-474 PRINCIPLES OF CHEMISTRY 



the action of chlorine in the presence of water, do not give a salt of 

 .hypochlorous acid, but form a chloride and hypochlorous acid, which 

 fact shows the incapacity of this acid to combine with the given bases. 

 Therefore, if such oxides as those of zinc or mercury be shaken up in 

 water, and chlorine be passed through the turbid liquid, 32 a reaction 

 occurs which may be expressed in the following manner : 2HgO -f 2C1 2 

 =Hg 2 OCl 2 -f C1 2 O. In this case, a compound of mercury oxide with 

 anercury chloride, or the so-called mercury oxychloride, is obtained : 

 Hg 2 OCl 2 =HgO + HgCl 2 . This is insoluble in water, and is not affected 

 by hypochlorous anhydride, so that the solution will contain hypo- 

 chlorous acid only, but the greater part of it splits up into the anhydride 

 and water. 



A solution of hypochlorous anhydride is also obtained by the action 

 of chlorine on many salts ; for example, in the action of chlorine on a 

 solution of sodium sulphate the following reaction takes place : 

 Na 2 SO 4 + H 2 O + Cl 2 = NaCl + HClO + NaHSO 4 . Hence here the 

 hypochlorous acid is formed, together with HC1, at the expense of the 

 reaction of chlorine on water, for C1 2 +H 2 O=HC1 + HC1O. If the 

 crystallo-hydrate of chlorine be mixed with mercury oxide, then the 

 hydrochloric acid formed in the reaction gives mercury chloride, and 

 hypochlorous acid remains in solution. A dilute solution of hypo- 

 chlorous acid or chlorine monoxide may be concentrated by distillation, 

 and if a substance which takes up water (without destroying the acid) 

 for instance, calcium nitrate be added to the stronger solution 

 then the anhydride of hypochlorous acid i.e. chlorine monoxide is 

 disengaged. 



In the bleaching salts and hypochlorous salts which correspond 

 with chlorine monoxide and contain the two elements oxygen and 

 chlorine, which both act in an oxidising manner, we see a characteristic 

 example of a compound of elements which, in the majority of cases, act 

 chemically in an analogous manner. Chlorine monoxide, as prepared 

 from an aqueous solution by the abstraction of water or by the action 

 of dry chlorine on cold mercury oxide, is, at the ordinary temperature, 

 a gas or vapour which condenses into a red liquid boiling at + 20 and 

 giving a vapour whose density (43 referred to hydrogen) shows that 



52 Dry red mercury oxide acts on chlorine, forming dry hypochlorous anhydride 

 (chlorine monoxide) (Balard) ; when mixed with water, red mercury oxide acts feebly on 

 chlorine, and when freshly precipitated it evolves oxygen and chlorine. An oxide of 

 mercury which easily and abundantly evolves chlorine monoxide under the action of 

 -chlorine in the presence of water may be prepared as follows : the oxide of mercury, 

 precipitated from a mercuric salt by an alkali, is heated to 300 and cooled (Pelouze). If 

 a salt, MC1O, be added to a solution of mercuric salt, HgX 2 , then mercuric oxide is 

 liberated, because the hypochlorite is decomposed. 



