Role of gravity in the formation of liesegang patterns

We report the results obtained in four different kinds of experiments designed to test the effect of gravity on the formation of Liesegang patterns. Both reacting solutions (KI and Pb(NO3)2) were gelled with agarose L. The position of the PbI2 precipitates was determined by image analysis, and the kinetic coefficients k(m) = (X(n+1) - X(n))/X(n) and k(p) = (X(n)/A)(l/n) were obtained at different relative orientations of the gravitational field with respect to the direction of the advance of the precipitation front. We conclude that there is not an apparent influence of the gravitational forces on the kinetics of the pattern formation when it is obtained in gelled media at an agarose concentration of 1% (w/v). When the experiments were performed with agarose at 0.5% (w/v) or when one of the reacting solutions was ungelled, our tests show clearly the effect of gravity.