  We present transport measurements on long diffusive graphene-based Josephson
junctions. Several junctions are made on a single-domain crystal of CVD
graphene and feature the same contact width of ~9$\mu$m but vary in length from
400 to 1000 nm. As the carrier density is tuned with the gate voltage, the
critical current in the these junctions spans a range from a few nA up to more
than $5\mu$A, while the Thouless energy, ETh, covers almost two orders of
magnitude. Over much of this range, the product of the critical current and the
normal resistance IcRn is found to scale linearly with ETh, as expected from
theory. However, the ratio IcRn /ETh is found to be 0.1-0.2: much smaller than
the predicted ~10 for long diffusive SNS junctions.
