The reaction between these two ions is well-known to inorganic chemistry,
and is indeed one of the standard methods for preparing a whole range of
oxalato- complexes of Chromium(III). Admittedly the lab preps entail
heating, but this is just to speed up the process. I doubt that any
solution containing the two will remain unaltered for very long, even at
room temperature.
Keith has just described one consequence:
>KOx does not become
>exhausted. I don't know about the dichromate. I have found some green
>needle-like crystals in one of the bottles.
This is, very probably, potassium tris-oxalatochromate(III): K3Cr(C2O4)3.3H2O
The other consequence is that when the Cr(VI) of dichromate is thus reduced
to Cr(III) it will cease to have a 'contrast enhancing' effect.
Mike