Convective Fingering of an Autocatalytic Reaction Front

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We report experimental observations of the convection-driven fingering instability of an iodate-arsenous acid chemical reaction front. The front propagated upward in a vertical slab; the thickness of the slab was varied to control the degree of instability. We observed the onset and subsequent nonlinear evolution of the fingers, which were made visible by a pH indicator. We measured the spacing of the fingers during their initial stages and compared this to the wavelength of the fastest growing linear mode predicted by the stability analysis of Huang et. al. [Phys. Rev. E, 48, 4378 (1993), and unpublished]. We find agreement with the thickness dependence predicted by the theory.