Many Pt/Pl developer formulas call for a supersaturated solution of Potassium Oxalate - i.e., 350 grams per liter. The solubility of PO is 30 grams/100 grams of water (=300 grams/L). What benefit is there in supersaturating the developer when the excess will probably precipitate out of solution anyway? As a side note the B&S label says to dissolve 250 grams into 1 Liter.
Thomas
None. The only I can think of is that the solution will be more or less of the same concentration as the oxalate is slowly used up; a sort of auto-replenishment. But given the tolerances in development, I doubt this has much practical significance. The same with saturated dichromate solutions in various alt processes.
The question would be supersaturated at what temperature? Room temperature? Many use potassium oxalate significantly above room temperature. That said, I mix at 250g/l, warm to 90F, and develop for 120 seconds.
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I maybe wrong but the greater the temperature of the water the greater the amount of the compound dissolved. B&S says to dissolve 250 grams in 1L of water at 150F while others say to dissolve 350grams in 1L @ 120F.
Thomas
Solubility of PO is listed as 360g/l at 20C, so 350 at 120F should dissolve with relative ease. Upon cooling down, a little bit may crystallize out of solution, which can be reverted by reheating the solution. Of course all this doesn't answer your question, what the purpose is of a supersaturated solution. I can't think of any.
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