232 HISTORICAL INTRODUCTION TO CHEMISTRY CH. xi 



analogy is illustrated by the mutual displacement of chlorine, 

 sulphur and oxygen, for instance : 



HgS + C1 2 -> HgCl 2 + S. 



(Cinnabar.) (Corrosive 



sublimate.) 



CaO + C1 2 -> CaCl 2 + |O 2 . 



(Lime.) (Muriate of 



lime.) 



. 



Berthollet, by the action of chlorine on potash, prepared 

 ternary salts, containing metal, chlorine and oxygen : 



2KOH + C1 2 -> KC1 + KC1O + H 2 O. 



(Potassium 

 hypochlorite.) 



6KOH + 3C1 2 -> 5KC1 + KC1O 3 4- 3H 2 O. 



(Potassium 

 chlorate.) 



The potassium hypochlorite prepared from cold potash liberates 

 chlorine when acted on by acids, and was used as a convenient 

 source of chlorine for bleaching ; but it was soon displaced by 

 the bleaching powder, CaOCl 2 , which Tennant prepared by the 

 direct action of chlorine on slaked lime. The potassium 

 chlorate, which Berthollet prepared by the action of chlorine on 

 hot potash, is a crystalline salt, is readily decomposed by 

 heat and forms a convenient source for the preparation of small 

 quantities of oxygen : 



