  We report on infrared studies of the c-axis electrodynamics of Tl-Ba-Cu-O
(Tl-2201) crystals. A sum rule analysis reveals spectral weight shifts that can
be interpreted as a kinetic energy change at the superconducting transistion.
In optimally doped crystals, showing an incoherent normal state response, the
kinetic energy is lowered at T < Tc, but no significant change is found in the
over-doped samples, which have more coherent conductivity at T > Tc.
