Potassiumcyanide from darkroom chemicals?

In the distant past, KCN was used as a fixer for wet plate processes.

Thiosulfates are now the preferred fixer, whether sodium thiosulfate(hypo) or ammonium thiosulfate(rapid fixer). AFAIK, either of these will also work fine for wet plates.

I'd be interested to see how film would react to a KCN fixer...I'd be tempted to try it if not for the fact that I really, really don't like handling cyanides.

I have used potassium ferricyanide to enhance highlights on b&w prints, applying it with a paintbrush.

Potassium ferricyanide - Wikipedia

Its been decades since I used it and don't remember much about it, or if it was applied before or after fixing the print.

Potassium ferricyanide is virtually impossible to convert to a CN- ion and is pretty low down on the list of toxicity.

In my position at work, I have some responsibility for the chemistry teaching labs and as part of that actively liason with the hazardous waste coordinator. We moved our freshman teaching labs a couple of years ago to having two waste disposal drums. Each drum is 55 gallons, with one marked for acides/heavy metals and the other marked for bases. Initially, the base drums were marked "Bases and cyanides" because an acidic cyanide solution can release HCN. The problem was that we have an experiment where we use potassium ferricyanide, and another where we use potassium thiocyanate in a nitric acid solutions . The TAs were directing their students to put both of these in the base drum and as a consequence our base drums were coming out with very low pH(and I could talk to them until I was blue in the face without changing their minds).

I finally had the waste coordinator take "Cyanide" off the label as we don't use cyanides in lower level teaching labs. In fact, the only use we have for KCN(barring research lab use) is to do something called a Kaiser test, which tests for the completion of a peptide coupling reaction. It's a very dilute solution, and we use a small quantity in one upper level experiment where the students synthesize peptides. I use about 300mg every couple of years, and the bottle otherwise stays locked in a cabinet in my office(not in general stockroom circulation).

. . . potassiumcyanide. . . As far as I know there are no such ingredients in common darkrooms, and there is no use of cyanice. . . Is it possible?

Potassium Ferricyanide was (is) commonly used in the preparation of the more resilient two stage Sepia Toners in the (first stage) know as "Bleaching Solution"

The formula for the bleach that I most often used (still use sometimes now) is based on Kodak's "T7a" two step Sepia Toner:

BLEACH:

Water 2 litre (H2O)

Potassium Ferricyanide (K3[Fe(CN)6]) 75gms

Potassium Oxalate (C2K2O4)　200gms

Potassium Bromide (KBr) 75 grams

Acetic Acid (25% b.v. from Stock Glacial Acetic Acid) (CH3COOH) 40 ml

*

The same Bleaching Solution could be used for preparation of Blue Toned Prints if two stage toning were to be used.

However, many Darkroom Labs used a one stage Blue Toner, employing Ferric Ferrocyanide, to make the more commonly known toner/pigment “Prussian Blue” (C18Fe7N18), so this is yet another use of ‘cyanide’ in the Darkroom.

*

Although ‘cyanide’ appears to many as a dangerous chemical, and care and procedures would be adhered to in the preparation and use of the chemicals, it would be reasonable to say that “more care” needs to be employed when managing the acids, especially, the Stock Solutions of Acids: Sulphuric Acid being a very nasty Stock, requiring absolute care and procedural rigour.

WW

Potassium ferricyanide is virtually impossible to convert to a CN- ion and is pretty low down on the list of toxicity. . .

Yes, thanks.

We were writing at the same time.

I am not a chemist's bootlace, but I think that the Cyanide is "bonded very tightly" to the Iron in Ferric Ferrocyanide - hence my comments that whilst we were taught to be careful with these 'cyanide' chemicals, we were really taught to respect the Acids that we used. . . mind it's been a long time since I have been in a Darkroom Lab using Stock Solutions and with experience: I am careful with any chemical that I use.

*

Just returning to the OP and the TV show - I'd reckon to be "poisoned" by "potassiumcyanide" a solution would have to be ingested? I reckon that would taste vile. I think the TV show used some poetic licence?

WW

However, many Darkroom Labs used a one stage Blue Toner, employing Ferric Ferrocyanide, to make the more commonly known toner/pigment “Prussian Blue” (C18Fe7N18), so this is yet another use of ‘cyanide’ in the Darkroom.

Don't forget that Prussian Blue can be formed from mixing K3Fe(CN)6 and ferric ammonium citrate and then exposing the mixture to UV light. If you coat that on paper and let it dry, you can make the traditional cyanotype print or a blueprint.

BTW, Prussian Blue is used to treat certain types of heavy metal poisoning. I have a work friend who very nearly died of thallium poisoning before they found out what it was(strange set of circumstances, as he had worked with thallium in the past but wasn't actively working with it). Once they figured it out, the treatment was huge doses of Prussian Blue-I want to say on the order of several grams a day-until his blood level had dropped to safe levels.

