Starting from this formula of Donald Qualls.
Sodium Sulfite is not available for me, and may be for others too. So, I propose following recipe:
250 ml Water 30 tablets @ 500 mg Acetaminophen 50 g Sodium Sulfite (anhydrous) 20 g Sodium Hydroxide (anhydrous) Mix in order indicated, let stand in sealed container 72 hours before using. Keep crystals from bottom of container with liquid when decanting, stir before drawing off concentrate for dilution. Use dilutions and times as for Agfa Rodinal. Use within 30 minutes of dilution.
2x100 ml Water
20 g Sodium Hydroxide
30 tablets @ 500 mg Acetaminophen (Paracetamol)
40 g Sodium Carbonate (Potash)
500 ml Sulfurous Acid at 6% or equivalent to 30 g of pure acid
First of all, with a mortar, transform the Acetaminophen in powder.
Put 100 ml water in a beaker and 20 g Sodium Hydroxide inside and stir. While hot pour the acetaminophen and stir, one tsp each time until all powder is inside. This solution will be brownish. Let the beaker by side, let us call it beaker A.
Put another 100 ml water in another beaker and add 40g Sodium Carbonate and stir. It will not dissolve all but it doesn't matter. Now go on pouring the sulfurous acid slowly because you will get a lot of bubbles. In this reaction CO2 is produce in large quantity. You will end with less than 500 ml of a solution of Sodium sulfite. Put the solution in a pirex jar and heat it to get the CO2 out, stirring with a spoon. Let the solution cool down.
In a 500 ml bottle pour the content of beaker A. Then wash the beaker with solution B and pour in the 500 ml bottle until this is full. You may have more sulfite left but not much. You have now 500 ml of Parodinal. Let it rest for the same 72 hours before use.
When preparing the work solution, take in account that you end with 500 ml instead of the 250 ml of Donald's recipe. So, you need to double the concentration of the solution, instead of 1:100, use 1:50 and so on.