^" CHEMISTRY. 



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Chlorine forms four compounds with oxygen ; none of them are 

 very permanent, but they are all easily decomposed 



Hijioochlorous acid, CIO, or protoxide of chlorine, is obtained by 

 the action of chlorme gas on peroxide of mercury, thus :— 



2 Chlorine \ SI"!"'!"^ —^Chloride of Mercury. 



t Chlorine ^-"^ 



Oxide of \ Mercury ^^ ^ 



Mercury ) Oxygen r_ ^ Hypochlorous acid, 



It is a pale yellowish gas,— possesses powerful bleaching pro- 

 perties, and forms bleaching salts. 



Chhroiis acid, C10„ peroxide of chlorine ;_prepared bv heating a 

 mixture of sulphuric acid and chlorate of potassa ; the chloric acid 

 which IS set free is spontaneously decomposed into chlorous acid 

 and hypochloric acid, the latter remaining in union with the potassa. 

 It has a richer colour than chlorine, and is very explosive. 



Chhric acid, ClO^, the most important compound of the series; — 

 prepared by adding sulphuric acid to the chlorate of baryta. If 

 ch orine gas be transmitted through a solution of caustic potassa, a 

 chlorate of potassa crystallizes, and the chloride of potassium re- 

 mains in solution. The chlorates are easily recognised ;— they give 

 out pure oxygen when heated, passing into chlorides ; they yield 

 chlorous acid on being heated with sulphuric acid ; but give no pre- 

 cipitate with silver. 



Perchloric acid, CK\ prepared by acting on the perchlorate of 

 potassa with sulphuric acid. It has a very strong affinity for 

 moisture ; — forms salts resembling the chlorates. 



Ckloride of nitrogen, Cli\, prepared by transmitting chlorine 

 gas through a solution of muriate of ammonia ; globules of an oily 

 aspect are formed, which subside to the bottom ;— it is the most ex- 

 plosive substance known. 



Chlorine also forms compounds with carbon, carbonic acid, phos- 

 phorus, boron, and silicon. The important compound of chlorine 

 and hydrogen will be described subsequently. 



IODINE. 



Exists in sea-weeds and in certain saline springs ;— usually pre- 

 pared from kelp, an impure carbonate of soda ; the mother waters 

 of this contain iodine in combination with sodium or potassium. 

 From this the iodine may be evolved by the action of sulphuric acid 

 and peroxide of manganese ; the rationale is as follows :— 



Iodide of Uodine Iodine. 



Sodium ) Sodium _______^ 



2 Sulphuric S Sul ^huiic^tcid " ^ Sulphate of Soda. 



acid ^ Sulphuric acid — ^irr"^"^ 



Peroxide of \ Oxygen -—-'f'^ ~~ — ---, S Sulphate of Man- 



Manganese / Protoxide of Manganese J ganese. 



