Note 55 — Chapter XVIII · SILICON AND THE OTHER ELEMENTS OF THE FOURTH GROUP

Lead dioxide is often called lead peroxide, but this name leads to error, because PbO2 does not show the properties of true peroxides, like hydrogen or barium peroxides, but is endowed with acid properties—that is, it is able to form true salts with bases, which is not the case with true peroxides. Lead dioxide is a normal salt-forming compound of lead, as Bi2O5 is for bismuth, CeO2 for cerium, and TeO3 for tellurium, &c. They all evolve chlorine when treated with hydrochloric acid, whilst true peroxides form hydrogen peroxide. The true lead peroxide, if it were obtained, would probably have the composition Pb2O5, or, in combination with peroxide of hydrogen, H2Pb2O7 = H2O2 + Pb2O5, judging from the peroxides corresponding with sulphuric, chromic, and other acids, which we shall afterwards consider.

As a proof of the fact, that the form PbO₂, or PbX₄, is the highest normal form of any combination of lead, it is most important to remark that it might be expected that the action of lead chloride, PbCl₂, on zinc-ethyl, ZnEt₂, would result in the formation of zinc chloride, ZnCl₂, and lead-ethyl, PbEt₂, but that in reality the reaction proceeds otherwise. Half of the lead is set free, and lead tetrethyl, PbEt₄, is formed as a colourless liquid, boiling at about 200° (Butleroff, Frankland, Buckton, Cahours, and others). The type PbX₄ is not only expressed in PbEt₄ and PbO₂, but also in PbF₄, obtained by Brauner.