Wow!

Aside - You obvioulsy passed the chemistry exam - I just scrapped through . . . I simply follow the directions on the many recipes that I have collected over the years!

Potassium ferricyanide is virtually impossible to convert to a CN- ion

Everything is possible - but the good thing is that in a darkroom the chemicals and tools needed for that reaction to take place aren't present.

In the distant past, KCN was used as a fixer for wet plate processes.

True, but I wonder if one can still obtain the chemical (potassium cyanide) today.

BTW, potasium cyanide and potassium ferricyanide aren't as closely related as the names suggest (as is so often the case when improper nomenclature is used). The former can readily kill you, the latter is much less dangerous unless exposed to conditions not usually present in a darkroom.

Ferric Ferrocyanide, to make the more commonly known toner/pigment “Prussian Blue” (C18Fe7N18), so this is yet another use of ‘cyanide’ in the Darkroom.

And there is another improper naming of a chemical.

William Michael said: ↑

Ferric Ferrocyanide, to make the more commonly known toner/pigment “Prussian Blue” (C18Fe7N18), so this is yet another use of ‘cyanide’ in the Darkroom.

. . . And there is another improper naming of a chemical.

Well then, please correct my error. It's no use leaving it there and just saying that I made a mistake.

I was simply copying from my book of Toning recipes - if those notes are in error and if you can correct them, we all will learn something, won't we?

True, but I wonder if one can still obtain the chemical (potassium cyanide) today.

With the proper credentials, most any chemical can be obtained. KCN has its place in research labs. I bought some in March, and as I mentioned have a specific real-world use for it.

I have the proper credentials, however, and also didn't purchase it for personal use. Photographers Formulary doesn't carry it, and I doubt any member of the general public can get it.

BTW, let's not get too picky about chemical names. If we are going to be sticklers for names, the only correct way to name a chemical is using the IUPAC name. In that case, we should call K3Fe(CN)6 potassium hexacyanoferrate(III). Potassium ferricyanide is an older systematic name, but those names(particularly the ones which use ic/ous to indicate the oxidation state of a metal) are now technically obsolete. They are still widely used even in literature and of course are understood. I'd say most "chemically fluent" people would recognize the ferricyanide ion much more readily than the IUPAC name.

Wow!

Aside - You obvioulsy passed the chemistry exam - I just scrapped through . . . I simply follow the directions on the many recipes that I have collected over the years!

I live and breathe chemistry. I have a masters in analytical chemistry. In my full time job in the chemistry department at a large research university, I split my time as a bench chemist mostly doing lab preps for teaching labs(along with frequent "special projects" that involve developing new experiments, synthesizing unavailable or expensive chemicals, or the like) and as the scientific specialist for my department. I also teach general chemistry when I get the chance.

Sorry to ramble a bit, but needless to say I enjoy chemistry :) . Darkroom work is a natural extension of that.

William Michael said: ↑

Sorry William, it is not you making the mistake. Unfortunately, the use "common names" for chemicals is about as old as chemistry itself and continues to create confusion. Unfortunately, the proper names are often quite complicated (I am not going to start a chemistry lecture here, suffice it to say that a more appropriate (but still not totally proper) name would be ferric hexacyanoferrate. The main distinction is that "cyanide" in proper use refers to a salt of a positively charged kation (K) and a negatively charged anion (CN); from such a salt, CN can readily be liberated. In a "cyanoferrate" the CN is bound differently and much less readily liberated (it's actually a complex compound).

As I said, "common names" are often used in the (non-scientific) literature and create nothing but confusion. They have proven to be impossible to eradicate though.

Thanks. . . reminds me of the tale - "Mum and Dad bought him a chemistry set for his 8th Birthday... after he blew up the house he never looked back"

More seriously, and in the case that Dieter does not reply, where are my lab notes in error when I copied this:

"Ferric Ferrocyanide, to make the more commonly known toner/pigment “Prussian Blue” (C18Fe7N18), so this is yet another use of ‘cyanide’ in the Darkroom."

WW

ferric hexacyanoferrat

That name is totally incorrect-the cation is potassium, not Iron(III) and even if it were correct you'd be guilty of using a classical name to indicate the oxidation state of the cation.

Aside from that, the IUPAC name for the anion you gave is meaningless because you do not indicate the oxidation state of the iron. To be correct, you need to call it hexacyanoferrate(III). Otherwise, you could either be referring to either the anions classically known as ferricyanide or ferrocyanide. Granted it can be inferred from the cation.

As I said, ferricyanide is still a commonly accepted name for the this particular cation under discussion, and you will find it all over the place in literature. Classical names are still quite common, and in fact Langmuir seems to be taking no issues with my exclusive use of classical names in a recently submitted paper.

That name is totally incorrect-the cation is potassium, not Iron(III) and even if it were correct you'd be guilty of using a classical name to indicate the oxidation state of the cation.

