From: Liam Lawless (liam.lawless@blueyonder.co.uk)
Date: 02/23/03-06:39:55 PM Z
Joe & All,
Now, this is interesting. I've seen various MSDSs for pot. ferri. (though
none recently) and I do not remember any dire warnings not to mix with
strong acids. Did some searching tonight and found several that almost
casually mention that p.f. is incompatible with acids. But go to
http://www.rpi.edu/dept/cieem/mcrusers/msds/db/msds/potassiumferricyanide.ht
ml and you'll find:
10. Stability and Reactivity
Stability:
Stable under ordinary conditions of use and storage. The aqueous solution
decomposes slowly on standing.
Hazardous Decomposition Products:
When heated to decomposition or comes in contact with acid or acid fumes it
emits toxic fumes of cyanides. Emits toxic fumes of cyanide and oxides of
nitrogen when heated to decomposition.
Hazardous Polymerization:
Will not occur.
Incompatibilities:
Ammonia, chromium trioxide + heat, cupric nitrate, sodium nitrite + heat,
acids and acid fumes.
Conditions to Avoid:
Light, heat, incompatibles
In the anhydrous form it's explosive in contact with strong ammonia, and the
combination caused a fatality at a tannery near here many years ago. I
always thought p.f. was not one to worry about overmuch - apart from mixing
with ammonia! - and it is not regarded as particularly toxic (another MSDS
states "Information on the human health effects from exposure to this
substance is limited. Used information for a related compound, potassium
ferrocyanide, as a guide. Potassium ferrocyanide is apparently benign and
does not decompose to cyanide in the body.") So, if this particular data
sheet, from the University of Iowa, is true, it would seem that some of the
others ought to be a little more hysterical than they actually are.
It's probably 15-20 years since I looked up this substance and it would
appear that *some* authorities are more wary of it now than was the case
back then. Several of the online MSDSs I looked at do not appear to show
the R&S (Risk & Safety) phrases, but one that did had R20, R21, R22 and R32:
Harmful by inhalation, in contact with skin or if swallowed, and contact
with acids emits very toxic gas. The Aldrich catalogue gives R phrases
32-36/37/38: contact with acids liberates very toxic gas; irritating to
eyes, respiratory system and skin. ("Irritating" is a lower hazard than
"Harmful".)
The blue toner formula I have used for years, and published in Post-Factory,
contains a relatively large proportion of sulphuric acid, and many similar
formulae exist in old (and newer) books. The toner consists of two stock
solutions and the ferri. and the acid are actually separate until they are
combined to prepare a working toner, but the two stock solutions *could* be
combined before diluting with water, in which case the ferri. would for a
time be in a pretty acidic environment. Having done lots of blue toning,
I'm sure I've done this more than once, yet I find myself still here. Nor
have I ever seen any warning against this. What gives? I feel I know less
than I did 20 minutes ago.
Liam
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