RE: PotassiumOxalate and pH
Cor, I recall the pH of fresh Pot Ox as I recorded it to be closer to 5.4. I can't find my paper that has that note on it right now. I need to do a little filing : ( In doing a quick google, several listed it at 7 +/- 1 but I did see references to 5.5 and some msds show no information under pH. Eric Neilsen Photography 4101 Commerce Street Suite 9 Dallas, TX 75226 http://e.neilsen.home.att.net http://ericneilsenphotography.com Skype ejprinter > -----Original Message----- > From: C.Breukel@lumc.nl [mailto:C.Breukel@lumc.nl] > Sent: Monday, February 19, 2007 6:01 AM > To: alt-photo-process-l@usask.ca > Subject: PotassiumOxalte and pH > > In the past I was well advised about how to keep the PotOx solution for > pure Pt printing alive: > > Regularly filter off the debris > Replenish with fresh 25% PotOX (keep the end volume constant) > Keep the pH on the acid side (around pH 4) with oxalic acid > > Today I was checking the pH again (got some problems with pt printing), > and the solution was around pH7, so I added the oxalic acid. > > At the same time I made some fresh 25% PotOx, checked the pH, and saw > that it was pH 8.0! I was surprised, because I assumed it to be on the > acid side. (Checked the literature, and indeed potOx is neutral to > slightly basic, and off course no buffer). > > This seems to be contradicting: when your used PotOx solution gives > problems: use oxalic acid to lower the pH (and that sure works), but > OTOH: the pH of the fresh starting solution is neutral/slightly basic? > > What am I missing? I guess when the developer gets used, a lot of other > stuff gets introduced: ferric compounds, Pt compounds, perhaps paper > compounds, and then a lower pH is necessary. > > Best, > > Cor
|