HYPOCHLOROUS ACID. 367 



Hypochlorous acid. The discovery of this compound was 

 made by M. Balard in 1834.* It is formed by the action of 

 chlorine upon the red oxide of mercury. If to a two-pound 

 bottle of chlorine gas, 6 drachms of red oxide of mercury in fine 

 powder be added, with 1 Jounce of water, the chlorine will be found 

 to be rapidly absorbed on agitation. One portion of the chlorine 

 unites with the oxygen of the metallic oxide, and becomes hy- 

 pochlorous acid, which is dissolved by the water, while another 

 portion forms a chloride with the metal, which chloride unites 

 with a portion of undecomposed oxide, and forms an insoluble 

 oxichloride. The liquid may be poured off and allowed to settle ; 

 it is a solution of hypochlorous acid, with generally a little 

 chloride of mercury. This reaction is expressed in the follow- 

 ing diagram : 



FORMATION OF HYPOCHLOROUS ACID. 



Before decomposition. After decomposition. 



Chlorine .... Chlorine . . . Hypochlorous acid 



Chlorine .... Chlorine . . " *-. Chloride of Merc. 1 J 

 Oxide of Merc. Oxide of Merc Oxide of Mercury j| 



8 



Or in symbols ; 2 Cl and 2 HgO = CIO and HgCl, HgO. But 

 the oxichloride formed, seems not always to contain the same 

 proportion of oxide. The proportion of hypochlorous acid in 

 the liquid may be increased, by introducing the same solution 

 into a second bottle of chlorine, with an additional quantity of 

 red oxide of mercury The oxide of zinc and black oxide of 

 copper, diffused through water, and exposed to chlorine, give 

 rise to a similar formation of hypochlorous acid. 



The pure hypochlorous acid is a gas, which Balard succeeded 

 in disengaging by passing up fragments of nitrate of lime into 

 the liquid acid above mercury, in a jar of the mercurial trough. 

 By dissolving in the water, that salt causes the evolution of the 

 gas, which collects in the upper part of the jar, and is defended 

 from contact with the mercury, which absorbs it, by the inter- 

 vention of the saline solution. 



* An. de Ch. et de Ph. t. 57, p. 225, or Taylor's Scientific Memoirs, vol. I, 

 p. 269. 



