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PirateDocBrown
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The gluteraldehyde is likely a few ppt, as a biocide.
The oxalic acid is likely there, just to keep it near pH 7.
I would imagine the stuff to be over 95% of the dry mass the ferric ferrocyanide.
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JJay
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I'm going to try heating part of it to 300 C on a hotplate and see if it is still water soluble and acidic.
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JJay
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... doing some reading, it looks like 300 C will actually scorch Prussian Blue... http://adsabs.harvard.edu/abs/1989HyInt..46..723I
I'm not seeing a lot of clear information on the temperature for boiling/subliming oxalic acid, but every source I am seeing suggests a temperature
under 200 C.
I can easily reach a temperature of 225 C in my oven.
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JJay
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Reading over that paper (as opposed to just glancing at the abstract), it looks as though temperatures up to 300 C mainly affect the electron
configuration of the iron, changing the electrical conductivity of Prussian blue, and have little to no effect on the bound cyanide of pure Prussian
blue. I suspect that high temperatures might affect the solubility too.
I checked, and a sample of the dried bluing is soluble in water prior to any heat treatment. So I dried a clean 50 mL beaker in an oven and weighed it
at 35.46 grams and then added 0.19 grams of dried Mrs. Smith's bluing. There is an unknown amount of water in the mix, and with such a small sample,
it is not really feasible to accurately assay the impurities with a cheap pocket scale, but I'd like to retain most of the bluing for future
experiments such as checking the effect of different temperatures on the bluing's properties.
I then heated it in an oven at 260 C for 30 minutes in a ventilated area. Upon removing it from the oven, the blue sample had disappeared and been
replaced by a slightly alkaline orangish brown powder that was virtually insoluble in water, with no blue color visible anywhere. This is assumed to
be iron oxide with a small amount of potassium carbonate. The beaker weighed 35.55 grams.
[Edited on 10-2-2017 by JJay]
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chemplayer...
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Those needle crystals do indeed look like an oxalate salt.
HCN is famous for having a variety of odors depending on the individual. We dropped a little (VERY little - like about 30mg) alkali CN salt into
dilute sulfuric acid just to see. We figured that is would be worth knowing what it smelt like just in case we ever encountered a lot of it
accidentally!
The salt bubbles on contact with the acid (not super-vigorously like a carbonate, but more gently with bubbles also coming out of the acid around).
Two of us cautiously wafted some of the air-diluted vapours and had a sniff to see, and compared notes.
Our perceptions were the same - it is distinctive, but weird and hard to describe. Musty, dusty, mouldy, very slightly bitter, not very acrid/acid at
all. You get a strong weird feeling of something on the top of your mouth and throat - and here there is 'something' which is almond-like but it's
difficult to describe. Definitely not sweet and nothing like benzaldehyde or your stereotypical almond flavouring aroma. You'll know if it's there,
but if you're not used to it you're not going to obviously identify it (perhaps unless you're genetically predisposed to smelling something stronger).
So worth being a bit careful, but yields of HCN from heating even strong mineral acids with cyanoferrate compounds are normally that good due to
side-reactions, and the conditions seem to be quite sensitive to the formation.
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JJay
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I just ran across this entry on Prussian blue. If true, it seems to clear up a lot of questions that I've had about its soluble form: https://books.google.com/books?id=vEwj1WZKThEC&pg=PA1444...
I wonder if perhaps there may have been some alkali cyanide and ferric cyanide in the mix. I actually didn't smell any cyanide at all while the
compound was heating in the oven, but I left it mostly unattended. It is surely not a good idea to breath the gaseous byproducts from strong heating
of bluing solution.
I think I might try adding some iron salts to a concentrated solution of bluing and see if there is a precipitate. I'm also curious as to the effects
of lower temperatures--and was there actually a small amount of alkali cyanide present? I wouldn't ordinarily expect the temperatures to be high
enough to produce any, but alkali cyanide does have an elevated pH.
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Velzee
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Using Fe salts would be a good idea to test if they are present, although I doubt if any are. As chemplayer said, it is extremely difficult to
describe the scent of HCN; I personally think it is akin to a metallic, old musty odor. Quite weird, frankly.
I look forward to seeing the test results and the dried Prussian blue!
Check out the ScienceMadness Wiki: http://www.sciencemadness.org/smwiki/index.php/Main_Page
"All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident."
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Velzee
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Quote: Originally posted by JJay  | ... doing some reading, it looks like 300 C will actually scorch Prussian Blue... http://adsabs.harvard.edu/abs/1989HyInt..46..723I
I'm not seeing a lot of clear information on the temperature for boiling/subliming oxalic acid, but every source I am seeing suggests a temperature
under 200 C.
I can easily reach a temperature of 225 C in my oven.
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I don't think 225°C would scorch the salt
Check out the ScienceMadness Wiki: http://www.sciencemadness.org/smwiki/index.php/Main_Page
"All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident."
—Arthur Schopenhauer
"¡Vivá Cristo Rey!"
—Saint José Sánchez del Río |
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JJay
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I don't think so either, but I'm not 100% sure... 260 C was too hot.
Oh, and as far as the scent goes, I thought the bluing smelled like kind of like watery almonds when I was boiling it down, but I took care not to
smell it more than once. At the time, I attributed the watery aspect to water vapor, and in retrospect, I'm not sure what to think about that. I'm not
about to try smelling boiling laundry bluing again, but I will pull this experiment out at some point and try further purification steps.
[Edited on 4-5-2018 by JJay]
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