xi MURIATIC ACID AND CHLORINE 229 



SUMMARY AND SUPPLEMENT 

 A. THE DISCOVERY OF CHLORINE 



Scheele, in 1774, described the properties of the mineral 

 "manganese," now known as pyrolusite or black oxide of 

 manganese, MnO 2 . It is insoluble in dilute nitric or sulphuric 

 acid, but liberates oxygen and is converted into a sulphate by 

 baking with oil of vitriol. 



MnO 2 +H 2 SO 4 - 



(Manganese (Manganous 



dioxide.) sulphate.) 



It also liberates oxygen when heated (Berthollet, 1785), giving 

 rise to an oxide analogous with smithy scale, Fe 3 O 4 . 



It dissolves in cold muriatic acid to a dark solution, which 

 contains an unstable manganic salt and from which the black 

 oxide can be recovered by dilution ; this reversible action may 

 perhaps be represented by the equation : 



but no chloride of the formula MnCl 4 has yet been isolated. 

 When the liquid is heated, a pungent, green gas escapes, to 

 which Davy, in 1810, gave the name chlorine. 



(Manganous (Chlor- 

 chloride.) ine) 



The gas bleaches coloured flowers, extinguishes flame, and 

 unites directly with nearly all metals, thus : 



Lead Pb + CL->PbCl 2 . 



(Lead 

 chloride.) 



Iron 2Fe + 3Cl 2 ->2FeCl 3 . 



(Ferric 

 chloride.) 



Gold 2Au + 3Cl 2 ->2AuCl 3 . 



(Auric 

 chloride) ^) 



Berthollet, in 1785, collected chlorine-water free from muri- 

 atic acid and showed that the gas is not an acid. From the 



