Lead Periodates

In common with many other metals lead forms several periodates, most of which may be regarded as basic salts, or salts of polybasic periodic acids.

By precipitating lead nitrate solution with sodium iodate, Rammelsberg obtained a white, microcrystalline salt, to which he attributed the formula Pb(IO₄)₂.2PbO.2H₂O or Pb₃I₂O₁₀.2H₂O. When strongly heated this salt loses water, iodine, and oxygen, leaving PbI₂.5PbO. According to Kimmins, however, it gradually loses its water at 275° C., leaving the dark yellow anhydro-salt Pb(IO₄)₂.2PbO; and it is converted into the red normal salt Pb(IO₄)₂ by prolonged heating with concentrated nitric acid.

Giolitti has obtained rather different results. According to this observer, the salt obtained by adding a dilute acetic acid solution of lead acetate to a cold solution of the salt K₂HIO₅, to which the formula Pb₃I₂O₁₀.2H₂O was attributed by Rammelsberg, is PbHIO₅; and this when heated to 130°-140° C. yields the anhydro-salt Pb₂I₂O₉ as a red powder. The hydrated salt PbHIO₅.H₂O is formed when a solution of periodic acid is added to a dilute acetic acid solution of lead acetate; and Pb₂HIO₆ results from the prolonged heating of PbHIO₅ with water. Lastly, the salt Pb₃I₂O₁₀.H₂O, containing one molecule of water less than Rammelsberg's salt, is probably formed when PbHIO₅ is heated in dilute nitric acid with lead hydroxide.