The instantaneous, chemical reaction between a sparingly soluble gaseous species and a liquid-phase reactant is known to occur at a moving reaction plane to which both the reacting species diffuse. This study investigates the motion of such a reaction front, in thin tubes, where the liquid-phase reactant is present as a slurry of sparingly soluble, fine particles. The movement of the reaction boundary is well-understood quantitatively only in the absence of particles and this paper attempts to provide a theoretical model and its experimental validation, for the case of slurries. The agreement between theory and experiment is found to be reasonable. The relevance of this problem arises from the more general context of gas-liquid-solid reactors where the theory for computing the specific rates of absorption requires the simultaneous modeling of reactant diffusion, motion of the reaction plane and the effects of particle dissolution in the vicinity of the gas-liquid-interface, within a rigid ’surface penetration element’. Thus, the situation prevailing in such a penetration element is sought to be physically ’simulated’ by the use of a thin glass tube.