Gearhead_Shem_Tov
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"Bluo" optical brightener -- ferric ferrocyanide?
I just bought a bottle of Pascoe's Bluo here in Australia in hopes
it contains ferric ferrocyanide, (as with Mrs. Stewart's Bluing in
the States). When I checked the MSDS, though, it told me
NOTHING about its contents other than the following:
Appearance CLEAR NAVY BLUE LIQUID
Solubility (water) SOLUBLE
Odour SLIGHT ODOUR
Specific Gravity 0.998
pH 3.0 - 4.0
% Volatiles > 60 % (Water)
Vapour Pressure 18 mm Hg @ 20°C
Flammability NON FLAMMABLE
Boiling Point 100°C (Approximately)
Melting Point < 0°C
Is there a way to make an educated guess whether this contains
ferric ferrocyanide with just the above information?
I gather that Bluing usually is ferrocyanide dissolved in dilute
oxalic acid, and that would match the low ph, I suppose, but I'm
at a loss how to interpret the lower MP when the BP is the same
as water.
Failing that I guess I could test for Fe(III) with a thiocyanate,
though I don't know if my local photo supply store carries any of
the usual suspects. And, I dunno, maybe test for oxalic acid,
too?
Or is it more likely to contain a synthetic dye instead of good old
Prussian Blue?
-Bobby
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densest
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If you want Prussian Blue, what about a tube of watercolor or gouache from a hobby/artist supply store? Unless, of course, they've taken it off the
shelf there... It should say "PB27" somewhere on it - that's the international Colo(u)r Index name.
The binder is often gum arabic.
[Edited on 2-9-2010 by densest]
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Mr. Wizard
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I remember my old Chemcraft Chemistry set would use sodium carbonate to make the blue color disappear.
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Rich_Insane
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I suppose that adding sodium carbonate would cause precipitation of the most likely insoluble ferric carbonate. I know that ferrous carbonate (Fe 2+
instead of 3+, am I right?) is quite insoluble.Your best bet would be to add sodium carbonate. The resulting solution should appear yellowish, because
sodium ferrocyanide is yellowish.
Then you could go on to verify the presence of ferric carbonate somehow.
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Gearhead_Shem_Tov
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I made up a soln. of a couple grams of Bluo to about 25 ml of de-ionised water, then added 2g of sodium carbonate. A little effervescence, not much
(if any) colour change and not much apparent precipitate, though. I'll add some more when it has settled down to see what happens.
-B
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woelen
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If it really contains prussian blue, then addition of sodium carbonate quickly and very clearly changes the color from deep blue to pale brown/yellow.
This reaction is fast and complete. If your solution does not show such a reaction, then it does not contain prussian blue and then the blue color
probably is some organic dye.
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Rich_Insane
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Try a little more carbonate. If nothing happens, woelen is right, it's probably some dye. I'd expect that most bluing today would contain organic dyes
though.
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Gearhead_Shem_Tov
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Quote: Originally posted by Rich_Insane  | | Try a little more carbonate. If nothing happens, woelen is right, it's probably some dye. I'd expect that most bluing today would contain organic dyes
though. |
I left the test tube overnight after my first test, and I noticed the bottom cm or so did turn clear, with a fairly sharp demarcation with
the blue fluid above. I've now added some more carbonate (half a teaspoon?); I'll report what it does once it stops fizzing...
-Bobby
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