TIIK HALOGENS 475 



:'2 vols. of chlorine and 1 vol. of oxygen give 2 vols. of chlorine 

 monoxide. In an anhydrous form the gas or liquid easily explodes, 

 splitting up into chlorine and oxygen. This explosiveness is determined 

 by the fact that heat is evolved in the decomposition to the amount of 

 .about 15000 heat units for C1 2 O. 33 The explosion may even take place 

 accidentally, and also in the presence of many oxidisable substances 

 (for instance, sulphur, organic compounds, etc.), but the solution, 

 although unstable and showing strong oxidising properties, does not 

 give any explosion. 34 



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, 

 -even in their origin, 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,O 5 , NaClO 3 , HC1O 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 the addition of any- 



33 All explosive substances are of this kind ozone, hydrogen peroxide, chloride of 

 nitrogen, nitro-compounds, &c. Hence they cannot be formed directly from the elements 

 or their simplest compounds, but, on the contrary, decompose into them. In a liquid 

 state chlorine monoxide even explodes on contact with powdery substances, or when 

 rapidly agitated for instance, if a file be rasped over the vessel in which it is. 



34 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 9000 

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



The capacity of hypochlorous acid for entering into combination with the unsaturated 

 hydrocarbons (Carius and others) is very often taken advantage of in organic chemistry. 

 'Thus its solution absorbs ethylene, forming the chlorhydrin C 2 H 4 C1'OH. 



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, HClOo (judging from 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 ana- 

 logous to nitrous acid, HNO 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, C1O 2 , which is ob- 

 tained 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 pre- 

 rsent known is that pure chlorine dioxide C1O 2 (see Notes 89-48) is gradually converted 

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



