From: Alan \"Uncle Al\" Schwartz <uncleal0@ix.netcom.com>
Newsgroups: sci.chem
Subject: Re: Q: Iron idicator - Sodium Ferrocyanide?
Date: 24 Jan 1996 18:42:53 GMT

Ferrocyanide will grab just about any divalent transition metal to form 
an insoluble and often strongly-colored "Prussian Blue" type of complex. 
 However...

The levels of free soluble iron, Fe^(2+) in anything are vanishingly 
small because of its ready oxidation to insoluble Fe^(+3) hydroxo-oxides 
(rust).  If there is iron in solution, it is probably complexed and may 
be unavailable for your reaction.  In any case, nominal levels are only 
parts-per-million.  There is nothing to be seen.

If you want a nice experiment, take a cup of Total or other "high iron" 
cereal, buzz it up in a blender with a few volumes of water to make a 
thin mush, then swish a good magnet covered with aluminum foil through 
the muck (or pour it into a glass and run a strong magnet along the 
side).  Son of a gun - iron filings!

Colorimetric determinations generally employ reaction of the desired 
species into a derivative which can be solvent extracted from the water 
phase and then concentrated, such as nickel dimethylglyoxime or Cuproin 
for iron and copper.  18th Century science aside, modern determinations 
are usually done by atomic absorption or other physical instrumental 
technique which is fast, labor-lite, generates minimal waste, and which 
accomodates mostly untreated matrices.

-- 
Alan "Uncle Al" Schwartz
UncleAl0@ix.netcom.com  ("zero" before "@")
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