  The high frequency collective dynamics of molten potassium has been
investigated by inelastic x-ray scattering, disclosing an energy/momentum
transfer region unreachable by previous neutron scattering experiments (INS).
We find that a two-step relaxation scenario, similar to that found in other
liquid metals, applies to liquid potassium. In particular, we show how the
sound velocity determined by INS experiments, exceeding the hydrodynamic value
by $\approx 30 %$, is the higher limit of a speed up, located in the momentum
region $1<Q<3$ nm$^{-1}$, which marks the departure from the isothermal value.
We point out how this phenomenology is the consequence of a microscopic
relaxation process that, in turn, can be traced back to the presence of
''instantaneous'' disorder, rather than to the crossover from a liquid to
solid-like response.

Disordered Systems and Neural Networks