Parodinal Variations in Chemicals

Discussion in 'Black and White' started by dennis_o'connor|5, Nov 9, 2009.

  1. I have been making 'Parodinal' using the formula given. I have been following the directions very carefully, at least I thought I had! Until about 30 mins ago I have had a problem with very large volumes of crystals forming in the glass bottle, at least 30% of the volume. I posted this problem in another thread and recieved helpful responses. This morning I tried a slightly different approach. One of the variations of processing I have seen was to dissolve the sodium sulphite in half the volume of water separately. I tried this but did not get any significant improvement. I used capsules rather that the tablet form of paracetamol. That was the problem. If you simply convert the number of tablets to an equivalent number of capsules you get more chemical in the mix. This morning I actually weighed the total paracetemol powder on an accurate set of scales as I emptied each capsule into my weighing container. I was making 300ml of parodinal, which, on a pro-rata basis called for 36 tablets! This should give 18g of paracetamol (including the filler)! I actually got 18g of paracetamol powder from '33' capsules. So I have made up the latest batch using that amount. Initial visual appearance shows a totally different solution. Much less initial reaction to crystal formation and a much 'clearer' liquid.
    I hope I am not 'teaching granny to suck eggs'. I hope that this information proves useful to other 'home-brewers'.
  2. I've had that same problem, so this is very useful. I had the additional problem that as I was boiling the mixture, the volume of water evaporated concentrated the liquid too much. I had to keep adding water to maintain the liquid level.
    Incidentally, I've made parodinal using commerical grade caustic soda (sold as drain cleaner!) and it worked fine.
  3. I actually got 18g of paracetamol powder from '33' capsules.​
    Just a thought - you got 18g of powder, but, without a chemical assay, can you be sure it was paracetamol? Some of that powder may be added to improve the handling, like an anti-caking agent.
    It's almost certain (because of strict quality control) that a 500mg Paracetamol tablet contains exactly 500mg of Paracetamol as the active ingredient. Accurate pharmacology would be impossible if manufacturers short-changed the contents of their drugs.
  4. Alec. Yes I considered that as it is a medicine. The point I am trying to make is that my mistake was using tablet number to capsule number. I dont know how much filler there is in a 500mg tablet or the capsule. If I knew that I could be more accurate in the capsule powder weight.
    Chris. I also use drain cleaner (caustic soda) for the sodium hydroxide chemical.
  5. The point I am trying to make is that my mistake was using tablet number to capsule number.​
    It's not clear to my why you consider that to be a mistake. If a tablet is listed as 500mg paracetamol as the active ingredient, then that's exactly what's in it. 500mg paracetamol per tablet. Ditto for a 500mg capsule.
    I dont know how much filler there is in a 500mg tablet or the capsule. If I knew that I could be more accurate in the capsule powder weight.​
    Again, why do you care how much filler there is? The filler will not affect your film developing (you hope).
    If you want to know how much filler there is, it's easy to find out: take the powder from 10 tablets, weight it. 5g of that is paracetamol (because they're 500mg tablets - 500mg of the active ingredient, paracetamol) - and the rest is filler. Divide by 10 to find the filler per tablet.
  6. Example: I just weighed out 10 500mg USP tablets from the bottle in my cupboard. The total mass was 5.6g. Ergo each tablet contains in addition to the 500mg paracetamol a further 60mg of binding agent, sugar coating, red dye and whatever else the manufacturer wants to include.
  7. Alec. Thank you for your detailed reply. I can only hazard a guess that it is the reduction of the paracetamol powder ratio in my latest mix that has given me the 'improved' (visually) version.
    I notice that Chris in his reply stated that he boiled the water when making parodinal. I have never seen that mentioned in any of the homebrew recipies I have read. In fact I have seen it stated that the sodium sulphite should be mixed at room temperature and only added to the sodium hydroxide/paracetamol when both had cooled. I am thinking that variations in perhaps water quality in different countries, or the quality of the sodium hydroxide, or changes in processing techniques is what is giving the variations. I always use distilled or deionized water.
    I know that the quantity of sodium sulphite stated in the 'original parodinal formula' exceeds the solubility level in water at room temperature. I always have sediment in the bottom of the mixing container, which I add anyway to the mixture. Perhaps I should make it a saturated solution by boiling the water like Chris has stated he does.
    I have seen one statement that the final solution should be filtered before storage, again, only one mention by one contrbuter. Perhaps there is a difinitive procedure script somewhere that could shed some light.
  8. I think the following which I found whilst 'surfing' answers my question about the crystal formation. However. The crystals in my solution start to form within an hour, not a couple of weeks! I wonder if this means I could reduce the percentage of paracetamol or one or both of the other two ingredients. Just curious.
    "After standing for a week or so, clear, needle like crystals will deposit in the container; be sure to keep these with the liquid if you decant, as they’re the excess of p-aminophenol sufonate that ensures against rapid oxidation of the developer by keeping the solution saturated"
