If chlorine is passed through a solution of caustic potash or soda, the hypochlorite produced so long as the liquid remains alkaline is rapidly converted with evolution of heat into chlorate when excess of chlorine is present: 3KOCl = KClO3 + 2KCl.
Expt. 2. - The apparatus is shown in Fig. 160. Chlorine generated from manganese dioxide and hydrochloric acid is washed with a little water, and passed into caustic potash solution (20 gm. of KOH in 40 c.c. of water) in the beaker. Crystals separate, and to prevent the delivery tube becoming choked, an inverted funnel is used. When the liquid smells strongly of chlorine, it is cooled and decanted from the crystals of potassium chlorate, KClO 3, which separate. The crystals are washed once or twice with a little cold water and then recrystallised from hot water. They are sparingly soluble in cold water (8.395 gm. per 100 gm. water at 25°), are monoclinic in shape  | Fig: Crystal of potassium chlorate |
easily distinguishable from the cubes of chloride, and on heating in a test-tube melt and evolve oxygen, leaving potassium chloride.
- Solutions give no precipitate with silver nitrate, but on heating the dry salt it gives off oxygen, and the residue when dissolved in water gives a white curdy precipitate of silver chloride with silver nitrate and dilute nitric acid: 2KClO3 = 2KCl + 3O2; KCl + AgNO3 = AgCl + KNO3.
- If a solution of potassium chlorate is mixed with indigo solution and sulphuric acid, and a few drops of sodium sulphite solution are added, the colour of the indigo is discharged. The chlorate is reduced by the sulphurous acid to a lower oxide of chlorine, which has strong bleaching properties.
- A little potassium chlorate treated with concentrated sulphuric acid in a test-tube turns orange-yellow, and evolves a yellow explosive gas (chlorine dioxide, ClO2), having a peculiar odour: 3KClO3 + 2H2SO4 = KClO4 + 2KHSO4 + H2O + 2ClO2. On warming there is a crackling noise, due to explosions of the ClO2.
- Potassium chlorate warmed with concentrated hydrochloric acid gives off a yellow gas (euchlorine), consisting of a mixture of Cl2 and ClO2: 8KClO8 + 24HCl = 8KCl + 12H2O +9Cl2 + 6ClO2.
Potassium chlorate detonates violently when triturated with phosphorus or sulphur. (Dangerous). A mixture of the chlorate and sulphur detonates on percussion.
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