CHAPTER XI THE HALOGENS: CHLORINE, BROMINE, IODINE, AND FLUORINE

fact that heat is evolved in the decomposition to the amount of about 15,000 heat units for Cl 2 O. The explosion may even take place spontaneously, and also in the presence of many oxidisable substances (for instance, sulphur, organic compounds, &c.), but the solution, although unstable and showing a strong oxidising tendency, does not explode. It is evident that the presence of hypochlorous acid, HClO, may be assumed in an aqueous solution of Cl 2 O, since Cl 2 O + H 2 O = 2HClO.

Hypochlorous acid, its salts, and chlorine monoxide serve as a transition between hydrochloric acid, chlorides, and chlorine, and a whole series of compounds containing the same elements combined with a still greater quantity of oxygen. The higher oxides of chlorine, as their origin indicates, are closely connected with hypochlorous acid and its salts:

When heated, solutions of hypochlorites undergo a remarkable change. Themselves so unstable, they, without any further addition, yield two fresh salts which are both much more stable; one contains more oxygen than MClO, the other contains none at all.

Part of the salt—namely, two-thirds of it—parts with its oxygen in order to oxidise the remaining third.³⁹ From an intermediate substance, RX, two extremes, R and RX₃ are formed, just as nitrous anhydride splits up into nitric oxide and nitric anhydride (or nitric acid). The resulting salt, MClO₃, corresponds with chloric acid and potassium chlorate, KClO₃. It is evident that a similar salt may be obtained directly by the action of chlorine on an alkali if its solution be heated, because RClO will be first formed, and then RClO₃; for example, 6KHO + 3Cl₂ = KClO₃ + 5KCl + 3H₂O. Chlorates are so prepared; for instance, potassium chlorate, which is easily separated from potassium chloride, being sparingly soluble in cold water.⁴⁰