increases with the electrolyte concentration and is about 0.43 M in a saturated magnesium tetrafluoroborate solution. Magnesium solutions which exhibit the characteristic blue color of the solvated electron, are less stable than those of alkali metals. Their stability which increases with their concentration and the concentration of the supporting electrolyte, is quite good for concentrations higher than 0.05 M (rate constant for the decomposition of the solution lower than 10(-4) s(-1)). Magnesium and alkali metals solutions have the same reducing power since (i) the potential ranges of solutions of sodium or magnesium tetrafluoroborate in liquid ammonia are the same at a gold electrode and (ii) the diffusion coefficient of the solvated electron in the presence of magnesium tetrafluoroborate salt is not significantly different from that of sodium under the same conditions (only 1.7 times lower).