480 PRINCIPLES OF CHEMISTRY 



combine with the bases mentioned. 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 + 2C1 2 = Hg 2 001 2 + C1 2 O. In this case, a 

 compound of mercury oxide with mercury chloride, or the socalled 

 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 hypochlorous acid only, but the greater 

 part of it splits up into the anhydride and water. 32 bis 



Chlorine monoxide, which corresponds to bleaching and hypo- 

 chlorous salts, containing as it does the two elements oxygen and 

 chlorine, forms 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 con- 

 denses into a red liquid boiling at -f 20 and giving a vapour whose 

 density (43 referred to hydrogen) shows that 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 1 5,000 heat units 

 for C1 2 O. 33 The explosion may even take place spontaneously, and also 



32 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, MC10, be added to a solution of mercuric salt, HgX 2 , mercuric oxide is liberated, 

 because the hypochlorite is decomposed. 



52 bis 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 3O 4 + H-jO + C1 2 = NaCl + HC10 + NaHSO 4 . Here 

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

 water, for Cl e + H 2 O = HC1 + HC10. If the crystallo-hydrate of chlorine be mixed with 

 mercury oxide, the hydrochloric acid formed in the reaction gives mercury chloride, 

 and hypochlorous acid remains in solution. A dilute solution of hypochlorous 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 mon- 

 oxide is disengaged. 



53 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 explodes even on contact with powdery substances, or when 

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



