  The validity of fluctuation dissipation relations in an aging system is
studied in a colloidal glass during the transition from a fluid-like to a
solid-like state. The evolution of the rheological and electrical properties is
analyzed in the range $1Hz - 40Hz$. It is found that at the beginning of the
transition the fluctuation dissipation relation is strongly violated in
electrical measurements. The amplitude and the persistence time of this
violation are decreasing functions of frequency. At the lowest frequencies of
the measuring range it persists for times which are about 5% of the time needed
to form the colloidal glass. This phenomenology is quite close to the recent
theoretical predictions done for the violation of the fluctuation dissipation
relation in glassy systems. In contrast in the rheological measurements no
violation of the fluctuation dissipation relation is observed. The reasons of
this large difference between the electrical and rheological measurements are
discussed.
