What is the difference betwwen Parformaldehyde and Paraformaldehyde sodium bisulphite

[Marek Warunkiewicz]

I know it seems like a dumb question, different names etc. What I am looking for is if there is a way of substituting one for the other or making the Paraformaldehyde sodium bisulphite.

Thanks!

Marek

 

[Photo Engineer]

Well, paraformaldehyde is a white solid that is a polymer of formaldehyde. Sodium Formaldehyde bisulfite is called an "adduct". It is a while solid also that is a loose chemical combination of formaldehyde and Sodium Bisulfite. The Adduct is soluble in water and the polymer generally is not. Both decompose into formalin, but the adduct also gives Sodium Sulfite in solution. There is no such thing as Sodium Parformaldehyde Bislufite.

There is Trioxymethylene which is a trimer of Formaldehyde. It is made up of 3 molecules of Formaldehyde in a ring structure.

They are all inter convertible with the right conditions, usually alkali or acid.

PE

 

[Marek Warunkiewicz]

Thanks for your answer! This is the formula I am trying to make:

PACKO LITH DEVELOPER

Water (< 32 C) 500 ml
Sodium Sulfite (anhydrous) 3.0 gr
Sodium Formaldehyde bisulphite 25.0 gr
Hydroquinone 12.0 gr
Sodium Bromide 2.6 gr
Sodium Carbonate (monohydrate) 23.0 gr
Ascorbic Acid 5 gr
Cold water to make 1 L

So the "Sodium Formaldehyde bisulphite" confused me. Should I just add 45 Gr of Paraformaldehyde and not worry?

Thanks!

Marek

 

[Photo Engineer]

Some of the buffering and sulfite in the developer is coming from the adduct so NO, use of Paraforomaldehyde is not exactly equivalent and I don't know for sure what the change will do! I suggest that you get the adduct and use it, or learn to make it using the wikipedia references. There was a long discourse about this here with references.

PE

 

[An Le-qun]

Marek,
ChlorAmEx (I think I have the spelling right) is Sodium Formaldehyde bisulfite. It is available here: http://www.angelsplus.com/SuppliesWater.htm
It's sold as an ammonia remover for fish tanks. Not expensive, and IMHO easier to work with than any of the other options for the buffer in this formula.
Cheers!
An

 

[Marek Warunkiewicz]

Thanks all!

Marek

 

[nworth]

Paraformaldehyde-hydroquinone developers were once very popular for lithographic work. They were rumored to be cleaner working than other formulas and had the advantage of hardening the emulsion a bit. Paraformaldehyde is soluble in alkalies, and sodium sulfite is apparently alkaline enough to do the job. It would probably be possible to make an equivalent solution by dissolving paraformaldehye in the appropriate amount of sodium sulfite and then adjusting the pH of the final solution. A fairly similar developer to the one you showed appeared in a 40s era Photo Lab Index:

Water (<90F) 500 ml
Sodium sulfite (anh) 30 g
Paraformaldehyde 7.5 g
Potassium metabisulfite 2.6 g
Boric acid (crystals) 7.5 g
Hydroquinone 22.5 g
Potassium bromide 1.6 g
Water to make 1 l

Something more similar to the Packo formula might start with the Packo formula, but using 25 g of sodium sulfite, 5 g of paraformaldehyde, and three 3 g of sodium metabisulfite instead of the quantities of sodium sulfite and sodium formaldehyse bisulfite listed.

 

[Gerald C Koch]

High contrast paraformaldehyde developers work because the formaldehyde combines with sulfite ions and keeps the sulfite ion level very low. This promotes infectious development which causes high contrast. Paraformaldehyde and its sulfite adduct are not interchangeable unless the compositions of the developers are changed. The adduct already contains sulfite and so cannot remove any more.

 

[Photo Engineer]

Just a bit of clarification.

Paraformaldehyde does not form an adduct with sulfite. If it is decomposed by acid in the presence of bisulfite then it can form the Formaldehyde bisulfite addition product (adduct). This is due to the fact that paraformaldehyde decomposes into formaldehyde in acid and then reacts with bisulfite.

The bisulfite adduct reversibly decomposes into formalin and sulfite - bisulfite, and the ratio of the latter two is dependent on the pH of the solution.

This decomposition is taken advantage of in the developers being discussed and in the E6 pre-bleach to yield formalin, but for widely different purposes.

PE

 

[Gerald C Koch]

PE is correct! Thanks. I should have proof read my post better. The process is a bit confusing for in one case you are speaking of sulfite and in another bisulfite.

 

[Photo Engineer]

Jerry;

I don't blame you one bit. This is a messy area of chemistry and I had to look it up even though I did some Research on it for an EK patent years ago.

PE