SURFACE-TENSION DRIVEN OSCILLATORY MOTION OF A MERCURY DROP IN THE PRESENCE OF CONCENTRATION GRADIENT OF K2CR2O7 IN HNO3 SOLUTION

An experimental and theoretical study is made on the translational osc illation of a mercury drop in a horizontally placed petri dish filled with HNO3 solution, where solid state K2Cr2O7 is dissolved from a cert ain fixed position. The latter diffuses gradually into the former solu tion, so that almost steady spatial distribution of K2Cr2O7 with conce ntration c is achieved. When the mercury drop is exposed to the soluti on where both c and grade are small, it is pulled toward a higher c re gion. On the other hand when it reaches a very high c region, it under goes stronger chemical reaction accompanied by a cloud of precipitatio n and recedes toward lower c region. This process is repeated and the oscillatory motion is established. Hydrodynamical analysis taking acco unt of the non-uniform distribution of surface tension associated with chemical reaction is given to explain this phenomenon.