Re: ferro vs ferri
I've already wrote about this in the past. Search the archive for more info. "Potassium hexacyanoferrate" is an incomplete description of the compound. There is "potassium hexacyanoferrate (II)" and "potassium hexacyanoferrate (III)." The old name for the former is potassium ferrOcyanide and the latter potassium ferrIcyanide. They have different oxidation numbers of the iron and they behave differently. For all practical purposes, regard them as different chemicals. The one that makes prussian blue pigment when free ferric ion is present is the former, hexacyanoferrate (II). The one that has strong oxidizing power and often used as a bleach is the latter, hexacyanoferrate (III). I see no availability problem for these chemicals. It's just that a lot of alternative process literatures continue to use old nomenclature made obsolete in chemistry and the rest of the world is moving forward. Generally cyano ligands are tightly bound to the iron in these compounds, but they can be liberated and give off toxic cyanide gas when mixed with strong acids or exposed to UV irradiation. This type of agents are removed from color film and print processing, decades ago, and all emulsion manufacturers in the western economy block claim that they are also eliminated from commercial emulsion manufacturing, although they are frequently used in emulsion research and also described very heavily in patent literature. (The quantity used in emulsion making is quite small anyway, not like those used in color processing decades ago.) I believe that the use of "potassium ferricyanide" or potassium hexacyanoferrate (III) as a bleaching agent in black-and-white darkroom work should be made obsolete, especially because there are a number of alternative compounds that work well as a b&w bleach and present much less environmental damage. Actually there are a range of agents that work from mild to strong bleach, depending on the application. The only difference I can see is that ... they cost a couple pennies more. However, the market for these is quite small and no one (so far) wants to make a b&w bleach (even after seeing the success of Silvergrain products) and most authors are not updating their books to include new recommendations... furthermore, my website is now gone and so is my place to promote new technology... oh well. -- Ryuji Suzuki http://silvergrain.org From: Trevor Cunningham <tr_cunningham@yahoo.com> Subject: ferro vs ferri Date: Wed, 29 Aug 2007 23:40:51 -0700 (PDT) > Hey gang...trying to get back into things in a new location. > I recently moved to Jakarta and have found a bulk chemical > supplier. I am able to find ferric ammonium citrate, but > cannot find potassium ferricyanide. Instead, they have > hexacyanoferrate, or potassium FERROcyanide...wikipedia > mentions that several suspicious Morrocans in Rome were > arrested with the stuff and some waterway maps and also says > it reacts quite unpleasantly with acid (which I find highly > unusual that I can get it so easily). However, the article > does mention that potassium FERRIcyanide can be made from it > with the introduction of chlorine (process completely > unknown to me). Availability seems to be an issue if I'm to > make cyanotypes, but if I can make my own chemical, then the > project factor seems almost irresistable. > > Thoughts? > > Trevor Cunningham > > > "The optimist believes this is the best of all possible worlds. The pessimist fears it's true" - J Robert Oppenheimer > > --------------------------------- > Ready for the edge of your seat? Check out tonight's top picks on Yahoo! TV.
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