ScienceAsia 31 (2005): 329-333 |doi: 10.2306/scienceasia1513-1874.2005.31.329

Mechanical oscillations of an oxidizing agent
over a mercury surface

Bjorn Maiworm and Mario Markus^*

 
ABSTRACT:A drop of a solution of potassium dichromate and sulphuric acid was placed on the surface of mercury around an iron needle immersed in the mercury. We observed circular, as well as irregularly swirling oscillations of this drop. We could explain this phenomenon as follows. Electrochemical oscillations occur at the iron-solution interface; these cause oscillations of the potential at the drop’s bottom, and thus of the drop’s shape by virtue of electrocapillarity. Our measurements allowed us to determine the surface tension and the capacity of the double-layer at the mercury-solution interface, as functions of voltage. We observed and explain a much faster electrical loading, as compared to the unloading, of the double-layer. Furthermore,we observed a negative differential electrical capacity.

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Max-Planck-Institut fur Molekulare Physiologie, Postfach 500247, D-44202 Dortmund, Germany.

* Corresponding author, E-mail: markus@mpi-dortmund.mpg.de

Received 31 Mar 2005, Accepted 12 Jul 2005