Thanks Gayle, for such a clear, balanced account of how EDTA,
  despite the last word in its its name, does not work as an
  acid, and decalcifies most effectively from an alkaline
  solution. I haven't read the Harris reference, but will do
  so next week! The place where I learned this wisdom was
  Chaberek, S. and Martell, A. E. 1959. Organic Sequestering
  Agents. Wiley, New York. Much longer, and perhaps a bit out 
  of date compared with your 1982 ref, but not difficult to
  understand at a descriptive level. 
 
On Sun, 13 Aug 2000, Gayle Callis wrote:

> I strongly suggest reading of the following chapter in order to understand
> how EDTA works.  A bit chemical, but wow!  sure is worth the read.  Had to
> thank my P Chem hubby for this info, plus some impromptu lectures on
> chelators, particularly how they work as a function of pH.  
> 
> Harris DE  EDTA Titrations:  In Quantitative Chemical Analysis.  WH Freeman
> and Co, 1982 pp 271-289.

  ... Much wisdom followed but is not quoted in this reply ...
 
> Another thought is why put EDTA in an HCl solution when it cannot chelate
> below pH 3???  ...
>                    ...  I have never been convinced that EDTA is
> necessary in HCl solutions, although decalcifying solution mfrs maintain
> otherwise plus say the decalcification is better than with just acid alone.
> When using these HCl with EDTA reagents, it is the acid that ...
> as the active ingredient. 

  It's obviously ridiculous to add EDTA if the pH is low. It seems
  reasonable to use a wee bit of HCl to bring the pH of Na4EDTA
  down to about 7.5 or 8, but your suggestion of acetic acid is
  better because it won't cause an excessive change of pH with just
  a few drops. 
> 
> How's that for confusion, enough on EDTA   

  There's no confusion, only clarification!  I guess that you will
  soon get one of Phil Oshel's emails, asking you to write something
  about EDTA for Microscopy Today! 

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1