  We derived Potassium abundances in red giant branch stars in the Galactic
globular clusters NGC104 (144 stars), NGC6752 (134 stars) and NGC6809 (151
stars) using high-resolution spectra collected with FLAMES at the ESO - Very
Large Telescope. In the considered samples we do not find significant intrinsic
spreads in [K/Fe] (confirming the previous findings by Carretta et al.), at
variance with the cases of the massive clusters NGC2419 and NGC2808.
Additionally, marginally significant [K/Fe]-[O/Fe] anti-correlations are found
in NGC104 and NGC6809, and [K/Fe]-[Na/Fe] correlations are found in NGC104 and
NGC6752. No evidence of [K/Fe]-[Mg/Fe] anti-correlation are found. The results
of our analysis are consistent with a scenario in which the process leading to
the multi-populations in globular clusters implies also enrichment in the K
abundance, the amplitude of the associated [K/Fe] enhancement becoming
measurable only in stars showing the most extreme effects of O and Mg
depletion. Stars enhanced in [K/Fe] have been found so far only in clusters
harbouring some Mg-poor stars, while the other globulars, without a Mg-poor
sub-population, show small or null [K/Fe] spreads.
