  We present the first resonant x-ray reflectivity measurements from a liquid
surface. The surface structure of the liquid Hg-Au alloy system just beyond the
solubility limit of 0.14at% Au in Hg had previously been shown to exhibit a
unique surface phase characterized by a low-density surface region with a
complicated temperature dependence. In this paper we present reflectivity
measurements near the Au LIII edge, for 0.2at% Au in Hg at room temperature.
The data are consistent with a concentration of Au in the surface region that
can be no larger than about 30at%. These results rule out previous suggestions
that pure Au layers segregate at the alloy surface.
