Evidently you didn't see my reply to the original question. Your old book
is pure Victorian misinformation! (I am repeating the explanation after
this msg.)
> It's also called pure Prussian blue. When you
>mix the salts of iron with cyanide, the by-product is Prussian blue.
Perhaps that's the way they did it back 100 yrs ago, but Prussian blue is
made today by mixing potassium (or sodium) ferrocyanide and ferric sulfate
(or any other soluble ferric salt). The "cyanide" in this is not what we
normally consider as the poisonous material, but represents the "cyan"
radical, named originally because of the blue pigment, the word "cyan"
meaning "blue" in Greek.
This was my reply to the original question:
>Okay I get the potassium ferro part, what is sesquincyanuret?
The Victorians liked fancy names, and often made them up as rococo as their
household furnishings! That is Potassium ferrocyanide. How did they make up
the name? Well, the formula (sorry I can't do subscripts) is K4Fe(CN)6. We
know now that this is the structure, but if you'll note, the (CN) is 1.5
times the amount of K. "Sesqui" means one and one-half, and 6 is 1.5x 4,
right? The true chemists' name for this compound is "tetrapotassium
hexakis(cyano-C)ferrate(4-)"! Also known as "yellow prussiate of potash" -
Lotsa names.
Just for the record, the stuff we mostly use is potassium ferricyanide,
which has the formula K3Fe(CN)6. Note this has twice as much (CN) as K. It
can be converted to the the ferro-, which is what happens when we use it as
a bleach, or in cyanotypes.
There's much more to this, but I'm sensing a lack of interest in my audience!
<<sil>>
<silh@iag.net>
<webmaster@psa-photo.org>
Sil Horwitz, FPSA
Technical Editor, PSA Journal
check out <http://www.psa-photo.org>