Double-diffusive fingering instability of a surfactant-glycerine-water drop in water

We present an experimental setup that allows easy visualization of single f ingers formed by double diffusive convection. This setup consists of a drop ( containing water and two solutes) that is injected at the bottom of a di sh filled with water. The gravity-driven expansion of the drop induces a to roidal bulk ow of the surrounding water. This ow straightens and confines t he fingers horizontally and quasi two-dimensionally. An extremely low diffu sion coefficient of one of the two solutes (a surfactant in our case) cause s unusually stable configurations. This stability is robust within a wide r ange of concentrations. Wavelength measurements agree well with theoretical estimations.