Silver periodates

A solution of sodium periodate, Na₄I₂O₉, gives with Silver nitrate a precipitate of a silver periodate. It crystallizes from dilute nitric acid in straw-coloured, hexagonal crystals of the formula 2Ag₂O,I₂O₇,3H₂O, transformed at 100° C. into the corresponding mono- hydrate, a dark-red, crystalline powder. Prolonged boiling of the trihydrate with water yields 3Ag₂O,I₂O₇ or 5Ag₂O,I₂O₇. The substance with the second formula is also produced as a black, crystalline powder by the action of Silver nitrate on the trihydrate. Evaporation with nitric acid converts the trihydrate into the yellow, crystalline anhydrous salt, Ag₂O,I₂O₇. Ammonia transforms the trihydrate into a black powder, 4Ag₂O,I₂O₇. The trihydrate, 2Ag₂O,I₂O₇,3H₂O, is also formed by the interaction at ordinary temperatures of Silver nitrate and a nitric-acid solution of the periodate Na₂H₃IO₆. At 100° C. the action produces a black precipitate, 3Ag₂O,I₂O₇.