  Lagrangian chaos is experimentally investigated in a convective flow by means
of Particle Tracking Velocimetry. The Finite Size Lyapunov Exponent analysis is
applied to quantify dispersion properties at different scales. In the range of
parameters of the experiment, Lagrangian motion is found to be chaotic.
Moreover, the Lyapunov depends on the Rayleigh number as Ra^(1/2). A simple
dimensional argument for explaining the observed power law scaling is proposed.
