We present the experimental part of a study of the permanganate-hydroxylamine system at a supercritical Hopf bifurcation aiming at deriving a mechanism for the reaction. We report quenching data for the addition of a number of essential species and for substances supposed to remove essential species, as well as for dilution. In particular, we report successful quenchings with colloid manganese dioxide and with Arabic gum, which is supposed to inactivate the surface of the colloid.