Is there any reason that Dimezone S should not be substituted for Phenidone in formulas that call for Phenidone and are the two chemicals substituted equally weight for weight?
Denise Libby
All of the Ilford liquid developers that used to contain Phenidone have contained Dimezone S since the early 1990's. PQU was the last to change in about 1993. The replacements were made to give much longer shelf lives.
Phenidone hydrolyses in alkaline solution. The higher the pH the greater the rate of hydrolysis. For Dimezone and Dimezone S the rate of hydrolysis is slower. Since the molecular weight of each is larger than that of phenidone more must be used to get the same activity. I have read one claim that says that the activity of the Dimezones are less than that for phenidone even when compensation is made for the differing MW's.