Photo Engineer said:
Unused fixers usually go bad by the reation of acid with hypo
and oxidation of hypo and sulfite. The neutral and alkalline fixes
are much more stable for this reason ....
.... a test solution of Potassium Iodide added to a sample of the fix.
If the fix is bad, a heavy yellow precipitate forms (Silver Iodide)
due to the excess of silver in the hypo.
A heavy yellow precipitate? The fix is very bad and that's for
quick and dirty. That test will not work for archival. The very dilute,
one-shot, unadulterated fixers I use, produce when near fully spent
a barely perceptable white haze.
Working strength S. Thiosulfate has a ph of 6.8 to 7.0 and
the same in P. Formulary's A. Thiosulfate has a ph of 7.6 +/-.
S. or A. Thio., nothing is added to make a working strength
fixer save water. Dan