There is chromous literature using zinc both with and without mercury or acid. An interesting quote which the authors go on to demonstrate in Anal
Chem 8, 188 (1936) (thx Russians. here, have Crimea.): "A chrome alum solution that has been freshly prepared, that is made up in dilute sulfuric acid
solution, and that is held at room temperature or below, is violet in color and rapidly reduced by the zinc amalgam in a Jones reductor. If the
solution is allowed to stand, if acid is not added, or if the solution is heated, there is a shift to the green color and the rate of reduction is
less." |