  This paper presents a theoretical description of diffusion growth of a gas
bubble after its nucleation in supersaturated liquid solution. We study systems
where gas molecules completely dissociate in the solvent into two parts, thus
making Sievert's solubility law valid. We show that the difference between
Henry's and Sievert's laws for chemical equilibrium conditions causes the
difference in bubble growth dynamics. Assuming that diffusion flux is steady we
obtain a differential equation on bubble radius. Bubble dynamics equation is
solved analytically for the case of homogeneous nucleation of a bubble, which
takes place at a significant pressure drop. We also obtain conditions of
diffusion flux steadiness. The fulfillment of these conditions is studied for
the case of nucleation of water vapor bubbles in magmatic melts.