 

Aside from that, the IUPAC name for the anion you gave is meaningless because you do not indicate the oxidation state of the iron. To be correct, you need to call it hexacyanoferrate(III). Otherwise, you could either be referring to either the anions classically known as ferricyanide or ferrocyanide. Granted it can be inferred from the cation.

 

As I said, ferricyanide is still a commonly accepted name for the this particular cation under discussion, and you will find it all over the place in literature. Classical names are still quite common, and in fact Langmuir seems to be taking no issues with my exclusive use of classical names in a recently submitted paper.

Ben, as I indicated in my post, I am well aware that the name I gave is not the IUPAC name (that I have no trouble providing) - I didn't want to get into that level of detail as it doesn't help those who "don't live and breathe chemistry". The fact that common names are still widely used doesn't make things any better and, as should be obvious from this thread, just adds confusion. The fact that a renowned Journal still admits paper that don't exclusively use IUPAC names is doing everyone a big disservice and I can't help but wonder what good it does to still teach and use the classic names at universities (small wonder that many students can't properly balance a redox equation or think that methylchlorid is a salt). Be glad I wasn't the reviewer of your paper or I would have recommended against publication until proper name corrections have been made.

Sorry to all, I should have stayed out of this thread since it appears that instead of clearing things up I just added to the confusion. Even when approached correctly, chemistry isn't an easy matter to master; using obsolete and rather incorrect nomenclature certainly doesn't make understanding it any easier. So by all means, let's get picky about chemical names. Very picky indeed.

To be correct, you need to call it hexacyanoferrate(III)

Not to put to fine a point on it, but for some time now, the correct name would be hexacyanidoferrate (III) or hexacyanidoferrate (3-) to indicate that the cyanide is coordinated. Must admit not something I have seen used often but certainly in accordance with IUPAC recommendations. Has been a while though that I had to deal with IUPAC naming conventions. They become rather laborious when naming larger organic molecules. I doubt anyone would recognize caffeine from its IUPAC name (I'll spare everyone).

Why are we even giving this any brain time?

TV shows are fiction!

They're made up by airhead writers with little to no knowledge of science, technology, or anything much else they write about.

Yes potassium cyanide was once used in photographic darkrooms, back in the C19th, along with mercury vapour, carbide lamps, gun-cotton, black lead, lead paint, and a whole host of other stuff we wouldn't go near these days.

IIRC one of the victims in the film "Kind hearts and coronets" was killed with darkroom chemicals. So the plot isn't even original.

. . .Why are we even giving this any brain time? . . .

That's possibly a tongue-in-cheek question, but anyway - for me, I have found all the responses most interesting including yours, which I found quite humorous, especially the quip about the plot.

I rather like reading and being involved in conversations like this one: there are lots of interesting tit-bits to learn. for me it was not a waste of time by a nice diversion from my normal day's working - kind of relaxing really.

WW

I rather like reading and being involved in conversations like this one: there are lots of interesting tit-bits to learn. for me it was not a waste of time by a nice diversion from my normal day's working - kind of relaxing really.

 

WW

That's fair enough Michael.

I'd just put a question such as this in much the same category as one asking "How exactly do the Star Trek tansporter and phaser work?"

I thought a bit of a reality-check was needed.

Re the "question category"

I understood that the OP was asking more about the chemicals that were used in Photography and not about TV shows - i.e. (lay terms) "Was cyanide really used in the darkroom?" . . . and from that question flowed a fountain of interesting photographic information.

(William)

Not to put to fine a point on it, but for some time now, the correct name would be hexacyanidoferrate (III) or hexacyanidoferrate (3-) to indicate that the cyanide is coordinated. Must admit not something I have seen used often but certainly in accordance with IUPAC recommendations. Has been a while though that I had to deal with IUPAC naming conventions. They become rather laborious when naming larger organic molecules. I doubt anyone would recognize caffeine from its IUPAC name (I'll spare everyone).

So, how is "ferric hexacyanoferrate" is in any way an IUPAC name for the compound known commonly as "Potassium ferricyanide." I don't see you referring to the presence of a potassium at all.

In addition, as I said, in the name you provided you are guilty of using a classical name for an Iron(III) ion.

Using cumbersome IUPAC names in literature, especially large molecules, is not terribly common. Even when organic(or inorganic) chemists submit a previously unknown compound they will often only give the IUPAC name as part of the record of the compound(along with things like spectral data) and then refer to it by an abbreviation.

So, how is "ferric hexacyanoferrate" is in any way an IUPAC name

I never said it was, please go back and read what I wrote. All I intended to point out was that the cyanide in potassium cyanide is not of the same nature as that in ferricyanide (since treating both as equals is what I saw happening in this thread), a fact that is hidden by the use of an archaic naming scheme and I attempted to do so without giving a chemistry lecture at a level I deemed inappropriate for this forum.