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Sodium metabisulfite in glycol - problem with dissolving

skljocnulbumte

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Hello!
I started to dissolve a powder chemistry for pyrocat-hd in glycol. From the start I had a problem with sodium metabisulfite. I couldn't dissolve it. Temperature was 65C. After 30min of mixing it is the same like on the start. Is there any trick to dissolve it? I didn't add any other chemistry yet. Thanks a lot for any advise.
 
http://www.pyrocat-hd.com/html/mixing.html
The metabisulfite and bromide are meant to be dissolved separately in water before adding to the glycol.
If you let the undissolved metabisulfite settle out overnight it may be possible to pour off the clear glycol and dissolve the residue metabisulfite-glycol slurry in water as per the instructions.
 
Last edited:
If you are mixing in glycol, I recommend Pyrocat-HDC. Here is the recipe from the website, pyrocat-hd.com:

B. Pyrocat-HDC (Solution A mixed in glycol)
Stock A
Propylene Glycol at 150F 750ml
Pyrocatechin 50 g
Phenidone 2.5g
Ascorbic Acid 4.0g
Propylene Glycol to 1000ml

Pyrocat-HDC gives almost identical results as Pyrocat-HD with most films and development methods.
 
There is a saying in chemistry, "Like dissolves like." What it means is that organic solvents like a glycol dissolve organic substances while water being ionic dissolves ionic substances like sodium chloride. The solubility of sodium metabisufite in glycols is very low.
 
FWIW, this is how I've mixed Pyrocat-HD in glycol for years:

1. Weigh out all the dry chemicals for Stock A.

2. Pre-heat the glycol to about 150F in a water bath or hot plate stirrer.

3. Add the pyrocatechin to the warm glycol and stir until dissolved. Should take no more than about a minute.

4. Add the phenidone and stir. Should dissolve completely in about a minute.

5. Add the bromide and sodium metabisulfite to about 50-75ml (for 1L final volume) of hot distilled water at about 120F. Stir until completely dissolved, and then add this solution to the glycol solution.

6. Top off the solution with glycol to final volume.

I've never had any issues with any of the dry chemicals dissolving completely using this method. Hope it helps.
 

However you are dissolving the bromide and metabisulfite in water so this really doesn't really help the OP's problem.
 

Sodium metabisulfite is soluble in glycerol, which might be preferable to water to add to the Pyrocat.
 
Does that mean that glycerol could be used instead of the propylene glycol?
 
Yes, agreed. It just occurred to me that maybe one could perhaps replace the glycol with glycerol, and if so would there be any advantage?
 
Raghu Kuvempunagar said:
Isn’t glycerol hygroscopic? It’s probably impossible to get water free Pyrocat developer Part A that has Metabisulphite in it.
Click to expand...
It's my belief that you use just enough "glycerol" to get the Sodium Metasulfite into solution. You could do the same with a small amount of H2O also. These tiny amounts of water have very little or maybe even "NO" effects on shelf life. I have finally settled on Pyrocat-HDC and see no reason to try the other forms of Pyrocat after using HDC version for a while. I've used the PC version, HD version and the MC version and they are all good. That's just me of course. JohnW
 
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