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strange salt (fwd)

updated thu 16 dec 99 on wed 15 dec 99


> -------- Forwarded message ----------
> Date: Tue, 14 Dec 1999 09:49:21 EST
> From: Michael Banks
> Reply-To: Ceramic Arts Discussion List
> Subject: strange salt
> Resent-Subject: strange salt
> ----------------------------Original message----------------------------
> This thread is taking some strange twists and turns lately...
> I would like to point out that the stuff in question, sodium ferrocyanide
> (yellow prussate of soda pickling salt) is nothing to do with common salt
> (NaCl). Pickling salts are used in the electroplating industry to prepare
> items for plating.
> It is my belief that ferrocyanide salts are a lot less toxic than cyanides
> (but would welcome correction), -so no hysteria please. Monona may be able
> to enlighten?

There is no melting point or boiling point in any standard reference or even
in the Handbook of Chemistry and Physics! Sax says of the ferrocyanides in

Ferrocyanides in general have low toxicity, but highly toxic decomposition
products can form upon mixing them with hot concentrated acids. Acid, basic
or neutral solutions of ferrocyanides liberate hydrocyanic acid upon strong
irradiation.* Fusion of mixtures of metal cyanides with metal chlorates,
perchlorates, nitrates, or nitrites may cause violent explosions. When
heated to decomposition or on contact with acid fumes they emit toxic fumes
of CN-.

* I know about the problem of irradiation in neutral water solutions because
Kodak had a holding lagoon with a very small amount of ferrocyanide in the
water which was waste water from their photo manufacturing process. They
were demonstrating that their waste was not all that toxic so they had fish
swimming in the water. One day the sun was really strong--and all the fish
died from HCN liberation.

The nitrate reaction is funny at this point in Clayart's discussions. It
sounds like mixing the ferrocyanide with the nitrate fertilizer and firing it
as a glaze might not be so smart!!

The most relevant piece of information is that when heated to decomposition
it will release CN-. We don't know what that decomposition temperature is
from the literature, but we can rest assured it is exceeded in the kiln.

> I seem to recall from high school biology, that cyanide ions knock out the
> ferredoxin (a respiration enzyme?) in cells with disasterous consequences
> (like instant death). <

Exactly. And the change in the body is observed as turning blue which is
still called "cyanosis" whether it is caused by cyanide or not.

> Ferrocyanide ions conversely have little affinity for
> the iron atoms in ferredoxin because the CN radical is already bonded to
> iron in the salt.

The formula is Na4Fe(CN)6.10HOH. So the only thing that will remain in a
glaze is the sodium and a little iron. Surely we can find better ways to get
these elements into our glazes. Call the bomb squad and move on.


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