I have found what I believe is the patent for Kodak Hypo Clearing Agent. It is U.S.P. 2,860,978 The patent discusses the use of EDTA Tetra Sodium Salt and has a formula containing it. It also briefly mentions citrates but none of the sample formulas in the patent includes it. If I interpret it correctly a citrate, even by itself, has some effect on removing thiosulfate and silver complexes. Keep in mind that patents are legal not scientific papers and are written in a rather peculiar jargon often intended to obscure as much as to elucidate. Nonetheless, its often possible to learn something from them. U.S. patents are available from the United States Patent and Trade-Mark Office at http://www.uspto.gov You will need a plug-in to read the FAX TIFF files they download as. The best is freeware called Alternatiff available from the web. Do a Google search to find it. The other source of patents is the new Google patents search. Google for "Google Patents" to find it. The google site is better than the USPTO site for old patents because one can do text searches where the USPTO site allows them only for patent issued in 1976 and later. The Google site goes back to 1790. I found this one by searching for Richard Henn, who was one of Kodak's top researchers.
--- Richard Knoppow Los Angeles, CA, USAdickburk@xxxxxxxxxxxxx
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