Hypochlorites, when heated, undergo conversion into a mixture of chlorate and chloride: jNaOCLAq = NaClOg.Aq + zNaCLAq. The usual method of preparing chlorates, however, is to pass a current of chlorine through hot " milk of lime "-that is, calcium hydroxide suspended and partially dissolved in water0 Potassium chloride equivalent to one-sixth of the lime is also present. The following reaction occurs: 6Ca ( O H).,. Aq + 2KCI. Aq + 6C12 = 6CaCl2. Aq + 2KC10r Aq + 6H2O. On evaporation, the sparingly soluble potassium chlorate deposits in crystals, leaving the very soluble calcium chloride in solution. The potassium chlorate is purified by recrystallisa-tion. It is a white, lustrous salt, crystallising in flat plates. It fuses readily, and, at a somewhat higher temperature than its melting-point, it evolves oxygen. At the same time some of the chlorate is oxidised by the oxygen, and perchlorate is formed: *KC1CK»2KCI+ 3®* and KC10q + 0 = KC1O4.
Sodium chlorate, NaC1O3, is now largely produced by electrolysis of a hot solution of common salt. The initial products are sodium and chlorine. The sodium, however, immediately on liberation at the kathode, yields hydrogen and caustic soda. The latter reacts with the chlorine, giving hypochlorite, which at the high temperature changes into chlorate. On evaporation, the sparingly soluble NaCl crystallises out and is removed; and from the mother-liquors, the sodium chlorate deposits. Its use is chiefly for the manufacture of lucifer matches. Mixed with antimony sulphide, Sb2S3, it gives an easily kindled mixture.