We investigated traveling fronts of the oxidation of sulfite by iodate
and by bromate. Isothermal density changes (Delta rho(c)) and enthalp
ies were determined, the latter being negative in both cases. The Delt
a rho(c) is negative in the iodate-sulfite system but positive in the
bromate-sulfite system. Double-diffusive convection was expected in th
e bromate system and was observed. The effect of tube diameter and the
orientation of the tube on the wave velocity and wave shape were stud
ied, and a gravitational anisotropy was found in both systems. Accordi
ng to the Pojman-Epstein model, only simple convection should have occ
urred in the iodate-sulfite system. In fact, curved descending fronts
with velocities greater than the ascending ones and ''fingering'' were
observed. Several explanations were considered, including the possibi
lity that the current model must be expanded to explicitly treat the e
ffect of a moving interface on the stability of the fluid.