Kämmerer showed that a solution of sp. gr. 2·127 at 14°, containing 2HIO3,9H2O, solidified completely in the cold. On comparing solutions HI + mH2O with HIO3 + mH2O, we find that the specific gravity increases but the volume decreases, whilst in the passage of solutions HCl + mH2O to HClO3 + mH2O both the specific gravity and the volume increase, which is also observed in certain other cases (for example, H3PO3 and H3PO4).
Ditte (1890) obtained many iodates of great variety. A neutral salt, 2(LiIO3)H2O, is obtained by saturating a solution of lithia with iodic acid. There is an analogous ammonium salt, 2(NH4IO3)H2O. He also obtained hydrates of a more complex composition, such as 6(NH4IO3)H2O and 6(NH4IO3)2H2O. Salts of the alkaline earths, Ba(IO3)2H2O and Sr(IO3)2H2O, may be obtained by a reaction of double decomposition from the normal salts of the type 2(MeIO3)H2O. When evaporated at 70° to 80° with nitric acid these salts lose water. A mixture of solutions of nitrate of zinc and an alkaline iodate precipitates Zn(IO3)22H2O. An anhydrous salt is thrown out if nitric acid be added to the solutions. Analogous salts of cadmium, silver, and copper give compounds of the type 2Me′IO34NH3 and Me″(IO3)24NH3, with gaseous ammonia (Me′ and Me″ being elements of the first (Ag) and second (Cd, Zn, Cu) groups).
With an aqueous solution of ammonia the above salts give substances of a different composition, such as Zn(IO3)2(NH4)2O, Cd(IO3)2(NH4)2O. Copper gives Cu(IO3)24(NH4)2O and Cu(IO3)2(NH4)2O. These salts may be regarded as compounds of I2O5, and MeO and (NH4)2O; for example, Zn(IO3)2(NH4)2O may be regarded as ZnO(NH4)2OI2O5, or, as derived from the hydrate, I2O52H2O = 2(HIO3)H2O.
If sodium iodate be mixed with a solution of sodium hydroxide, heated, and chlorine passed through the solution, a sparingly soluble salt separates out, which corresponds with periodic acid, and has the composition Na4I2O9,3H2O. 6NaHO + 2NaIO3 + 4Cl = 4NaCl + Na4I2O9 + 3H2O. This compound is sparingly soluble in water, but dissolves easily in a very dilute solution of nitric acid. If silver nitrate be added to this solution a precipitate is formed which contains the corresponding compound of silver, Ag4I2O9,3H2O. If this sparingly soluble silver compound be dissolved in hot nitric acid, orange crystals of a salt having the composition AgIO4 separate on evaporation. This salt is formed from the preceding by the nitric acid taking up silver oxide—Ag4I2O_9 + 2HNO3 = 2AgNO3 + 2AgIO4 + H2O. The silver salt is decomposed by water, with the re-formation of the preceding salt, whilst iodic acid remains in solution— 4AgIO4 + H2O = Ag4I2O9 + 2HIO4.
The structure of the first of these salts, Na4I2O9,3H2O, presents itself in a simpler form if the water of crystallisation is regarded as an integral portion of the salt; the formula is then divided in two, and takes the form of IO(OH)3(ONa)2—that is, it answers to the type IOX5, or IX7, like AgIO4 which is IO3(OAg). The composition of all the salts of periodic acids are expressed by this type IX7. Kimmins (1889) refers all the salts of periodic acid to four types—the meta-salts of HIO4 (salts of Ag, Cu, Pb), the meso-salts of H3IO5 (PbH, Ag2H, CdH), the para-salts of H5IO6 (Na2H3, Na3H2), and the di-salts of H4I2O9 (K4, Ag4, Ni2). The three first are direct compounds of the type IX7, namely, IO3(OH), IO2(OH)3, and IO(OH)5, and the last are types of diperiodic salts, which correspond with the type of the meso-salts, as pyrophosphoric salts correspond with orthophosphoric salts—i.e. 2H3IO5-H2O = H4I2O9.