  9. See if you can find a brand of caplets where the powder contents can be tipped out.
    Using this powder I made clear PaRodinal using the procedure given in the first post below, with slight modification including filtering through cotton wool at the end.Also I made a saturated sodium sulfite solution and set this aside.Formula was from
    Also see attached sodium hydroxide hazard note,it is caustic.
  10. Alan. Thanks for the reply. I do use capsules and tip out the powder filling to get the paracetamol. I have not seen mentioned the saturated solution of sodium sulphite. I will follow the links you generously provided.
    Do you keep the filtered crystals and put some back into the solution or discard them.
  11. Alan. I forgot to ask in my previous post about the saturated sodium sulphite solution. Do you manage to get all of the sulphite into solution or is there a residue in the bottom of the container. When you add the saturated solution to the hydroxide/paracetamol solution do you include any residue or leave it behind in the container?
  12. I used this formula,but with powder tipped out of caplets and Zorkikat's mixing instructions to get a clear solution:
    I found that 50g sodium sulfite would not dissolve in 125ml water,as implied by Zorkikat,so I put 50g in 150ml water to get a saturated solution,it still did not all dissolve, and decanted 125 ml of clear solution from this to add to the acetaminophen lye solution,then filtered through cotton wool to get a clear solution.
    I did not add any sodium sulfite crystals to the clear solution.
    I have not developed a film in this clear PaRodinal yet but at 1+50 it blackened a film leader in a few minutes.
  13. Thank you Alan for this information.
  14. Alan. In your reply you gave me the solution (no pun intended) to my 'excessive crystal formation'. In any instructions I have read on the preparation of parodinal it usually states mix etc - and leave standing for 72 hrs. Up to the point where I read your reply, I never thought of filtering after the chemicals have been mixed. I have left the mixed solution for 72 hrs then filtered. This is why I have been getting the excessive crystal formation. I have just made another batch and using your filtering as soon as the chemicals are mixed technique, I now have a crystal clear bottle of parodinal. Not a crystal in sight (yet).
    Thanks very much for your help.
  15. Dennis,
    I'm taking it, then, from what you have said that you brew the parodinal at room temperature - is that right? And that once mixed, you just let the mixture stand for 72 hours for the reaction to proceed?
  16. Chris. Yes that is what I have done up to yesterday. This was when I was getting the excessive crystal formation (within 20 minutes). After reading Alan's last post I made a 'brew' but I filtered it through cotton wool within a couple of minutes of mixing the sodium sulphite and sodium hydroxide/paracetamol solutions together. I hope I got it correct this time. The solution is clear and a slight pink colour this morning. I have processed negatives in the previous mixes, and they work fine. I will have to wait a couple of days before I can test this version. If I made a mistake in the filtering, all I will have lost is a bit of time, the chemical cost is negligable.
  17. Dennis,
    Could you please summarise you process (quantities, sequence of mixing etc.)? I want to give your method a try.
  18. Chris.
    I use paracetamol capsules.
    1. I dissolve 50g of sodium sulphite in 150ml of deionized or distilled water at room temperature. You will not be able to dissolve all of it and there will be some residue in the base of the container. Put this solution to one side.
    2. Remove the paracetamol powder from the capsules (I put mine into an empty 35mm film canister) into a container and put the lid on it.
    3. Quickly weigh and pour the sodium hydroxide into a graduated glass container containing 125ml of deionized or distilled water, stirring quickly to dissolve it. The sodium hydroxide is hygroscopic so it will quickly absorb atmospheric moisture if left standing in an open container.
    4. Add the paracetamol powder whilst the sodium hydroxide solution is still hot. It tends to float on the top of the water so you have to work your stiring device quickly at the surface to get it into the solution. The colour will cloudy and may have a very slight 'pink' tinge. Once dissolved you need to quickly cool the solution. I place the container into my darkroom sink and play cold tapwater on the outside of the container with a small hose.
    5. Measure 125ml of the sodium sulphite solution and add it to the sodium hydroxide/paracetamol solution. Pour into a suitable glass bottle and cap it. Up to Alan's post I used to include the residue as well. Now I do not.
    At this point I used to (up until Alan's post) let the solution stand for 72hrs. This is when I was getting excessive crystal growth I have mentioned previously. After 72hrs (approx) I was filtering the solution into a clean glass bottle and I added half a teaspoon of the crystals left behind in the filter.
    My last batch was prepared exactly the same BUT this time I filtered it a couple of minutes after the final mix into a clean glass bottle and capped it. The resulting solution is crystal clear, a light pink colour, no sign of any crystals 'yet'.
    I hope this helps
  19. Dennis,
    Thank you very much for that. I'll give that a try some time over the next few weeks.
  20. Chris.
    You are very welcome. By the way I forgot to say the amounts are as published.
  21. Remember the label on old Rodinal bottles said:" slight flocculations are of no importance".

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