My scale broke and haven't got the chance to buy a new one, thats why I can't make the parodinal right now.
My current approach takes advantage of the fact that paracetamol (acetaminophen) in tablet form is already premeasured, most tablets being 500 mg. While I don't know the precision of that measurement, for the purposes of a DIY film developer I've simply assumed that, given it's for human drug consumption, it's probably close enough.
Here's what I am trying in my latest batch:
(1) Measure 400 ml of methyl alcohol (methanol) into a sealable container. I've been using glass wide-mouth Kerr canning jars with a quadruple fold of Saran food wrap as a gasket. 400 ml is approximately four times the minimum requirement at 20C/68F, but is a minimum for my workaround procedure.
(2) Add 80 500 mg tablets to the methanol and seal the jar. No crushing is required. Just drop them in, then shake the jar every few minutes. In about two hours the paracetamol will have separated completely from the binder. This puts about 40 grams into the 400 ml solution.
(3) Set the mixture aside for about 3-4 days. Leave it completely untouched so that gravity can do its work. The solids will completely settle out leaving a near crystal clear liquid. If you want true crystal clear, wait about a week. This is my workaround for not owning a vaccum filter flask or centrifuge. If I was going to do this on a regular basis, I'd invest in a flask and hand-pump or aspirator.
(4) Since the Parodinal formula calls for 30 mg of paracetamol for 500 ml of developer, I next use a 60 ml syringe (intended for livestock, not humans, so it's easy to source) to carefully remove 300 ml of clear solution from the jar. This is why I need 400 ml to start. The residual solids fit comfortably into that remaining 100 ml at the bottom and don't contaminate the 300 ml I've removed. 300 ml contains 30 mg of paracetamol. No scale is thus required.
(5) Place the removed 300 ml of solution into a 500 ml beaker and allow the methanol to completely evaporate. I help this process along by immersing the beaker into a waterbath held at exactly 52C/125F by a one of those Corning hot plate stirrers equipped with a feedback thermometer. I chose 52C/125F because the boiling point of methanol is 65C/149F and I don't know enough chemistry to anticipate whether boiling the methanol away more quickly will alter the crystallizing paracetamol at that temperature. Make certain there is sufficient ventilation in place to remove the methanol fumes. If not, perform this step outside. I've never tried using the sun on a warm day, but it might work.
(6) When the methanol is gone, add 400 ml of distilled water at 7C/45F into the beaker containing the crystallized paracetamol. Place the beaker into an ice bath for safety. Place a thermometer into the beaker.
(7) Using eye protection, gloves, and protective clothing, slowly add 40 grams of anhydrous sodium hydroxide into the beaker. Watch the temperature on the thermometer. Go slowly enough that any excess heat bleeds out into the ice water, but leave enough heat to help dissolve the sodium sulfite in the next step. I aim for the usual 52C/125F. The solution should turn a slight pinkish, but still be transparently clear.
(8) Once the paracetamol is completely dissolved, adjust the temperature to 52C/125F and add 50 grams of sodum sulfite. This is only half the amount called for in the original Parodinal formula. My experience has been that 100 grams sulfite per 500 ml of solution is beyond saturation at room temperature. I always seemed to have a significant excess that would not dissolve. So I'm trying the more standard developer concentraton of 100 grams per liter to see how that works out.
(9) Once the sodium sulfite is completely dissolved, add cold distilled water to bring the total volume up to 500 ml. Store as you would any other film developer.
I'm trying several new things with this, so if the above steps end up producing a failure - or disaster - I'll ask the moderators to remove this post.
Ken
I was pointing out that they were inert and would not effect the keeping properties of the developer. Certainly the two most common fillers cellulose and starch are not soluble in water. Sometimes the word soluble is used when the more exact term disperse should be used. Cookbooks will commonly say "dissolve the starch in a small amount of water."
