If it does not, add another drop of acid. When all solid is added, dilute this to 100 ml and this will make a 37% (weight / volume). Be careful as Formaldehyde is a gas and can overcome you in a closed space. Wear eye and hand protection and use a breath mask or work outdoors if possible.

PE

iranzi · Jul 31, 2011

Thank you very much, PE.
I have 10% Sulfuric Acid, so I'd have to use more of it. Would that be a problem?

michaelbsc · Jul 31, 2011

If you are doing it for fun ignore me.

If you just want 37% formalin and you're in the US there is a chemical supply house on eBay that sells 500ml bottles with reasonable shipping.

Photo Engineer · Jul 31, 2011

Michael has a point. Just buy it!

If you have to make it, then for the acid, if you can, get automobile battery acid, but if not then use 3 - 6 drops of the 10% for starters. The formula that I gave is a guesstimate anyhow and you will probably have to adjust it a bit to get it right.

PE

brianmquinn · Jul 31, 2011

Formaldehyde is a gas. It will dissolve in water and when the water is saturated it is 37% formaldehyde. Formalin is a water saturated with formaldehyde (37%) with some methanol added to stabilize the formaldehyde. When this saturated solution is diluted 10 fold you get a 3.7% solution. Usually rounded to 4%.

So you see that 10% formalin is really 3.7% formaldehyde.

lungovw · Mar 22, 2018

PE, I followed your instruction with the following adaptation: I had only Sulfuric Acid 98%, so I started with ~130 ml water at 40ºC and added a drop. Then I introduced a first coffee spoon of Paraformaldehyde in a beaker with a magnetic stirrer. It didn't dissolve at all. I added a second and a third drop and nothing happened. Is 40ºC too cold? How far should I go in temperature or would you have any other point for me to check?

lantau · Mar 22, 2018

I had the same problem. It requires constant heating, but I didn't have a means to properly do it in a ventilated place. Eventually I produced Formaldehyde but didn't get near dissolving the required quantity of paraformaldeyhde without poisoning myself. I simply used more of the solution as is and added it to the bottle with surfactant. It'll have to be good enough. I can smell Formaldehyde when final rinsing film with that. Maybe in summer when I can work outside I'll try again.

Makes me wonder if any of those lith developer recipes with Paraformaldehyde would actually work.

Photo Engineer · Mar 22, 2018

As I said above, this formula is a guess.

PE

desertrat · Mar 22, 2018

10% formalin (4% formaldehyde) is widely used in pathology and biology labs to prepare tissue samples for sectioning, staining, and mounting on microscope slides. They routinely make formalin from paraformaldehyde but not at full strength. They use just enough paraformaldehyde to make a the 10% formalin solution. It might be that trying to make a full strength solution just won't work.

There are instructions on the web for this, but formalin used in histology labs usually contains buffers, which may not be appropriate for photo use. PE's formula might work for making a 10% solution instead of full strength. Also, from what I've seen on the web, dilute sodium hydroxide is added in small amounts to help the paraformaldehyde dissolve. After it's all dissolved, small amounts of dilute HCL are added to bring the ph to neutral.

Making formalin from paraformaldehyde - help

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