THE HALOGENS 481 



in the presence of many oxidisable substances (for instance, sulphur, 

 organic compounds, <feo.), but the solution, although unstable and 

 showing a strong oxidising tendency, does not explode. 34 It is evident 

 that the presence of hypochlorous acid, HC10, may be assumed in an 

 aqueous solution of C1 2 O, since C1 2 O + H 2 O = 2HC10. 



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 



C1 2 , -NaCl, HC1, hydrochloric acid, 

 C1 2 O, NaCIO, HC1O, hypochlorous acid 

 C1 2 O 3 , NaClO 2 , HC1O 2 , chlorous acid. 35 

 C1 2 O 5 , NaClO 3 , HC10 3 , chloric acid. 

 C1 2 O 7 , NaClO 4 , HC1O 4 , perchloric acid. 



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 MC1O, the other contains none at all. 



3MG10 = MC10 3 + 2MC1 



hypochlorite chlorate chloride 



s * A solution of chlorine monoxide, or hypochlorous acid, does not explode, owing to 

 the presence of the mass of water. In dissolving, chlorine monoxide evolves about 9,000 

 heat units, so that its store of heat becomes less. 



The capacity of hypochlorous acid (studied by Carius and others) for entering into com- 

 bination with the unsaturated hydrocarbons is very often taken advantage of in organic 

 Chemistry. Thus its solution absorbs ethylene, forming the chlorhydrin C 2 H 4 C10H. 



The oxidising action of hypochlorous acid and its salts is not only applied to bleaching" 

 but also to many reactions of oxidation. Thus it converts the lower oxides of manganese 

 into the peroxide. 



35 Chlorous acid, HC1O 2 (according to the data given by Millon, Brandau, and 

 others) in many.respects resembles hypochlorous acid, HC1O, whilst they both differ from 

 chloric and perchloric acids in their degree of stability, which is expressed, for instance, 

 in their bleaching properties ; the two higher acids do not bleach, but both the lower 

 ones do so (oxidise at the ordinary temperature). On the other hand, chlorous acid is 

 analogous to nitrous acid, HN0 2 The anhydride of chlorous acid, C1 2 O 3 , is not known 

 in a pure state, but it probably occurs in admixture with chlorine dioxide, C102, which is 

 obtained by the action of nitric and sulphuric acids on a mixture of potassium chlorate 

 with such reducing substances as nitric oxide, arsenious oxide, sugar, &c. All that is at 

 present known is that pure chlorine dioxide ClO<j (see Notes 89-43) is gradually converted 

 into a mixture of hypochlorous and chlorous acids under the action of water (and alkalis) ; 

 that is, it acts like nitric peroxide, NO 2 (giving HNO 3 and HNO 2 ), or as a mixed anhy- 

 dride, 2C1O 2 + H 3 O = HC1O 3 + HClOo. The silver salt, AgClO 2 , is sparingly soluble in 

 water. The investigations of Garzarolli-Thurnlackh and others seem to show that the 

 anhydride C1 2 O 3 does not exist in a free state. 



