The onset of oscillatory convection in a binary fluid mixture.

Flow-visualization experiments are described which study the onset of convection in ethanol-water mixtures. It is shown that the conducting state becomes unstable to oscillatory convection, in a pattern of parallel rolls, having an onset Rayleigh number, a growth rate and frequency which are consistent with linear instability theory. In this case, however, the onset of convection is not a forward bifurcation: the oscillatory fluid motion does not stabilize at a finite amplitude, but continues to grow exponentially with time until large-amplitude, overturning convection is triggered.