The oxidation of iodic acid to periodic acid is accomplished by means of a solution of sodium hypochlorite; it is easier to dissolve iodine in a solution of sodium carbonate, when hypoiodite is formed, and to saturate the solution with chlorine. The iodate at first formed is converted into the periodate : NaIO₃.Aq + NaOCl. Aq = NaCl.Aq + NaIO₄.Aq. As the periodate is sparingly soluble in water, it crystallises out on concentrating the solution. On mixing the solution of the sodium salt with silver nitrate, tri-hydrogen di-argentic periodate is precipitated; it is dissolved in hot dilute nitric acid and evaporated, when mono-argentic periodate, AgIO₄, crystallises out. On mixing with water, this salt undergoes the change : 2AgIO₄ + ₄H₂O - H₈Ag₂IO₆ + H₅IO₆.Aq. The silver salt, which is insoluble in water, is removed by filtration, and the periodic acid deposits in crystals on evaporation. The acid forms white prisms; on heating it to 130°, it decomposes into iodine pentoxide, I₂O₅, a white solid, also produced on heating iodic acid to 170% together with water and oxygen; at 18o° the pentoxide decomposes slowly into iodine and oxygen.