Mercury drop attacks an oxidant crystal

We report the autonomous motion of a mercury drop in the concentration field of a dissolving oxidant crystal. A mercury drop and a K2Cr2O7 crystal were placed similar to 10 mm apart in a Petri dish filled with 1 M HNO3 or H2SO4. When the front of the dissolving bichromate reached the edge of the circular Hg drop, the latter began to elongate and to move toward the crystal. This happened in the form of one (for H2SO4) Or several (for HNO3) rapid attacks. By analogy with the beating mercury heart we conclude that the shape and motion of the Hg drop are related to the anisotropy of the interfacial tension.