We studied the spatiotemporal dynamics of a new system consisting of sulfide ions (outer electrolyte) diffusing into an organic gel (gelatin) containing mercaptoethanol-capped cadmium ions (inner electrolyte), The product, cadmium sulfide, exhibits a faint yellow transparent propagating front starting at the gel-outer electrolyte interface. When subjected to UV light, this system reveals fluorescing US nuclei localized spatially in a narrow region, called pulse, that leads the front and propagates down the tube. We show that the pulse consists of US nanoclusters of an average size of about 4 rim, whereas the trailing front consists of 6-8 nm cubic-phase US crystallites. The width of the pulse remains constant in time, t, at about 2 mm and independent of the outer concentration S-0. It was found that the speed of the pulse fluctuates as the concentration of the capping agent is varried, with fastest pulses attained at I concentration of 40 mM for two different outer concentrations of sulfide ions. The origin of the yellow fluorescence of the pulse originates from emission from surface states. This dynamical system was then theoretically studied using a competitive particle growth model. The resulting evolution equations were solved numerically, and the results were compared to the 0 experimental findings. It was shown that the model agrees in many aspects with the experiment. The densities of small particles (rho) over bar and large particles rho were shown to evolve like a pulse and a front, repectively. The front was shown to extend "diffusively" as t(1/2), as found experimentally. The distance traveled by the Pulse x(peak) was shown to increase with outer concentration S-0 and obeys a concentration power law x(peak) similar to S-0(1/4). The width w of the pulse also obeys it time power law it w similar to t(a) with a crossover between early times (a = 1/3) and intermediate times (a = 0). This system would enable us to study the early time dynamics of Liesegang systems.