Density oscillations in precipitate domains of a propagating Cr(OH)3 ring

A propagating Cr(OH)3 band in 1D and a circular ring in 2D were observed and studied in PVA/GDA gels. In a recent simulation (Al-Ghoul and Sultan, J. Phys. Chem. A 107 (2003) 1095) using the model of Müller and Polezhaev, the precipitate density of the 1D pulse exhibited temporal oscillations at early times. We present here new experiments to verify this theoretical finding. Oscillations were indeed observed in the density and width of the precipitate ring, suggesting that the obtained pattern is that of a breathing pulse. The properties of the pulse studied in this Letter, capture the characteristics of a pulse of mineral deposit conjectured earlier (Earth-Sci. Rev. 29 (1990) 163) using a model of geochemical pattern formation.