Talk:Potassium ferricyanide

Prussian blue
it was stated that it is the presence of iron (III) ions (Fe3+) that cause potassium hexacyanoferrate to form a blue complex. It is in fact iron (II) ions (Fe2+). This is a very important difference and quite a major error to make. I have corrected the article as such.

No you are incorrect. I think you need to be clear as to the difference between ferrous ferrate and ferric compounds. I have corrected the article from your blunder.

I think you are both inaccurate. Potassium hexacyanoferrate(II), AKA potassium ferrocyanide or yellow prussate, reacts with ferric iron to form ferric ferrocyanide, or Prussian blue. Potassium hexacyanoferrate(III), AKA potassium ferricyanide or red prussate, reacts with ferrous iron to form ferrous ferricyanide, or Turnbull blue. Aristaea 17:32, 13 June 2007 (UTC)


 * I think Aristea is correct, see Prussian blue, a better article than this one! Walkerma 16:32, 2 August 2007 (UTC)
 * The consensus (see Dunbar review cited in Prussian blue) is that Turnbull's Blue and Prussian Blue are the same. They differ only in terms of the reagents - the details of the mixing gives rise to differing particle sizes hence slightly differing colors. In other words, the same compound can be made by adding Fe(II) salts to [[Fe(CN)6]3- or, complementarily and more typically, by treating Fe(III) salts with [Fe(CN)6]4-:
 * a precipitation process:
 * 4 [Fe(H2O)6]3+ +  3 [Fe(CN)6]4-  →  Fe7(CN)18  = (Fe3+)4([Fe(CN)6]4-)3
 * redox followed by precipitation:
 * 4 [Fe(H2O)6]2+ +  4  [Fe(CN)6]3-  →  [Fe(CN)6]4-  +  Fe7(CN)18  = (Fe3+)4([Fe(CN)6]4-)3

At least I think this is the way it is. BTW, I noticed that we lack a page on "nonstoichiometric compound," which describes Prussian Blue.--Smokefoot 17:18, 2 August 2007 (UTC)


 * Of course, you're right Smokefoot - I was giving a very quick answer before running to lab. I was recalling books I read in my youth - some time ago - which differentiated the two in the way Aristaea described.  I had heard of the "new" knowledge, but it slipped my mind.  As Prussian blue makes clear, they are chemically the same, although they may well be called different things based on the method of preparation, which can make all the difference! (as with Purple of Cassius).  Sorry for my mistake. Walkerma 01:41, 3 August 2007 (UTC)

density of negative what?
"It is also used with sodium thiosulfate (hypo) to reduce the density of negative where the mixture is known as Farmer's reducer."

Density of Negative what? I think this is incomplete and should be completed for when people like myself come on here to get information about a specfic property of the compound.

Alexzander
 * It's a photographic negative - I've reworded it, because it was very unclear. Walkerma 16:26, 2 August 2007 (UTC)

Color photography
"In color photography, potassium ferricyanide is used to reduce the size of color dots without reducing their number, as a kind of manual color correction." - W H A T ? This does not make any sense. Never heard of such a process. What are color dots? —Preceding unsigned comment added by 94.237.95.75 (talk) 01:50, 14 November 2010 (UTC) The term color photography is a bit of a misnomer.

The dots are in reference to the halftone printing process. During the days of analog film separations, the colors of Yellow, Magenta, Cyan, and Black were represented by 4 separate photographic film’s consisting of differing size dots. Using a printing press, the size of the dots would indicate the amount of ink printed on the substrate. Combinations of the dots together would create all the different colors available within the printing process. If an area within the image required a color correction,  a dot etcher would be engaged to use the solution to “etch” or reduce the size of the dot. If an enlargement was to be made, a positive film would be made from the negative and the positive dots would be etched. Once completed, the corrected film positive would be used to make a newly corrected negative separation. These individuals were typically the highest paid and most highly skilled in the industry as they would be able to look at a proof, and then look at the corresponding dots on the films to determine what correction was required.

As a professional educator within the area of graphic communications, I was able to view the process of dot etching back in the late 1970’s on a tour of a color separation house that supported the industry. With the introduction of the electronic dot generating scanners, this technology was soon made obsolete.

--Pixelpete56 (talk) 15:32, 5 June 2015 (UTC)

Genesis of hydrogen cyanide
I've used various acids (hydrochloric, nitric, sulfuric) to dissolve this compound, at concentrations up to 10M, and have not noticed any fumes of cyanide -- I'm not unable to smell it, if anything, I'm overly sensitive. The equation provided is feasible enough, but it must have a ridiculously low equilibrium constant (or high, depending on the direction of the equation). Pure hydrochloric acid must have a molarity of around 35 (estimated on the spot, so maybe off), so I doubt concentration is the problem. It'd be nice if someone could clear this up, either by providing an equilibrium constant for the equation 6H+ plus ferricyanide anion --> etc etc., or by specifying the exact conditions under which the compound produces HCN. For the record, heating the solid under a Bunsen burner provided a distinct and unmistakable presence of cyanide gas. Disclaimer: I am a chemist, do not try this at home. Mr0t1633 (talk) 11:05, 13 January 2010 (UTC)


 * I'll have to second the concern for accuracy here. Ferrocyanic Acid and Ferricyanic Acid are isolatable entities and in superacids the Ferrocyanide complex can be protonated. In Acid strong enough to form Ferricyanic acid, free Hydrogen Cyanide is protonated then hydrolyzed to Ammonia and Formic Acid. Note that Common Table Salt contains Ferrocyanide as anti-caking agent and does not release cyanide in the stomach's Hydrochloric Acid. Strong Alkali does react with Ferricyanide creating Potassium Cyanide and Ferric Hydroxide eventually (then eventually hydrolyzing the Cyanide to Formate and Ammonia) because the formation constant for Ferric Hydroxide is more favorable than formation of Ferricyanide complex. (Chemical Rubber Handbook had [Fe][OH] at ~10^33 and [Fe][CN] at ~10^27) 2001:4898:80E8:ED31:0:0:0:2 (talk) 07:11, 15 June 2015 (UTC)
 * Wikipedia has zero interest in your experimental results - that's a rule around here called WP:NOR. If you think that there is a problem with the article, then revise or remove the suspect section.  --Smokefoot (talk) 12:26, 15 June 2015 (UTC)

Assessment comment
Substituted at 03:17, 30 April 2016 (UTC)